Secondary battery and electric device
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-02-07
- Publication Date
- 2026-08-13
Smart Images
Figure CN2025076145_13082026_PF_FP_ABST
Abstract
Description
Secondary batteries and electrical equipment Technical Field
[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Technology
[0002] In secondary batteries, the outermost electrode of the stacked electrode assembly is usually coated with an active material layer only on one side of the current collector, while the inner electrode is coated with an active material layer on both sides of the current collector. This is to make full use of the active material layer, reduce material costs, and increase the energy density of the battery. Summary of the Invention
[0003] Regarding existing secondary batteries, the inventors discovered that because the outermost electrode uses a single-layer coating while the inner electrode uses a double-sided coating, and the proportions of various substances in the active material layers of the inner and outer electrodes are generally the same, the conductivity of the outermost electrode is greater than that of the inner electrode, and the current density of the outermost electrode is significantly higher than that of the inner electrode. During the cycling process of the secondary battery, the electrolyte at the outermost electrode is consumed faster, making lithium plating more likely to occur on the outermost electrode, resulting in a decrease in the cycle performance and safety performance of the secondary battery.
[0004] In view of the above situation, it is necessary to provide a secondary battery that can reduce the current density of the outermost electrode to reduce the possibility of lithium plating.
[0005] In a first aspect, this application provides a secondary battery, including a housing, an electrode assembly, and an adapter. The housing houses the electrode assembly and the adapter. The electrode assembly includes multiple electrodes and a separator. The multiple electrodes are stacked along a first direction, with a separator between any two adjacent electrodes. The polarities of any two adjacent electrodes are opposite, and the first direction is the thickness direction of the electrodes. The multiple electrodes consist of two outer electrode layers and multiple inner electrode layers. The outer electrode layers are located in the outermost layer of the electrode assembly, and the inner electrode layers are located in the inner layers of the electrode assembly. Each electrode includes a current collector and an active material layer. For the outer electrode layers, the active material layer is disposed on one surface of the current collector facing the interior of the electrode assembly along the thickness direction. For the inner electrode layers, the active material layer is disposed on two opposing surfaces of the current collector along the thickness direction. One of the two outer electrode layers is a first electrode, and one of the multiple inner electrode layers is a second electrode. The first and second electrode layers have the same polarity. A first electrode plate is connected to a first electrode tab, which extends from the first electrode plate along a second direction. A second electrode plate is connected to a second electrode tab, which extends from the second electrode plate along the second direction. The first and second electrode tabs are connected to an adapter. The second direction is perpendicular to the first direction. The first electrode tab includes a first connecting portion connected to the first electrode plate, a second connecting portion connected to the adapter, and a first portion located between the first and second connecting portions. The length of the first portion along the extending direction of the first electrode tab is L1, and the volume of the first portion is V1. The second electrode tab includes a third connecting portion connected to the second electrode plate, a fourth connecting portion connected to the adapter, and a second portion located between the third and fourth connecting portions. The length of the second portion along the extending direction of the second electrode tab is L2, and the volume of the second portion is V2. S1 = V1 / L1, S2 = V2 / L2, S1 < S2.
[0006] The first electrode is connected to the first tab, and the second electrode is connected to the second tab. The first and second tabs are connected to an adapter, allowing current to be distributed to the first and second tabs via the adapter and flow to the first and second electrodes respectively. By setting S1 < S2, the resistance of the first tab along its extension direction can be made greater than that of the second tab along its extension direction. This helps to reduce the current density distributed to the first tab, thereby reducing the current density through the first electrode, slowing down the electrolyte consumption rate, and reducing the possibility of lithium plating on the first electrode.
[0007] In one or more of the above embodiments, 0.5 ≤ S1 / S2 ≤ 0.9.
[0008] In the above embodiments, it is beneficial to ensure that the first tab has sufficient current carrying capacity and to better reduce the possibility of lithium plating on the first electrode.
[0009] In one or more of the above embodiments, 0.05mm 2 ≤S2≤0.5mm 2 .
[0010] In the above embodiment, 0.05mm is set. 2 Setting S2 ≤ 0.5mm helps ensure the current-carrying capacity of the first electrode tab. 2 This helps maintain the energy density of the secondary battery.
[0011] In one or more of the above embodiments, the first part is provided with a through hole, which extends through the first part along the thickness direction of the first electrode tab.
[0012] In the above embodiment, by providing a through hole in the first part, it is advantageous to make the volume of the first part smaller than that of the second part, thereby making S1 < S2. Furthermore, at the through hole, the cross-sectional area of the first part along the extension direction perpendicular to the first electrode tab is smaller, and the impedance at the corresponding position is higher. Thus, by adjusting the opening position of the through hole, it is advantageous to adjust the current density distribution on the first part, thereby improving the current carrying capacity of the first electrode tab.
[0013] In one or more of the above embodiments, the size of the through hole along the width direction of the first electrode tab is d1, where 0.5mm≤d1≤2mm.
[0014] In the above embodiments, setting 0.5mm≤d1 facilitates the machining of through holes in the first part, which improves the ease of manufacturing the secondary battery. Setting d1≤2mm ensures that the effective size of the first tab in the width direction is not too small, which helps to improve the strength of the first tab and thus reduces the possibility of the first tab breaking when the secondary battery is dropped.
[0015] In one or more of the above embodiments, the through hole is arc-shaped and extends along the direction of the first electrode tab. The size of the through hole is d2, where 0.5mm≤d2≤2mm.
[0016] In the above embodiments, the arc-shaped through-hole helps to make the current distribution on the first part more uniform, reducing the possibility of the first electrode tab melting due to excessively high local current density, thereby further improving the current carrying capacity of the first electrode tab. Furthermore, it helps to reduce stress concentration in the first part, thus improving the structural strength of the first electrode tab.
[0017] In one or more of the above embodiments, there are multiple through holes, and the distance between two adjacent through holes is D, along the line connecting the geometric centers of two adjacent through holes, where 1mm≤D≤8mm.
[0018] In the above embodiments, setting D to 1mm≤D ensures that the distance between two adjacent vias is not too short, which helps reduce the possibility of the first tab melting due to excessively high local current density between two adjacent vias, thereby further improving the current carrying capacity of the first tab. Setting D≤8mm ensures that the distance between the via and the width edge of the first tab is not too short, which helps reduce the possibility of the first tab melting due to excessively high local current density between the via and the width edge of the first tab, also helping to further improve the current carrying capacity of the first tab.
[0019] In one or more of the above embodiments, the first portion includes a punched area, and a through hole is provided in the punched area. Along the extending direction of the first tab, the first connecting portion is closer to the punched area than the second connecting portion.
[0020] In the above embodiments, it is beneficial to avoid the second connecting part, improve the connection strength between the first electrode and the adapter, and improve the stability of current distribution to the first electrode through the adapter.
