Secondary battery and electric device

Abstract

The application discloses a secondary battery and a power consumption device. The secondary battery comprises an electrode assembly, the electrode assembly is in a winding structure and comprises a first pole piece, the first pole piece comprises a first current collector, a first active material layer arranged on the surface of the first current collector, and a plurality of first pole lugs. The first current collector comprises a plurality of first current collecting portions and a plurality of second current collecting portions, the plurality of first current collecting portions and the plurality of second current collecting portions are alternately arranged along the winding direction of the electrode assembly, the first pole lugs are connected to the first current collecting portions, each first current collecting portion is connected with at least one first pole lug, and the thickness of the second current collecting portions is greater than that of the first current collecting portions. The technical scheme can reduce the overall internal resistance in the secondary battery, improve the consistency of the internal resistance, and thus lower the temperature rise and make the temperature distribution more uniform.

Description

Technical Field

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

[0002] Secondary batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, power tools, and energy storage devices.

[0003] Improving the heat accumulation caused by internal resistance in secondary batteries is a research direction in battery technology. Summary of the Invention

[0004] In view of the above problems, this application provides a secondary battery and an electrical device that can reduce the overall internal resistance of the secondary battery and improve the consistency of internal impedance, resulting in lower temperature rise and more uniform temperature distribution.

[0005] In a first aspect, this application provides a secondary battery, including an electrode assembly. The electrode assembly has a wound structure and includes a first electrode sheet. The first electrode sheet includes a first current collector, a first active material layer disposed on the surface of the first current collector, and a plurality of first tabs. The first current collector includes a plurality of first current collection sections and a plurality of second current collection sections, which are arranged alternately at intervals along the winding direction of the electrode assembly. The first tabs are connected to the first current collection sections, and each first current collection section is connected to at least one first tab. The thickness of the second current collection sections is greater than the thickness of the first current collection sections.

[0006] The technical solution of this application embodiment achieves precise control of the internal resistance and optimized thermal management of the electrode assembly by setting a first current collector and a second current collector with alternating thicknesses in the wound electrode assembly, and connecting the first tab to the thinner first current collector. The thicker second current collector reduces the bulk resistance of the current collector itself, effectively improving the current carrying capacity of the local area and avoiding local overheating and abnormal temperature rise caused by excessive current density. The thinner first current collector, combined with the tab lead-out structure, ensures current collection efficiency while avoiding the increase in weight and cost caused by excessive thickness of the overall current collector. This alternating thickness current collector layout makes the resistance distribution of the electrode assembly more uniform in the winding direction, fundamentally balancing the overall resistance, weakening the heat accumulation caused by the bottleneck effect on the current transmission path, thereby improving the battery rate performance and overcurrent capacity while effectively suppressing the temperature rise during charging and discharging, ensuring the safety and cycle stability of the secondary battery under high power conditions.

[0007] In some embodiments, the electrode assembly includes a flat region and a bent region. A plurality of first current collectors include a first flat portion located in the flat region, and a plurality of second current collectors include a second flat portion located in the flat region. Each first current collector includes a first flat portion, and each second current collector includes a second flat portion. This structure confines the alternating thick and thin current collectors within the flat region, utilizing the flat area to leverage the low-resistance, high-current-carrying capacity of the thick current collectors while reducing the risk of stress concentration and fracture in the bent region.

[0008] In some embodiments, the first active material layer includes a first portion and a second portion. The first portion is coated on the surface of a plurality of first current collectors, and the second portion is coated on the surface of a plurality of second current collectors. The thickness of the first portion is C1, and the thickness of the second portion is C2, satisfying 1 / 2C1≤C2≤C1. In the above structure, C2=C1, with a uniformly thick active layer and a thick current collector, directly reduces the overall internal resistance; C2=1 / 2C1, with a thinner active layer and a thicker current collector, shortens the ion diffusion path while maintaining low resistance.

[0009] In some embodiments, the thickness of the first current collector is W1, and the thickness of the second current collector is W2, satisfying: 1μm≤|W2-W1|≤4μm. In the above structure, the lower limit of 1μm ensures effective compensation for the resistance difference between the thick and thin current collectors, avoiding uneven current distribution; the upper limit of 4μm prevents sudden thickness changes from causing winding stress concentration or electrode breakage.

[0010] In some embodiments, C1 and C2, W1 and W2 satisfy: 0≤|(C1+W1)-(C2+W2)|≤0.1×(C1+W1).

[0011] In some embodiments, the difference between the thickness of the second part and the thickness of the first part is C2-C1, and the absolute value of the difference is ΔC=|C2-C1|. ΔC and the thickness C1 of the first part satisfy: 1%≤ΔC / C1≤15%. The above structure, by limiting the total electrode thickness deviation to ≤10%, allows the current collector and active layer thicknesses to be adjusted collaboratively within a reasonable range to optimize resistance distribution, while avoiding winding misalignment, interface peeling, or localized stress concentration caused by excessive total thickness differences. This ensures both uniform current transmission and maintains the structural stability and cycle reliability of the electrode assembly.

[0012] In some embodiments, the first current collector includes a plurality of third current collectors located in the bending region, and each third current collector connects the first current collector and the second current collector; wherein the thickness of the third current collector is greater than the thickness of the first current collector. The above structure, by providing third current collectors with a thickness greater than that of the first current collector in the bending region, enhances the structural support of the bending region and reduces the risk of wrinkling or breakage of the electrode at the bending point.

