Secondary battery and electronic device

Abstract

The application discloses a secondary battery and an electronic device. An isolation film is stacked between a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a negative active material layer facing the positive electrode sheet. The positive electrode sheet includes a positive active material layer facing the negative active material layer. The negative active material layer is provided with a first groove. A negative electrode tab includes a first part and a second part connected to each other. The first part is arranged in the first groove, and the second part extends out of the negative electrode sheet. In a first direction, the first part is divided into a first section and a second section. The first section is connected between the second section and the second part. In a reverse direction of the first direction, the width of the first section in a second direction is arranged to increase, and the width of the second section in the second direction is arranged to decrease. In the second direction, the minimum width of the first section is W a1 , the maximum width of the second section is W b2 , the width of the second part is W2, W a1 ≥ W2, and W b2 ≥ W2. This can reduce lithium precipitation and improve the safety of the secondary battery.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in electronic devices such as smartphones, laptops, wearable devices, and smart home devices due to their high energy density and environmental friendliness. Lithium-ion batteries consist of a positive electrode and a negative electrode, typically requiring positive and negative tabs to lead out the positive and negative terminals. For example, grooves are created in the active material layer of the negative electrode to connect to the negative tabs and lead out the negative electrode. However, creating these grooves requires removing part of the negative electrode active material layer, increasing the risk of lithium plating. Summary of the Invention

[0003] This application aims to provide a secondary battery and electronic device that reduces the technical problem of lithium plating in secondary batteries.

[0004] In one aspect, this application proposes a secondary battery, including a positive electrode, a separator, a negative electrode, and a negative electrode tab. A separator is stacked between the positive and negative electrode. The negative electrode includes a negative active material layer facing the positive electrode, and the positive electrode includes a positive active material layer facing the negative active material layer. The negative active material layer has a first groove. The negative electrode tab includes a first portion and a second portion connected together. The first portion is disposed in the first groove, and the second portion extends out of the negative electrode. Along a first direction, the first portion is divided into a first segment and a second segment, where the first direction is the direction from the negative electrode to the second portion. The first segment connects the second segment and the second portion. Along the opposite direction of the first direction, the width of the first segment increases in the second direction, and the width of the second segment decreases in the second direction. Along the second direction, the minimum width of the first segment is W. a1 The maximum width of the second segment is W. b2 The width of the second part is W2, W a1 ≥W2, W b2 >W2. Wherein, the third direction is the thickness direction of the negative electrode sheet, and the first direction, the second direction, and the third direction are mutually perpendicular.

[0005] In the above technical solution, W is limited. a1 ≥W2, and W b2The increased connection area between W2 and the first section and the negative electrode plate provides more pathways for current transmission between the negative electrode tab and the negative electrode plate. Current that might have been concentrated at the edge of the first groove can now be dispersed across the negative electrode active material layer over a larger area, mitigating excessive current concentration in localized areas and resulting in a more uniform current distribution near the first groove, thus reducing lithium plating. Simultaneously, the increased width of the first section diffuses the current from the connection point with the negative electrode plate, while the decreased width of the second section further adjusts the current distribution within the first groove, complementing the diffusion effect of the first section to create a reasonable current density gradient, resulting in a more uniform current distribution near the first groove. This uniform current density facilitates the uniform insertion and extraction of lithium ions into the negative electrode active material layer, reducing lithium plating problems caused by abnormal lithium ion deposition due to localized current density anomalies, and improving the safety of the secondary battery.

[0006] In some embodiments, along the second direction, the width of the first groove is W1, and the maximum width of the first segment is W. b1 ,0mm≤W1-W b1 A width of ≤4mm ensures sufficient connection area for the first segment within the first groove to conduct current, thereby improving current conduction efficiency and reducing energy loss within the secondary battery. Furthermore, it allows for a closer match between the width of the first segment and the width of the first groove, resulting in a more uniform current distribution near the first segment. This helps reduce situations where local current density is too high or too low, thus minimizing lithium plating and improving the safety and stability of the secondary battery.

