Secondary battery, manufacturing method and electrical apparatus

Abstract

The present disclosure relates to the technical field of lithium batteries, in particular to a secondary battery, a manufacturing method, and an electrical apparatus. The secondary battery comprises a negative electrode sheet. A current collector comprises a first region and a second region, the second region being close to a tab, a first active substance layer being located in the first region, and a second active substance layer being located in the second region. The mass fraction of a silicon-based material in the second active substance layer is greater than the mass fraction of the silicon-based material in the first active substance layer, and the mass fraction of a first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer. The present application can improve the capacity of the second region, increase the charging speed of the second region, and mitigate precipitation of lithium dendrites in the second region.

Description

Secondary battery, preparation method and power-using device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application 202311641487.7, filed on November 30, 2023, entitled “Positive Secondary Battery, Preparation Method and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the technical field of lithium batteries, and in particular to a secondary battery, a preparation method, and an electrical device. Background Art

[0004] Lithium-ion batteries have made significant progress in recent years, finding widespread application in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in electric vehicles, power tools, military equipment, and aerospace. In particular, lithium-ion batteries are being used in electric vehicles, such as electric bicycles, electric motorcycles, and electric cars. As the market demands for higher battery life, the demand for lithium-ion batteries' cycle performance and fast charging capabilities continues to increase.

[0005] Summary of the Invention

[0006] In view of this, the main technical problem solved by the present disclosure is to improve the cycle performance and fast charging capability of lithium-ion batteries, thereby providing a secondary battery, a preparation method and an electrical device that can improve the cycle performance and fast charging capability of secondary batteries.

[0007] A first aspect of the present disclosure provides a secondary battery, comprising a negative electrode pole piece, the negative electrode pole piece comprising a current collector and an active material layer arranged on the surface of the current collector, the active material layer comprising a silicon-based material and a carbon-containing material, the carbon-containing material comprising a first carbon material; the current collector comprising a main body and a tab located on one side of the main body, the main body comprising a first region and a second region, the second region being located between the first region and the tab; the active material layer comprising a first active material layer and a second active material layer, the first active material layer being located in the first region, and the second active material layer being located in the second region; the mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer; the mass fraction of the first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer.

[0008] In the disclosed embodiment, the active material layer of the negative electrode plate includes a silicon-based material and a carbon-containing material. By adding a high-capacity silicon-based material to the carbon-containing material, the capacity of the negative electrode plate can be increased. In the disclosed embodiment, first, by setting the mass fraction of the silicon-based material in the second active material layer to be greater than the mass fraction of the silicon-based material in the first active layer, the active material layer unit volume capacity of the negative electrode plate in the area near the edge of the electrode (the second area) is higher than that in the main area (the first area), which can increase the capacity of the second area and significantly improve the occurrence of the negative electrode plate capacity reduction caused by the second area being thinned relative to the first area due to the influence of the manufacturing process of the negative electrode plate. Secondly, the expansion coefficient of the silicon-based material is greater than that of the carbon-containing material. By increasing the mass fraction of the silicon-based material in the second region to be higher than that in the first region, the expansion degree of the second active material layer in the second region is greater than that of the first active material layer in the first region during the charge and discharge process, so that the porosity of the second active material layer in the second region increases, the specific surface area increases to a greater extent, and the contact area between the second active material layer and the electrolyte increases, which can improve the transmission capacity of lithium ions, reduce the lithium ion deposition in the second region, and improve the lithium deposition of the negative electrode in the second region. Thirdly, since the lithium insertion potential of the silicon-based material is relatively high, the potential of the electrode is higher during charging, which significantly improves the fast charging capability of the negative electrode. In the embodiment of the present disclosure, the carbon-containing material includes a first carbon material, and the first carbon material is a fast-charging high-kinetic carbon material, which can improve the fast charging capability of the second region. In the embodiment of the present disclosure, by controlling the mass fraction of the silicon-based material in the second active material layer to be greater than the mass fraction of the silicon-based material in the first active material layer, and controlling the mass fraction of the first carbon material in the second active material layer to be greater than the mass fraction of the first carbon material in the first active material, the capacity of the second region can be increased and the charging speed of the second region can be increased, so as to improve the problem caused by the thin second active material layer in the second region of the negative electrode sheet during the battery manufacturing process; thereby, the overall fast charging capability and cycle stability of the secondary battery can be improved.

[0009] In any embodiment, the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than 1:1 and less than or equal to 80:1. In the embodiment of the present disclosure, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer to the silicon-based material in the first active material layer within the above range, the problem caused by the thin second active material layer in the second region due to process reasons can be improved, the difference in capacity per unit area between the second active material layer and the first active material layer can be reduced, the situation of lithium dendrite precipitation in the second active material layer can be improved, and the fast charging capability of the second active material layer can be improved.

[0010] In the embodiments of the present disclosure, the capacity per unit area refers to the capacity of the active material layer in a unit area divided by a plane parallel to the plane where the current collector is located.

[0011] In any embodiment, the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than or equal to 1.3 and less than or equal to 30:1. In the embodiment of the present disclosure, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer to the silicon-based material in the first active material layer within the above range, the problem caused by the thin second active material layer in the second region due to process reasons can be better improved, so that the difference in capacity per unit area between the second active material layer and the first active material layer is reduced, and the situation of local precipitation of lithium dendrites in the negative electrode plate is improved. The second active material layer has a smaller difference in fast charging capacity than the first active material layer, so that the second active material layer has a larger capacity and higher stability.

[0012] In any embodiment, the mass fraction of the silicon-based material in the first active material layer is 0.5% to 30%, and optionally 1% to 20%. In the embodiments of the present disclosure, by controlling the mass fraction of the silicon-based material in the first active material layer within the above range, the reversible gram capacity of the first active material layer of the negative electrode plate is improved, the energy density of the secondary battery is improved, the stability of the first active material layer is improved, and the cycle performance of the secondary battery is improved.

[0013] In any embodiment, the mass fraction of the silicon-based material in the second active material layer is 1% to 40%, optionally 1.5% to 30%. In the embodiment of the present disclosure, by controlling the mass fraction of the silicon-based material in the second active material layer and making the mass fraction of the silicon-based material in the second active material layer greater than the mass fraction of the silicon-based material in the first active material layer, the reversible capacity of the second active material layer is improved, the stability of the second active material layer is improved, and the capacity per unit volume of the second active material layer in the second region is greater than the capacity per unit volume of the first active material layer in the first region, thereby reducing the occurrence of lithium plating in the second region of the secondary battery.

[0014] In any embodiment, the mass fraction of the first carbon material in the carbon-containing material in the second region is 40% to 100%, and optionally 50% to 90%. In the embodiments of the present disclosure, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second region, the content of the first carbon material in the second region is optimized, thereby improving the stability and fast charging performance of the second active material layer in the second region.

[0015] In any embodiment, the mass fraction of the first carbon material in the first region of the carbon-containing material is 20% to 99%, and optionally 35% to 89%. In the disclosed embodiments, by controlling the mass fraction of the first carbon material in the carbon-containing material in the first region, the content of the first carbon material in the first region is optimized, and the difference in the fast-charging performance of the active material per unit area in the first region and the second region is minimized, thereby improving the fast-charging capability and stability of the negative electrode sheet.

[0016] In any embodiment, the mass fraction of the first carbon material in the second region 1413 in the second active material layer 1422 is 24% to 96%, and optionally 35% to 89%. In the disclosed embodiment, by controlling the mass fraction of the first carbon material in the second region 1413 in the second active material layer 1422 within the above range, the content of the first carbon material in the second region 1413 in the second active material layer 1422 is optimized, resulting in better stability and fast charging performance of the second active material layer 1422 in the second region 1413.

[0017] In any embodiment, the mass fraction of the first carbon material in the first region 1412 in the first active material layer 1421 is 14% to 79%, and optionally 24% to 69%. By controlling the mass fraction of the first carbon material in the first region 1412 in the first active material layer 1421 within the above range, the content of the first carbon material in the first region 1412 in the first active material layer 1421 is optimized, thereby improving the stability and fast charging performance of the second active material layer 1422 in the first region 1412.

[0018] In any embodiment, the carbon-containing material further includes a second carbon material, and the reversible gram capacity of the first carbon material is less than the reversible gram capacity of the second carbon material. In the disclosed embodiment, the second carbon material is a high-capacity carbon material, and the first carbon material is a fast-charging carbon material. By controlling the content of the first and second carbon materials, the capacity and fast-charging performance of the secondary battery can be coordinated and controlled to a certain extent.

[0019] In any embodiment, the volume average particle size Dv50 of the first carbon material is smaller than the volume average particle size Dv50 of the second carbon material. In the embodiment of the present disclosure, the volume average particle size Dv50 of the first carbon material is smaller than the volume average particle size Dv50 of the second carbon material. The first carbon material has a larger specific surface area, which makes the channels for lithium ion migration more numerous and the paths shorter during the charge and discharge process, and the rate performance is better, so that the fast charging capability of the first carbon material is greater than the fast charging capability of the second carbon material. The second carbon material has a larger volume average particle size Dv50, a smaller specific surface area, a high compaction density, and a large capacity, so that the reversible gram capacity of the second carbon material is greater than the reversible gram capacity of the first carbon material.

[0020] In any embodiment, the volume average particle size DV50 of the first carbon material is greater than or equal to 1 μm and less than or equal to 15 μm. In the embodiment of the present disclosure, by controlling the volume average particle size DV50 of the first carbon material within the above range, the fast charging performance of the first carbon material is improved.

[0021] In any embodiment, the volume average particle size DV50 of the second carbon material is greater than or equal to 7 μm and less than or equal to 22 μm. In the embodiment of the present disclosure, by controlling the volume average particle size DV50 of the first carbon material within the above range, the reversible specific capacitance performance of the second carbon material is improved.

[0022] In any embodiment, the reversible gram capacity of the first carbon material is 330 mAh / g to 360 mAh / g, and optionally 330 mAh / g to 360 mAh / g. In the disclosed embodiment, the reversible gram capacity of the first carbon material is within the above range, so that the formed negative electrode sheet has a larger reversible gram capacity and better stability.

