Secondary battery, method for manufacturing the same, and electric device

Abstract

The application relates to the field of secondary batteries, and provides a secondary battery, a manufacturing method of the secondary battery, and an electric device, at least the cycle performance of the secondary battery being improved. At least one of a positive plate or a negative plate in a roll core of the secondary battery comprises: a current collector, a first end of the current collector corresponding to a starting end of a winding treatment; a first active layer located on a surface of the current collector, an edge of the first active layer close to the first end being aligned with the first end; and a second active layer located on the surface of the current collector, a shape of a normal projection of the second active layer on the surface of the current collector being a "U" type, the first active layer being located in an opening of the "U" type of the second active layer; the first active layer comprises a heat conduction auxiliary material, and the second active layer does not comprise the heat conduction auxiliary material; or the first active layer and the second active layer both comprise the heat conduction auxiliary material, and a mass ratio of the heat conduction auxiliary material in the first active layer to the first active layer is greater than a mass ratio of the heat conduction auxiliary material in the second active layer to the second active layer.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, and in particular to a secondary battery, its manufacturing method, and electrical equipment. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, have received widespread attention and use due to their advantages such as high voltage, high energy density, good cycle performance, and no memory effect. Their application areas have also expanded from traditional digital products to high-rate power tools, electric bicycles, electric cars, and other products, which has placed higher demands on secondary batteries. Summary of the Invention

[0003] This application provides a secondary battery, a method for manufacturing the same, and an electrical device thereof, which at least helps to improve the cycle performance of the secondary battery.

[0004] According to some embodiments of this application, one aspect of this application provides a secondary battery, including: a core formed by winding a positive electrode sheet, a separator, and a negative electrode sheet stacked sequentially, wherein at least one of the positive electrode sheet or the negative electrode sheet includes: a current collector, the current collector including a first end and a second end disposed opposite to each other along the winding direction of the winding process, the first end corresponding to the starting end of the winding process; a first active layer, the first active layer being located on the surface of the current collector, the edge of the first active layer near the first end being aligned with the first end; a second active layer, the second active layer being located on the surface of the current collector, the orthographic projection shape of the second active layer on the surface of the current collector being "U"-shaped, the first active layer being located in the "U"-shaped opening of the second active layer; the first active layer includes thermally conductive auxiliary materials, and the second active layer does not include thermally conductive auxiliary materials; or, both the first active layer and the second active layer include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary materials in the first active layer to the first active layer is greater than the mass ratio of the thermally conductive auxiliary materials in the second active layer to the second active layer.

[0005] In some embodiments, in the first active layer, the mass percentage of the thermally conductive auxiliary material per unit volume gradually decreases in the direction from the first end to the second end.

[0006] In some embodiments, the thermally conductive auxiliary material includes aluminum nitride or aluminum oxide.

[0007] In some embodiments, both the first active layer and the second active layer include active materials, and the average particle size of the active materials in the first active layer is smaller than the average particle size of the active materials in the second active layer.

[0008] In some embodiments, both the first active layer and the second active layer include a conductive agent, and the mass ratio of the conductive agent in the first active layer to the mass ratio of the conductive agent in the second active layer is greater than the mass ratio of the conductive agent in the second active layer to the mass ratio of the conductive agent in the second active layer.

[0009] In some embodiments, both the first active layer and the second active layer include a lithium replenishing agent, and the mass ratio of the lithium replenishing agent in the first active layer to the mass ratio of the lithium replenishing agent in the second active layer is less than the mass ratio of the lithium replenishing agent in the second active layer.

[0010] In some embodiments, the ratio of the width of the first active layer to the width of the second active layer is 3:1 to 5:1 in the direction from the first end to the second end.

[0011] In some embodiments, the compaction density of the first active layer is less than that of the second active layer.

[0012] In some embodiments, in the first active layer, the compaction density of the first active layer gradually increases in the direction from the first end to the second end.

[0013] In some embodiments, the thickness of the first active layer is greater than the thickness of the second active layer in a direction perpendicular to the surface of the current collector.

[0014] According to some embodiments of this application, another aspect of this application provides a method for manufacturing a secondary battery, including: preparing a positive electrode sheet or a negative electrode sheet, the preparation steps including: dry shearing and mixing a first active mixed material, extruding and hot rolling to form a first active film, the first active mixed material including a thermally conductive auxiliary material; dry shearing and mixing a second active mixed material, extruding and hot rolling to form a second active film, the second active mixed material not including a thermally conductive auxiliary material, or the second active mixed material including a thermally conductive auxiliary material, and the mass percentage of the thermally conductive auxiliary material in the second active mixed material is small. The mass ratio of thermally conductive auxiliary materials in the first active mixed material; cutting the first active film and the second active film; calendering and laminating the cut first active film and the second active film with the current collector to form a first active layer and a second active layer on the surface of the current collector, the current collector including a first end and a second end disposed opposite to each other, the edge of the first active layer near the first end being aligned with the first end, the orthographic projection shape of the second active layer on the surface of the current collector being "U" shaped, the first active layer being located in the "U" shaped opening of the second active layer; sequentially stacking the positive electrode sheet, the separator and the negative electrode sheet, and winding them from the first end of the current collector to form a core.

[0015] In some embodiments, the first active layer is formed by calendering multiple layers of first active film; and / or, the second active layer is formed by calendering multiple layers of second active film.