[0007] In some embodiments, 1mm≤W1-W b1 With a diameter of ≤2mm, the current dispersion and uncontrolled flow caused by a large remaining space in the first groove can be reduced. This is conducive to maintaining a relatively uniform current distribution near the first section and making full use of the space. It can reduce lithium plating and reduce the energy density loss of the secondary battery.

[0008] In some embodiments, 6mm≤W b1 The diameter is ≤10mm, which allows the first section to fit properly with the first groove while effectively adapting to the area where the current is concentrated near the first groove. This enables the current to be more evenly distributed to the negative electrode active material layer, reducing the risk of lithium plating caused by excessive local current, improving the safety of the secondary battery, and helping to improve the charge and discharge performance of the secondary battery.

[0009] In some embodiments, 8mm≤W b1 With a thickness of ≤9mm, it is easier to precisely control the current distribution, reduce the uneven embedding of lithium ions in the negative electrode active material layer caused by uneven current distribution, thereby further reducing the possibility of lithium plating and improving the safety and stability of the secondary battery.

[0010] In some embodiments, the maximum length of the first portion along the first direction is L. b1 The length of the first groove is L1, where 0mm ≤ L1 - L b1 A thickness of ≤3mm is beneficial for more uniform diffusion of lithium ions in the first direction, which improves the charge and discharge efficiency and cycle stability of the secondary battery and reduces lithium plating caused by uneven distribution of lithium ions.

[0011] In some embodiments, 1mm ≤ L1-L b1 A thickness of ≤2mm allows for a more uniform concentration distribution of lithium ions around the first part, reducing diffusion resistance caused by the concentration gradient and decreasing lithium plating.

[0012] In some embodiments, 12mm≤L b1 The diameter is ≤15mm, which allows the negative electrode tab to better fit with the first groove, facilitating the uniform transmission of current between the negative electrode tab and the negative electrode sheet. This reduces the current concentration in local areas, optimizes the distribution of lithium ions, and allows lithium ions to be more evenly embedded in the negative electrode active material layer, thereby reducing lithium plating.

[0013] In some embodiments, 13mm≤L b1 A thickness of ≤14mm helps to make the current distribution more uniform and reduce the fluctuation of the current density, thereby allowing lithium ions to be embedded more uniformly in the negative electrode active material layer and further reducing the risk of lithium plating.

[0014] In some embodiments, viewed along a third direction, the first groove is divided into a first region and a second region along a first direction. Along the opposite direction of the first direction, the width of the first region is increased in the second direction, and the width of the second region is decreased in the second direction. A first segment is disposed in the first region, and a second segment is disposed in the second region. This allows the negative electrode tab to be more tightly embedded in the first groove, reducing the gap between the first groove and the negative electrode tab, thereby improving the utilization rate of the internal space of the secondary battery and increasing the energy density of the secondary battery.

[0015] In some embodiments, the secondary battery further includes a second adhesive layer disposed on the surface of the positive electrode active material layer facing the first groove. Along a first direction, the second adhesive layer is divided into a third portion and a fourth portion; along the opposite direction of the first direction, the width of the third portion increases in the second direction, and the width of the fourth portion decreases in the second direction. Along a third direction, the third portion covers the first region, and the fourth portion covers the second region. This reduces the space occupied by the second adhesive layer and reduces the amount of negative electrode active material layer covered by the second adhesive layer, and facilitates the uniform distribution of lithium ions near the first groove, contributing to the full utilization of the negative electrode active material layer and improving the energy density of the secondary battery.

[0016] In some embodiments, the secondary battery further includes a first adhesive layer that covers a first portion along a third direction, thereby reducing direct contact between burrs and the separator, thus reducing the risk of burrs puncturing the separator and consequently reducing the occurrence of short circuits.

[0017] In some embodiments, along the first direction, the first adhesive layer is divided into a fifth portion and a sixth portion; along the opposite direction of the first direction, the fifth portion is wider in the second direction, and the sixth portion is narrower in the second direction. Along the third direction, the fifth portion covers the first segment, and the sixth portion covers the second segment. This allows the first adhesive layer to adhere more tightly to the negative electrode tab, effectively covering burrs while reducing space waste caused by excessive use of the first adhesive layer and reducing the amount of negative electrode active material layer covered by the first adhesive layer, thus helping to reduce the energy density loss of the secondary battery.