[0023] In any embodiment, the reversible gram capacity of the second carbon material is 350 mAh / g to 380 mAh / g, and optionally 350 mAh / g to 380 mAh / g. In the disclosed embodiment, the reversible gram capacity of the second carbon material is within the above range, so that the formed negative electrode sheet has a larger reversible gram capacity and better stability.

[0024] In any embodiment, the ratio of the area of ​​the second region to the area of ​​the first region is (3-20):100. The ratio of the area of ​​the second region to the area of ​​the first region can optionally be (5-15):100. In the embodiment of the present disclosure, by controlling the area ratio of the second region to the first region within the above range, the content of the silicon-based material and the first carbon material in the first region and the second region of the negative electrode plate is appropriate, which can better alleviate the lithium deposition in the second region of the negative electrode plate, and make the reversible gram capacity of the negative electrode plate higher and the stability higher.

[0025] In any embodiment, the width of the second region, as measured from the first region toward the tab, is greater than zero and less than or equal to 20 mm. Alternatively, the width of the second region is greater than zero and less than or equal to 10 mm. In the disclosed embodiment, the width of the second region, as measured from the first region toward the tab, is within the above range, resulting in a smaller width of the second region and a smaller impact of the second active material layer in the second region on the overall negative electrode sheet.

[0026] In any embodiment, the secondary battery further includes a positive electrode sheet, and the CB value of the second active material layer is greater than or equal to the CB value of the first active material layer. The CB value is the ratio of the lithium insertion capacity of the negative electrode sheet per unit area to the lithium extraction capacity of the positive electrode sheet per unit area. In the embodiment of the present disclosure, by controlling the CB value of the second active material layer to be greater than or equal to the CB value of the first active material layer, the lithium insertion capacity per unit area of ​​the second active material layer is increased, thereby reducing the occurrence of lithium deposition in the second region during the charge and discharge process of the secondary battery.

[0027] In any embodiment, the first active material layer includes a first surface and a second surface, the first surface is close to the negative electrode current collector, and the second surface is away from the negative electrode current collector. The thickness of the first active material layer is recorded as H, then the first active material layer satisfies: the area from the first surface to 0.1H is the first sub-region, the area from the second surface to 0.1H is the second sub-region, and the mass fraction of the silicon-based material in the second sub-region is greater than the mass fraction of the silicon-based material in the first sub-region. In the embodiment of the present disclosure, by controlling the mass fraction of the silicon-based material in the second sub-region to be greater than the mass fraction of the silicon-based material in the first sub-region, that is, the silicon content in the upper surface layer (close to the second surface) is greater than that in the lower surface layer (close to the first surface), so that the silicon content is larger, the silicon-based material expands during the charge and discharge process, so that the specific surface area of ​​the active material layer in the first sub-region of the upper surface is larger, which is beneficial to increase the contact area with the electrolyte, increase the capacity of the negative electrode plate, and improve the charging effect of the negative electrode plate.

[0028] In any embodiment, based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region, the mass fraction of the silicon-based material in the first sub-region is greater than or equal to 0 and less than or equal to 25%. In the embodiments of the present disclosure, by controlling the mass fraction of the silicon-based material in the first sub-region within the above range, the negative electrode plate has a higher capacity and higher stability.

[0029] In any embodiment, based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region, the mass fraction of the silicon-based material in the second sub-region is greater than or equal to 1% and less than or equal to 35%. In the embodiments of the present disclosure, by controlling the mass fraction of the silicon-based material in the second sub-region within the above range, the negative electrode plate has a higher capacity and higher stability.

[0030] In any embodiment, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the second subregion is greater than the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first subregion. By controlling the mass fraction of the first carbon material in the carbon-containing material in the second subregion to be greater than the mass fraction of the first carbon material in the carbon-containing material in the first subregion, the fast charging performance of the negative electrode plate can be improved.

[0031] In any embodiment, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the second sub-region is 20% to 85%, more preferably 30% to 75%. In the embodiment of the present disclosure, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region within the above range, the second sub-region has better fast charging performance and better stability, thereby improving the fast charging performance of the negative electrode plate and reducing the occurrence of lithium plating in the negative electrode plate.

[0032] In any embodiment, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region is 0-75%, more preferably 20-65%. In the embodiment of the present disclosure, by controlling the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region, the capacity of the first sub-region is increased, the stability of the first sub-region is increased, and the stability of the negative electrode sheet is improved.

[0033] In any embodiment, the active material layer includes a base layer and a supplementary layer, the base layer being located in the first region and the second region; the supplementary layer being located on the side of the base layer in the second region facing away from the current collector, the mass fraction of the silicon-based material in the supplementary layer being greater than the mass fraction of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer being greater than the mass fraction of the first carbon material in the base layer. In the disclosed embodiments, the provision of the supplementary layer can increase the content of the silicon-based material and the first carbon material in the second region, thereby improving the problem caused by a thin second active material layer in the second region of the negative electrode during battery manufacturing; thereby improving the overall fast charging capability and cycle stability of the secondary battery.

[0034] In any embodiment, the active material layer includes a base layer and an additional layer, the additional layer integrally extends to cover the side of the base layer away from the current collector and the side of the base layer close to the tab, and the portion of the additional layer covering the side of the base layer close to the tab is located in the second region. In the embodiment of the present disclosure, the active material layer includes a two-layer structure or a layer structure of more than two layers, so that the additional layer covers the end of the base layer close to the tab, and controls the mass fraction of the silicon-based material of the additional layer to be greater than the mass fraction of the silicon-based material of the base layer, and the mass fraction of the first carbon material of the additional layer to be greater than the mass fraction of the first carbon material of the additional layer. The mass fraction of the silicon-based material in the second region can be controlled to be greater than the mass fraction of the silicon-based material in the first region, and the mass fraction of the first carbon material in the second region can be controlled to be greater than the mass fraction of the first carbon material in the first region. In the embodiment of the present disclosure, the active material layer is provided with a two-layer structure, which facilitates the production of the active material layer, and at the same time facilitates the improvement of the unit area capacity and fast charging capability of the second region, and reduces the occurrence of lithium deposition in the second region.

[0035] In any embodiment, the silicon-based material includes any one or more of silicon, a silicon-carbon composite material, silicon monoxide, and a silicon monoxide-carbon composite material.

[0036] In any embodiment, the carbon-containing material includes graphite. The first carbon material includes hard carbon, which refers to carbon materials that are difficult to graphitize at temperatures above 2500°C. Hard carbon includes resin carbon, organic polymer pyrolytic carbon, carbon black, and biomass carbon. The interlayer spacing of hard carbon is greater than the thickness of a single layer of graphite. This large interlayer spacing facilitates the insertion and extraction of lithium ions. Therefore, hard carbon has excellent charge and discharge performance, good rate capability and cycling stability, and rapid charge and discharge performance. Based on the formation method, the first carbon material also includes a portion of artificial graphite. The second carbon material includes soft carbon, which refers to amorphous carbon materials that can be graphitized at temperatures above 2500°C. Depending on the precursor sintering temperature, soft carbon can produce three different crystal structures: amorphous, turbostratic, and graphite. The graphite structure is also commonly found in artificial graphite. The amorphous structure has low crystallinity, large interlayer spacing, and good compatibility with the electrolyte, resulting in excellent low-temperature performance and good rate performance. Based on the formation method, the second carbon material also includes another portion of artificial graphite.

[0037] A second aspect of the present disclosure further provides a method for preparing a secondary battery, comprising:

[0038] A current collector is provided, the current collector comprising a main body and a tab located on one side of the main body, the main body having a first region and a second region, the second region being located between the first region and the tab;

[0039] A slurry containing an active substance is coated on the first and second regions of the current collector to form an active substance layer; the slurry containing the active substance includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material and a second carbon material, and the reversible gram capacity of the first carbon material is less than the reversible gram capacity of the second carbon material; the active substance layer includes a first active substance layer and a second active substance layer, the first active substance layer is located in the first region, and the second active substance layer is located in the second region, so that the mass fraction of the silicon-based material in the second active substance layer is greater than the mass fraction of the silicon-based material in the first active substance layer, and the mass fraction of the first carbon material in the second active substance layer is greater than the mass fraction of the first carbon material in the first active substance layer.

[0040] The embodiments of the present disclosure can form the secondary battery of the first aspect, and thus have at least the same advantages as the secondary battery of the first aspect.

[0041] In any embodiment, coating a slurry containing an active material on the first region and the second region of the current collector to form an active material layer includes:

[0042] Coating a base slurry on the current collector to form a base layer, wherein the base layer is located in the first region and the second region;

[0043] A supplementary slurry is applied to the side of the base layer in the second region facing away from the current collector to form a supplementary layer. The mass fraction of the silicon-based material in the supplementary layer is greater than the mass fraction of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than the mass fraction of the first carbon material in the base layer. Providing the supplementary layer can increase the content of the silicon-based material and the first carbon material in the second region.

[0044] In any embodiment, coating a slurry containing an active material on the first region and the second region of the current collector to form an active material layer includes:

[0045] Coating a base slurry on the current collector to form a base layer, wherein the base layer is located in the first region and the second region;

[0046] An additional slurry is coated on the side of the base layer away from the current collector to form an additional layer, and the additional layer covers the side of the base layer close to the pole ear; wherein the portion of the additional layer covering the side of the base layer close to the pole ear is in the second region, the mass fraction of the silicon-based material in the additional slurry is greater than the mass fraction of the silicon-based material in the basic slurry, and the mass fraction of the first carbon material in the additional slurry to the carbon-containing material is greater than the mass fraction of the first carbon material in the basic slurry to the carbon-containing material.

[0047] In the embodiment of the present disclosure, by adopting a coating method of two or more layers, the mass fraction of the silicon-based material and the mass fraction of the first carbon material in the base slurry and the additional slurry can be controlled. The additional slurry is made to cover the end of the base layer close to the tab side, and the additional slurry is made to be located in the second region, so that the additional slurry forms an additional layer, thereby controlling the difference between the content of the silicon-based material and the second carbon material in the second region per unit area and the content of the silicon-based material and the second carbon material per unit area in the first region, thereby improving the occurrence of lithium deposition caused by the thin thickness of the second region due to the manufacturing process.