[0021] In one or more of the above embodiments, in the extension direction of the first electrode tab, the punched area includes a first edge and a second edge disposed opposite to each other. Compared with the first edge, the second edge is closer to the second connecting part. Along the extension direction of the first electrode tab, the minimum distance between the first edge and the first connecting part is d3, and the minimum distance between the second edge and the second connecting part is d4, where 0.05×L1≤d3≤0.1×L1 and 0.05×L1≤d4≤0.1×L1.
[0022] In the above embodiments, setting 0.05×L1≤d3 and 0.05×L1≤d4 allows for a greater distance between the through-holes in the punching area and the first and second connecting portions, which is beneficial for improving the connection strength between the first electrode tab and the first electrode plate and the adapter, and improving the reliability of the electrical connection between the first electrode tab and the first electrode plate and the adapter. Setting d3≤0.1×L1 and d4≤0.1×L1 ensures that the area of the punching area is not too small, which is beneficial for increasing the number of through-holes that can be set in the punching area.
[0023] In one or more of the above embodiments, in the flattened state, the total projected area of the through hole along the thickness direction of the first electrode tab is S3, and the projected area of the second part along the thickness direction of the second electrode tab is S4, 1.1≤S4 / S3≤5.
[0024] In the above embodiments, setting 1.1≤S4 / S3 ensures that the area of the through-hole on the first tab is not too large, which helps to improve the strength of the first tab and thus reduces the possibility of the first tab breaking when the secondary battery is dropped. Setting S4 / S3≤5 ensures that the area of the through-hole on the first tab is not too small, which helps to ensure that the current density through the first electrode is not too large and thus helps to reduce the possibility of lithium plating on the first electrode.
[0025] In one or more of the above embodiments, the minimum width of the first portion along the width direction of the first tab is W1. The width of the second portion along the width direction of the second tab is W2. 0.1≤W1 / W2≤0.9.
[0026] In the above embodiments, setting W1 to 0.1 ≤ W1 / W2 ensures that W1 is not too small, which is beneficial to improving the mechanical strength of the first tab and thus reducing the possibility of the first tab breaking when the secondary battery is dropped. Setting W1 / W2 ≤ 0.9 helps to reduce the possibility of lithium plating on the first electrode and also helps to increase the usable space inside the casing, thereby increasing the energy density of the secondary battery.
[0027] In one or more of the above embodiments, the width of the first portion is equal everywhere along the width direction of the first tab, 0.5≤W1 / W2≤0.9.
[0028] In the above embodiments, setting 0.5≤W1 / W2 is beneficial to further improve the mechanical strength of the first electrode tab, thereby further reducing the possibility of the first electrode tab breaking when the secondary battery is dropped.
[0029] In one or more of the above embodiments, 1mm≤W2≤10mm.
[0030] In one or more of the above embodiments, the minimum thickness of the first portion along the thickness direction of the first electrode tab is H1. The thickness of the second portion along the thickness direction of the second electrode tab is H2. H1 < H2.
[0031] In the above embodiments, setting H1 < H2 is beneficial to make S1 < S2 and to increase the usable space inside the casing, thereby increasing the energy density of the secondary battery.
[0032] In one or more of the above embodiments, 0.05mm ≤ H1.
[0033] In the above embodiments, setting H1 to 0.05mm ≤ H1 ensures that the first part is not too thin, which is beneficial to improving the mechanical strength of the first tab.
[0034] In a second aspect, this application provides an electrical device including the secondary battery described in the first aspect. The secondary battery of this application can reduce the likelihood of lithium plating, thus improving the cycle life of the secondary battery and consequently extending the service life of the electrical device. Attached Figure Description
[0035] Figure 1 is a front view of a secondary battery provided in an embodiment of this application.
[0036] Figure 2 is a cross-sectional view along section line Ⅱ-Ⅱ in Figure 1.
[0037] Figure 3 is an enlarged view of region III in Figure 2.
[0038] Figure 4 is a schematic diagram of the first part in the flattened state provided in the first embodiment of this application.
[0039] Figure 5 is a schematic diagram of the first part in the flattened state provided in the second embodiment of this application.
[0040] Figure 6 is a schematic diagram of the first part in the flattened state provided in the third embodiment of this application.
[0041] Figure 7 is a schematic diagram of the second part in a flattened state according to an embodiment of this application.
[0042] Figure 8 is a schematic diagram of an electrical device provided in an embodiment of this application.
[0043] Key Component Symbols: Secondary Battery 100; Casing 10; Electrode Assembly 20; Electrode 21; First Electrode 201; Second Electrode 202; Positive Electrode 211; Positive Current Collector 2111; Positive Active Material Layer 2112; Negative Electrode 212; Negative Current Collector 2121; Negative Active Material Layer 2122; Separator 22; Adapter 30; First Tab 40; First Connecting Part 41; Second Connecting Part 42; First Section 43; Perforated Area 431; Second Centerline 4311; First Edge 4312; Second Edge 4313; First Centerline 432; Through Hole 44; Second Tab 50; Third Connecting Part 51; Fourth Connecting Part 52; Second Section 53; Electrical Equipment 1000; First Direction X; Second Direction Y Detailed Implementation
[0044] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.
[0045] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an element interposed in between. When an element is considered to be "set" on another element, it can be directly set on the other element or there may be an element interposed in between. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
[0047] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0048] In the description of the embodiments of this application, the term "perpendicular" is used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately perpendicular. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be approximately straight lines or planes. From a macroscopic perspective, if the overall extension direction is a straight line or plane, the component can be considered as a "straight line" or "plane".
[0049] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment 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 mutually exclusive, independent, or alternative embodiment. Where there is no conflict, the various embodiments in this application can be combined with each other.
[0050] This application discloses a secondary battery, including a casing, an electrode assembly, and an adapter. The casing houses the electrode assembly and the adapter. The electrode assembly includes multiple electrodes and a separator. The multiple electrodes are stacked along a first direction, with a separator between any two adjacent electrodes. The polarities of any two adjacent electrodes are opposite. The first direction is the thickness direction of the electrodes. The multiple electrodes consist of two outer electrode layers and multiple inner electrode layers. The outer electrode layers are located at the outermost layer of the electrode assembly, and the inner electrode layers are located at the innermost layer of the electrode assembly. Each electrode includes a current collector and an active material layer. For the outer electrode layers, the active material layer is disposed on one surface of the current collector facing the interior of the electrode assembly along the thickness direction. For the inner electrode layers, the active material layer is disposed on two opposing surfaces of the current collector along the thickness direction. One of the two outer electrode layers is a first electrode, and one of the multiple inner electrode layers is a second electrode. The first and second electrode layers have the same polarity. A first electrode plate is connected to a first electrode tab, which extends from the first electrode plate along a second direction. A second electrode plate is connected to a second electrode tab, which extends from the second electrode plate along the second direction. The first and second electrode tabs are connected to an adapter. The second direction is perpendicular to the first direction. The first electrode tab includes a first connecting portion connected to the first electrode plate, a second connecting portion connected to the adapter, and a first portion located between the first and second connecting portions. The length of the first portion along the extending direction of the first electrode tab is L1, and the volume of the first portion is V1. The second electrode tab includes a third connecting portion connected to the second electrode plate, a fourth connecting portion connected to the adapter, and a second portion located between the third and fourth connecting portions. The length of the second portion along the extending direction of the second electrode tab is L2, and the volume of the second portion is V2. S1 = V1 / L1, S2 = V2 / L2, S1 < S2.