[0018] In some embodiments, the projection of the first adhesive layer along a third direction is located within the first groove, which can reduce the space occupied by the first adhesive layer and improve the energy density of the secondary battery.

[0019] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0020] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0021] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0022] Figure 1 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application; Figure 2 This is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application; Figure 3 This is a schematic diagram of the stacked structure of electrode assemblies in some embodiments of this application; Figure 4 This is a schematic diagram of the stacked structure of the positive electrode, separator, and negative electrode in some embodiments of this application; Figure 5 This is a schematic diagram showing the connection between the negative electrode tab and the negative electrode plate in some embodiments of this application; Figure 6 This is a schematic diagram of the current density of the negative electrode active material layer at the first groove in some embodiments of this application; Figure 7This is a schematic diagram showing the connection between the negative electrode tab and the negative electrode plate in some embodiments of this application; Figure 8 This is a schematic diagram showing the connection between the negative electrode tab and the negative electrode plate in some embodiments of this application; Figure 9 This is a schematic diagram showing the connection between the negative electrode tab and the negative electrode plate in some embodiments of this application; Figure 10 This is a schematic diagram of the bonding between the first adhesive layer and the positive electrode active material layer in some embodiments of this application.

[0023] Explanation of reference numerals in the attached figures: 1000, secondary battery; 100. Electrode assembly; 10. Positive electrode sheet; 11. Positive current collector; 111. First surface; 112. Second surface; 12. Positive active material layer; 20. Negative electrode sheet; 20a. First end; 20b. Second end; 21. Negative current collector; 211. Third surface; 212. Fourth surface; 22. Negative active material layer; 221. First groove; 2211. First region; 2212. Second region; 222. First edge; 30. Separating membrane; 40. Negative electrode tab; 41. First part; 411. First section; 412. Second section; 42. Second part; 50. First adhesive layer; 51. Fifth part; 52. Sixth part; 60. Second adhesive layer; 61. Third part; 62. Fourth part; 200. Shell; X, first direction; Y, second direction; Z, third direction. Detailed Implementation

[0024] 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.

[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 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.

[0027] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0028] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0029] Firstly, this application proposes a secondary battery 1000, please refer to... Figure 1 The secondary battery 1000 includes an electrode assembly 100, a housing 200, and an electrolyte (not shown in the figure). The housing 200 can accommodate the electrode assembly 100 and the electrolyte, and the electrolyte wets the electrode assembly 100 inside the housing 200.

[0030] For the electrode assembly 100 mentioned above, please refer to... Figures 1 to 3 The electrode assembly 100 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10, the separator 30, and the negative electrode 20 are stacked and wound together. Figure 2 The diagram illustrates a wound structure of the electrode assembly 100, for example, stacked along the thickness direction of the positive electrode 10 and / or the negative electrode 20 and wound along their length direction to form a wound electrode assembly 100. In some other embodiments, the electrode assembly 100 may also employ a stacked structure, wherein... Figure 3 The electrode assembly 100 is shown in a stacked structure. Along the third direction Z (the thickness direction of the positive electrode 10 and / or the negative electrode 20), multiple positive electrode 10 and multiple negative electrode 20 are stacked alternately, and a separator 30 is provided between adjacent positive electrode 10 and negative electrode 20.

[0031] It should be noted that, in the embodiments of this application, the first direction X is the width direction of the positive electrode 10 and / or the negative electrode 20, the second direction Y is the length direction of the positive electrode 10 and / or the negative electrode 20, and the third direction Z is the thickness direction of the positive electrode 10 and / or the negative electrode 20. The first direction X, the second direction Y, and the third direction Z are all perpendicular to each other. In the stacked electrode assembly 100, the first direction X may also be the width direction of the positive electrode 10 and / or the negative electrode 20, and the second direction Y may also be the length direction of the positive electrode 10 and / or the negative electrode 20.