[0048] In any embodiment, after the additional slurry is applied to the side of the base layer facing away from the current collector to form the additional layer, the method further includes applying a supplementary slurry to the side of the additional layer in the second region facing away from the current collector to form a supplementary layer. By providing the supplementary layer, the content of the silicon-based material and the first carbon material in the second region can be increased.

[0049] The third aspect of the present disclosure further provides an electrical device comprising the secondary battery of the first aspect and / or the secondary battery prepared by the method of the second aspect. Since the electrical device of the present disclosure comprises the secondary battery provided by the present disclosure, it has at least the same advantages as the secondary battery. The embodiments of the present disclosure include the secondary battery of the first aspect or the secondary battery of the second aspect, so that the electrical device of the present disclosure has at least the advantages of the secondary battery of the first aspect and / or the advantages of the secondary battery prepared by the method of the second aspect.

[0050] The above description is only an overview of the technical solution of the present disclosure. In order to more clearly understand the technical means of the present disclosure, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present disclosure more obvious and easy to understand, the specific implementation methods of the present disclosure are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG1 is a schematic structural diagram of an embodiment of a related negative electrode plate.

[0052] FIG2 is a schematic structural diagram of an embodiment of a current collector disclosed herein.

[0053] FIG3 a is a schematic structural diagram of an embodiment of a negative electrode plate disclosed herein.

[0054] FIG3 b is a schematic structural diagram of another embodiment of the negative electrode plate disclosed in the present invention.

[0055] FIG4 is a schematic structural diagram of an embodiment of a secondary battery disclosed herein.

[0056] FIG5 is a schematic diagram of the exploded structure of an embodiment of the battery pack disclosed herein.

[0057] FIG6 is a schematic diagram of a partial structure of an embodiment of the vehicle disclosed herein.

[0058] 10. Secondary battery; 11. Cell assembly; 12. End cap; 12a. Electrode terminal; 13. Shell; 20. Case; 21. First part; 22. Second part; 100. Battery pack; 200. Controller; 300. Motor; 1000. Vehicle; 14. Negative electrode sheet; 141. Current collector; 142. Active material layer; 1411. Main body; 1414. Tab; 1412. First region; 1413. Second region; 1421. First active material layer; 1422. Second active material layer; 1423. First surface; 1424. Second surface; 1425. First sub-region; 1426. Second sub-region; 143. Base layer; 144. Additional layer; 146. Supplementary layer. DETAILED DESCRIPTION

[0059] Below, the embodiments of the secondary battery, battery, and electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0060] The "ranges" disclosed in this disclosure are defined in the form of lower limits and upper limits, where 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 manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., 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 contemplated. In addition, if the minimum range values ​​listed are 1 and 2, and if the maximum range values ​​listed are 3, 4, and 5, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this disclosure, unless otherwise specified, the numerical range "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "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 disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0063] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, a method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, a method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b), and (c), or may comprise steps (a), (c), and (b), or may comprise steps (c), (a), and (b), etc.

[0064] Unless otherwise specified, the terms "include" and "comprising" used in this disclosure may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components may be included.

[0065] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0066] As shown in Figure 1, during the electrode production process, a slurry containing active material is generally coated on the current collector 141 and further dried to form the electrode. However, due to the coating process, the active material layer 142 formed near the tab 1414 of the electrode is easily thinner. That is, as shown in the figure, the second active material layer 1422 is thinner than the first active material layer 1421. During the battery charge and discharge process, the charge density of the negative electrode near the tab 1414 is higher, and lithium dendrites are easily formed in this area of ​​the negative electrode, affecting the battery's cycle performance. In addition, improving the rapid charge and discharge performance of secondary batteries is of great significance.

[0067] Based on this, as shown in Figures 2, 3a and 3b, the present disclosure proposes that the first aspect of the present disclosure provides a secondary battery 10 (see Figure 4), including a negative electrode sheet 14, the negative electrode sheet 14 includes a current collector 141 and an active material layer 142 provided on the surface of the current collector 141, the active material layer 142 includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material; the current collector 141 includes a main body 1411 and a tab 1414 located on one side of the main body 1411, the main body 1411 includes a first region 1412 and a second region 1413, the second region 141 3 is located between the first region 1412 and the tab 1414; the active material layer 142 includes a first active material layer 1421 and a second active material layer 1422, the first active material layer 1421 is located in the first region 1412, and the second active material layer 1422 is located in the second region 1413; the mass fraction of the silicon-based material in the second active material layer 1422 is greater than the mass fraction of the silicon-based material in the first active material layer 1421; the mass fraction of the first carbon material in the second active material layer 1422 is greater than the mass fraction of the first carbon material in the first active material layer 1421.

[0068] In the disclosed embodiment, the active material layer 142 of the negative electrode plate 14 includes a silicon-based material and a carbon-containing material. By adding a high-capacity silicon-based material to the carbon-containing material, the capacity of the negative electrode plate 14 can be increased. In the disclosed embodiment, first, by setting the mass fraction of the silicon-based material in the second active material layer 1422 to be greater than the mass fraction of the silicon-based material in the first active layer, the active material layer 142 of the negative electrode plate 14 near the edge of the tab 1414 (the second region 1413) has a higher unit volume capacity than the main region (the first region 1412). This can increase the capacity of the second region 1413 and significantly improve the situation where the capacity per unit area of ​​the second region 1413 is less than that of the first region 1412. Secondly, the expansion coefficient of the silicon-based material is greater than the expansion coefficient of the carbon-containing material. By increasing the mass fraction of the silicon-based material in the second region 1413 to a higher mass fraction than that in the first region 1412, the second active material layer 1422 in the second region 1413 expands more than the first active material layer 1421 in the first region 1412 during the charge and discharge process, thereby increasing the porosity and specific surface area of ​​the second active material layer 1422 in the second region 1413. The contact area between the second active material layer 1422 and the electrolyte is increased, thereby improving the lithium ion transmission capacity, reducing the lithium ion deposition in the second region 1413, and improving the lithium deposition in the second region 1413 of the negative electrode plate 14. Thirdly, since the lithium insertion potential of the silicon-based material is higher, the potential of the plate is higher during charging, which significantly improves the fast charging capability of the negative electrode plate 14. In the embodiment of the present disclosure, the carbon-containing material includes a first carbon material, which is a fast-charging high-kinetic carbon material that can improve the fast charging capability of the second region 1413. In the disclosed embodiments, by controlling the mass fraction of the silicon-based material in the second active material layer 1422 to be greater than the mass fraction of the silicon-based material in the first active material layer 1421, and controlling the mass fraction of the first carbon material in the second active material layer 1422 to be greater than the mass fraction of the first carbon material in the first active material, the capacity of the second region 1413 can be increased, and the charging speed of the second region 1413 can be increased. The secondary battery 10 of the disclosed embodiments can increase the capacity and fast charging capability of the negative electrode plate 14, and improve the lithium deposition in a localized area of ​​the negative electrode plate 14; thereby, the overall fast charging capability and cycling stability of the secondary battery can be improved.

[0069] In some embodiments, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 is greater than 1:1 and less than or equal to 80:1. In the disclosed embodiments, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 within the above range, the difference in capacity per unit area between the second active material layer 1422 and the first active material layer 1421 can be reduced, the formation of lithium dendrites in the second active material layer 1422 can be improved, and the fast charging capability of the second active material layer 1422 can be enhanced. Among them, the ratio of the mass fraction of the base material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 can be 1.1:1, 1.5:1, 1.8:1, 2:1, 5:1, 10:1, 30:1, 50:1, 80:1, etc., or a range consisting of any two of the above values, for example, 1.1:1~2:1, 2:1~50:1, 50:1~80:1, etc.

[0070] In some embodiments, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 is greater than 1:1 and less than or equal to 80:1. In the disclosed embodiments, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 within the above range, the difference in capacity per unit area between the second active material layer 1422 and the first active material layer 1421 can be reduced, the formation of lithium dendrites in the second active material layer 1422 can be improved, and the fast charging capability of the second active material layer 1422 can be enhanced. Among them, the ratio of the mass fraction of the base material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 can be 1.1:1, 1.5:1, 1.8:1, 2:1, 5:1, 10:1, 30:1, 50:1, 80:1, etc., or a range consisting of any two of the above values, for example, 1.1:1~2:1, 2:1~50:1, 50:1~80:1, etc.

[0071] In some embodiments, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 is greater than or equal to 1.3 and less than or equal to 30:1. In the disclosed embodiments, by controlling the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 within the above range, the capacity difference per unit area between the second active material layer 1422 and the first active material layer 1421 can be reduced, thereby improving the localized precipitation of lithium dendrites on the negative electrode sheet 14. This results in a smaller difference in the fast charging capability of the second active material layer 1422 and the first active material layer 1421, resulting in a larger capacity and higher stability for the second active material layer 1422. Among them, the ratio of the mass fraction of the silicon-based material in the second active material layer 1422 to the mass fraction of the silicon-based material in the first active material layer 1421 can be 1.3:1, 2:1, 5:1, 8:1, 10:1, 18:1, 20:1, 30:1, etc., or a range consisting of any two of the above values, for example, 1.3:1~8:1, 8:1~18:1, 18:1~30:1, etc.

[0072] In some embodiments, the mass fraction of the silicon-based material in the first active material layer 1421 is 0.5% to 30%, or alternatively, 1% to 20%. In the disclosed embodiments, by controlling the mass fraction of the silicon-based material in the first active material layer 1421 within the above range, the reversible gram capacity of the first active material layer 1421 of the negative electrode sheet 14 is improved, the energy density of the secondary battery 10 is improved, the stability of the first active material layer 1421 is improved, and the cycle performance of the secondary battery 10 is improved. Among them, the mass fraction of the silicon-based material in the first active material layer 1421 can be 0.5%, 1%, 1.48%, 1.5%, 1.8%, 2%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 25%, 26%, 30%, etc., or a range composed of any two of the above values, for example, 0.5% to 1%, 1% to 1.48%, 1.48% to 8%, 8% to 13%, 13% to 20%, 20% to 30%, etc.