[0016] In some embodiments, the number of layers of the first active film in the first active layer gradually increases in the direction from the first end to the second end.

[0017] In some embodiments, during the process of calendering and laminating the cut first and second active films with the current collector, in the overlapping area of ​​the first and second active films, the first active film is closer to the current collector than the second active film.

[0018] According to some embodiments of this application, another aspect of this application provides an electrical device, including: a secondary battery and a load, wherein the secondary battery is the secondary battery in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments; or, it includes an energy storage system and a load, wherein the energy storage system includes the secondary battery in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments.

[0019] The technical solution provided in this application has at least the following advantages:

[0020] In the secondary battery, its preparation method, and the electrical device provided in this application embodiment, at least one of the positive or negative electrode sheet includes a current collector and a first active layer and a second active layer located on the surface of the current collector. The first active layer is aligned with the edge of the starting end of the current collector winding process, and the second active layer is arranged in a "U" shape around the other edge positions of the first active layer. Thus, after the positive or negative electrode sheet is wound to form a core, the first active layer is located in the central region of the core along the circumferential direction or along the winding axis Y, and the second active layer is located in the peripheral region of the core. Since the central region of the core is the most difficult place for heat to dissipate in a wound battery, the heat generated by the electrochemical reaction will accumulate here, forming a "hot spot," resulting in extremely uneven temperature distribution inside the secondary battery. By setting the first active layer to include thermally conductive auxiliary materials and the second active layer not to include thermally conductive auxiliary materials; or by setting both the first and second active layers to include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary materials in the first active layer to the mass ratio of the thermally conductive auxiliary materials in the second active layer to the mass ratio of the thermally conductive auxiliary materials in the second active layer, it is beneficial to enhance the thermal conductivity of the central region and dissipate the heat generated by charging and discharging more quickly. Attached Figure Description

[0021] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional technology, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1A cross-sectional structural diagram of a core provided in an embodiment of this application;

[0023] Figure 2 A top view of an electrode sheet provided in an embodiment of this application;

[0024] Figure 3 A top view of another electrode provided in an embodiment of this application;

[0025] Figure 4 for Figure 2 or Figure 3 A schematic diagram of a cross-sectional structure along the CC1 direction;

[0026] Figure 5 for Figure 2 or Figure 3 Another cross-sectional view along the CC1 direction.

[0027] Explanation of reference numerals in the attached figures:

[0028] 12. Diaphragm; 11. Electrode; 21. Inner side; 22. Outer side; 100. Current collector; 101. First active layer; 102. Second active layer; A. First end; B. Second end; X. Winding direction; Y. Winding axis direction. Detailed Implementation

[0029] The assembly process of secondary batteries mainly includes winding and stacking. In the winding process, the positive and negative electrodes of the secondary battery are elongated strips. Under high-rate charging, due to the uneven current density within the electrodes and the influence of the electrode impedance on lithium intercalation behavior, a large amount of heat cannot be transferred in time. This leads to uneven heating of the electrodes, which may cause local overheating of the secondary battery cell, thereby reducing the service life of the secondary battery and increasing safety risks.

[0030] Figure 1 This is a cross-sectional structural diagram of a core provided in an embodiment of this application.

[0031] refer to Figure 1 The electrodes 11 on both sides of the separator 12 are the positive and negative electrodes, respectively. After the electrodes 11 and the separator 12 are stacked, they are wound to form a core. After winding, one end of the electrode 11 is located on the inner side 21 of the core, and the other end is located on the outer side 22 of the core. During the charging and discharging process of the secondary battery, the inner side 21 (central area) of the core is more prone to local overheating, which leads to a reduction in the service life of the secondary battery and an increase in safety risks.

[0032] This application provides a secondary battery, its manufacturing method, and an electrical device. By precisely enhancing the thermal conductivity in the heat dissipation bottleneck area of ​​the secondary battery core, the heat dissipation problem in the central area of ​​the core is efficiently solved, thereby improving the overall heat dissipation capacity, temperature uniformity, and safety of the secondary battery. This, in turn, helps to improve the cycle life of the secondary battery and reduce the negative impact on the energy density of the secondary battery.

[0033] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0034] In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0037] In the description of the embodiments of this application, technical terms such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0038] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. When describing a component on another component or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0039] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included.

[0040] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "component" is also intended to include the plural form unless the context clearly indicates otherwise.

[0041] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0042] Figure 2 A top view of an electrode sheet provided in an embodiment of this application; Figure 3 A top view of another electrode provided in an embodiment of this application; Figure 4 for Figure 2 or Figure 3 A schematic diagram of a cross-sectional structure along the CC1 direction; Figure 5 for Figure 2 or Figure 3 A schematic diagram of another cross-sectional structure along the CC1 direction. The electrode can be either a positive or negative electrode.

[0043] According to some embodiments of this application, one aspect of this application provides a secondary battery, including: a core formed by winding a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence.

[0044] refer to Figures 2 to 5 At least one of the positive or negative electrode includes: current collector 100, first active layer 101 and second active layer 102.

[0045] The current collector 100 includes a first end A and a second end B disposed opposite to each other along the winding direction X of the winding process, with the first end A corresponding to the starting end of the winding process. Accordingly, the winding axis direction Y is perpendicular to the winding direction X.