[0032] Please refer to Figure 4 The positive electrode 10 includes a positive current collector 11 and a positive active material layer 12. The positive current collector 11 can be made of a flat aluminum foil, titanium foil, nickel foil, or stainless steel foil. The positive active material layer 12 can be disposed on at least one surface of the positive current collector 11 in the thickness direction, for example, along the third direction Z. The positive current collector 11 includes a first surface 111 and a second surface 112 disposed opposite to each other. The positive active material layer 12 can be disposed on the first surface 111 and / or the second surface 112. The positive active material layer 12 includes a positive active material, a conductive agent, and a binder. The above material components are mixed, stirred evenly, and coated on the first surface 111 and / or the second surface 112 to obtain the positive active material layer 12. The positive active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate.

[0033] Please refer to Figure 4 The negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 can be made of a flat copper foil, titanium foil, nickel foil, stainless steel foil, or silver foil. The negative electrode active material layer 22 can be disposed on at least one surface of the negative electrode current collector 21 in the thickness direction, for example, along the third direction Z. The negative electrode current collector 21 includes a third surface 211 and a fourth surface 212 disposed opposite to each other, and the negative electrode active material layer 22 can be disposed on the third surface 211 and / or the fourth surface 212. The negative electrode active material layer 22 includes a negative electrode active material, a conductive agent, and a binder, etc. These materials are mixed, stirred evenly, and coated on the third surface 211 and / or the fourth surface 212 to obtain the negative electrode active material layer 22. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, silicon alloy, etc.

[0034] In some embodiments, the separator 30 includes a substrate layer (not shown) and a ceramic layer (not shown). The substrate layer includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, polyimide, or polyamide, and the ceramic layer includes at least one of alumina, magnesium oxide, or zirconium oxide. This allows the separator 30 to adapt to the electrolyte environment inside the secondary battery 1000, extending the service life of the separator 30.

[0035] In some other embodiments, the separator 30 may not require a ceramic layer, meaning it may consist only of a substrate layer. A separator 30 without a ceramic layer offers better flexibility, facilitating the expansion of the negative electrode 20. Furthermore, it exhibits higher ionic conductivity, reducing the internal resistance of the secondary battery 1000 and improving secondary cycle life. Simultaneously, the separator 30 exhibits a lower thermal shrinkage rate, maintaining good dimensional stability under high-temperature conditions and reducing the risk of internal short circuits in the secondary battery 1000 due to thermal shrinkage.

[0036] The 1000 rechargeable battery also includes a 40 negative electrode tab; please refer to [link / reference]. Figure 4 and Figure 5 The negative electrode tab 40 is connected to the aforementioned negative electrode sheet 20. For example, a first groove 221 is provided on the aforementioned negative electrode active material layer 22. The first groove 221 can be formed by laser cleaning on the negative electrode active material layer 22, or by using foaming adhesive process and mechanical processing to remove part of the negative electrode active material layer 22, thereby forming the first groove 221, so that the negative electrode current collector 21 is exposed from the first groove 221. The negative electrode tab 40 includes a first part 41 and a second part 42 connected to each other. The first part 41 is disposed in the first groove 221 and connected to the negative electrode current collector 21. The connection method includes, but is not limited to, welding or conductive adhesive bonding. The second part 42 extends out of the negative electrode sheet 20, wherein the first direction X is the direction from the negative electrode sheet 20 to the second part 42.

[0037] Please refer to Figure 4 The secondary battery 1000 also includes a first adhesive layer 50, which is disposed on the surface of the positive electrode active material layer 12 facing the negative electrode active material layer 22. Along the third direction Z, the first adhesive layer 50 covers the first groove 221. The portion of the positive electrode active material layer 12 corresponding to the first groove 221 is covered by the first adhesive layer 50, which reduces or prevents the extraction of lithium ions from this portion of the positive electrode active material layer 12. This allows the negative electrode active material layer 22 to have sufficient margin for lithium ion insertion, thereby reducing the risk of lithium plating.