[0013] In some embodiments, the thickness of the third current collector is less than or equal to the thickness of the second current collector. The third current collector does not have an active material layer; or, the thickness of the active material layer on the third current collector is less than the thickness of the first portion. The above structure limits the thickness of the third current collector to no more than that of the second current collector and employs an uncoated or thin-coated design, reducing the local stiffness of the bending region, mitigating the abrupt change in electrode stacking height caused by excessive thickness in the bending region, and ensuring the structural flatness and winding tightness of the electrode assembly.

[0014] In some embodiments, the conductivity of the first current collector is S1, the conductivity of the second current collector is S2, the thickness of the first current collector is W1, and the thickness of the second current collector is W2, satisfying: S1×W1≤S2×W2. This structure, by defining the relative relationship of the conductivity (S×W) of the current collector surface, ensures that the current-carrying capacity of the second current collector is not lower than that of the first current collector. Simultaneously, through the synergistic matching of conductivity and thickness, it reduces current bottlenecks and abnormal temperature rises caused by insufficient local current-carrying capacity, ensuring the uniformity of current transmission and thermal stability of the electrode assembly in the winding direction.

[0015] In some embodiments, the equivalent impedance of the first current collector is R1, and the equivalent impedance of the second current collector is R2; under rated current, R1 and R2 satisfy the relationship: 0≤|R2–R1|≤0.1×R1. The above structure, by controlling the equivalent impedance deviation between the first and second current collectors to within 10%, improves the uniformity of current distribution along the electrode length, reduces polarization unevenness and abnormal temperature rise caused by excessive local current density, and reduces the risk of capacity loss or lithium plating due to impedance mismatch, thereby improving the battery's charge / discharge efficiency, rate performance, and cycle life.

[0016] In some embodiments, the electrode assembly further includes a second electrode, which includes a second current collector, a second active material layer disposed on the surface of the second current collector, and a plurality of second tabs. The second current collector includes a plurality of fourth current collectors and a plurality of fifth current collectors. Each second tab is connected to at least one fourth current collector, and the thickness of the fifth current collector is greater than the thickness of the fourth current collector. The first and second electrodes are electrodes of opposite polarity. The first and second electrodes are stacked and wound together. The first and fourth current collectors are alternately stacked along a first direction. The first and second tabs are staggered along a second direction, where the first direction is the thickness direction of the electrode and the second direction is perpendicular to the first direction. The above structure, through the alternating stacking of opposite polarity current collectors along the thickness direction and the staggered arrangement of the tabs, constructs a low-impedance three-dimensional conductive network, shortening the electron transport path and reducing internal resistance. This staggered arrangement optimizes the space utilization of the wound structure, reduces local current accumulation, and improves the electrochemical performance and structural stability of the electrode assembly.

[0017] In some embodiments, the secondary battery includes two electrode assemblies; the first straight portions of the two electrode assemblies are arranged adjacent to each other along a first direction, and the corresponding first tabs of the two electrode assemblies are stacked. This structure, by arranging the first straight portions of the two electrode assemblies adjacent to each other and stacking the tabs, achieves coplanar connection of the tabs, shortens the current transmission path, and reduces contact resistance. This stacked layout optimizes the tab welding process, enhances the mechanical strength and reliability of the connection, and improves the utilization rate of the battery's internal space.

[0018] Secondly, this application provides an electrical device that includes the secondary battery described in the above embodiments.

[0019] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0020] The features, advantages, and technical effects of exemplary embodiments of this application will now be described with reference to the accompanying drawings.

[0021] Figure 1 This is a schematic diagram of the structure of a secondary battery according to an embodiment of this application; Figure 2 This is a schematic diagram of the structure of an electrode assembly according to an embodiment of this application; Figure 3 This is a partial structural diagram of the first and second pole pieces according to an embodiment of this application; Figure 4 This is a partial structural schematic diagram of the first and second electrodes according to another embodiment of this application; Figure 5 This is a schematic diagram of the structure of an electrode assembly according to another embodiment of this application; Figure 6 This is a schematic diagram of the structure of an electrode assembly according to another embodiment of this application.

[0022] Detailed Explanation of Reference Numerals 1. Secondary battery; 10. Electrode assembly; 101. First electrode; 102. Tab; 103. First current collector; 104. First active material layer; 105. First tab; 106. First current collector; 107. Second current collector; 108. Straight region; 109. Bending region; 111. First part; 112. Second part; 113. Third current collector; 114. Second electrode; 115. Second tab; 20. Housing; 30. Terminal assembly; 31. Electrode terminal; 33. Seal. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0024] The terms "first," "second," "third," etc., used in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy. In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0025] In this application, the reference to "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 in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0026] In the description of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0027] In the embodiments of this application, "parallel" includes not only the case of absolute parallelism, but also the case of approximate parallelism as commonly understood in engineering; similarly, "perpendicular" also includes not only the case of absolute perpendicularity, but also the case of approximate perpendicularity as commonly understood in engineering. For example, if the angle between two directions is 80°-90°, the two directions can be considered perpendicular; if the angle between two directions is 0°-10°, the two directions can be considered parallel.

[0028] The secondary battery of this application is described below with reference to the accompanying drawings.

[0029] Reference Figures 1 to 2 This application provides a secondary battery 1. The secondary battery 1 can refer to a battery that can be used again after being discharged by recharging to activate the active materials.