[0046] The first active layer 101 is located on the surface of the current collector 100, and the edge of the first active layer 101 near the first end A is aligned with the first end A.

[0047] The second active layer 102 is located on the surface of the current collector 100. The orthographic projection of the second active layer 102 on the surface of the current collector 100 is U-shaped. The first active layer 101 is located in the U-shaped opening of the second active layer 102.

[0048] In one example, the first active layer 101 includes thermally conductive materials, while the second active layer 102 does not include thermally conductive materials.

[0049] In another example, both the first active layer 101 and the second active layer 102 include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary materials in the first active layer 101 to the mass ratio of the thermally conductive auxiliary materials in the second active layer 102 is greater than that in the second active layer 102.

[0050] It should be noted that the positions and shapes of the first active layer 101, the second active layer 102, and the current collector 100 are all in the context of the unfolded state of the positive or negative electrode sheet.

[0051] In the secondary battery provided in this application embodiment, at least one of the positive or negative electrode includes a current collector 100 and a first active layer 101 and a second active layer 102 located on the surface of the current collector 100. The first active layer 101 is aligned with the edge of the starting end of the current collector 100 winding process, and the second active layer 102 is arranged in a "U" shape around the other edge positions of the first active layer 101. Thus, after the positive or negative electrode is wound to form a core, the first active layer 101 is located in the central region of the core along the circumferential direction or along the winding axis Y, and the second active layer 102 is located in the outer region of the core. Since the central region of the core is the most difficult place for heat to dissipate in a wound battery, the heat generated by the electrochemical reaction will accumulate here, forming a "hot spot," resulting in extremely uneven temperature distribution inside the secondary battery. By setting the first active layer 101 to include thermally conductive auxiliary materials and the second active layer 102 not to include thermally conductive auxiliary materials; or by setting both the first active layer 101 and the second active layer 102 to include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary materials in the first active layer 101 to the first active layer 101 is greater than the mass ratio of the thermally conductive auxiliary materials in the second active layer 102 to the second active layer 102, it is beneficial to enhance the thermal conductivity of the central region and dissipate the heat generated by charging and discharging more quickly.

[0052] After being wound, the positive and negative electrode sheets form a three-dimensional core. The geometric center of the core corresponds to the center of the core in the height direction and the center in the thickness direction. The area where the geometric center of the three-dimensional core is located corresponds to the central area of ​​the core.

[0053] refer to Figure 2 In one example, the edge of the first active layer 101 near the first end A is aligned with a portion of the edge of the first end A of the current collector 100, and the edge of the "U"-shaped opening of the second active layer 102 is aligned with the remaining edge of the first end A of the current collector 100. In this way, the central region of the core can be cooled using the first active layer 101 to avoid heat concentration in the core.

[0054] refer to Figure 3 In another example, the first active layer 101 has a "T" shaped structure, and the edge of the first active layer 101 near the first end A is aligned with the entire edge of the first end A of the current collector 100. Thus, except for the central region of the core, the portions of the core located at the circumferential center at both ends along the winding axis Y can dissipate heat, further improving the core's heat dissipation capacity.

[0055] It should be noted that, in Figure 4 and Figure 5 In this example, the first active layer 101 and the second active layer 102 are located on only one side of the current collector 100. In other embodiments, the first active layer and the second active layer can be located on both sides of the current collector, and the first active layer on both sides of the current collector is mirror-image of the current collector, and the second active layer on both sides of the current collector is mirror-image of the current collector.

[0056] When the electrode is a positive electrode, the current collector 100 is a positive current collector, and both the first active layer 101 and the second active layer 102 include positive active material, conductive agent and binder; when the electrode is a negative electrode, the current collector 100 is a negative current collector, and both the first active layer 101 and the second active layer 102 include negative active material, conductive agent and binder.

[0057] The positive current collector can be selected from aluminum foil; the negative current collector can be selected from copper foil.

[0058] Positive electrode active materials include layered LiM x O2 (M=Co, Ni, Mn) positive electrode active material, spinel structure LiMn2O4 positive electrode active material or olivine structure LiFePO4 positive electrode active material.

[0059] Negative electrode active materials include carbon-based materials and non-carbon-based materials. Carbon-based materials include natural graphite, artificial graphite, mesophase carbon spheres, hard carbon, soft carbon, or graphene. Non-carbon-based materials include titanium-based materials, silicon-based materials, tin-based materials, nitrides, and metallic lithium.

[0060] The conductive agent includes at least one of Super P, acetylene black, Super S, KS-6, KS-15, SFG-6, SFG-15, or Ketjen black.

[0061] The adhesive includes at least one of polyvinylidene fluoride (PVDF), polyimide (PI), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC).

[0062] Thermally conductive materials include aluminum nitride or aluminum oxide.

[0063] The thermally conductive auxiliary material accounts for 2% to 8% of the mass of the first active layer 101, for example, it can be 2%, 3%, 4%, 5%, 6%, 7% or 8%.

[0064] In some embodiments, in the first active layer 101, the mass percentage of the thermally conductive auxiliary material per unit volume gradually decreases from the first end A to the second end B. For the first active layer 101, the portion closer to the first end A, after winding, is located closer to the center region of the core. Therefore, placing a thermally conductive auxiliary material with a higher mass percentage closer to the center region of the core can improve the thermal conductivity of the central region, achieve faster and more uniform temperature distribution of the electrode, and avoid localized overheating.