[0051] The first electrode is connected to the first tab, and the second electrode is connected to the second tab. The first and second tabs are connected to an adapter, allowing current to be distributed to the first and second tabs via the adapter and flow to the first and second electrodes respectively. By setting S1 < S2, the resistance of the first tab along its extension direction can be made greater than that of the second tab along its extension direction. This helps to reduce the current density distributed to the first tab, thereby reducing the current density through the first electrode, slowing down the electrolyte consumption rate, and reducing the possibility of lithium plating on the first electrode.
[0052] Some embodiments of this application will now be described with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.
[0053] Referring to Figure 1, one embodiment of this application provides a secondary battery 100, including a housing 10, an electrode assembly 20, and an adapter 30. The housing 10 houses the electrode assembly 20 and the adapter 30.
[0054] In some embodiments, the housing 10 is a flexible packaging bag, such as an aluminum-plastic film. In other embodiments, the housing 10 is a rigid outer shell, such as a plastic shell, or a metal shell comprising at least one of steel alloys, aluminum alloys, and copper alloys.
[0055] Referring to Figure 2, the electrode assembly 20 includes multiple electrode sheets 21 and a separator 22. The multiple electrode sheets 21 are stacked along a first direction X. Any two adjacent electrode sheets 21 have opposite polarities, and a separator 22 is disposed between any two adjacent electrode sheets 21. The first direction X is the thickness direction of the electrode sheets 21.
[0056] In some embodiments, depending on the polarity, the plurality of electrodes 21 are composed of positive electrode 211 and negative electrode 212.
[0057] In some embodiments, based on the relative positions of the electrode sheets 21, the plurality of electrode sheets 21 are composed of two outer electrode sheets and a plurality of inner electrode sheets. The outer electrode sheets are located at the outermost layer of the electrode assembly 20, and the inner electrode sheets are located at the inner layer of the electrode assembly 20. "Outermost layer" refers to the outermost layer of the plurality of electrode sheets 21, and there is one "outermost layer" disposed opposite to each other along the thickness direction of the electrode assembly 20. "Inner layer" refers to the layer located inside the two outer electrode sheets along the opposite direction.
[0058] It should be noted that the terms "outermost layer" and "inner layer" are determined based on the relative positional relationship between the multiple electrodes 21, without considering the relative positional relationship between the separator 22 and the electrodes 21.
[0059] In some embodiments, referring to FIG2, the electrode 21 includes a current collector and an active material layer. For the outer electrode, the active material layer is disposed on one surface of the current collector, which faces the interior of the electrode assembly 20 along the thickness direction of the current collector. For the inner electrode, the active material layer is disposed on both surfaces of the current collector, which are disposed opposite to each other along the thickness direction of the current collector.
[0060] In some embodiments, depending on the polarity, the current collector includes a positive current collector 2111 and a negative current collector 2121, and the active material layer includes a positive active material layer 2112 and a negative active material layer 2122.
[0061] Referring to Figure 2, the positive electrode 211 includes a positive current collector 2111 and a positive active material layer 2112. The positive active material layer 2112 is disposed on one or both sides of the positive current collector 2111 along its thickness direction. When the positive electrode 211 is an inner electrode, the positive active material layer 2112 is disposed on two opposite sides of the positive current collector 2111 along its thickness direction; when the positive electrode 211 is an outer electrode, the positive active material layer 2112 is disposed only on the side of the positive current collector 2111 facing the interior of the electrode assembly 20 along its thickness direction. The negative electrode 212 includes a negative current collector 2121 and a negative active material layer 2122, which is disposed on one or both sides of the negative current collector 2121 along its thickness direction. When the negative electrode 212 is an inner electrode, the negative current collector 2121 is disposed on two opposite sides of the negative current collector 2121 along the thickness direction; when the negative electrode 212 is an outer electrode, the negative active material layer 2122 is disposed only on the side of the negative current collector 2121 facing the inside of the electrode assembly 20 along the thickness direction.
[0062] In some embodiments, at least one of the positive current collector 2111 and the negative current collector 2121 is a metal layer. As an example, the positive current collector 2111 may be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil. The negative current collector 2121 may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.
[0063] In some embodiments, at least one of the positive current collector 2111 and the negative current collector 2121 is a composite current collector.
[0064] In some embodiments, the positive electrode active material layer 2112 includes a positive electrode active material. The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.
[0065] In some embodiments, the negative electrode active material layer 2122 includes a negative electrode active material. The negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials.
[0066] In some embodiments, along the first direction X, a separator 22 is disposed between the positive electrode active material layer 2112 and the negative electrode active material layer 2122. The separator 22 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.
[0067] In some embodiments, the secondary battery 100 includes an electrolyte (not shown) contained within the housing 10. The electrolyte facilitates ion conduction between the positive electrode active material layer 2112 and the negative electrode active material layer 2122.
[0068] In some embodiments, the electrolyte comprises an electrolyte salt. The electrolyte salt comprises at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide LiN(CF3SO2)2 (LiTFS I), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).
[0069] One of the two outer electrode layers is a first electrode 201, and one of the multiple inner electrode layers is a second electrode 202. The first electrode 201 and the second electrode 202 have the same polarity. In some embodiments, both the first electrode 201 and the second electrode 202 are negative electrodes 212. In other embodiments, both the first electrode 201 and the second electrode 202 are positive electrodes 211.
[0070] Referring to Figure 2, a first electrode 201 is connected to a first electrode tab 40, which extends out of the first electrode 201 along a second direction Y. The first electrode tab 40 includes a first connecting portion 41 connected to the first electrode 201. A second electrode 202 is connected to a second electrode tab 50, which extends out of the second electrode 202 along a second direction Y. The second electrode tab 50 includes a third connecting portion 51 connected to the second electrode 202. The second direction Y is perpendicular to the first direction X.
[0071] In some embodiments, the current collector of the first electrode 201 is integrally formed with the first tab 40. For example, the current collector of the first electrode 201 and the first tab 40 are die-cut from a sheet. In this case, the first connection portion 41 is the interface between the current collector of the first electrode 201 and the first tab 40 along the second direction Y. In other embodiments, the first tab 40 is welded to the current collector of the first electrode 201 along the first direction X. In this case, the first connection portion 41 is the solder joint between the first tab 40 and the current collector of the first electrode 201.