[0030] As an example, the secondary battery 1 of this application can be a lithium-ion battery, a sodium-ion battery, a sodium-lithium-ion battery, a lithium metal battery, a sodium metal battery, a lithium-sulfur battery, a magnesium-ion battery, etc.

[0031] As an example, the secondary battery 1 of this application can be a prismatic battery, a pouch battery, or a battery of other shapes. Prismatic batteries include prismatic batteries and polyprismatic batteries, such as hexagonal prismatic batteries.

[0032] As an example, refer to Figure 1 The secondary battery 1 can be a prismatic battery, including a housing 20 and an electrode assembly 10 housed within the housing 20.

[0033] Electrode assembly 10 is a component in the secondary battery 1 where an electrochemical reaction occurs. The secondary battery 1 may include one or more electrode assemblies 10. Exemplarily, electrode assembly 10 may be a wound structure.

[0034] The electrode assembly 10 includes a positive electrode, a negative electrode, and a separator. The positive and negative electrodes have opposite polarities, and the separator separates them. During the charging and discharging process of the secondary battery 1, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0035] The positive electrode includes a positive current collector and a positive active material layer, the positive active material layer being disposed on the surface of the positive current collector. The negative electrode includes a negative current collector and a negative active material layer, the negative active material layer being disposed on the surface of the negative current collector.

[0036] The positive electrode tab is connected to the positive current collector. In some examples, the positive electrode tab and the positive current collector are a single piece; for example, a layer of positive active material can be coated onto the surface of a metal foil first, and then the positive current collector and the positive electrode tab can be formed by die-cutting the metal foil after coating. In other examples, the positive electrode tab and the positive current collector are formed separately and connected separately; for example, the positive electrode tab is welded to the positive current collector.

[0037] The negative electrode tab is connected to the negative electrode current collector. In some examples, the negative electrode tab and the negative electrode current collector are a single piece; for example, a layer of negative electrode active material can be coated onto the surface of a metal foil first, and then the negative electrode current collector and the negative electrode tab can be formed by die-cutting the metal foil after coating. In other examples, the negative electrode tab and the negative electrode current collector are formed separately and connected; for example, the negative electrode tab is welded to the negative electrode current collector.

[0038] Optionally, the positive current collector is aluminum foil, and the negative current collector is copper foil.

[0039] In some embodiments, the secondary battery 1 can be rectangular, square, or other irregularly shaped.

[0040] In some embodiments, the secondary battery 1 includes a terminal assembly 30, which includes electrode terminals 31. One end of the electrode terminal 31 is located inside the housing 20, and the other end is located outside the housing 20. The electrode terminal 31 is connected to a tab 102 (generally referring to a positive or negative tab). The electrode terminal 31 is used to connect to an external circuit to enable charging and discharging of the secondary battery 1.

[0041] In some embodiments, electrode terminal 31 is soldered to electrode tab 102.

[0042] In some embodiments, the terminal assembly 30 further includes a seal 33 surrounding the electrode terminal 31 and disposed between the electrode terminal 31 and the housing 20. The seal 33 can be used to weld with the encapsulation layer of the packaging film 21 to achieve a sealed connection between the terminal assembly 30 and the housing 20.

[0043] In some embodiments, there are multiple terminal assemblies 30, with a portion of the multiple terminal assemblies 30 connected to the positive electrode tab and another portion of the multiple terminal assemblies 30 connected to the negative electrode tab.

[0044] In the winding structure of electrode assemblies, to improve the welding stability of the tabs, the tabs are usually concentrated on one side. This design means that the even-numbered electrode layers cannot be directly led out through the tabs; the current must first be transmitted laterally through the current collector to the adjacent odd-numbered electrode layers, and then led out through the odd-numbered electrode layers. This inherent difference in the transmission path makes the electron transmission distance of the even-numbered electrode layers significantly longer than that of the odd-numbered electrode layers, resulting in a higher equivalent impedance for the even-numbered electrode layers compared to the odd-numbered electrode layers.

[0045] Impedance mismatch between electrodes can lead to uneven interlayer current distribution, resulting in excessively high local current density, exacerbating electrochemical polarization and Joule heating, and causing abnormal temperature rise. This not only weakens the battery's charge and discharge efficiency and rate performance but also accelerates the degradation of active materials and interfacial side reactions, ultimately impairing the battery's cycle life and operational safety.

[0046] To address the aforementioned issues, this application provides a secondary battery that incorporates alternating thicknesses of a first current collector and a second current collector within a wound electrode assembly. A first tab is connected to the thinner first current collector, enabling precise control of the internal resistance and optimized thermal management of the electrode assembly. The thicker second current collector reduces the bulk resistance of the current collector itself, effectively improving the current carrying capacity in local areas and preventing localized overheating and abnormal temperature rise due to excessive current density. Meanwhile, the thinner first current collector, combined with the tab lead-out structure, ensures efficient current collection while avoiding the increased weight and cost associated with excessively thicker current collectors. This alternating thickness current collector layout results in a more uniform resistance distribution along the winding direction of the electrode assembly, fundamentally balancing the overall resistance and mitigating heat accumulation caused by bottlenecks in the current transmission path. This effectively suppresses temperature rise during charging and discharging while improving the battery's rate performance and overcurrent capacity, ensuring the safety and cycle stability of the secondary battery under high-power conditions.