[0065] In some embodiments, both the first active layer 101 and the second active layer 102 include active materials, and the average particle size of the active material in the first active layer 101 is smaller than the average particle size of the active material in the second active layer 102. The active material can be selected as either a positive or negative electrode active material depending on the polarity of the electrode. By setting the average particle size of the active material in the first active layer 101 to be smaller, the diffusion path of metal ions in the first active layer 101 is shortened, the specific surface area in contact with the electrolyte is increased, the electronic or ion conductivity of the core center region is enhanced, the ion transport rate and reaction kinetics of the center region are improved, the current density of the center region and the peripheral region is balanced, and the stability of the secondary battery is improved.

[0066] Average particle size refers to the particle size at which the cumulative particle size distribution percentage reaches 50%.

[0067] The average particle size of the active material in the first active layer 101 can be 0.5μm to 0.8μm, for example, it can be 0.5μm, 0.6μm, 0.7μm or 0.8μm.

[0068] The average particle size of the active material in the second active layer 102 can be 0.8μm to 1.2μm, for example, it can be 0.8μm, 0.9μm, 1μm, 1.1μm or 1.2μm.

[0069] In some embodiments, both the first active layer 101 and the second active layer 102 include a conductive agent, and the mass ratio of the conductive agent in the first active layer 101 to the mass ratio of the conductive agent in the second active layer 102 is greater than that in the second active layer 102. By setting a larger mass ratio of the conductive agent in the first active layer 101, more and more efficient electron transport channels are formed between the active material particles, reducing the contact resistance in the core center region. Combined with the synergistic effect of the thermally conductive auxiliary materials, the electrochemical performance and thermal management capability of the core center region are jointly optimized, promoting a convergence of current density and electrochemical reaction rate between the core center region and the peripheral region.

[0070] In some embodiments, both the first active layer 101 and the second active layer 102 include a lithium replenishing agent, with the mass ratio of the lithium replenishing agent in the first active layer 101 being less than the mass ratio of the lithium replenishing agent in the second active layer 102. Because the temperature in the central region of the core is relatively high, the lithium replenishing agent content in the first active layer 101 is relatively small, which avoids excessive lithium replenishing agent reacting violently in the high-temperature, high-stress central region (such as reacting with the electrolyte to produce gas). The second active layer 102 in the peripheral region has a higher lithium replenishing agent content, which can utilize the edge heat dissipation advantage to safely and efficiently compensate for lithium loss.

[0071] In some embodiments, in the direction from the first end A to the second end B, the width ratio of the first active layer 101 to the width ratio of the second active layer 102 is 3:1 to 5:1, specifically 3:1, 4:1, or 5:1. (See reference) Figure 2 and Figure 3 The width of the second active layer 102 refers to the width of the second active layer 102 located on the side of the first active layer 101 near the second end B.

[0072] In some embodiments, the ratio of the width of the first active layer 101 to the total width of the second active layer 102 along the winding axis direction Y is 3:1 to 5:1, specifically 3:1, 4:1, or 5:1. (See reference) Figure 2 and Figure 3 The total width of the second active layer 102 refers to the sum of the widths of the two second active layers 102 located on both sides of the first active layer 101 along the winding axis direction Y.

[0073] refer to Figure 3When the first active layer 101 is T-shaped, the width of the first active layer 101 along the winding axis direction Y refers to the width of the first active layer 101 located between the second active layers 102. In some embodiments, the compaction density of the first active layer 101 is less than the compaction density of the second active layer 102. This allows the porosity of the first active layer 101 to be lower than that of the second active layer 102, enhancing the spontaneous absorption and wetting of the electrolyte in the central region of the core and ensuring uniform electrolyte distribution between the central and peripheral regions.

[0074] The compaction density of the first active layer 101 can be 2.3 g / cm³. 3 ~2.4g / cm 3 For example, it could be 2.3 g / cm³. 3 2.32 g / cm 3 2.35g / cm 3 2.38g / cm 3 Or 2.4g / cm 3 .

[0075] The porosity of the first active layer 101 is 30% to 35%, specifically 30%, 31%, 32%, 33%, 34%, or 35%.

[0076] The compaction density of the second active layer 102 can be 2.45 g / cm³. 3 ~2.6g / cm 3 For example, it could be 2.45 g / cm³. 3 2.48 g / cm 3 2.5g / cm 3 2.53g / cm 3 2.56 g / cm 3 2.58g / cm 3 Or 2.6g / cm 3 .

[0077] The porosity of the second active layer 102 is 25% to 30%, specifically 25%, 26%, 27%, 28%, 29%, or 30%.

[0078] In some embodiments, in the first active layer 101, the compaction density of the first active layer 101 gradually increases in the direction from the first end A to the second end B. For the first active layer 101, the portion of the first active layer 101 closer to the first end A, after the winding process, is located closer to the center region of the core. The closer the position is to the center region of the core, the lower the compaction density of the first active layer 101, which can facilitate the spontaneous absorption and wetting of electrolyte into the central region, and further balance the consistency of electrolyte portion at different positions of the first active layer 101.

[0079] In some embodiments, the thickness of the first active layer 101 is greater than the thickness of the second active layer 102 in a direction perpendicular to the surface of the current collector 100. Thus, after the winding process forms the core, gaps can be formed between the second active layers 102 to prevent the second active layers 102 from hindering the diffusion of the electrolyte to the central region.