[0038] The inventors of this application have discovered that there is an uneven current density at the first groove 221 of the negative electrode active material layer 22. Please refer to... Figure 6 , Figure 6This diagram illustrates the current density near the first groove 221 in the negative electrode active material layer 22; darker colors indicate higher current densities. Figure 5 As can be seen, the current density increases closer to the first groove 221. When the current density of the negative electrode active material layer 22 is high, the electrochemical reaction is intense, and a large number of lithium ions are released and reach the surface of the negative electrode active material layer 22 per unit time. This easily leads to the accumulation of lithium ions on the surface of the negative electrode active material layer 22, resulting in lithium plating. Furthermore, high current density can cause increased local polarization of the negative electrode active material layer 22 (the potential in the local area deviates from the equilibrium potential), which may lower the negative electrode potential. When the negative electrode potential is lower than the potential for lithium ions to be reduced to metallic lithium, lithium plating may occur. Lithium plating may cause safety problems such as internal short circuits and overheating in the secondary battery 1000.

[0039] To reduce the above problems, please refer to Figure 5 Along the first direction X, the first part 41 is divided into a first segment 411 and a second segment 412. The first segment 411 connects the second segment 412 and the second part 42. Along the opposite direction of the first direction X, the width of the first segment 411 in the second direction Y is increased; for example, the width of the first segment 411 gradually increases in the second direction Y, or the first segment 411 is divided into multiple segments, with the width increasing closer to the second segment 412. Along the opposite direction of the first direction X, the width of the second segment 412 in the second direction Y is decreased; for example, the width of the second segment 412 gradually decreases in the second direction Y, or the second segment is divided into multiple segments, with the width decreasing further away from the first segment 411. The minimum width of the first segment 411 along the second direction Y is W. a1 The maximum width of the second segment 412 is W. b2 The width of the second part 42 is W2, W a1 ≥W2, W b2 >W2.

[0040] In the embodiments of this application, W is defined as follows: a1 ≥W2, and W b2 >W2, that is, the increased connection area between the first part 41 and the negative electrode 20, allows for more paths to be chosen when the current is transmitted between the negative electrode tab 40 and the negative electrode 20. The current that might have been concentrated at the edge of the first groove 221 can be dispersed onto the negative electrode active material layer 22 over a larger area, thereby alleviating the excessive concentration of current in local areas and making the current distribution near the first groove 221 more uniform, thus reducing lithium plating.

[0041] Furthermore, from Figure 6As can be seen, the current density is greater closer to the first groove 221, and the current density is also greater closer to the edge of the negative electrode active material layer 22 (first edge 222). In the embodiments of this application, the width of the first segment 411 is increased in the second direction Y along the opposite direction of the first direction X. This makes the cross-sectional area of ​​the conduction path gradually increase when the current is transmitted between the first segment 411 and the negative electrode plate 20. The current tends to pass through the path with lower resistance, thus guiding the current to diffuse away from the edge of the negative electrode active material layer 22. This is beneficial for a more uniform distribution of the current near the first groove 221, reducing the concentration of current at the edge of the negative electrode active material layer 22, and thus reducing lithium plating.

[0042] Simultaneously, as the current conducts into the negative electrode 20, the amount of current it needs to carry gradually decreases. In this embodiment, the width of the second segment 412 in the second direction Y is reduced along the opposite direction of the first direction X. When the current is conducted from the first segment 411 to the second segment 412, the current is relatively evenly dispersed after diffusion through the first segment 411. At this time, the width of the second segment 412 in the second direction Y is reduced, which prevents the current from being too dispersed due to the large cross-sectional area of ​​the path during the continued conduction process, and reduces the current accumulation on the side of the first groove 221 away from the first edge 222.

[0043] The increased width of the first segment 411 is responsible for diffusing the current from the connection point with the negative electrode 20. The decreased width of the second segment 412, based on the diffusion effect of the first segment 411, further adjusts the current distribution within the first groove 221. Together with the current diffusion effect of the first segment 411, they form a reasonable current density gradient, resulting in a more uniform current distribution near the first groove 221. This uniform current density facilitates the uniform insertion and extraction of lithium ions into the negative electrode active material layer 22, reducing lithium plating problems caused by abnormal lithium ion deposition due to localized current density anomalies, and improving the safety of the secondary battery 1000.