[0047] like Figures 1 to 3 As shown, the secondary battery 1 provided in this application embodiment includes an electrode assembly 10. The electrode assembly 10 has a wound structure and includes a first electrode 101. The first electrode 101 includes a first current collector 103, a first active material layer 104 disposed on the surface of the first current collector 103, and a plurality of first tabs 105. The first current collector 103 includes a plurality of first current collectors 106 and a plurality of second current collectors 107. The plurality of first current collectors 106 and the plurality of second current collectors 107 are arranged alternately at intervals along the winding direction of the electrode assembly 10. The first tabs 105 are connected to the first current collectors 106. Each first current collector 106 is connected to at least one first tab 105. The thickness of the second current collectors 107 is greater than the thickness of the first current collectors 106.

[0048] For example, the electrode assembly 10 is mainly formed by winding a first electrode 101 (such as a positive electrode), a second electrode 114 (such as a negative electrode) and a separator. The first electrode 101 includes a first current collector 103, a first active material layer 104 coated on its surface, and a plurality of first tabs 105.

[0049] The first current collector 103 adopts a segmented differentiated design, specifically including a first current collector 106 and a second current collector 107 arranged alternately along the winding direction. In this embodiment, the alternate arrangement means that in the straight region of the electrode assembly, the first and second current collectors are arranged in an ABAB sequence along the winding direction, while the section located in the bending region (i.e., the third current collector mentioned below) serves as a transition structure connecting adjacent first and second current collectors in the straight region. A first tab 105 is only provided on the first current collector 106, meaning each first current collector 106 is connected to at least one first tab 105 for current conduction or conduction; while the second current collector 107 does not have tabs 102 and mainly serves as the load for the active material.

[0050] First, by increasing the thickness of the second current collector 107 without tabless, the ohmic impedance in this region is effectively reduced, compensating for the path resistance caused by the lateral transmission of current to the adjacent tab 102. This balances the current density of the electrode along the winding direction, reducing local overheating and polarization. Second, the thickened second current collector 107 enhances the mechanical strength of the electrode in the non-welded area, better resisting winding tension and expansion stress during battery charging and discharging, preventing current collector breakage. Finally, this structure improves the rate performance, cycle life, and safety of the secondary battery 1 while ensuring the stability of the welding process.

[0051] In some embodiments of this application, the electrode assembly 10 includes a flat region 108 and a bent region 109, a plurality of first current collectors 106 include a first flat portion located in the flat region 108, a plurality of second current collectors 107 include a second flat portion located in the flat region 108, each first current collector 106 includes a first flat portion, and each second current collector 107 includes a second flat portion.

[0052] The first current collector 106 and the second current collector 107 are both disposed in the flat region 108, forming a first flat section and a second flat section respectively. Each first current collector 106 corresponds to a first flat section in the flat region 108, and each second current collector 107 corresponds to a second flat section in the flat region 108.

[0053] For example, the electrode assembly 10 of the prismatic battery is flattened after being wound. In the large plane (flat region 108) of the secondary battery 1, the first current collector 106 and the second current collector 107 are arranged alternately. Assuming that the first current collector 106 is segment A and the second current collector 107 is segment B, then on the cross-section of the flat region 108, the material distribution presents an alternating sequence of ABAB. Segment A is the first flat region, and segment B is the second flat region. This one-to-one correspondence ensures that in the main reaction region of the battery, the current collector regions of different thicknesses are clearly defined and completely cover the flat region 108.

[0054] The aforementioned structure, through a clearly defined distribution of the flat region 108, achieves uniform control of current and heat. Firstly, the flat region 108 is the area where the electrochemical reaction is most concentrated and heat generation is most significant within the battery. By designing the second current collector 107 (typically thicker) to cover the flat region 108, the ohmic impedance of the main body region during high-current discharge is effectively reduced, improving heat dissipation performance. Secondly, this one-to-one correspondence ensures a highly regular and consistent current transmission path within the flat region 108, avoiding excessively high local current density caused by misalignment of the current collectors, thus improving the performance of the secondary battery 1.

[0055] like Figure 3 As shown, in some embodiments of this application, the first active material layer 104 includes a first portion 111 and a second portion 112. The first portion 111 is coated on the surface of a plurality of first current collectors 106, and the second portion 112 is coated on the surface of a plurality of second current collectors 107. The thickness of the first portion 111 is C1, and the thickness of the second portion 112 is C2, satisfying 1 / 2C1≤C2≤C1.

[0056] For example, assume that the thickness C1 of the active material layer 111 coated on the first current collector 106 (thinner) is 100 μm. According to this embodiment, the thickness C2 of the active material layer 112 coated on the second current collector 107 (thicker aluminum foil) should be controlled between 50 μm and 100 μm. For example, C2 can be designed to be 80 μm. In this case, although the foil thickness of the second current collector 107 increases, the thickness C2 (80 μm) of the active material coating on its surface is slightly less than or equal to the thickness C1 (100 μm) of the first portion 111, but it is not excessively thinned and remains more than half of C1.

[0057] When C2 = C1, the uniformly thick active layer and the thickened current collector work synergistically to directly reduce the overall internal resistance. When C2 = 1 / 2C1, the thinner active layer, combined with the thicker current collector, shortens the ion diffusion path while maintaining low resistance. By limiting the thickness difference between the two active material layers at these two endpoints, it ensures that the thick foil region has sufficient active material to maintain high energy density, while preventing localized overheating caused by excessive electrode thickness. This also avoids the impedance reduction and cooling effect failure caused by current collector thinning.