[0080] The thickness of the first active layer 101 is 70μm to 100μm, for example, it can be 70μm, 75μm, 80μm, 84μm, 90μm, 93μm, 98μm or 100μm.

[0081] The thickness of the second active layer 102 is 70μm to 100μm, for example, it can be 70μm, 75μm, 80μm, 84μm, 90μm, 93μm, 98μm or 100μm.

[0082] The thickness difference between the first active layer 101 and the second active layer 102 is less than 5 μm, which helps to maintain the uniformity of the electrode.

[0083] exist Figure 4 In this example, the junction of the first active layer 101 and the second active layer 102 is taken as an example. In other embodiments, refer to... Figure 5 The first active layer 101 and the second active layer 102 are overlapped at the junction, and in the overlapping part, the first active layer 101 is closer to the current collector 100 than the second active layer 102.

[0084] In the secondary battery provided in this application embodiment, at least one of the positive or negative electrode includes a current collector 100 and a first active layer 101 and a second active layer 102 located on the surface of the current collector 100. The first active layer 101 is aligned with the edge of the starting end of the current collector 100 winding process, and the second active layer 102 is arranged in a "U" shape around the other edge positions of the first active layer 101. Thus, after the positive or negative electrode is wound to form a core, the first active layer 101 is located in the central region of the core along the circumferential direction or along the winding axis Y, and the second active layer 102 is located in the outer region of the core. Since the central region of the core is the most difficult place for heat to dissipate in a wound battery, the heat generated by the electrochemical reaction will accumulate here, forming a "hot spot," resulting in extremely uneven temperature distribution inside the secondary battery. By setting the first active layer 101 to include thermally conductive auxiliary materials and the second active layer 102 not to include thermally conductive auxiliary materials; or by setting both the first active layer 101 and the second active layer 102 to include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary materials in the first active layer 101 to the first active layer 101 is greater than the mass ratio of the thermally conductive auxiliary materials in the second active layer 102 to the second active layer 102, it is beneficial to enhance the thermal conductivity of the central region and dissipate the heat generated by charging and discharging more quickly.

[0085] Accordingly, another embodiment of this application also provides a method for manufacturing a secondary battery, which can be used to manufacture the secondary battery provided in the above embodiments. For parts that are the same as or corresponding to the previous embodiment, please refer to the corresponding descriptions of the foregoing embodiments, which will not be repeated in detail below.

[0086] The preparation method of a secondary battery includes: preparing a positive electrode sheet or a negative electrode sheet, sequentially stacking a positive electrode sheet, a separator and a negative electrode sheet, and winding the positive electrode sheet or the current collector from the first end of the current collector to form a core.

[0087] The steps for preparing a positive or negative electrode include:

[0088] S201. The first active mixed material is dry sheared and mixed, and then extruded and hot rolled to form a first active film. The first active mixed material includes thermally conductive auxiliary materials.

[0089] S202. The second active mixture is dry sheared and mixed, and then extruded and hot rolled to form a second active film. The second active mixture does not include thermally conductive auxiliary materials, or the second active mixture includes thermally conductive auxiliary materials, and the mass percentage of thermally conductive auxiliary materials in the second active mixture is less than the mass percentage of thermally conductive auxiliary materials in the first active mixture.

[0090] S203. Cut the first active membrane and the second active membrane.

[0091] S204. The cut first active film and second active film are calendered and laminated with the current collector to form a first active layer and a second active layer on the surface of the current collector. The current collector includes a first end and a second end that are disposed opposite to each other. The edge of the first active layer near the first end is aligned with the first end. The orthographic projection shape of the second active layer on the surface of the current collector is "U". The first active layer is located in the "U"-shaped opening of the second active layer.

[0092] In the secondary battery preparation method provided in this application embodiment, during the preparation of the electrode sheet, the first active mixed material and the second active mixed material are prepared by dry shearing and mixing, and then extrusion molding and hot rolling molding to form the first active film and the second active film. Compared with wet coating, solvent residue can be avoided, which is beneficial to improving the ionic conductivity of the electrode sheet. Moreover, dry mixing and film formation does not require drying, resulting in lower manufacturing costs, simpler process, and greater suitability for large-scale mass production. After cutting the first and second active films, they are compounded and calendered with the current collector, which can precisely control the shape and position of the first and second active films, so that the first active layer is located in the "U"-shaped opening of the second active layer. After the positive or negative electrode sheet is wound to form a core, the first active layer can be located in the central area of ​​the core, and the second active layer can be located in the outer area of ​​the core. Since the central area of ​​the core is the most difficult place for heat to dissipate in the wound structure battery, the heat generated by the electrochemical reaction will accumulate here, forming a "hot spot", resulting in extremely uneven temperature distribution inside the secondary battery. By setting the first active layer to include thermally conductive auxiliary materials and the second active layer not to include thermally conductive auxiliary materials; or by setting both the first and second active layers to include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary materials in the first active layer to the mass ratio of the thermally conductive auxiliary materials in the second active layer to the mass ratio of the thermally conductive auxiliary materials in the second active layer, it is beneficial to enhance the thermal conductivity of the central region and dissipate the heat generated by charging and discharging more quickly.

[0093] In step S201 or S202, the temperature range of hot roll forming is 60℃~130℃, for example, it can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃ or 130℃.