[0073] In some embodiments, the mass fraction of the silicon-based material in the second active material layer 1422 is 1% to 40%. Alternatively, it can be 1.5% to 30%. In the disclosed embodiments, by controlling the mass fraction of the silicon-based material in the second active material layer 1422 and ensuring that the mass fraction of the silicon-based material in the second active material layer 1422 is greater than that in the first active material layer 1421, the reversible capacity of the second active material layer 1422 is improved, the stability of the second active material layer 1422 is improved, and the capacity per unit volume of the second active material layer 1422 in the second region 1413 is greater than the capacity per unit volume of the first active material layer 1421 in the first region 1412, thereby reducing the occurrence of lithium deposition in the second region 1413 of the secondary battery 10. Among them, the mass fraction of the silicon-based material in the second active material layer 1422 can be 1%, 1.48%, 1.5%, 1.8%, 2%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 25%, 26%, 28%, 30%, 31%, 34%, 35%, 38%, 40%, etc., or a range composed of any two of the above values, for example, 1% to 1.5%, 1.5% to 13%, 13% to 20%, 20% to 28%, 28% to 30%, 30% to 40%, etc.

[0074] In some embodiments, the mass fraction of the first carbon material in the second region 1413 to the carbon-containing material is 40% to 100%, optionally 50% to 90%. In the embodiment of the present disclosure, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second region 1413, the content of the first carbon material in the second region 1413 is optimized, so that the second active material layer 1422 in the second region 1413 has better stability and better fast charging performance. Among them, the mass fraction of the first carbon material in the second region 1413 to the carbon-containing material can be 40%, 50%, 55%, 60%, 70%, 80%, 85%, 90%, 98%, 100%, etc., or a range consisting of any two of the above values, for example, 40% to 50%, 50% to 70%, 70% to 90%, 90% to 100%, etc.

[0075] In some embodiments, the mass fraction of the first carbon material in the first region 1412 to the carbon-containing material is 20% to 80%, optionally 30% to 70%. In the embodiment of the present disclosure, by controlling the mass fraction of the first carbon material in the carbon-containing material in the first region 1412, the content of the first carbon material in the first region 1412 is optimized, so that the fast charging performance of the active material per unit area in the first region 1412 and the second region 1413 is relatively small, thereby improving the fast charging capability and stability of the negative electrode plate 14. Among them, the mass fraction of the first carbon material in the first region 1412 to the carbon-containing material can be 20%, 30%, 40%, 50%, 60%, 68%, 70%, 78%, 80%, etc., or a range consisting of any two of the above values, for example, 20% to 30%, 30% to 40%, 40% to 70%, 70% to 80%, etc.

[0076] In some embodiments, the mass fraction of the first carbon material in the second region 1413 in the second active material layer 1422 is 24% to 96%, and optionally 35% to 89%. In the disclosed embodiments, by controlling the mass fraction of the first carbon material in the second region 1413 in the second active material layer 1422 within the above range, the content of the first carbon material in the second region 1413 in the second active material layer 1422 is optimized, resulting in better stability and fast charging performance of the second active material layer 1422 in the second region 1413. Among them, the mass fraction of the first carbon material in the second region 1413 to the second active material layer 1422 can be 24%, 30%, 35%, 40%, 50%, 60%, 68%, 70%, 78%, 80%, 89%, 90%, 96%, etc., or a range consisting of any two of the above values, for example, 24% to 35%, 35% to 60%, 60% to 80%, 80% to 89%, 89% to 96%, etc.

[0077] In some embodiments, the mass fraction of the first carbon material in the first region 1412 in the first active material layer 1421 is 14% to 79%, optionally 24% to 69%. By controlling the mass fraction of the first carbon material in the first region 1412 in the first active material layer 1421 within the above range, the content of the first carbon material in the first region 1412 in the first active material layer 1421 is optimized, thereby improving the stability and fast charging performance of the second active material layer 1422 in the first region 1412. The mass fraction of the first carbon material in the first region 1412 in the first active material layer 1421 can be 14%, 18%, 20%, 24%, 30%, 35%, 40%, 50%, 60%, 69%, 70%, 78%, 79%, etc., or a range consisting of any two of the above values, for example, 14% to 24%, 24% to 60%, 60% to 69%, 69% to 79%, etc.

[0078] In some embodiments, the carbon-containing material includes a second carbon material, and the reversible gram capacity of the first carbon material is less than the reversible gram capacity of the second carbon material. In the disclosed embodiments, the second carbon material is a high-capacity carbon material, and the first carbon material is a fast-charging carbon material. By controlling the content of the first and second carbon materials, the capacity and fast-charging performance of the secondary battery can be coordinated and controlled to a certain extent.

[0079] In some embodiments, the reversible gram capacity of the first carbon material is 320mAh / g to 370mAh / g, optionally 330mAh / g to 360mAh / g. In the embodiment of the present disclosure, the reversible gram capacity of the first carbon material is within the above range, so that the reversible gram capacity of the formed negative electrode plate 14 is large and the stability is good. Among them, the reversible gram capacity of the first carbon material can be 320mAh / g, 330mAh / g, 340mAh / g, 350mAh / g, 355mAh / g, 358mAh / g, 360mAh / g, 365mAh / g, 368mAh / g, 370mAh / g, etc., or a range consisting of any two of the above values, for example, 320mAh / g to 330mAh / g, 330mAh / g to 340mAh / g, 340mAh / g to 350mAh / g, 350mAh / g to 360mAh / g, 360mAh / g to 370mAh / g, etc.

[0080] In some embodiments, the reversible gram capacity of the second carbon material is 340 mAh / g to 390 mAh / g, optionally 350 mAh / g to 380 mAh / g. In the embodiment of the present disclosure, the reversible gram capacity of the second carbon material is within the above range, so that the reversible gram capacity of the formed negative electrode plate 14 is large and the stability is good. Among them, the reversible gram capacity of the second carbon material can be 340 mAh / g, 350 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 378 mAh / g, 380 mAh / g, 390 mAh / g, etc., or a range consisting of any two of the above values, for example, 340 mAh / g to 350 mAh / g, 350 mAh / g to 360 mAh / g, 360 mAh / g to 370 mAh / g, 370 mAh / g to 380 mAh / g, 380 mAh / g to 390 mAh / g, etc.

[0081] In some embodiments, the volume average particle size Dv50 of the first carbon material is smaller than the volume average particle size Dv50 of the second carbon material. In the embodiment of the present disclosure, the volume average particle size Dv50 of the first carbon material is smaller than the volume average particle size Dv50 of the second carbon material. The first carbon material has a larger specific surface area, which makes the channels for lithium ion migration more numerous and the paths shorter during the charge and discharge process, and the rate performance is better, so that the fast charging capability of the first carbon material is greater than the fast charging capability of the second carbon material. The second carbon material has a larger volume average particle size Dv50, a smaller specific surface area, a high compaction density, and a large capacity, so that the reversible gram capacity of the second carbon material is greater than the reversible gram capacity of the first carbon material.

[0082] In some embodiments, the volume average particle size DV50 of the first carbon material is greater than or equal to 1 μm and less than or equal to 15 μm. In the embodiment of the present disclosure, the fast charging performance of the first carbon material is better by controlling the volume average particle size DV50 of the first carbon material within the above range. In the embodiment of the present disclosure, the volume average particle size DV50 of the first carbon material can be 1 μm, 1.8 μm, 2 μm, 5 μm, 7 μm, 8 μm, 10 μm, 13 μm, 14 μm, 14.9 μm, etc., or a range consisting of any two of the above values, for example, 1 μm to 7 μm, 7 μm to 13 μm, 13 μm to 15 μm, etc.

[0083] In some embodiments, the volume average particle size DV50 of the second carbon material is greater than or equal to 7 μm and less than or equal to 22 μm. In the embodiment of the present disclosure, by controlling the volume average particle size DV50 of the first carbon material within the above range, the reversible gram capacity performance of the second carbon material is better. In the embodiment of the present disclosure, the volume average particle size DV50 of the second carbon material can be 7 μm, 8 μm, 9 μm, 10 μm, 13 μm, 14 μm, 15 μm, 18 μm, 20 μm, 21 μm, 21.9 μm, etc., or a range consisting of any two of the above values, for example, 7 μm to 13 μm, 13 μm to 15 μm, 15 μm to 22 μm, etc.

[0084] In some embodiments, the ratio of the area of ​​the second region 1413 to the area of ​​the first region 1412 is (3-20): 100. In the disclosed embodiments, by controlling the area ratio of the second region 1413 to the first region 1412 within the above range, the contents of the silicon-based material and the first carbon material in the first region 1412 and the second region 1413 of the negative electrode plate 14 are appropriate, which can effectively alleviate the lithium deposition in the second region 1413 of the negative electrode plate 14 and increase the reversible gram capacity and stability of the negative electrode plate 14. Among them, the ratio of the area of ​​the second region 1413 to the area of ​​the first region 1412 can be 3:100, 5:100, 8:100, 10:100, 13:100, 15:100, 18:100, 20:100, etc., or a range consisting of any two of the above values, for example, (3~10):100, (10~15):100, (15~20):100, etc.

[0085] In some embodiments, the ratio of the area of ​​the second region 1413 to the area of ​​the first region 1412 is (5-15):100. In the embodiment of the present disclosure, by controlling the area ratio of the second region 1413 to the first region 1412 within the above range, the content of the silicon-based material and the first carbon material in the first region 1412 and the second region 1413 of the negative electrode plate 14 is appropriate, which can effectively alleviate the lithium deposition in the second region 1413 of the negative electrode plate 14, and make the reversible gram capacity of the negative electrode plate 14 higher and the stability higher. Among them, the ratio of the area of ​​the second region 1413 to the area of ​​the first region 1412 can be 5:100, 8:100, 10:100, 13:100, 15:100, or a range consisting of any two of the above values, for example, (5-8):100, (8-13):100, (13-15):100, etc.