[0058] like Figure 4 As shown, in some embodiments of this application, the thickness of the first current collector 106 is W1 and the thickness of the second current collector 107 is W2, satisfying: 1μm≤|W2-W1|≤4μm.

[0059] For example, assume the thickness W1 of the first current collector 106 (at the connection tab 102) is 12 μm. According to this scheme, the thickness W2 of the second current collector 107 (not at the connection tab 102) should be controlled between 13 μm and 16 μm. For example, a 15 μm aluminum foil can be used as the second current collector 107, in which case the thickness difference is 3 μm, which falls within the preferred range of 1 μm to 4 μm.

[0060] |W2-W1|=1μm, which limits the minimum effective range of thickness difference. If the difference is less than 1μm, the increase in conductivity brought about by the increase in the cross-sectional area of ​​the current collector is negligible, which is difficult to offset the additional impedance generated by the long-distance lateral transmission of current by even-numbered electrode layers, and cannot effectively improve the problem of uneven current distribution.

[0061] |W2-W1|=4μm, which limits the maximum tolerance for thickness abrupt changes. If the difference exceeds 4μm, a noticeable step will form at the boundary where the current collector thickness changes alternately. During high-speed winding, this step can easily lead to electrode breakage, misalignment, or excessive cell thickness (interference), severely affecting production yield.

[0062] The aforementioned technical solution, by ensuring a thickness difference of at least 1 μm, reduces the ohmic impedance of the solderless region (second current collector 107), balances the current density of the electrode along the winding direction, and alleviates local polarization and temperature rise. Secondly, limiting the thickness difference to within 4 μm reduces mechanical stress concentration caused by excessive abrupt changes in substrate thickness, ensures the stability of winding tension, and reduces the risk of electrode breakage and cell deformation. Ultimately, this design achieves impedance homogenization while also considering the process window and safety for large-scale manufacturing.

[0063] In some embodiments of this application, C1 and C2, W1 and W2 satisfy: 0≤|(C1+W1)-(C2+W2)|≤0.1×(C1+W1).

[0064] For example, the total electrode thickness (C1+W1) of the first current collector 106 region is 120 μm. According to the formula, the difference between the total electrode thickness (C2+W2) of the second current collector 107 region and 120 μm must not exceed 12 μm (120 μm × 0.1), and the final electrode thickness of the second current collector 107 region must be controlled between 108 μm and 132 μm to ensure that the overall electrode thickness fluctuation is within the above range.

[0065] When (C1+W1)=(C2+W2), the thickness of the current collector and the coating inside are different, but the overall thickness of the electrode surface is completely consistent. This is the most ideal state in the winding process, which can eliminate internal stress to the greatest extent.

[0066] The difference is 0.1 × (C1 + W1)), which sets the maximum allowable range for electrode thickness fluctuation. If this ratio is exceeded, the electrode will form a significant alternating thickness structure during winding, resulting in periodic bulges inside the cell, which can easily lead to electrode misalignment, diaphragm wear, or even cell deformation.

[0067] The aforementioned range limitation, by controlling the electrode thickness difference to within 10%, reduces mechanical stress concentration during winding, thus lowering the risk of electrode breakage or separator puncture caused by abrupt thickness changes. Secondly, the highly uniform electrode thickness ensures a uniform distribution of porosity within the cell, which is beneficial for electrolyte wetting and uniform lithium-ion transport, reducing localized lithium plating. This design, while allowing for variations in current collector and coating thickness, ensures both the smoothness of the cell's appearance and the compactness of its internal structure, improving battery cycle life and safety.

[0068] In some embodiments of this application, the difference between the thickness of the second part 112 and the thickness of the first part 111 is C2-C1, and the absolute value of the difference is ΔC=|C2-C1|. ΔC and the thickness C1 of the first part 111 satisfy: 1%≤ΔC / C1≤15%.

[0069] For example, the thickness C1 of the first part 111 active material layer is 100 μm. The difference ΔC between the thickness C2 and C1 of the second part 112 active material layer should be controlled between 1 μm and 15 μm. For example, if C2 is designed to be 110 μm, then ΔC is 10 μm, and ΔC / C1 = 10%, which falls within the preferred range of 1% to 15%. Although the thicknesses of the two coating parts are not exactly the same, the difference is strictly limited to a small range.

[0070] ΔC / C1=1% ensures that there is a measurable difference in coating thickness. If the difference is less than 1%, the physical properties of the two coatings are similar, and it is difficult to compensate for the difference in capacity or impedance caused by the different current collector thicknesses (W1 and W2) through the thickness difference, thus losing the meaning of differentiated design.

[0071] ΔC / C1=15% sets the limit for abrupt changes in coating thickness. If the difference exceeds 15%, a noticeable step will form at the junction of C1 and C2. During electrode rolling, this step can cause cracking or powdering at the coating edges; during winding, it may lead to stress concentration inside the cell due to localized thickness abrupt changes.

[0072] In the above technical solution, odd-numbered layers and even-numbered layers use current collectors of different thicknesses. To compensate for the impact of the current collector thickness difference on the total electrode thickness, the coating thickness of the active material layer is adjusted accordingly, ensuring that the total thickness of the two types of electrodes remains consistent. Therefore, in the subsequent cold pressing process, odd-numbered and even-numbered layer electrodes can be processed using uniform rolling parameters without differentiation, simplifying the manufacturing process while effectively ensuring the consistency of electrode thickness and the flatness of the winding.