[0094] In step S304, the calendering temperature can be 40℃~100℃, specifically 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃.

[0095] In some embodiments, the first active layer can be formed by calendering multiple layers of a first active film. Similarly, the second active layer can be formed by calendering multiple layers of a second active film. Calendering multiple active films helps to control the uniform distribution of the thickness of the first and second active layers.

[0096] When it is necessary to prepare a first active layer in which the mass percentage of thermally conductive auxiliary material in a unit volume gradually decreases from the first end to the second end, multiple first sub-active films with decreasing mass percentages of thermally conductive auxiliary material can be prepared. Then, during the calendering and lamination process, the multiple first sub-active films are arranged sequentially along the direction from the first end to the second end of the current collector according to the rule of decreasing mass percentage of thermally conductive auxiliary material, so that the multiple first sub-active films are sequentially connected to form the first active layer.

[0097] When preparing a first active layer with gradually increasing compaction density from the first end to the second end, multiple first sub-active films with the same mass percentage of thermally conductive auxiliary materials but different areas can be prepared. Then, during calendering and lamination, first sub-active films with progressively decreasing areas are sequentially stacked on the current collector, and the number of stacked first sub-active films on the current collector increases sequentially along the direction from the first end to the second end. Thus, after calendering and lamination, the thickness of the first active layer is uniformly distributed. Because the number of first sub-active films corresponding to the first active layer near the first end is less, and the number of first sub-active films corresponding to the first sub-active layer near the second end is more, the compaction density of the first active layer gradually increases from the first end to the second end.

[0098] During the calendering and lamination process of the cut first and second active films with the current collector, in the overlapping area of ​​the first and second active films, the first active film is closer to the current collector than the second active film. In other words, during calendering and lamination, at the interface between the first and second active films, the second active film is placed on the side of the first active film furthest from the current collector. This allows the first active layer to have more contact with the current collector, enabling the thermally conductive auxiliary material in the first active layer to more quickly and uniformly distribute the temperature of the electrode.

[0099] According to some embodiments of this application, another aspect of this application provides an electrical device, including: a secondary battery and a load, wherein the secondary battery is the secondary battery in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments; or, it includes an energy storage system and a load, wherein the energy storage system includes the secondary battery in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments.

[0100] The following are specific embodiments of this application.

[0101] Example 1

[0102] Preparation of positive electrode:

[0103] (1) A first active mixture consisting of 96% lithium iron phosphate (D50 of 0.6μm), 1% conductive carbon black SP, 0.5% carbon nanotubes, 2% PVDF and 0.5% aluminum nitride by mass is dry sheared and mixed, and then extruded and hot rolled to form a first active film.

[0104] (2) A second active mixture consisting of 95% lithium iron phosphate (D50 is 1μm), 1% conductive carbon black SP, 2% PVDF and 2% lithium iron phosphate by mass ratio is dry sheared and mixed, and then extruded and hot rolled to form a second active film.

[0105] (3) The first and second active films are cut, and the cut first and second active films are rolled and laminated with aluminum foil to form a first active layer and a second active layer on the aluminum foil. The first active layer is aligned with the edge of the first end of the aluminum foil, and the second active layer is U-shaped in the orthographic projection of the aluminum foil. The first active layer is located in the U-shaped opening of the second active layer. The shapes of the first and second active layers are as follows: Figure 2 As shown. The compaction density of the first active layer is 2.35 g / cm³. 3 The porosity is 33% and the thickness is 80 μm; the compaction density of the second active layer is 2.5 g / cm³. 3 It has a porosity of 28% and a thickness of 80μm.

[0106] A negative electrode sheet is provided, which consists of copper foil and a negative electrode active layer on the surface of the copper foil. The negative electrode active layer consists of 94.5% graphite, 1% Ketjen superconducting carbon black, 2.25% SBR and 2.25% CMC by mass.

[0107] After the positive electrode, separator and negative electrode are stacked in sequence, they are wound from the first end of the positive electrode to form a core. The core is then placed in the casing and injected with electrolyte to obtain a secondary battery.

[0108] Example 2

[0109] The difference between Example 2 and Example 1 is that the first active mixed material is composed of 96.2% lithium iron phosphate, 1% conductive carbon black SP, 0.5% carbon nanotubes, 2% PVDF and 0.3% aluminum nitride.

[0110] Example 3

[0111] The difference between Example 3 and Example 1 is that the first active mixed material is composed of 95.8% lithium iron phosphate, 1% conductive carbon black SP, 0.5% carbon nanotubes, 2% PVDF and 0.7% aluminum nitride.

[0112] Example 4

[0113] The difference between Example 4 and Example 1 is that the second active mixed material is composed of 94.8% lithium iron phosphate, 1% conductive carbon black SP, 2% PVDF, 2% lithium supplementer and 0.2% aluminum nitride.

[0114] Example 5

[0115] The difference between Example 5 and Example 1 is that the first active layer in the positive electrode is formed by sequentially splicing together the first active film made of the first active mixed material of Example 3, Example 1 and Example 2. That is, in the direction from the first end to the second end of the aluminum foil, the mass ratio of the thermally conductive auxiliary material in the unit volume of the first active layer decreases sequentially.