[0086] In some embodiments, the secondary battery 10 further includes a positive electrode sheet, and the CB value of the second active material layer 1422 is greater than or equal to the CB value of the first active material layer 1421. The CB value is the ratio of the lithium insertion capacity per unit area of ​​the negative electrode sheet 14 to the lithium extraction capacity per unit area of ​​the positive electrode sheet. In the embodiments of the present disclosure, by controlling the CB value of the second active material layer 1422 to be greater than or equal to the CB value of the first active material layer 1421, the lithium insertion capacity per unit area of ​​the second active material layer 1422 is increased, thereby reducing the occurrence of lithium deposition in the second region 1413 during the charge and discharge process of the secondary battery 10.

[0087] In some embodiments, the first active material layer 1421 includes a first surface 1423 and a second surface 1424, the first surface 1423 is close to the negative electrode current collector 141, and the second surface 1424 is far away from the negative electrode current collector 141. The thickness of the first active material layer 1421 is recorded as H, then the first active material layer 1421 satisfies: the area from the first surface 1423 to 0.1H is the first sub-region 1425, the area from the second surface 1424 to 0.1H is the second sub-region 1426, and the mass fraction of the silicon-based material in the second sub-region 1426 is greater than the mass fraction of the silicon-based material in the first sub-region 1425. In the embodiment of the present disclosure, by controlling the mass fraction of the silicon-based material in the second sub-region 1426 to be greater than the mass fraction of the silicon-based material in the first sub-region 1425, that is, the silicon content in the upper surface layer (close to the second surface 1424) is greater than that in the lower surface layer (close to the first surface 1423), the silicon content is larger, and the silicon-based material expands during the charging and discharging process, so that the specific surface area of ​​the active material layer 142 in the first sub-region 1425 of the upper surface is larger, which is beneficial to increase the contact area with the electrolyte, increase the capacity of the negative electrode plate 14, and improve the charging effect of the negative electrode plate 14.

[0088] In some embodiments, based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region 1425, the mass fraction of the silicon-based material in the first sub-region 1425 is greater than or equal to 0 and less than or equal to 25%. In the disclosed embodiments, by controlling the mass fraction of the silicon-based material in the first sub-region 1425 within the above range, the negative electrode plate 14 has a higher capacity and higher stability. Based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region 1425, the mass fraction of the silicon-based material in the first sub-region 1425 can be 0, 1%, 2%, 3%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 24%, 25%, etc., or a range consisting of any two of the above values, for example, 0-8%, 8%-13%, 13%-20%, or 20%-25%.

[0089] In some embodiments, based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region 1426, the mass fraction of the silicon-based material in the second sub-region 1426 is greater than or equal to 1% and less than or equal to 35%. In the disclosed embodiments, by controlling the mass fraction of the silicon-based material in the second sub-region 1426 within the above range, the negative electrode plate 14 has a higher capacity and higher stability. Based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region 1426, the mass fraction of the silicon-based material in the second sub-region 1426 can be 1%, 2%, 3%, 5%, 8%, 10%, 12%, 13%, 15%, 18%, 20%, 25%, 30%, 31.03%, 35%, or a range consisting of any two of the above values, for example, 0.99% to 10%, 10% to 13%, 13% to 31.03%, or 31.03% to 35%.

[0090] In some embodiments, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the second sub-region 1426 is greater than the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region 1425. By controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region 1426 to be greater than the mass fraction of the first carbon material in the carbon-containing material in the first sub-region 1425, the fast charging performance of the negative electrode sheet 14 can be improved.

[0091] In some embodiments, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the second sub-region 1426 is 20% to 85%, more preferably 30% to 75%. In the embodiments of the present disclosure, by controlling the mass fraction of the first carbon material in the carbon-containing material in the second sub-region 1426 within the above range, the second sub-region 1426 has better fast charging performance and better stability, thereby improving the fast charging performance of the negative electrode plate 14 and reducing the occurrence of lithium plating in the negative electrode plate 14. The mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the second sub-region 1426 is 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 83%, 85%, or the like, or a range consisting of any two of the above values, for example, 20% to 30%, 30% to 40%, 40% to 70%, 70% to 75%, 75% to 85%, or the like.

[0092] In some embodiments, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region 1425 is 0-75%, more preferably 20-65%. In the disclosed embodiments, by controlling the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region 1425, the capacity and stability of the first sub-region 1425 are increased, thereby improving the stability of the negative electrode sheet 14. The mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region 1425 is 0, 10%, 20%, 30%, 40%, 50%, 55%, 58%, 60%, 65%, 68%, 70%, 75%, etc., or a range consisting of any two of the above values, for example, 0-20%, 20%-40%, 40%-65%, 65%-75%, etc.

[0093] In any embodiment, the active material layer 142 includes a base layer 143 and a supplementary layer 146. The base layer 143 is located in the first region 1412 and the second region 1413. The supplementary layer 146 is disposed on the side of the base layer 143 in the second region 1413 facing away from the current collector 141. The mass fraction of the silicon-based material in the supplementary layer 146 is greater than the mass fraction of the silicon-based material in the base layer 143, and the mass fraction of the first carbon material in the supplementary layer 146 is greater than the mass fraction of the first carbon material in the base layer 143. In the disclosed embodiment, the provision of the supplementary layer 146 can increase the content of the silicon-based material and the first carbon material in the second region 1413, thereby improving the problem caused by the thin second active material layer 142 in the second region 1413 of the negative electrode during battery manufacturing. This can thereby improve the overall fast charging capability and cycle stability of the secondary battery.

[0094] In some embodiments, the active material layer 142 includes a base layer 143 and an additional layer 144. The additional layer 144 integrally extends to cover the side of the base layer 143 facing away from the current collector 141 and the side of the base layer 143 near the tab 1414. The portion of the additional layer 144 covering the side of the base layer 143 near the tab 1414 is located in the second region 1413. In the embodiment of the present disclosure, the active material layer 142 includes a two-layer structure or a structure of more than two layers, so that the additional layer 144 covers the end of the base layer 143 near the tab 1414. The mass fraction of the silicon-based material in the additional layer 144 is controlled to be greater than the mass fraction of the silicon-based material in the base layer 143, and the mass fraction of the first carbon material in the additional layer 144 is controlled to be greater than the mass fraction of the first carbon material in the additional layer 144. This can control the mass fraction of the silicon-based material in the second region 1413 to be greater than the mass fraction of the silicon-based material in the first region 1412, and the mass fraction of the first carbon material in the second region 1413 to be greater than the mass fraction of the first carbon material in the first region 1412. In the embodiment of the present disclosure, the active material layer 142 is provided with a two-layer structure, which facilitates the production of the active material layer 142 , and at the same time facilitates improving the unit area capacity and fast charging capability of the second region 1413 , thereby reducing the occurrence of lithium deposition in the second region 1413 .

[0095] In some embodiments, the active material layer 142 includes a base layer 143, an additional layer 144 and a supplementary layer 146, which have the above-mentioned effects and will not be described in detail. In addition, by setting the base layer 143, the additional layer 144 and the supplementary layer 146 at the same time, it is convenient to regulate the process parameters of the base layer 143, the additional layer 144 and the supplementary layer 146, which facilitates production.

[0096] In some embodiments, the silicon-based material includes any one or more of silicon, a silicon-carbon composite material, silicon monoxide, and a silicon monoxide-carbon composite material.

[0097] In some embodiments, the carbon-containing material includes graphite. The first carbon material includes hard carbon, which refers to carbon materials that are difficult to graphitize at temperatures above 2500°C. Hard carbon includes resin carbon, organic polymer pyrolytic carbon, carbon black, biomass carbon, etc. The interlayer spacing of hard carbon is greater than the thickness of a single layer of graphite. This large interlayer spacing facilitates the insertion and extraction of lithium ions. Therefore, hard carbon has excellent charge and discharge performance, good rate capability and cycling stability, and rapid charge and discharge performance. Based on the formation method, the first carbon material also includes a portion of artificial graphite. The second carbon material includes soft carbon, which refers to amorphous carbon materials that can be graphitized at temperatures above 2500°C. Depending on the precursor sintering temperature, soft carbon will produce three different crystal structures: amorphous structure, turbostratic disordered structure, and graphite structure. Graphite structure is also the common artificial graphite. The amorphous structure has low crystallinity, large interlayer spacing, and good compatibility with the electrolyte, resulting in excellent low-temperature performance and good rate performance. Based on the formation method, the second carbon material also includes another portion of artificial graphite.

[0098] A second aspect of the present disclosure further provides a method for preparing a secondary battery 10, comprising:

[0099] A current collector 141 is provided. The current collector 141 includes a main body 1411 and a tab 1414 located on one side of the main body 1411 . The main body 1411 has a first region 1412 and a second region 1413 . The second region 1413 is located between the first region 1412 and the tab 1414 .

[0100] A slurry containing an active substance is coated on the first region 1412 and the second region 1413 of the current collector 141 to form an active substance layer 142; the slurry containing the active substance includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material and a second carbon material, and the reversible gram capacity of the first carbon material is less than the reversible gram capacity of the second carbon material; the active substance layer 142 includes a first active substance layer 1421 and a second active substance layer 1422, the first active substance layer 1421 is located in the first region 1412, and the second active substance layer 1422 is located in the second region 1413, so that the mass fraction of the silicon-based material in the second active substance layer 1422 is greater than the mass fraction of the silicon-based material in the first active substance layer 1421, and the mass fraction of the first carbon material in the second active substance layer 1422 is greater than the mass fraction of the first carbon material in the first active substance layer 1421.

[0101] The embodiment of the present disclosure can form the secondary battery 10 of the first aspect, and thus has at least the same advantages as the secondary battery 10 of the first aspect.

[0102] In some embodiments, coating the first region 1412 and the second region 1413 of the current collector 141 with a slurry containing an active material to form the active material layer 142 includes:

[0103] A base slurry is coated on the current collector 141 to form a base layer 143 , and the base layer 143 is located in the first region 1412 and the second region 1413 ;

[0104] A supplementary slurry is applied to the side of the base layer 143 in the second region 1413 facing away from the current collector 141 to form a supplementary layer 146. The mass fraction of the silicon-based material in the supplementary layer 146 is greater than the mass fraction of the silicon-based material in the base layer 143, and the mass fraction of the first carbon material in the supplementary layer 146 is greater than the mass fraction of the first carbon material in the base layer 143. By providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased. By providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased.