[0073] like Figure 2 As shown, in some embodiments of this application, the first current collector 103 includes a plurality of third current collectors 113, the plurality of third current collectors 113 are located in the bending region 109, and each third current collector 113 is connected to the first current collector 106 and the second current collector 107; wherein, the thickness of the third current collector 113 is greater than the thickness of the first current collector 106.

[0074] For example, the thickness of the first current collector 106 located in the straight region 108 is 12 μm. The thickness of the third current collector 113 located in the bending region 109 should be greater than 12 μm, for example, designed to be 15 μm or 16 μm.

[0075] The third current collector 113 serves as a support component for the bending region 109. Its increased thickness resists tensile stress during the winding process, reducing the risk of electrode breakage or wrinkling at corners and lowering the production scrap rate. Secondly, the thickened bending region 109 better maintains the overall shape of the cell, reducing the probability of cell deformation (such as bulging) during long-term use or thermal expansion. This design, through localized reinforcement, addresses the vulnerability of the bending region 109 in square batteries without significantly increasing overall weight, improving battery safety and cycle life. In some embodiments of this application, the thickness of the third current collector 113 is less than or equal to the thickness of the second current collector 107. The third current collector 113 does not have an active material layer; or, the thickness of the active material layer in the third current collector 113 is less than the thickness of the first portion 111.

[0076] For example, the thickness of the active material layer in the first portion 111 is 100 μm, and the thickness of the third current collector 113 located in the bending region 109 can be selected to be 15 μm (equal to the thickness of the second current collector 107). In the coating process, it is possible to leave the third current collector 113 blank (i.e., not coated), or to coat only a very thin transition layer (e.g., with a thickness of 50 μm, less than the 100 μm of the first portion 111). In this way, the total thickness of the electrode at the bending point will be controlled at a low level.

[0077] The coating thickness is less than the thickness of the first part 111. The coating is usually more brittle than the metal foil. If the coating thickness at the bend is close to or exceeds that of the straight area 108 (C1), the coating is very prone to cracking or peeling when the winding is under stress. Keeping its thickness less than C1 (or even 0) is to ensure that the bend area 109 has sufficient flexibility.

[0078] By limiting the thickness of the third current collector 113 and the coating thickness, the total thickness of the electrode at the bend is reduced, lowering the bending stress during winding and preventing electrode breakage and active material shedding. Secondly, the thinner bend region 109 design avoids the problem of excessive thickness at the corners of the wound cell, improving the utilization rate of the internal space of the cell and making the winding tension more uniform. Therefore, the above technical solution maximizes the flexibility of the bend region 109 while ensuring it has a certain mechanical strength, reducing the risk of microcracks and lithium plating in the bend region 109 of the square battery.

[0079] In some embodiments of this application, the conductivity of the first current collector 106 is S1, the conductivity of the second current collector 107 is S2, the thickness of the first current collector 106 is W1, and the thickness of the second current collector 107 is W2, satisfying: S1×W1≤S2×W2.

[0080] For example, the first current collector 106 uses aluminum foil with a thickness W1 of 12 μm and a conductivity S1 of 35 MS / m. The second current collector 107 uses high-strength aluminum alloy with a slightly lower conductivity S2 of 30 MS / m. According to this scheme, S1×W1≤S2×W2, i.e., 35×12≤30×W2, it is calculated that W2 must be greater than or equal to 14 μm. Therefore, a second current collector 107 with a thickness of 15 μm can be selected in the design. In this case, 30×15=450>35×12=420, which meets the requirement of conductivity compensation.

[0081] When S1×W1=S2×W2, the surface conductance of the two current collectors is exactly the same. Despite the difference in materials or thickness, the ohmic impedance encountered by the current when it propagates laterally in the two regions is the same, achieving ideal current distribution uniformity without local bottlenecks.

[0082] S2×W2 > S1×W1. In practical applications, the upper limit is limited by cost and weight. If S2×W2 is much larger than S1×W1, it means that the second current collector 107 provides excessive conductivity. Although this can further reduce internal resistance, it will waste current collector material and reduce the overall energy density of the battery. Therefore, their relative values ​​should be controlled within a certain range.

[0083] By setting S2×W2≥S1×W1, the second current collector 107 (typically located at the far end of the tab 102) for long-distance current transmission is ensured to have a sufficient conductive cross-section, effectively compensating for the increased resistance due to the longer path and reducing overall polarization. Secondly, this design allows for greater flexibility in material selection; for example, alloys with slightly lower conductivity but higher mechanical strength can be used as thick foils, as long as the product relationship is satisfied by increasing the thickness. Ultimately, this design balances low internal resistance and high rate performance with the mechanical strength and manufacturing cost of the electrode, improving the overall electrochemical performance of the battery.

[0084] For example, the four-terminal method can be used to measure the volume resistivity of metal foil. In the four-terminal method, a constant DC current is passed through the outer two terminals, and the voltage drop is measured at the inner two terminals. This effectively eliminates the influence of lead resistance and contact resistance on the measurement results, accurately reflecting the intrinsic volume resistivity characteristics of the foil. The volume resistivity is calculated from the measured resistance value combined with the foil's geometric dimensions, and then converted into conductivity.

[0085] The specific testing steps include: Dimension measurement: Use a digital micrometer or laser thickness gauge to measure the sample thickness T, select at least 5 evenly distributed positions along the sample length direction for measurement, and take the arithmetic mean; Use a vernier caliper to measure the sample width W, and similarly take the average of multiple points.