[0116] Example 6

[0117] The difference between Example 6 and Example 1 is that the first active layer in the positive electrode is formed by rolling multiple layers of first active films with different areas. The number of first active film layers gradually increases in the direction from the first end to the second end of the aluminum foil; that is, the compaction density of the first active layer gradually increases in the direction from the first end to the second end of the aluminum foil. Furthermore, the compaction density at any position in the first active layer is 2.3 g / cm³. 3 ~2.4g / cm 3 Within the range.

[0118] Example 7

[0119] The difference between Example 7 and Example 1 is that the thickness of the second active layer is 78 μm.

[0120] Example 8

[0121] The difference between Example 8 and Example 1 is that the shapes of the first active layer and the second active layer are as follows: Figure 3 As shown.

[0122] Comparative Example 1

[0123] The difference between Comparative Example 1 and Example 1 is that the second active mixed material is composed of 95.5% lithium iron phosphate, 1% conductive carbon black SP, 0.5% carbon nanotubes, 2% PVDF and 1% aluminum nitride.

[0124] Comparative Example 2

[0125] The difference between Comparative Example 2 and Example 1 is that the second active mixed material is composed of 94% lithium iron phosphate, 1% conductive carbon black SP, 1% carbon nanotubes, 2% PVDF and 2% lithium-rich lithium iron phosphate.

[0126] Comparative Example 3

[0127] The difference between Comparative Example 3 and Example 1 is that the first active mixed material consists of 93% lithium iron phosphate, 1% conductive carbon black SP, 0.5% carbon nanotubes, 2% PVDF, 0.5% aluminum nitride, and 3% lithium-rich lithium iron phosphate.

[0128] Comparative Example 4

[0129] The difference between Comparative Example 4 and Example 1 is that the first active mixture consists of 95% lithium iron phosphate, 1% conductive carbon black SP, 2% PVDF and 2% lithium-rich lithium iron phosphate; the second active mixture consists of 96% lithium iron phosphate, 1% conductive carbon black SP, 0.5% carbon nanotubes, 2% PVDF and 0.5% aluminum nitride.

[0130] Comparative Example 5

[0131] The difference between Comparative Example 5 and Example 1 is that the compaction density of the second active layer is 2 g / cm³. 3 The porosity is 38%.

[0132] Comparative Example 6

[0133] The difference between Comparative Example 6 and Example 1 is that the compaction density of the first active layer is 2.5 g / cm³. 3 The porosity is 28%; the compaction density of the second active layer is 2.35 g / cm³. 3 The porosity is 33%.

[0134] Comparative Example 7

[0135] The difference between Comparative Example 7 and Example 1 is that the D50 of lithium iron phosphate in the first active mixed material is 1.5 μm.

[0136] Comparative Example 8

[0137] The difference between Comparative Example 8 and Example 1 is that the D50 of lithium iron phosphate in the first active mixed material is 1 μm, while the D50 of lithium iron phosphate in the second active mixed material is 0.6 μm.

[0138] Comparative Example 9

[0139] The difference between Comparative Example 9 and Example 1 is that the thickness of the second active layer is 82 μm.

[0140] The capacity retention and energy efficiency of the secondary batteries from Examples 1 to 7 and Comparative Examples 1 to 9 were tested after 500 cycles at 0.5P. The test results are shown in Table 1.

[0141] Table 1

[0142]

[0143] According to Examples 1 to 8 and Comparative Example 1, in the secondary battery provided by this application, by setting a first active layer with higher thermal conductivity in the core center region of the secondary battery, the heat dissipation problem in the core center region can be solved, which is conducive to improving the overall temperature uniformity of the secondary battery, improving the cycle life of the secondary battery, and reducing the negative impact of uneven temperature distribution on the energy efficiency of the secondary battery.

[0144] Based on Examples 1 to 8 and Comparative Examples 2 to 4, it can be found that setting a higher content of conductive agent in the first active layer is more beneficial to improving the cycle life of the secondary battery than setting a higher content of conductive agent in the second active layer, and setting a higher content of lithium replenishing agent in the second active layer is more beneficial to improving the cycle life of the secondary battery than setting a higher content of lithium replenishing agent in the first active layer.

[0145] According to Examples 1 to 8 and Comparative Examples 5 and 6, it can be found that when the compaction density of the first active layer is lower than that of the second active layer, it is more conducive to the spontaneous absorption of electrolyte into the central area of ​​the core, which in turn is beneficial to the improvement of the cycle life and energy efficiency of the secondary battery.

[0146] According to Examples 1 to 8 and Comparative Examples 7 and 8, it can be found that when the average particle size of the active material in the first active layer is smaller, it can help shorten the diffusion path of lithium ions in the first active layer, thereby strengthening the reaction kinetics in the central region of the core and improving the cycle performance of the secondary battery.

[0147] According to Comparative Example 9, when the thickness of the second active layer is too thick, it may block the diffusion of electrolyte to the center area of ​​the core, thereby reducing the cycle performance of the secondary battery.