[0072] In some embodiments, the current collector of the second electrode 202 is integrally formed with the second tab 50. For example, the current collector of the second electrode 202 and the second tab 50 are die-cut from a sheet. In this case, the third connection portion 51 is the contact surface between the current collector of the second electrode 202 and the second tab 50 along the second direction Y. In other embodiments, the second tab 50 is welded to the current collector of the second electrode 202 along the first direction X. In this case, the third connection portion 51 is the solder joint between the second tab 50 and the current collector of the second electrode 202.
[0073] Referring to Figures 2 and 3, the first tab 40 and the second tab 50 are connected to the adapter 30. The first tab 40 includes a second connecting portion 42 connected to the adapter 30, and the second tab 50 includes a fourth connecting portion 52 connected to the adapter 30. In some embodiments, the first tab 40 and the second tab 50 are stacked and fused together to form part of a tab bundle, and the adapter 30 is welded to the tab bundle along its thickness direction. In this case, the second connecting portion 42 is the solder joint between the first tab 40 and the adapter 30, and the fourth connecting portion 52 is the solder joint between the second tab 50 and the adapter 30.
[0074] In some embodiments, the first tab 40 includes a first portion 43 located between the first connecting portion 41 and the second connecting portion 42. The length of the first portion 43 is L1, and its volume is V1, along the extending direction of the first tab 40. It should be noted that when the first tab 40 is integrally formed with the current collector of the first electrode 201, and the first tab 40 is welded to the adapter 30, the length of the first portion 43 is the minimum distance along the extending direction of the first tab 40 between the current collector of the first electrode 201 and the contact surface of the first tab 40 and the weld point of the second connecting portion 42. When the first tab 40 is welded to both the first electrode 201 and the adapter 30, the length of the first portion 43 is the minimum distance along the extending direction of the first tab 40 between the weld point of the first connecting portion 41 and the weld point of the second connecting portion 42.
[0075] In some embodiments, the second tab 50 includes a second portion 53 located between the third connecting portion 51 and the fourth connecting portion 52. The length of the second portion 53 is L2, and its volume is V2, along the extending direction of the second tab 50. It should be noted that when the second tab 50 is integrally formed with the current collector of the second electrode 202, and the second tab 50 is welded to the adapter 30, the length of the second portion 53 is the minimum distance along the extending direction of the second tab 50 between the current collector of the second electrode 202 and the contact surface of the second tab 50 and the weld point of the fourth connecting portion 52. When the second tab 50 is welded to both the second electrode 202 and the adapter 30, the length of the second portion 53 is the minimum distance along the extending direction of the second tab 50 between the weld point of the third connecting portion 51 and the weld point of the fourth connecting portion 52.
[0076] The first electrode 201 is connected to the first tab 40, and the second electrode 202 is connected to the second tab 50. The first tab 40 and the second tab 50 are connected to the adapter 30. The current can be distributed to the first tab 40 and the second tab 50 through the adapter 30, and flow to the first electrode 201 and the second electrode 202 respectively.
[0077] In some embodiments, S1 = V1 / L1, S2 = V2 / L2, and S1 < S2. By setting S1 < S2, the resistance value of the first tab 40 along the extension direction can be made greater than the resistance value of the second tab 50 along the extension direction. This helps to reduce the current density distributed to the first tab 40, thereby helping to reduce the current density through the first electrode 201, slowing down the consumption rate of the electrolyte, and reducing the possibility of lithium plating on the first electrode 201.
[0078] In some embodiments, the volume of the first part 43 and the volume of the second part 53 are measured by the displacement method, specifically: (1) along the extension direction of the first tab 40, at the junction of the first connecting part 41 and the second connecting part 42 with the first part 43, the first part 43 is cut off from the first tab 40; along the extension direction of the second tab 50, at the junction of the third connecting part 51 and the fourth connecting part 52 with the second part 53, the second part 53 is cut off from the second tab 50; (2) the first part 43 and the second part 53 are placed into a container filled with water in sequence, and the volume of the overflowing water is measured respectively, which is the volume of the first part 43 and the second part 53.
[0079] In some embodiments, the lengths of the first part 43 and the second part 53 are measured using measuring instruments such as a ruler or micrometer in a flattened state.
[0080] In some embodiments, 0.5 ≤ S1 / S2 ≤ 0.9. For example, the value of S1 / S2 is 0.5, 0.6, 0.7, 0.8, or 0.9. This is beneficial for ensuring that the first tab 40 has sufficient current carrying capacity and for better reducing the possibility of lithium plating on the first electrode 201.
[0081] In some embodiments, 0.05mm 2 ≤S2≤0.5mm 2 For example, the value of S2 is 0.05 mm. 2 0.1mm 2 0.2mm 2 0.3mm 2 0.4mm 2 or 0.5mm 2 Set to 0.05mm 2 Setting S2 ≤ 0.5mm helps ensure the current-carrying capacity of the first tab 40. 2 This helps maintain the energy density of the secondary battery at 100%.
[0082] In some embodiments, referring to Figures 4 to 6, the first portion 43 is provided with a through hole 44, which extends through the first portion 43 along the thickness direction of the first tab 40. By providing a through hole 44 in the first portion 43, it is advantageous to make the volume of the first portion 43 smaller than the volume of the second portion 53, thereby facilitating S1 < S2. Furthermore, at the through hole 44, the cross-sectional area of the first portion 43 along the extension direction perpendicular to the first tab 40 is smaller, and the impedance at the corresponding position is higher. Thus, by adjusting the opening position of the through hole 44, it is advantageous to adjust the current density distribution on the first portion 43, thereby improving the current carrying capacity of the first tab 40.
[0083] In some embodiments, the through-hole 44 is arc-shaped. For example, referring to Figure 4, the through-hole 44 is circular; referring to Figure 5, the through-hole 44 is elliptical. This facilitates a more uniform current distribution on the first portion 43, reducing the possibility of excessive local current density causing the first tab 40 to melt, thereby further improving the current-carrying capacity of the first tab 40. Furthermore, it helps reduce stress concentration in the first portion 43, thereby improving the structural strength of the first tab 40. In other embodiments, the through-hole 44 is in a regular or irregular shape, such as rectangular (see Figure 6), triangular, rhomboid, trapezoidal, pentagonal, hexagonal, or star-shaped.
[0084] In some embodiments, the size of the through hole 44 along the width direction of the first tab 40 is d1, where 0.5mm ≤ d1 ≤ 2mm. For example, the value of d1 is 0.5mm, 1mm, 1.5mm, or 2mm. Setting 0.5mm ≤ d1 facilitates the machining of the through hole 44 on the first portion 43, which improves the ease of manufacturing the secondary battery 100. Setting d1 ≤ 2mm ensures that the effective size of the first tab 40 in the width direction is not too small, which helps to improve the strength of the first tab 40 and thus helps to reduce the possibility of the first tab 40 breaking when the secondary battery 100 is dropped.