[0044] In some embodiments, along the second direction Y, the width of the first groove 221 is W1, and the maximum width of the first segment 411 is W. b1 ,0mm≤W1-W b1≤4mm, any value from 0mm to 4mm can be selected, such as 0mm, 1mm, 2mm, 3mm, or 4mm. This ensures that the first segment 411 has sufficient connection area within the first groove 221 to conduct current, thereby improving current conduction efficiency and reducing energy loss within the secondary battery 1000. Furthermore, it allows for a closer match between the width of the first segment 411 and the width of the first groove 221, resulting in a more uniform current distribution near the first segment 411. This helps reduce situations where local current density is too high or too low, thus reducing lithium plating and improving the safety and stability of the secondary battery 1000. It can be understood that the maximum width of the first segment 411 is equal to the maximum width of the second segment 412, i.e., W. b1 =W b2 .

[0045] If W1-W b1 If the diameter is large, for example, greater than 4mm, then the first segment 411 occupies a small proportion within the first groove 221. When current is conducted from the first segment 411 to the negative electrode 20, uneven current dispersion is likely to occur in the remaining space of the first groove 221. When the current is conducted to the negative electrode active material layer 22, it can easily lead to excessively high or low local current density, thereby affecting the uniform embedding of lithium ions in the negative electrode active material layer 22 and increasing the risk of lithium plating. Furthermore, the first groove 221 is relatively wider than the first segment 411, meaning that a significant amount of space in the first groove 221 region is not effectively utilized by the first segment 411 or the negative electrode active material layer 22, resulting in a waste of the active material layer and a loss of energy density of 1000 in the secondary battery.

[0046] And if W1-W b1 A smaller size, such as less than 0 mm, means that the width of the negative electrode tab 40 is larger. The negative electrode tab 40 will interfere with the negative electrode active material layer 22, making it difficult to weld the negative electrode tab 40 to the negative electrode sheet 20, and will also damage the negative electrode active material layer 22.

[0047] In the embodiments of this application, further, 1mm≤W1-W b1 ≤2mm, this range allows for more precise control of the current distribution within the first groove 221. W1-W b1 A diameter of ≥1mm reduces overcrowding of the first segment 411 within the first groove 221, facilitating electrical connection between negative electrode plates 20 and allowing current to diffuse smoothly from the first segment 411 to the surrounding area. This promotes a more uniform current density distribution, reduces the risk of localized current concentration, and consequently minimizes lithium plating. Simultaneously, W1-W b1≤2mm can reduce the current dispersion and runaway caused by the large remaining space in the first groove 221, which is conducive to the current maintaining a relatively uniform distribution near the first section 411, and can make full use of the space, which can reduce lithium plating and reduce the energy density loss of the secondary battery 1000.

[0048] The maximum width of the first segment 411 is W. b1 In the embodiments of this application, 6mm≤W is selected. b1 The width can be ≤10mm, and any value between 6mm and 10mm can be selected, such as 6mm, 7mm, 8mm, 9mm, or 10mm. Within this range, the maximum width of the first segment 411 can be well adapted to the first groove 221. The range of 6mm to 10mm allows the first segment 411 to fit reasonably with the first groove 221 while effectively adapting to the area of ​​concentrated current near the first groove 221. This enables the current to be more evenly distributed to the negative electrode active material layer 22, reducing the risk of lithium plating caused by excessive local current, improving the safety of the secondary battery 1000, and also helping to improve the charge and discharge performance of the secondary battery 1000.

[0049] Furthermore, 8mm≤W b1 ≤9mm, within this range, it is more conducive to the precise matching of the width of the first segment 411 with the structure of the first groove 221 and the entire negative electrode plate 20. When current is transmitted through the negative electrode tab 40, a width of 8mm to 9mm allows the current to be more evenly distributed within the first segment 411, reducing the occurrence of local current densities that are too high or too low. Compared to 6mm ≤W b1 ≤10mm range, 8mm≤W b1 A thickness of ≤9mm allows for more precise control of current distribution, reducing uneven lithium ion embedding in the negative electrode active material layer 22 caused by uneven current distribution. This further reduces the possibility of lithium plating and improves the safety and stability of the secondary battery 1000. Furthermore, this width range makes it easier for lithium ions to travel along a more regular and orderly path under the influence of an electric field, contributing to improved charge and discharge efficiency of the secondary battery 1000.