[0148] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A secondary battery, characterized in that, include: A wound core formed by winding a positive electrode sheet, a separator, and a negative electrode sheet stacked sequentially, wherein at least one of the positive electrode sheet or the negative electrode sheet comprises: The current collector includes a first end and a second end disposed opposite to each other along the winding direction of the winding process, wherein the first end corresponds to the starting end of the winding process. A first active layer is located on the surface of the current collector, and the edge of the first active layer near the first end is aligned with the first end. The second active layer is located on the surface of the current collector, and its orthographic projection on the current collector surface is U-shaped. The first active layer is located in the U-shaped opening of the second active layer. Along the winding axis of the core, the first active layer is located in the central region of the core, and the second active layer is located in the peripheral region of the core. The region where the geometric center of the core is located corresponds to the central region of the core. Along the winding axis, the ratio of the width of the first active layer to the total width of the second active layer is 3:1 to 5:

1. The total width of the second active layer is the sum of the widths of the two second active layers located on either side of the first active layer along the winding axis. The first active layer includes a thermally conductive auxiliary material, while the second active layer does not include a thermally conductive auxiliary material; or, both the first active layer and the second active layer include thermally conductive auxiliary materials, and the mass ratio of the thermally conductive auxiliary material in the first active layer to the mass ratio of the thermally conductive auxiliary material in the second active layer to the mass ratio of the thermally conductive auxiliary material in the second active layer is greater than that in the second active layer; wherein, the thermally conductive auxiliary material is aluminum nitride or aluminum oxide; Both the first active layer and the second active layer include a lithium replenishing agent, and the mass ratio of the lithium replenishing agent in the first active layer to the mass ratio of the lithium replenishing agent in the second active layer to the mass ratio of the lithium replenishing agent in the second active layer is smaller; both the first active layer and the second active layer include active materials, and the average particle size of the active materials in the first active layer is smaller than the average particle size of the active materials in the second active layer.

2. The secondary battery according to claim 1, characterized in that, In the first active layer, the mass percentage of the thermally conductive auxiliary material per unit volume gradually decreases in the direction from the first end to the second end.

3. The secondary battery according to claim 1, characterized in that, Both the first active layer and the second active layer contain conductive agents, and the mass ratio of the conductive agent in the first active layer to the mass ratio of the conductive agent in the second active layer is greater than that in the second active layer.

4. The secondary battery according to claim 1, characterized in that, The compaction density of the first active layer is less than that of the second active layer.

5. The secondary battery according to claim 1 or 4, characterized in that, In the first active layer, the compaction density of the first active layer gradually increases in the direction from the first end to the second end.

6. The secondary battery according to claim 4, characterized in that, In a direction perpendicular to the surface of the current collector, the thickness of the first active layer is greater than the thickness of the second active layer.

7. A method for manufacturing a secondary battery, characterized in that, include: The preparation steps for positive or negative electrode sheets include: The first active mixture is dry sheared and mixed, and then extruded and hot rolled to form a first active film. The first active mixture includes a thermally conductive auxiliary material, which is aluminum nitride or aluminum oxide. The second active mixture is dry sheared and mixed, and then extruded and hot rolled to form a second active film. The second active mixture does not contain thermally conductive auxiliary materials, or the second active mixture contains thermally conductive auxiliary materials, and the mass percentage of thermally conductive auxiliary materials in the second active mixture is less than the mass percentage of thermally conductive auxiliary materials in the first active mixture. The first active membrane and the second active membrane are cut; The cut first and second active films are calendered and laminated with the current collector to form a first active layer and a second active layer on the surface of the current collector. The current collector includes a first end and a second end disposed opposite to each other. The edge of the first active layer near the first end is aligned with the first end. The orthographic projection shape of the second active layer on the surface of the current collector is "U". The first active layer is located in the "U"-shaped opening of the second active layer. Both the first active layer and the second active layer include a lithium replenishing agent, and the mass ratio of the lithium replenishing agent in the first active layer to the mass ratio of the lithium replenishing agent in the second active layer to the mass ratio of the lithium replenishing agent in the second active layer is smaller; both the first active layer and the second active layer include active materials, and the average particle size of the active materials in the first active layer is smaller than the average particle size of the active materials in the second active layer. The positive electrode, the separator, and the negative electrode are sequentially stacked and wound from the first end of the current collector to form a core; Wherein, along the winding axis of the core, the first active layer is located in the central region of the core, and the second active layer is located in the peripheral region of the core. The region where the geometric center of the core is located corresponds to the central region of the core. Along the winding axis, the ratio of the width of the first active layer to the total width of the second active layer is 3:1 to 5:

1. The total width of the second active layer is the sum of the widths of the two second active layers located on both sides of the first active layer along the winding axis.

8. The method for manufacturing a secondary battery according to claim 7, characterized in that, The first active layer is formed by calendering multiple layers of the first active film; and / or, the second active layer is formed by calendering multiple layers of the second active film.

9. The method for manufacturing a secondary battery according to claim 8, characterized in that, From the first end to the second end, the number of layers of the first active film in the first active layer gradually increases.

10. The method for manufacturing a secondary battery according to claim 7, characterized in that, During the process of calendering and laminating the cut first active film and the second active film with the current collector, in the overlapping area of ​​the first active film and the second active film, the first active film is closer to the current collector than the second active film.

11. An electrical appliance, characterized in that, include: The secondary battery and the load, wherein the secondary battery is the secondary battery according to any one of claims 1 to 6, or the secondary battery prepared by the manufacturing method of the secondary battery according to any one of claims 7 to 10; or, the secondary battery includes an energy storage system and the load, wherein the energy storage system includes the secondary battery according to any one of claims 1 to 6, or the secondary battery prepared by the manufacturing method of the secondary battery according to any one of claims 7 to 10.

Images