[0086] Sample clamping: Clamp the sample in the four-end test fixture. The outer current terminals (I+, I-) are clamped at both ends of the sample, and the inner voltage terminals (V+, V-) are clamped at both ends of the gauge length L. Ensure that each probe makes good contact with the sample surface.

[0087] Test conditions: Ambient temperature: 25±2℃; Apply a constant DC current I, recommended current range: 100mA~1A (specifically, it is advisable to keep the voltage reading stable between 1mV and 100mV to avoid the Joule heating effect affecting the measurement accuracy). Forward and reverse measurement: Apply forward and reverse current respectively, and record the corresponding voltage values ​​V. fwd and V rev Take the average of the absolute values ​​of the two, V = (|V fwd |+|V rev |) / 2, to eliminate the influence of thermoelectric potential on the measurement results.

[0088] Multi-point measurement: On the same sample, select at least 3 different gauge length segments along the length direction for repeated measurement.

[0089] In some embodiments of this application, the equivalent impedance of the first current collector 106 is R1, and the equivalent impedance of the second current collector 107 is R2; under rated current, R1 and R2 satisfy the relationship: 0≤|R2–R1|≤0.1×R1.

[0090] The rated current is the nominal operating current of the product under standard test conditions. Its specific value can be obtained directly from the electrical parameter table in the product's specification sheet, instruction manual, or promotional brochure.

[0091] The aforementioned scheme effectively suppresses uneven interlayer current distribution by controlling the impedance difference between odd and even layers to within 10%, preventing intensified polarization, lithium plating, and active material failure caused by excessive local current. Secondly, the balanced current distribution reduces the concentrated generation of local Joule heat, avoiding hotspot effects and improving battery thermal safety. Finally, this design reduces the overall DC internal resistance of the battery while maintaining high energy density, thereby improving temperature uniformity and thermal stability during secondary battery operation.

[0092] DC internal resistance refers to the sum of ohmic impedance and polarization impedance exhibited by a battery to a direct current during charging and discharging. For example, the test method in this embodiment can employ the constant current pulse method, applying a short-time pulse current to the battery in a specific state of charge, recording the voltage response before and after the pulse, and calculating the DC internal resistance based on Ohm's law. This method can effectively characterize the battery's power output capability and internal impedance characteristics under actual operating conditions.

[0093] The specific testing steps include: Capacity calibration: Perform three capacity calibration cycles on the battery using the standard charge and discharge regime to confirm the battery's actual usable capacity.

[0094] SOC adjustment: 1) Charge the battery to 100% SOC using the standard charging procedure; 2) Discharge at a 1C current to 50% SOC (discharge capacity = rated capacity × 50%). 3) Let it stand for 1 hour to allow the battery voltage to stabilize.

[0095] DCR pulse test: 1) First, continuously record the battery terminal voltage at a sampling frequency of 10Hz or higher; 2) Apply a discharge pulse current I_pulse (e.g., 1C) with a duration of 10s; 3) Record the voltage response at the instant the pulse is applied; 4) After the pulse ends, let it stand for at least 30 minutes to allow the battery to return to its stable state before the pulse. To test the charging direction (DCR), apply a charging pulse of equal amplitude and repeat the above steps.

[0096] Multi-point testing: To obtain DCR values ​​at different SOCs, after the above resting period, continue discharging to the next target SOC (such as 35%, 20%, etc.) and repeat the DCR pulse test.

[0097] like Figure 5 As shown, in some embodiments of this application, the electrode assembly 10 further includes a second electrode 114. The second electrode 114 includes a second current collector, a second active material layer disposed on the surface of the second current collector, and a plurality of second tabs 115. The second current collector includes a plurality of fourth current collectors and a plurality of fifth current collectors. Each second tab 115 is connected to at least one fourth current collector, and the thickness of the fifth current collector is greater than the thickness of the fourth current collector. The first electrode 101 and the second electrode 114 are electrodes with opposite polarities. The first electrode 101 and the second electrode 114 are stacked and wound together. The first current collector 106 and the fourth current collector are alternately stacked along a first direction. The first tab 105 and the second tab 115 are staggered along a second direction. The first direction is the thickness direction of the electrode, and the second direction is perpendicular to the first direction.

[0098] The second electrode 114 has a similar structure to the first electrode 101. The first electrode 101, the separator, and the second electrode 114 are stacked and then wound to form the electrode assembly 10. To reduce the number of lines in the figure, Figure 5 The structure of the second electrode 114 is simplified and is only used as a schematic diagram of the position of the second electrode tab 115.

[0099] For example, the first electrode 101 is a positive electrode, with its first tab 105 located at the left end of the electrode width; the second electrode 114 is a negative electrode, with its second tab 115 located at the right end of the electrode width. During the winding process, the positive current collector and the negative current collector (fourth current collector) alternately adhere to each other. Since the first tab 105 and the second tab 115 are completely offset in the second direction (width direction), the welding areas of the positive tab 102 and the welding areas of the negative tab 102 do not overlap spatially, forming a physically isolated double-tab layout.

[0100] The fifth current collector does not have tabs and is larger than the fourth current collector. By increasing the thickness of the tabless fifth current collector, the ohmic impedance of this area is effectively reduced, compensating for the path resistance caused by the need for the current to be transmitted laterally to the adjacent tabs. This balances the current density of the electrode along the winding direction, reduces local overheating and polarization, and improves the rate performance, cycle life and safety of the secondary battery 1.