[0085] In some embodiments, the through hole 44 is arc-shaped and extends along the extension direction of the first tab 40. The size of the through hole 44 is d2, where 0.5mm ≤ d2 ≤ 2mm. For example, the value of d2 is 0.5mm, 1mm, 1.5mm, or 2mm.
[0086] In some embodiments, the through hole 44 is rectangular and extends along the direction of the first tab 40. The size of the through hole 44 is d2, where 2mm ≤ d2 ≤ 10mm. For example, the value of d2 is 2mm, 3mm, 5mm, 7mm, or 10mm.
[0087] In some embodiments, there are multiple vias 44. The distance between two adjacent vias 44 is D, where 1mm ≤ D ≤ 8mm, along the line connecting the geometric centers of two adjacent vias 44. For example, the value of D is 1mm, 2mm, 3mm, 5mm, 7mm, or 8mm. Setting D to 1mm ≤ D ensures that the current path between two adjacent vias 44 is not too short, which helps reduce the possibility of excessive local current density between two adjacent vias 44 causing the first tab 40 to melt, thereby further improving the current carrying capacity of the first tab 40. Setting D ≤ 8mm ensures that the distance between the via 44 and the width edge of the first tab 40 is not too short, which helps reduce the possibility of excessive local current density between the via 44 and the width edge of the first tab 40 causing the first tab 40 to melt, also helping to further improve the current carrying capacity of the first tab 40.
[0088] In some embodiments, the multiple vias 44 are uniformly distributed. This facilitates a more uniform current density distribution on the first portion 43. A uniform distribution of the multiple vias 44 means that the distance between the geometric centers of any two adjacent vias 44 is equal.
[0089] In some embodiments, referring to Figures 4 to 6, the first portion 43 includes a punched region 431, and a through hole 44 is provided in the punched region 431. Along the extending direction of the first tab 40, the first connecting portion 41 is closer to the punched region 431 than the second connecting portion 42. This facilitates avoiding the second connecting portion 42, improves the connection strength between the first tab 40 and the adapter 30, and enhances the stability of current distribution from the adapter 30 to the first tab 40.
[0090] In some embodiments, the first portion 43 has a first center line 432, and the perforated region 431 has a second center line 4311. The first center line 432 and the second center line 4311 are parallel to the width direction of the first tab 40. Along the extending direction of the first tab 40, the first connecting portion 41 being closer to the perforated region 431 than the second connecting portion 42 means that along the extending direction of the first tab 40, the second center line 4311 is located between the first connecting portion 41 and the first center line 432.
[0091] In some embodiments, in the extending direction of the first tab 40, the perforated region 431 includes a first edge 4312 and a second edge 4313 disposed opposite to each other. The second edge 4313 is closer to the second connecting portion 42 than the first edge 4312. In some embodiments, the first edge 4312 is tangent to the through hole 44 closest to the first connecting portion 41, and the second edge 4313 is tangent to the through hole 44 closest to the second connecting portion 42. The first edge 4312 and the second edge 4313 may be parallel or not parallel to the width direction of the first tab 40.
[0092] In some embodiments, along the extending direction of the first tab 40, the minimum distance between the first edge 4312 and the first connecting portion 41 is d3, and the minimum distance between the second edge 4313 and the second connecting portion 42 is d4, where 0.05×L1≤d3≤0.1×L1 and 0.05×L1≤d4≤0.1×L1. For example, the values of d3 and d4 are 0.05×L1, 0.06×L1, 0.07×L1, 0.08×L1, 0.09×L1, or 0.1×L1. Setting 0.05×L1≤d3 and 0.05×L1≤d4 allows the distance between the through hole 44 in the punching area 431 and the first connecting portion 41 and the second connecting portion 42 to be greater, which is beneficial to improving the connection strength between the first tab 40 and the first electrode 201 and the adapter 30, and improving the reliability of the electrical connection between the first tab 40 and the first electrode 201 and the adapter 30. Setting d3≤0.1×L1 and d4≤0.1×L1 ensures that the area of the punching region 431 is not too small, which is beneficial to increasing the number of through holes 44 that can be set on the punching region 431.
[0093] In some embodiments, in the flattened state, the total projected area of the through hole 44 along the thickness direction of the first tab 40 is S3, and the projected area of the second portion 53 along the thickness direction of the second tab 50 is S4, where 1.1 ≤ S4 / S3 ≤ 5. For example, the value of S4 / S3 is 1.1, 2, 3, 4, or 5. Setting 1.1 ≤ S4 / S3 ensures that the area of the through hole 44 on the first tab 40 is not too large, which helps to improve the strength of the first tab 40 and thus helps to reduce the possibility of the first tab 40 breaking when the secondary battery 100 is dropped. Setting S4 / S3 ≤ 5 ensures that the area of the through hole 44 on the first tab 40 is not too small, which helps to ensure that the current density through the first electrode 201 is not too large, thus helping to reduce the possibility of lithium plating on the first electrode 201.
[0094] In some embodiments, referring to Figures 4 to 7, the minimum width of the first portion 43 along the width direction of the first tab 40 is W1. The width of the second portion 53 along the width direction of the second tab 50 is W2. 0.1 ≤ W1 / W2 ≤ 0.9. For example, the value of W1 / W2 is 0.1, 0.2, 0.4, 0.6, 0.8, or 0.9. Setting 0.1 ≤ W1 / W2 ensures that W1 is not too small, thereby reducing the possibility of the first tab 40 breaking when the secondary battery 100 is dropped. Setting W1 / W2 ≤ 0.9 helps reduce the possibility of lithium plating on the first electrode 201 and increases the usable space inside the casing 10, thereby increasing the energy density of the secondary battery 100.
[0095] In some embodiments, the width of the first portion 43 is uniformly equal along the width direction of the first tab 40, with 0.5 ≤ W1 / W2 ≤ 0.9. For example, the value of W1 / W2 is 0.5, 0.6, 0.7, 0.8, or 0.9. Setting 0.5 ≤ W1 / W2 helps to further improve the mechanical strength of the first tab 40, thereby helping to further reduce the possibility of the first tab 40 breaking when the secondary battery 100 is dropped. It should be understood that the statement that the width of the first portion 43 is uniformly equal everywhere means that the difference between the maximum width and the minimum width of the first portion 43 is less than or equal to 10% × W1.
[0096] In some embodiments, the width of the first portion 43 gradually decreases along the extending direction of the first tab 40. In some embodiments, the width of the first portion 43 gradually increases along the extending direction of the first tab 40. In other embodiments, the width of the first portion 43 varies unevenly along the extending direction of the first tab 40.