[0105] In some embodiments, coating the first region 1412 and the second region 1413 of the current collector 141 with a slurry containing an active material to form the active material layer 142 includes:

[0106] A base slurry is coated on the current collector 141 to form a base layer 143 , and the base layer 143 is located in the first region 1412 and the second region 1413 ;

[0107] An additional slurry is coated on the side of the base layer 143 facing away from the current collector 141 to form an additional layer 144, and the additional layer 144 covers the side of the base layer 143 close to the pole tab 1414; wherein, the portion of the additional layer 144 covering the side of the base layer 143 close to the pole tab 1414 is in the second region 1413, the mass fraction of the silicon-based material in the additional slurry is greater than the mass fraction of the silicon-based material in the basic slurry, and the mass fraction of the first carbon material in the additional slurry to the carbon-containing material is greater than the mass fraction of the first carbon material in the basic slurry to the carbon-containing material.

[0108] In some embodiments, after forming the additional layer by coating an additional slurry on the side of the base layer 143 facing away from the current collector 141, a supplementary slurry is further coated on the side of the additional layer in the second region 1413 facing away from the current collector 141 to form a supplementary layer 146. By providing the supplementary layer 146, the content of the silicon-based material and the first carbon material in the second region 1413 can be increased.

[0109] In the embodiment of the present disclosure, by adopting a coating method of two or more layers, the mass fraction of the silicon-based material and the mass fraction of the first carbon material in the base slurry and the additional slurry can be controlled. The additional slurry is made to cover the end of the base layer 143 close to the tab 1414, and the additional slurry is made to be located in the second region 1413, so that the additional slurry forms an additional layer 144, thereby controlling the difference between the content of the silicon-based material and the second carbon material in the second region 1413 per unit area and the content of the silicon-based material and the second carbon material per unit area of ​​the first region 1412, thereby improving the occurrence of lithium deposition caused by the thin thickness of the second region 1413 due to the manufacturing process.

[0110] The third aspect of the present disclosure further provides an electrical device, comprising the secondary battery 10 of the first aspect and / or the secondary battery 10 prepared by the method of the second aspect. Because the electrical device of the present disclosure comprises the secondary battery 10 provided by the present disclosure, it has at least the same advantages as the secondary battery 10. The embodiments of the present disclosure include the secondary battery 10 of the first aspect or the secondary battery 10 of the second aspect, so that the electrical device of the present disclosure has at least the advantages of the secondary battery 10 of the first aspect and / or the advantages of the secondary battery 10 prepared by the method of the second aspect.

[0111] In addition, the secondary battery 10 , the battery pack 100 (see FIG. 5 ), and the electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0112] In the embodiment of the present disclosure, the secondary battery 10 also includes an electrolyte and a separator. The separator is provided between the positive electrode and the negative electrode 14, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. During the battery charge and discharge process, the active ions Li + The electrolyte is inserted and removed back and forth between the positive electrode sheet and the negative electrode sheet 14 , and plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet 14 .

[0113] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0114] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0115] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector 141. For example, aluminum foil may be used as the metal foil. The composite current collector 141 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 141 may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, when the secondary battery 10 is a lithium-ion battery, the positive electrode active material may be a positive electrode active material for lithium-ion batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as 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 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0117] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one 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.

[0118] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] 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 (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0120] The negative electrode current collector 141 has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector 141. The active material layer 142 of the negative electrode sheet 14 is disposed on at least one surface of the negative electrode current collector 141.

[0121] In some embodiments, the current collector 141 of the negative electrode plate 14 may be a metal foil or a composite current collector 141. For example, copper foil may be used as the metal foil. The composite current collector 141 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 141 may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments, the active material layer 142 may further include a binder. The binder may be selected from at least one 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 active material layer 142 may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the active material layer 142 may further include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0125] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet 14. The present disclosure has no specific limitation on the type of electrolyte, and the electrolyte can be selected according to needs.

[0126] In some embodiments, the electrolyte solution includes an electrolyte salt and a solvent.

[0127] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0128] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0129] 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.

[0130] In some embodiments, the secondary battery 10 further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be used.

[0131] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0132] In some embodiments, the positive electrode sheet, the negative electrode sheet 14 and the separator can be made into a battery cell assembly through a winding process or a lamination process.

[0133] In some embodiments, as shown in FIG4 , the secondary battery 10 may include an outer packaging. The outer packaging may be used to encapsulate the battery cell assembly 11 and the electrolyte. The outer packaging includes an end cap 12 , a housing 13 , and other functional components.

[0134] The end cap 12 refers to a component that covers the opening of the shell 13 to isolate the internal environment of the secondary battery 10 from the external environment. Without limitation, the shape of the end cap 12 can be adapted to the shape of the shell 13 to match the shell 13. Optionally, the end cap 12 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 12 is not easily deformed when squeezed or collided, so that the secondary battery 10 can have a higher structural strength and improved safety performance. Functional components such as electrode terminals 12a can be provided on the end cap 12. The electrode terminal 12a can be used to electrically connect to the battery cell assembly 11 for outputting or inputting electrical energy of the secondary battery 10. In some embodiments, the end cap 12 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of the secondary battery 10 reaches a threshold. The material of the end cap 12 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present disclosure do not impose any special restrictions on this. In some embodiments, an insulating member (not shown) may be provided inside the end cap 12 to isolate the electrical connection components in the housing 13 from the end cap 12 to reduce the risk of short circuits. For example, the insulating member may be made of plastic, rubber, or the like.

[0135] The shell 13 is a component used to cooperate with the end cap 12 to form the internal environment of the secondary battery 10, wherein the formed internal environment can be used to accommodate the battery cell assembly 11, electrolyte and other components. The shell 13 and the end cap 12 can be independent components. An opening can be set on the shell 13, and the internal environment of the secondary battery 10 is formed by covering the opening with the end cap 12. Without limitation, the end cap 12 and the shell 13 can also be integrated. Specifically, the end cap 12 and the shell 13 can form a common connection surface before other components are inserted into the shell. When the interior of the shell 13 needs to be encapsulated, the end cap 12 is then covered with the shell 13. The shell 13 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 13 can be determined according to the specific shape and size of the battery cell assembly 11. The material of the shell 13 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present disclosure do not impose any special restrictions on this.

[0136] The housing 13 may contain one or more battery cell assemblies 11. The portions of the positive and negative electrode sheets that do not contain active material each form a tab 1414. The positive and negative tabs may be located together at one end of the main body or separately at opposite ends. During the battery's charge and discharge processes, the positive and negative active materials react with the electrolyte, and the tabs 1414 connect to the electrode terminals to form a current circuit.

[0137] Referring to Figure 5 , the battery pack 100 includes a housing 20 and a secondary battery 10, with the secondary battery 10 housed within the housing 20. The housing 20 is used to provide a storage space for the secondary battery 10 and can have various structures. In some embodiments, the housing 20 can include a first portion 21 and a second portion 22, which overlap each other and together define a storage space for the secondary battery 10. The second portion 22 can be a hollow structure with one end open, and the first portion 21 can be a plate-like structure, with the first portion 21 overlapping the open side of the second portion 22, so that the first portion 21 and the second portion 22 together define a storage space. Alternatively, the first portion 21 and the second portion 22 can each be a hollow structure with one end open, with the open side of the first portion 21 overlapping the open side of the second portion 22. Of course, the housing 20 formed by the first portion 21 and the second portion 22 can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0138] The battery pack 100 may contain multiple secondary batteries 10, which may be connected in series, in parallel, or in a hybrid configuration. A hybrid configuration refers to a combination of series and parallel connections. Multiple secondary batteries 10 may be directly connected in series, in parallel, or in a hybrid configuration, and then the entire assembly of multiple secondary batteries 10 is housed within the housing 20. Alternatively, the battery pack 100 may be constructed by first connecting multiple secondary batteries 10 in series, in parallel, or in a hybrid configuration to form a battery module, which is then connected in series, in parallel, or in a hybrid configuration to form a single assembly, which is then housed within the housing 20. The battery pack 100 may also include other structures, such as a busbar assembly for electrically connecting the multiple secondary batteries 10.

[0139] The battery pack 100 in the embodiment of the present disclosure includes a lithium-ion battery as the secondary battery 10. In other embodiments, the battery pack 100 may further include any one or more of a lithium-sulfur battery, a sodium-ion battery, and a magnesium-ion battery, but is not limited thereto. The secondary battery 10 may be cylindrical, flat, rectangular, or in other shapes.

[0140] In addition, the present disclosure further provides an electrical device, which includes at least one of the secondary battery 10 and / or battery pack 100 provided in the present disclosure. The secondary battery 10 or battery pack 100 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0141] As an electric device, the secondary battery 10 and / or the battery pack 100 may be selected according to its usage requirements.

[0142] FIG6 shows an example of an electric device. The electric device is a vehicle such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. A structural schematic diagram of a vehicle 1000 is specifically provided. A secondary battery 10 (see FIG4 ) or a battery pack 100 is provided inside the vehicle 1000. The secondary battery 10 or the battery pack 100 can be provided at the bottom, head, or tail of the vehicle 1000. The secondary battery 10 or the battery pack 100 can be used to power the vehicle 1000. For example, the secondary battery 10 or the battery pack 100 can be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the secondary battery 10 or the battery pack 100 to power the motor 300, for example, for starting, navigating, and operating power requirements of the vehicle 1000.

[0143] In some embodiments of the present disclosure, the secondary battery 10 or the battery pack 100 can serve not only as the operating power source of the vehicle 1000, but also as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0144] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0145] Example 1

[0146] 1) Preparation method of positive electrode sheet:

[0147] Lithium iron phosphate, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) in a weight ratio of 90:10:3:1.5 were mixed with N,N-dimethylpyrrolidone (NMP) and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of aluminum foil. The electrode was cold pressed and sliced ​​to produce a positive electrode.