[0101] The aforementioned structure, by staggering the first tab 105 and the second tab 115 in the second direction, eliminates the physical path of direct contact between the positive and negative tabs 102, thus improving the safety of the battery cell. Secondly, the alternating stacked current collector design, combined with the staggered tab 102 layout, results in a more uniform thickness at both ends of the wound battery cell, avoiding localized bulging caused by overlapping tabs 102. Finally, this structure optimizes internal space utilization, facilitates automated assembly, and ensures current stability.

[0102] like Figure 6 As shown, in some embodiments of this application, the secondary battery 1 includes two electrode assemblies 10; the first straight portions of the two electrode assemblies 10 are arranged adjacent to each other along a first direction, and the first tabs 105 corresponding to the two electrode assemblies 10 are stacked.

[0103] The above structure, by stacking the first tabs 105 of the two electrode assemblies 10, achieves parallel connection of multiple components, reduces the overall AC internal resistance of the battery, and improves the high-current discharge capability. Secondly, the adjacent arrangement of the first flat portion increases the contact area between the components, which is beneficial for heat transfer and temperature equalization between the two components, and avoids local overheating.

[0104] An embodiment of this application also provides an electrical device that includes the secondary battery described in the above embodiments. This electrical device includes the aforementioned secondary battery and therefore also possesses the aforementioned technical effects.

[0105] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, The electrode assembly includes an electrode assembly with a wound structure and a first electrode sheet. The first electrode sheet includes a first current collector, a first active material layer disposed on the surface of the first current collector, and a plurality of first tabs. The first current collector includes a plurality of first current collectors and a plurality of second current collectors. The plurality of first current collectors and the plurality of second current collectors are arranged alternately at intervals along the winding direction of the electrode assembly. The first electrode tab is connected to the first current collector. Each first current collector is connected to at least one first electrode tab. The thickness of the second current collector is greater than the thickness of the first current collector.

2. The secondary battery according to claim 1, characterized in that, The electrode assembly includes a flat region and a bent region. The plurality of first current collectors include a first flat portion located in the flat region. The plurality of second current collectors include a second flat portion located in the flat region. Each first current collector includes a first flat portion, and each second current collector includes a second flat portion.

3. The secondary battery according to claim 1 or 2, characterized in that, The first active material layer includes a first part and a second part. The first part is coated on the surface of the plurality of first current collectors, and the second part is coated on the surface of the plurality of second current collectors. The thickness of the first part is C1, and the thickness of the second part is C2, satisfying 1 / 2C1≤C2≤C1.

4. The secondary battery according to claim 3, characterized in that, The thickness of the first current collector is W1, and the thickness of the second current collector is W2, satisfying: 1μm ≤ |W2-W1|≤ 4μm.

5. The secondary battery according to claim 4, characterized in that, C1 and C2, W1 and W2 satisfy: 0≤∣(C1+W1)-(C2+W2)∣≤0.1×(C1+W1).

6. The secondary battery according to any one of claims 3-5, characterized in that, The difference between the thickness of the second part and the thickness of the first part is C2-C1. The absolute value of the difference is ΔC=|C2-C1|. ΔC and the thickness of the first part C1 satisfy: 1%≤ΔC / C1≤ 15%.

7. The secondary battery according to any one of claims 4-6, characterized in that, The first current collector includes a plurality of third current collectors located in the bending region, and each third current collector connects the first current collector and the second current collector; wherein the thickness of the third current collector is greater than the thickness of the first current collector.

8. The secondary battery according to claim 7, characterized in that, The thickness of the third collector is less than or equal to the thickness of the second collector. The third current collector does not have an active material layer; or the thickness of the active material layer in the third current collector is less than the thickness of the first part.

9. The secondary battery according to any one of claims 1-8, characterized in that, The conductivity of the first current collector is S1, the conductivity of the second current collector is S2, the thickness of the first current collector is W1, and the thickness of the second current collector is W2, satisfying: S1×W1≤S2×W2.

10. The secondary battery according to any one of claims 1-9, characterized in that, The equivalent impedance of the first current collector is R1, and the equivalent impedance of the second current collector is R2. Under rated current, R1 and R2 satisfy the relationship: 0≤|R2–R1|≤ 0.1 × R1.

11. The secondary battery according to any one of claims 1-10, characterized in that, The electrode assembly further includes a second electrode sheet, which includes a second current collector, a second active material layer disposed on the surface of the second current collector, and a plurality of second tabs. The second current collector includes a plurality of fourth current collectors and a plurality of fifth current collectors. Each second tab is connected to at least one of the fourth current collectors, and the thickness of the fifth current collector is greater than the thickness of the fourth current collector. The first electrode and the second electrode are electrodes with opposite polarities. The first electrode and the second electrode are stacked and wound together. The first current collector and the fourth current collector are stacked alternately along a first direction. The first electrode tab and the second electrode tab are staggered along a second direction. The first direction is the thickness direction of the electrode, and the second direction is perpendicular to the first direction.

12. The secondary battery according to claim 11, characterized in that, The secondary battery includes two electrode assemblies; the first straight portions of the two electrode assemblies are arranged adjacent to each other along the first direction, and the first tabs corresponding to the two electrode assemblies are stacked.

13. An electrical appliance, characterized in that, Includes the secondary battery according to any one of claims 1-12.

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