[0097] In some embodiments, 1mm ≤ W2 ≤ 10mm. For example, the value of W2 is 1mm, 3mm, 5mm, 7mm or 10mm.
[0098] In some embodiments, referring to FIG3, the minimum thickness of the first portion 43 along the thickness direction of the first tab 40 is H1; the thickness of the second portion 53 along the thickness direction of the second tab 50 is H2; H1 < H2. Setting H1 < H2 is beneficial to make S1 < S2, and is beneficial to increase the usable space inside the housing 10, thereby increasing the energy density of the secondary battery 100.
[0099] In some embodiments, 0.05mm ≤ H1. For example, the value of H1 is 0.05mm, 0.06mm, 0.08mm, 0.1mm, or 0.15mm. Setting 0.05mm ≤ H1 ensures that the first portion 43 is not too thin, which is beneficial to improving the mechanical strength of the first tab 40.
[0100] In some embodiments, the thickness of the first portion 43 gradually decreases along the extending direction of the first tab 40. In some embodiments, the thickness of the first portion 43 gradually increases along the extending direction of the first tab 40. In other embodiments, the thickness of the first portion 43 varies unevenly along the extending direction of the first tab 40.
[0101] Referring to Figure 8, an embodiment of this application also provides an electrical device 1000, which includes the secondary battery 100 involved in any of the foregoing embodiments. The secondary battery 100 of this application can reduce the possibility of lithium plating, thus improving the cycle life of the secondary battery 100 and consequently improving the service life of the electrical device 1000. The electrical device 1000 includes, but is not limited to, electronic devices such as mobile phones, tablet computers, and laptop computers.
[0102] To verify the impact of the solution provided in this application on the secondary battery 100, the inventors of this application conducted the following experiments, which included 2 sets of comparative examples and 26 sets of implementation examples. Each set of comparative examples and implementation examples included 3 sets of secondary batteries 100, with 20 secondary batteries 100 in each set (60 in total). The 3 sets of secondary batteries 100 were used for long-cycle testing, electrical abuse testing and drop testing, respectively.
[0103] The preparation process of the secondary battery 100 in Example 1 includes the following steps:
[0104] (1) Preparation of positive electrode 211: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNTs (carbon nanotubes), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode active material with a solid content of 75 wt%, and the mixture was stirred evenly for later use. A 10 μm thick aluminum foil was used as the positive electrode current collector 2111. The above active material was uniformly coated onto one surface of the positive electrode current collector 2111 along its thickness direction using a slit coater, and then dried at 90°C to obtain a positive electrode 211 with a single-sided coating of the positive electrode active material. At this time, the thickness of the positive electrode active material layer 2112 along the thickness direction of the positive electrode current collector 2111 was 50 μm. The above coating steps were then repeated on the other surface of the positive electrode current collector 2111 along its thickness direction. The coated positive electrode sheet 211 is then cold-pressed, resulting in a positive electrode active material layer 2112 thickness of 35 μm. The area of the positive electrode current collector 2111 not covered by the positive electrode active material layer 2112 is the positive electrode empty foil area, which is then die-cut to obtain the positive electrode tab.
[0105] (2) Preparation of negative electrode 212: Artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC-Na (sodium carboxymethyl cellulose) were mixed in a weight ratio of 97:0.5:1.3:1.2. Deionized water was added as a solvent to prepare a negative electrode active material with a weight percentage of 50 wt%, and the mixture was stirred evenly for later use. A copper foil with a thickness of 10 μm was used as the negative electrode current collector 2121. The above negative electrode active material was uniformly coated onto one surface of the negative electrode current collector 2121 along its thickness direction using a slot coater, and then dried at 110°C to obtain a negative electrode 212 with a single-sided coating of the negative electrode active material layer 2122. At this time, the thickness of the negative electrode active material layer 2122 along the thickness direction of the negative electrode current collector 2121 was 55 μm. The above steps were then repeated on the other surface of the negative electrode current collector 2121 along its thickness direction. The coated negative electrode sheet 212 is then cold-pressed, resulting in a negative electrode active material layer 2122 thickness of 45 μm. The area of the negative electrode current collector 2121 not covered by the negative electrode active material layer 2122 is the negative electrode empty foil area. This area is die-cut to obtain the negative electrode tab, which has the same thickness as the negative electrode current collector 2121, approximately 10 μm. The width of the negative electrode tab is approximately 50 mm, and its length is approximately 8 mm. Multiple negative electrode sheets 212 are prepared, two of which are negative electrode sheets 212 with a negative electrode active material layer 2122 coated on one side. One of these negative electrode sheets 212 (serving as the first electrode sheet 201 in this experiment) has 20 through holes 44 (serving as the first electrode tab 40 in this experiment) on its negative electrode tab. The 20 through holes 44 are arranged in multiple rows along the length of the negative electrode tab, and the distance between two adjacent through holes 44 along the line connecting their geometric centers is 2 mm. The through holes 44 are rectangular, with a dimension of 1 mm along the width of the negative electrode tab and a dimension of 8 mm along the extension direction of the negative electrode tab. The remaining negative electrode sheets 212 are coated with the negative electrode active material layer 2122 on both sides.
[0106] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.
[0107] (4) Preparation of the isolation membrane 22: A 7 μm thick polyethylene porous polymer film was used as the isolation membrane 22.
[0108] (5) Preparation of electrode assembly 20: The positive electrode 211, the separator 22, and the negative electrode 212 are alternately stacked along the first direction X to obtain the electrode assembly 20. In the stacked structure of the electrode assembly 20, the two outermost electrode sheets are both negative electrode sheets 212 with a negative electrode active material layer 2122 coated on one side. Therefore, in the experiment of this application, the first electrode 201 and the second electrode 202 are negative electrode sheets 212. All the negative electrode tabs are gathered together to form a negative electrode tab bundle, and the adapter 30 is welded to the negative electrode tab bundle. Another adapter 30 is taken, all the positive electrode tabs are gathered together to form a positive electrode tab bundle, and the other adapter 30 is welded to the positive electrode tab bundle.
[0109] (6) Assembly of the secondary battery 100: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing upwards, place the electrode assembly 20 in the punch, and apply external force to press it firmly. Then, cover the electrode assembly 20 with another punched aluminum-plastic film with the punched surface facing downwards, and heat-seal the three edges of the two aluminum-plastic films by hot pressing. The unsealed edge is the side of the adapter 30 that extends out of the housing 10. Then, inject electrolyte through the unsealed edge, and after vacuum sealing, standing, hot pressing formation, shaping and other processes, the secondary battery 100 is obtained.
[0110] The preparation process of the secondary battery 100 in Comparative Example 1 and Comparative Example 2 is basically the same as that in Example 1. The difference is that the negative electrode tab of the outermost negative electrode sheet 212 of the secondary battery 100 in Comparative Example 1 does not have a through hole 44 and the width of the negative electrode tab is larger. The negative electrode tab of the outermost negative electrode sheet 212 of the secondary battery 100 in Comparative Example 2 does not have a through hole 44.