[0148] Among them, lithium iron phosphate is used as the positive electrode active material, conductive carbon black (Super~P) is used as the conductive agent, polyvinylidene fluoride (PVDF) is used as the binder, and N,N-dimethylpyrrolidone (NMP) is used as the slurry solvent.

[0149] 2) Preparation method of negative electrode sheet:

[0150] In the embodiment of the present disclosure, hard carbon (first carbon material), graphite (second carbon material), nano-silicon, conductive carbon black (Super-P), carbon nanotubes, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed with deionized water in a weight ratio of 54.04:13.51:28.95:0.5:0.1:1.1:1.8, and stirred evenly to obtain a base slurry for coating the negative electrode sheet. The viscosity can be adjusted by deionized water during the stirring process. Hard carbon (first carbon material), graphite (second carbon material), nano-silicon, conductive carbon black (Super-P), carbon nanotubes, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed with deionized water in a weight ratio of 54.04:13.51:28.95:0.5:0.1:1.1:1.8, and stirred evenly to obtain an additional slurry for coating the negative electrode sheet. Hard carbon (first carbon material), graphite (second carbon material), nano-silicon, conductive carbon black (Super~P), carbon nanotubes, sodium carboxymethyl cellulose (CMC~Na), and styrene-butadiene rubber (SBR) are mixed with deionized water in a weight ratio of 23.16:34.74:38.6:0.5:0.1:1.1:1.8, and stirred evenly to obtain a supplementary slurry for coating the negative electrode sheet. Then, the base slurry is coated on both sides of the negative electrode current collector with a certain width, and after drying, a base layer is formed. Then, an additional slurry is coated on the base layer to form an additional layer, and the additional layer covers the surface of the base layer away from the current collector to form a first active material layer; the supplementary slurry is coated on the additional layer in the second area, and then the negative electrode sheet is obtained by cold pressing and slicing. In the embodiment of the present disclosure, the negative electrode current collector is a 6μm thick copper foil. The embodiment of the present disclosure does not limit the material and thickness of the negative electrode current collector.

[0151] In the embodiment of the present disclosure, the volume average particle size DV50 of the hard carbon is 14 μm, and the reversible gram capacity of the hard carbon is 350 mAh / g. The volume average particle size DV50 of the graphite is 20 μm, and the reversible gram capacity of the graphite is 360 mAh / g.

[0152] 3) Preparation method of secondary battery:

[0153] The positive electrode sheet, the separator and the negative electrode sheet are wound into a battery cell assembly, and a secondary battery is obtained by welding the tabs, packaging in an aluminum shell, injecting liquid, packaging and vacuum forming. The width of the battery cell assembly is 148mm, the thickness is 28mm, the height is 98mm, and the capacity is 60Ah. Among them, the injected electrolyte is a 1mol / L LiPF6 solution, the solvent of the LiPF6 solution is ethylene carbonate (EC) and dimethyl carbonate (DMC), and the volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) is 1:2. In the embodiment of the present disclosure, the separator adopts 7μm thick polyethylene (PE). In the embodiment of the present disclosure, the energy density of the negative electrode active material of the negative electrode sheet is 1.07 times the energy density of the positive electrode active material of the positive electrode sheet.

[0154] The secondary battery obtained in the embodiment of the present disclosure includes a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a current collector and an active material layer disposed on the surface of the current collector. The active material layer includes a silicon-based material and a carbon-containing material. The carbon-containing material includes a first carbon material and a second carbon material. The reversible gram capacity of the first carbon material is less than the reversible gram capacity of the second carbon material. The current collector includes a main body and a tab located on one side of the main body. The main body includes a first region and a second region. The second region is located between the first region and the tab. In the embodiment of the present disclosure, the area ratio of the second region to the first region is 10:100. In the embodiment of the present disclosure, the active material layer includes a first active material layer and a second active material layer. The first active material layer is located in the first region and the second active material layer is located in the second region. The mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer. The mass fraction of the first carbon material (hard carbon) in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer. The CB value of the first active material layer is 1.07.

[0155] Comparative Example 1

[0156] The difference between the secondary battery and the preparation method of the secondary battery in this comparative example and Example 1 is that in the preparation method of the negative electrode sheet, the negative electrode active material, the conductive agent, the thickener and the binder are mixed with deionized water to form a slurry, the slurry is coated on both sides of the negative electrode collector with a certain width, and the negative electrode sheet is obtained by cold pressing and slicing. The obtained secondary battery negative electrode includes a positive electrode sheet and a negative electrode sheet, the negative electrode sheet includes a current collector and an active material layer arranged on the surface of the current collector, the active material layer includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material (hard carbon) and a second carbon material (soft carbon), the current collector includes a main body and a tab located on one side of the main body, the main body includes a first region and a second region, the second region is located between the first region and the tab; the active material layer includes a first active material layer and a second active material layer, the first active material layer is located in the first region, and the second active material layer is located in the second region; the mass fraction of the silicon-based material in the second active material layer is equal to the mass fraction of the silicon-based material in the first active material layer; the mass fraction of the first carbon material in the second active material layer is equal to the mass fraction of the first carbon material in the first active material layer. The CB value of the first active material layer is 1.07. The rest is the same as in Example 1 and will not be repeated here.

[0157] Comparative Example 2

[0158] The difference from Comparative Example 1 is that the negative electrode active material includes a silicon-based material and a carbonaceous material, the carbonaceous material includes a second carbon material (soft carbon) and does not contain a first carbon material (hard carbon). Other details are the same as in Comparative Example 1 and will not be repeated here.

[0159] Comparative Example 3

[0160] The difference from Comparative Example 1 is that the negative electrode active material includes a silicon-based material and a carbon-containing material, the carbon-containing material includes a first carbon material and does not contain a second carbon material. Other details are the same as in Comparative Example 1 and will not be repeated here.

[0161] The secondary batteries of Examples 1 to 14 and Comparative Examples 1 to 3 were subjected to relevant tests:

[0162] 1) Battery performance test. Specifically, the secondary battery cycle capacity retention rate test. The specific test conditions are:

[0163] At 25°C, charge at a constant current of 1 / 3C (nominal capacity) to a termination voltage of 3.8V, then charge at a constant voltage of 0.05C. 标 , let it sit for 5 minutes, then 1 / 3C 标Discharge to a discharge cutoff voltage of 2.0V, obtaining the discharge energy E and capacity C. The resulting capacity is recorded as the initial capacity C0. Repeat the above steps for the same secondary battery, and simultaneously record the battery's discharge capacity Cn after the nth cycle. The battery capacity retention rate after each cycle, Pn, = Cn / C0 × 100%. In this test, n = 1 for the first cycle, n = 2 for the second cycle, and n = 1500 for the 1500th cycle. The corresponding battery capacity retention rate data in Table 1 are measured after 1500 cycles under the above test conditions.

[0164] 2) Lithium deposition test.

[0165] At 25°C, charge at a constant current of 1 / 3C (nominal capacity) to a termination voltage of 3.8V, then charge at a constant voltage of 0.05C. 标 , let it sit for 5 minutes, then 1 / 3C 标 Discharge to a discharge cutoff voltage of 2.0 V to obtain the discharge energy E and capacity C, which is recorded as the initial capacity C0. Repeat the above steps for the same secondary battery. After cycling for 1500 cls, charge the battery to 3.8 V and disassemble the battery to observe whether there is lithium deposition on the surface of the negative electrode.

[0166] 3) Capacity test.

[0167] At 25°C, charge at a constant current of 1 / 3C (nominal capacity) to a termination voltage of 3.8V, then charge at a constant voltage of 0.05C. 标 , let it sit for 5 minutes, then 1 / 3C 标 Discharge to the discharge cut-off voltage of 2.0V, and obtain the discharge energy E and capacity C.

[0168] 4) Charging time test.

[0169] The full battery is charged at 35°C with a step-by-step decreasing current or a continuous decreasing current. The battery state of charge (SOC) range is 10% to 80% SOC. The boundary condition is that the anode potential is greater than 0mV. The equipment is a Xinwei charger and discharger. The specific test process is as follows: 1. During the battery preparation process, a lithium-plated copper wire is placed on the outside of the wound bare battery cell and wrapped with an isolation film to prevent overlap with the electrode or shell. The copper wire is led out to the outside of the battery cell as the third electrode. 2. The prepared battery is first tested for discharge capacity using the following capacity test method; 3. A voltage acquisition device is used to record the voltage between the third electrode and the negative electrode, i.e., the "anode potential." 4. The battery's initial SOC is adjusted to 10%, and then the battery is charged at an initial charge rate of 3C. When the anode potential drops to 0mV, the device automatically reduces the charge rate to 3-xC. Charging continues until the anode potential drops to 0mV. The device further reduces the charge rate to 3-2*xC, and so on. This method is called step-down current charging until the battery is charged to 80% SOC. When x is sufficiently small, such as 0.05C, it can be equivalent to continuous current charging. Finally, the total time from 10% SOC to 80% SOC is recorded.

[0170] 5) Volume average particle size Dv50 test.

[0171] Equipment model: Malvern 3000 (MasterSizer 3000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009, specific test process: Take an appropriate amount of sample to be tested (the sample concentration is sufficient to ensure 8% to 12% obscuration), add 20ml of deionized water, and simultaneously operate the external ultraviolet (53KHz / 120W) for 5 minutes to ensure that the sample is completely dispersed. Then, the sample is measured according to GB / T19077-2016 / ISO 13320:2009 standard.

[0172] The process parameters and performance of each embodiment and comparative example are shown in Table 1 and Table 2 below.

[0173] Table 1: Parameters and performance test results of Examples 1 to 14 and Comparative Examples 1 to 3.

[0174] Note: X2 represents the mass fraction of the silicon-based material in the second active material layer; X1 represents the mass fraction of the silicon-based material in the first active material layer; B represents the ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer; C2 represents the mass fraction of the first carbon material in the second region in the second active material layer; C1 represents the mass fraction of the first carbon material in the first region in the first active material layer; M2 represents the mass fraction of the first carbon material in the second region in the carbon-containing material; M1 represents the mass fraction of the first carbon material in the first region in the carbon-containing material; the first CB value represents the CB value of the second active material layer.