[0111] The preparation process of the secondary battery 100 in Examples 2 to 7 is basically the same as that in Example 1. The difference is that the size of the through hole 44 opened in Examples 2 to 7 is different from that in Example 1.
[0112] The preparation process of the secondary battery 100 in Examples 8 to 13 is basically the same as that in Example 1. The difference is that the distance between two adjacent through holes 44 along the geometric center line in Examples 8 to 13 is different from that in Example 1.
[0113] The preparation process of the secondary battery 100 in Examples 14 to 20 is basically the same as that in Example 11. The difference is that the size of the through hole 44 along the width direction of the negative electrode tab in Examples 14 to 20 is different from that in Example 11.
[0114] The preparation process of the secondary battery 100 in Examples 21 to 26 is basically the same as that in Example 1. The difference is that the first tab 40 of the secondary battery 100 in Examples 21 to 26 does not have a through hole 44. Instead, the negative tab of a negative electrode sheet 212 with a negative electrode active material layer 2122 coated on one side is flattened and narrowed to different degrees along the extension direction of the negative tab.
[0115] After the secondary batteries 100 in the comparative examples and embodiments were prepared, long-cycle tests were conducted on all secondary batteries 100 in each group, and the occurrence of lithium plating on the first electrode 201 was observed; electrical abuse tests were conducted on all secondary batteries 100 in each group, and the occurrence of melting of the first tab 40 was observed; drop tests were conducted on all secondary batteries 100 in each group, and the occurrence of drop failure of the secondary batteries 100 was observed.
[0116] The specific process of long loop testing is as follows:
[0117] 1) Maintain the test temperature at 25℃;
[0118] 2) Let the secondary battery 100 stand for 30 minutes;
[0119] 3) Charge at a constant current of 1.3C to 4.1V, then charge at a constant voltage of 1C;
[0120] 4) Charge at a constant current of 1C to 4.2V, then charge at a constant voltage of 0.7C;
[0121] 5) Charge at a constant current of 0.7C to 4.3V, then charge at a constant voltage to 0.025C;
[0122] 6) Let stand for 5 minutes;
[0123] 7) Discharge at a constant current of 0.7C to 3V;
[0124] 8) Let stand for 5 minutes;
[0125] 9) Repeat steps 3 through 8 800 times;
[0126] 10) Disassemble the secondary battery 100 and observe whether lithium plating occurs on the first electrode 201. Count the number of secondary batteries 100 with lithium plating on the first electrode 201 in each group. Count N as the number of secondary batteries 100 with lithium plating on the first electrode 201 in this group of experiments. Then the lithium plating rate of the secondary batteries 100 in this group of experiments is N / 20. Record the experimental data in Tables 1, 2 and 3.
[0127] The specific process of electrical abuse testing is as follows:
[0128] 1) Maintain the test temperature at 25℃;
[0129] 2) Let the secondary battery 100 stand for 30 minutes;
[0130] 3) Charge at a constant current of 5C to 4.1V, then charge at a constant voltage of 3C;
[0131] 4) Charge at 3C constant current to 4.2V, then charge at constant voltage to 1C;
[0132] 5) Charge at a constant current of 0.7C to 4.3V, then charge at a constant voltage to 0.025C;
[0133] 6) Let stand for 5 minutes;
[0134] 7) Discharge at a constant current of 5C to 3V;
[0135] 8) Let stand for 5 minutes;
[0136] 9) Repeat steps 3 through 8 800 times;
[0137] 10) Disassemble the secondary battery 100 and observe whether the first tab 40 has melted. Count the number of secondary batteries 100 in each group whose first tab 40 has melted. Count the number of secondary batteries 100 whose first tab 40 has melted in this group of experiments as N. Then the melting rate of the first tab 40 in this group of experiments is N / 20. Record the experimental data in Table 1, Table 2 and Table 3.
[0138] The specific process of the drop test is as follows:
[0139] 1) Under environmental conditions of 25±5℃, charge the secondary battery 100 to 100% SOC, and test the voltage of the secondary battery 100 before the drop test.
[0140] 2) Place the secondary battery 100 into the clamping chamber, and use an automatic drop device to drop the bottom, side and top of the secondary battery 100 sequentially from a position of 1.8m onto the steel plate. Each secondary battery 100 is dropped a total of 6 times, or 18 times.
[0141] 3) After the drop test, let it stand at room temperature for 24 hours, and measure and record the voltage of the secondary battery 100.
[0142] 4) Disassemble the secondary battery 100 and observe whether the first tab 40 is broken, whether the first tab 40 is detached from the negative current collector 2121, and whether the negative current collector 2121 around the first tab 40 is torn. If the voltage drop of the secondary battery 100 is greater than 30mV, or if the first tab 40 or the negative current collector 2121 around the first tab 40 is damaged or torn, then the corresponding secondary battery 100 fails the drop test. The number of secondary batteries 100 that fail in this group of experiments is N. The drop failure rate of the secondary batteries 100 in this group of experiments is N / 20. Record the experimental data in Tables 2 and 3.
[0143] Table 1
[0144] Table 2
[0145] Table 3
[0146] In Table 1, the lithium plating rate of the first electrode 201 in Examples 1 to 7 is significantly lower than that in Comparative Examples 1 and 2. That is, by setting S1 < S2, this application helps to reduce the possibility of lithium plating on the first electrode 201. The melting rate of the first tab 40 in Examples 1 to 5 is significantly lower than that in Example 6, and the lithium plating rate of the first electrode 201 in Examples 1 to 5 is significantly lower than that in Example 7. That is, by setting 0.5 ≤ S1 / S2 ≤ 0.9, this application not only helps to ensure sufficient current carrying capacity of the first tab 40 but also helps to better reduce the possibility of lithium plating on the first electrode 201.
[0147] In Table 2, the melting rate of the first tab 40 in Examples 9 to 12 is significantly lower than that in Examples 8 and 13. This is because when the distance between two adjacent through holes 44 or the distance between the through hole 44 and the width edge of the first tab 40 is small, the local current density is prone to be too high, leading to melting of the first tab 40. In other words, by setting 1mm≤D≤8mm, this application helps to reduce the possibility of the first tab 40 melting.
[0148] In Table 2, the drop failure rate of the secondary battery 100 in Example 8 is significantly higher than that in Examples 9 to 13. This is because when the distance between two adjacent through holes 44 is small, the connection strength between the two adjacent through holes 44 is weak. Thus, when the secondary battery 100 is dropped, the two adjacent through holes 44 are prone to interconnection, which can lead to tearing of the first tab 40. In other words, by setting 1mm≤D, this application also helps to reduce the possibility of the first tab 40 breaking when the secondary battery 100 is dropped.