[0175] Table 2 Part of the process parameters of Examples 7 to 14 and Comparative Examples 1 to 3.

[0176] Note: X3 represents the mass fraction of silicon-based materials in the first sub-region based on the total mass of silicon-based materials and carbon-containing materials in the first sub-region; X4 represents the mass fraction of silicon-based materials in the second sub-region based on the total mass of silicon-based materials and carbon-containing materials in the second sub-region; N2 represents the mass fraction of the first carbon material to the carbon-containing material per unit area in the second sub-region; N1 represents the mass fraction of the first carbon material to the carbon-containing material per unit area in the first sub-region.

[0177] As can be seen from the test results in Table 1, compared with the negative electrode sheets of Comparative Examples 1 to 3, the second active material layer in the second region is thinner during the coating process, causing the problem of lithium plating. In Examples 1 to 14 of the present disclosure, by setting the content of the silicon-based material and the content of the first carbon material in the second active material layer to be greater than the content of the silicon-based material and the content of the first carbon material in the first active material layer, respectively, the negative electrode sheet of the secondary battery has no lithium plating after cycling for 1500cls, and compared with Comparative Examples 1 to 3, the total time for charging from 10% SOC to 80% SOC of Examples 1 to 14 of the present disclosure is 13min to 19.5min, which is improved compared with Comparative Examples 1 to 3, indicating that the secondary batteries of Examples 1 to 14 of the present disclosure can improve the fast charging capability. The cycle capacity retention rate of the secondary batteries of Examples 1 to 14 of the present disclosure is 80% to 90% after cycling for 1500cls, which is improved compared with Comparative Examples 1 to 3.

[0178] As shown in Tables 1 and 2, in Examples 7-14 of the present disclosure, by controlling the mass fraction of the silicon-based material in the first subregion to be greater than the mass fraction of the silicon-based material in the second subregion, and controlling the mass fraction of the first carbon material in the first subregion to be greater than the mass fraction of the first carbon material in the carbon-containing material in the second subregion, the rapid charging capability of the secondary battery can be improved, such that the total time for charging from 10% SOC to 80% SOC is 13 minutes to 18 minutes. This can also improve the cycling performance of the secondary battery.

[0179] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a current collector and an active material layer disposed on a surface of the current collector, the active material layer comprising a silicon-based material and a carbon-containing material, the carbon-containing material comprising a first carbon material; The current collector includes a main body and a tab located on one side of the main body, the main body includes a first region and a second region, and the second region is located between the first region and the tab; The active material layer includes a first active material layer and a second active material layer, the first active material layer is located in the first region, and the second active material layer is located in the second region; The mass fraction of the silicon-based material in the second active material layer is greater than the mass fraction of the silicon-based material in the first active material layer; The mass fraction of the first carbon material in the second active material layer is greater than the mass fraction of the first carbon material in the first active material layer.

2. The secondary battery according to claim 1, wherein The ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than 1:1 and less than or equal to 80:

1.

3. The secondary battery according to claim 1 or 2, wherein: The ratio of the mass fraction of the silicon-based material in the second active material layer to the mass fraction of the silicon-based material in the first active material layer is greater than or equal to 1.3:1 and less than or equal to 30:

1.

4. The secondary battery according to any one of claims 1 to 3, wherein: The mass fraction of the silicon-based material in the first active material layer is 0.5% to 30%, optionally 1% to 20%; and / or, The mass fraction of the silicon-based material in the second active material layer is 1% to 40%, and optionally 1.5% to 30%.

5. The secondary battery according to any one of claims 1 to 4, wherein: The mass fraction of the first carbon material in the second region to the carbon-containing material is 40% to 100%, optionally 50% to 90%; or / and, In the first region, the mass fraction of the first carbon material to the carbon-containing material is 20% to 80%, optionally 30% to 70%; or / and, The mass fraction of the first carbon material in the second region in the second active material layer is 24% to 96%, optionally 35% to 89%; or / and The mass fraction of the first carbon material in the first region to the first active material layer is 14% to 79%, and optionally 24% to 69%.

6. The secondary battery according to any one of claims 1 to 5, wherein: The carbon-containing material includes a second carbon material, and a reversible gram capacity of the first carbon material is smaller than a reversible gram capacity of the second carbon material.

7. The secondary battery according to claim 6, wherein: The reversible gram capacity of the first carbon material is 320 mAh / g to 370 mAh / g, and optionally 330 mAh / g to 360 mAh / g; and / or, The reversible gram capacity of the second carbon material is 340 mAh / g to 390 mAh / g, and optionally 350 mAh / g to 380 mAh / g.

8. The secondary battery according to claim 6 or 7, wherein: The volume average particle size Dv50 of the first carbon material is larger than the volume average particle size Dv50 of the second carbon material.

9. The secondary battery according to claim 8, wherein: The volume average particle size DV50 of the first carbon material is greater than or equal to 1 μm and less than or equal to 15 μm; The volume average particle size DV50 of the second carbon material is greater than or equal to 7 μm and less than or equal to 22 μm.

10. The secondary battery according to any one of claims 1 to 9, wherein: The ratio of the area of ​​the second region to the area of ​​the first region is (3-20):100, and optionally is (5-15):

100.

11. The secondary battery according to any one of claims 1 to 10, wherein: Also includes a positive electrode plate; The CB value of the second active material layer is greater than or equal to the CB value of the first active material layer, and the CB value is the ratio of the lithium insertion capacity of the negative electrode plate per unit area to the lithium removal capacity of the positive electrode plate per unit area.

12. The secondary battery according to any one of claims 1 to 11, wherein: The first active material layer includes a first surface and a second surface, the first surface is close to the negative electrode current collector, and the second surface is far away from the negative electrode current collector. The thickness of the first active material layer is denoted as H. Then the first active material layer satisfies: the area from the first surface to 0.1H is the first sub-region, the area from the second surface to 0.1H is the second sub-region, and the mass fraction of the silicon-based material in the second sub-region is greater than the mass fraction of the silicon-based material in the first sub-region.

13. The secondary battery according to claim 12, wherein Based on the total mass of the silicon-based material and the carbon-containing material in the first sub-region, the mass fraction of the silicon-based material in the first sub-region is greater than or equal to 0 and less than or equal to 25%; and / or, Based on the total mass of the silicon-based material and the carbon-containing material in the second sub-region, the mass fraction of the silicon-based material in the second sub-region is greater than or equal to 1% and less than or equal to 35%.

14. The secondary battery according to claim 12 or 13, wherein: The mass fraction of the first carbon material per unit area of ​​the second sub-region to the carbon-containing material is greater than the mass fraction of the first carbon material per unit area of ​​the first sub-region to the carbon-containing material; Optionally, the mass fraction of the first carbon material per unit area of ​​the second sub-region to the carbon-containing material is 20% to 85%, more preferably 30% to 75%; Optionally, the mass fraction of the first carbon material per unit area of ​​the carbon-containing material in the first sub-region is 0-75%, and more optionally 20%-65%.

15. The secondary battery according to any one of claims 1 to 14, wherein: The active material layer includes a base layer and a supplementary layer, the base layer is located in the first region and the second region; the supplementary layer is arranged on the side of the base layer in the second region away from the current collector, the mass fraction of the silicon-based material in the supplementary layer is greater than the mass fraction of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than the mass fraction of the first carbon material in the base layer.

16. The secondary battery according to any one of claims 1 to 15, wherein: The active material layer includes a base layer and an additional layer, wherein the additional layer integrally extends to cover the side of the base layer away from the current collector and the side of the base layer close to the electrode tab, and the portion of the additional layer covering the side of the base layer close to the electrode tab is located in the second region.

17. A method for preparing a secondary battery as claimed in any one of claims 1 to 16, wherein: include: A current collector is provided, the current collector comprising a main body and a tab located on one side of the main body, the main body having a first region and a second region, the second region being located between the first region and the tab; A slurry containing active substances is coated on the first and second regions of the current collector to form an active substance layer; the slurry containing active substances includes a silicon-based material and a carbon-containing material, and the carbon-containing material includes a first carbon material; the active substance layer includes a first active substance layer and a second active substance layer, the first active substance layer is located in the first region, and the second active substance layer is located in the second region, so that the mass fraction of the silicon-based material in the second active substance layer is greater than the mass fraction of the silicon-based material in the first active substance layer, and the mass fraction of the first carbon material in the second active substance layer is greater than the mass fraction of the first carbon material in the first active substance layer.

18. The method of claim 17, wherein: The coating of a slurry containing an active material on the first region and the second region of the current collector to form an active material layer comprises: Coating a base slurry on the current collector to form a base layer, wherein the base layer is located in the first region and the second region; A supplementary slurry is coated on the side of the base layer in the second region facing away from the current collector to form a supplementary layer, wherein the mass fraction of the silicon-based material in the supplementary layer is greater than the mass fraction of the silicon-based material in the base layer, and the mass fraction of the first carbon material in the supplementary layer is greater than the mass fraction of the first carbon material in the base layer.

19. The method of claim 17, wherein: The coating of a slurry containing an active material on the first region and the second region of the current collector to form an active material layer comprises: Coating a base slurry on the current collector to form a base layer, wherein the base layer is located in the first region and the second region; An additional slurry is coated on the side of the base layer away from the current collector to form an additional layer, and the additional layer covers the side of the base layer close to the pole ear; wherein the portion of the additional layer covering the side of the base layer close to the pole ear is in the second region, the mass fraction of the silicon-based material in the additional slurry is greater than the mass fraction of the silicon-based material in the basic slurry, and the mass fraction of the first carbon material in the additional slurry to the carbon-containing material is greater than the mass fraction of the first carbon material in the basic slurry to the carbon-containing material; Optionally, the method further comprises: coating a supplementary slurry on a side of the additional layer in the second region away from the current collector to form a supplementary layer.

20. An electrical device comprising the secondary battery according to any one of claims 1 to 16 and / or the secondary battery prepared by the method according to any one of claims 17 to 19.

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