[0149] In Table 2, the drop failure rate of the secondary battery 100 in Example 20 is significantly higher than that in Examples 14 to 19. This is because when the size d1 of the through hole 44 is large, the first tab 40 is more prone to stress concentration in the width direction, making it more susceptible to tearing when the secondary battery 100 is dropped. In other words, by setting d1 ≤ 2 mm, this application helps reduce the likelihood of the first tab 40 breaking during a drop. Furthermore, by setting d1 ≤ 0.5 mm, this application facilitates the machining of the through hole 44 on the first portion 43, thus improving the ease of manufacturing the secondary battery 100.
[0150] In Table 2, the drop failure rate of the secondary battery 100 in Example 20 is significantly higher than that in Examples 14 to 19. This is because when the area of the through hole 44 in the first tab 40 is large, the first tab 40 is more prone to stress concentration in the width direction, thus making the first tab 40 more likely to tear when the secondary battery 100 is dropped. The lithium plating rate of the first electrode 201 in Example 14 is significantly higher than that in Examples 15 to 20. This is because when the area of the through hole 44 in the first tab 40 is small, the current density through the first electrode 201 is still relatively large, resulting in a higher probability of lithium plating on the first electrode 201. In other words, by setting 1.1≤S4 / S3, this application helps to reduce the possibility of the first tab 40 breaking when the secondary battery 100 is dropped. By setting S4 / S3≤5, it helps to reduce the probability of lithium plating on the first electrode 201.
[0151] In Table 3, when 0.5 ≤ W1 / W2, the melting rate and drop failure rate of the first tab 40 in Examples 21 to 26 begin to decrease significantly; when W1 / W2 ≤ 0.9, the lithium plating rate of the first electrode 201 in Examples 21 to 26 begins to decrease significantly. In other words, by setting 0.5 ≤ S1 / S2 ≤ 0.9, this application not only helps to ensure that the first tab 40 has sufficient current carrying capacity, thus reducing the possibility of breakage of the first tab 40 when the secondary battery 100 is dropped, but also helps to reduce the possibility of lithium plating on the first electrode 201.
[0152] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the substantive scope of this application fall within the scope of this application.
Claims
1. A secondary battery, characterized in that, The device includes a housing, an electrode assembly, and an adapter. The housing houses the electrode assembly and the adapter. The electrode assembly includes multiple electrodes and a separator. The multiple electrodes are stacked along a first direction, and the separator is provided between any two adjacent electrodes. The polarities of any two adjacent electrodes are opposite. The first direction is the thickness direction of the electrodes. The plurality of electrodes consists of two outer electrode layers and a plurality of inner electrode layers. The outer electrode layers are located on the outermost layer of the electrode assembly, and the inner electrode layers are located on the inner layers of the electrode assembly. Each electrode includes a current collector and an active material layer. For the outer electrode layer, the active material layer is disposed on one surface of the current collector facing the interior of the electrode assembly along the thickness direction. For the inner electrode layer, the active material layer is disposed on two opposing surfaces of the current collector along the thickness direction. One of the two outer electrode plates is a first electrode plate, and the plurality of inner electrode plates includes a second electrode plate. The first electrode plate and the second electrode plate have the same polarity. The first electrode plate is connected to a first electrode tab, which extends out of the first electrode plate along a second direction. The second electrode plate is connected to a second electrode tab, which extends out of the second electrode plate along a second direction. The first electrode tab and the second electrode tab are connected to the adapter. The second direction is perpendicular to the first direction. The first electrode tab includes a first connecting portion connected to the first electrode plate, a second connecting portion connected to the adapter, and a first portion located between the first connecting portion and the second connecting portion. Along the extending direction of the first electrode tab, the length of the first portion is L1, and the volume of the first portion is V1. The second electrode tab includes a third connecting portion connected to the second electrode plate, a fourth connecting portion connected to the adapter, and a second portion located between the third connecting portion and the fourth connecting portion. Along the extending direction of the second electrode tab, the length of the second portion is L2, and the volume of the second portion is V2. S1 = V1 / L1, S2 = V2 / L2, S1 < S2.
2. The secondary battery according to claim 1, characterized in that, 0.5≤S1 / S2≤0.
9.
3. The secondary battery according to claim 2, characterized in that, 0.05mm 2 ≤S2≤0.5mm 2 。 4. The secondary battery according to any one of claims 1 to 3, characterized in that, The first part is provided with a through hole, which extends through the first part along the thickness direction of the first electrode tab.
5. The secondary battery according to claim 4, characterized in that, Along the width direction of the first electrode tab, the size of the through hole is d1, 0.5mm≤d1≤2mm.
6. The secondary battery according to claim 5, characterized in that, The through hole is arc-shaped and extends along the direction of the first electrode tab. The size of the through hole is d2, where 0.5mm ≤ d2 ≤ 2mm.
7. The secondary battery according to any one of claims 4 to 6, characterized in that, The number of through holes is multiple, and the distance between two adjacent through holes is D, along the line connecting the geometric centers of two adjacent through holes, where 1mm≤D≤8mm.
8. The secondary battery according to any one of claims 4 to 7, characterized in that, The first portion includes a punched area, and the through hole is provided in the punched area; along the extending direction of the first tab, the first connecting portion is closer to the punched area than the second connecting portion.
9. The secondary battery according to claim 8, characterized in that, In the extending direction of the first electrode tab, the punched area includes a first edge and a second edge disposed opposite to each other. Compared with the first edge, the second edge is closer to the second connecting part. Along the extending direction of the first electrode tab, the minimum distance between the first edge and the first connecting part is d3, and the minimum distance between the second edge and the second connecting part is d4, where 0.05×L1≤d3≤0.1×L1 and 0.05×L1≤d4≤0.1×L1.
10. The secondary battery according to any one of claims 4 to 9, characterized in that, In the flattened state, the total projected area of the through hole along the thickness direction of the first electrode tab is S3, and the projected area of the second part along the thickness direction of the second electrode tab is S4, where 1.1≤S4 / S3≤5.
11. The secondary battery according to any one of claims 1 to 10, characterized in that, Along the width direction of the first electrode tab, the minimum width of the first portion is W1; along the width direction of the second electrode tab, the width of the second portion is W2; 0.1≤W1 / W2≤0.
9.
12. The secondary battery according to claim 11, characterized in that, Along the width direction of the first tab, the width of the first portion is equal everywhere, 0.5≤W1 / W2≤0.
9.
13. The secondary battery according to claim 11, characterized in that, 1mm≤W2≤10mm.
14. The secondary battery according to any one of claims 11 to 13, characterized in that, Along the thickness direction of the first electrode tab, the minimum thickness of the first portion is H1; along the thickness direction of the second electrode tab, the thickness of the second portion is H2; H1 < H2.
15. The secondary battery according to claim 14, characterized in that, 0.05mm≤H1.
16. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 15.