[0050] In some embodiments, please refer to Figure 7 Along the first direction X, the maximum length of the first part 41 is L. b1 The length of the first groove 221 is L1, 0mm≤L1-L b1The length difference is ≤3mm, and any value from 0 to 3mm can be selected, such as 0mm, 1mm, 2mm, or 3mm. In the first direction X, this length difference range facilitates efficient current collection and uniform transmission. The first portion 41 has sufficient space within the first groove 221, allowing for smoother current transmission and reducing the risk of current obstruction due to excessive length. Simultaneously, it reduces excessive current dispersion during transmission caused by the first groove 221 being too long relative to the first portion 41, enabling rapid current transmission from the first portion 41 to the negative electrode active material layer 22, thereby improving current transmission efficiency and reducing energy loss. Furthermore, this length difference range promotes more uniform diffusion of lithium ions in the first direction X, improving the charge / discharge efficiency and cycle stability of the secondary battery 100, and reducing lithium plating caused by uneven lithium ion distribution.

[0051] If L1-L b1 If the diameter is large, for example greater than 3 mm, then the first groove 221 is relatively long compared to the first portion 41, which may cause excessive current dispersion during transmission. For example, it may form an irregular distribution in the extra space of the first groove 221. This will lead to uneven embedding of lithium ions in the negative electrode active material layer 22, easily initiating lithium plating. Furthermore, L1−L b1 A larger size means that the first groove 221 occupies too much space. Given a fixed volume of the negative electrode 20, this will compress the proportion of active material, leading to a 1000 kcal / s energy density loss in the secondary battery. However, if L1-L... b1 If the diameter is small, for example, less than 0 mm, then the negative electrode tab 40 will interfere with the negative electrode active material layer 22 when it is installed in the first groove 221.

[0052] Furthermore, 1mm≤L1-L b1 ≤2mm allows for more precise control of current distribution in the negative electrode 20. When current passes through the first part 41, the 1mm to 2mm length difference makes the current transmission path within the first groove 221 more stable and uniform, compared to 0mm≤L1−L b1 Compared to ≤3mm, a smaller difference range can reduce current disturbance and loss during transmission, and reduce current concentration in certain local areas, thereby improving the charge and discharge efficiency of the secondary battery 1000. Furthermore, it allows for a more uniform concentration distribution of lithium ions around the first part 41, reducing diffusion resistance caused by concentration gradients and minimizing lithium plating.

[0053] In some embodiments, 12mm≤L b1The length can be ≤15mm, and any value between 12mm and 15mm can be selected, such as 12mm, 13mm, 14mm, or 15mm. This length range can better adapt to the first groove 221, facilitating uniform current transmission between the negative electrode tab 40 and the negative electrode sheet 20, reducing excessive current concentration in local areas, optimizing the distribution of lithium ions, and enabling lithium ions to be more uniformly embedded in the negative electrode active material layer 22, thereby reducing lithium plating.

[0054] Furthermore, 13mm≤L b1 ≤14mm allows for further optimization of the current conduction path between the first part 41 and the negative electrode 20, compared to 12mm≤L b1 The range is ≤15mm, limited to 13mm≤L b1 A thickness of ≤14mm helps to make the current distribution more uniform and reduce the fluctuation of the current density, thereby allowing lithium ions to be embedded more uniformly in the negative electrode active material layer 22, further reducing the risk of lithium plating.

[0055] Regarding the shape of the first groove 221, besides a square shape, it can also be a shape adapted to the negative electrode tab 40. Please refer to... Figure 8 Viewed along the third direction Z, the first groove 221 is divided into a first region 2211 and a second region 2212 in the first direction X. In the opposite direction of the first direction X, the width of the first region 2211 in the second direction Y is increased, allowing its shape to fit the first segment 411. The width of the second region 2212 in the second direction Y is decreased, allowing its shape to fit the second segment 412. The first segment 411 is located in the first region 2211, and the second segment 412 is located in the second region 2212.

[0056] In the embodiments of this application, the shape of the first region 2211 is adapted to the shape of the first segment 411, and the shape of the second region 2212 is adapted to the shape of the second segment 412, so that the negative electrode tab 40 can be more tightly embedded in the first groove 221. Compared with a square groove, the shape adaptation can better fit the contour of the negative electrode tab 40, reduce the gap between the first groove 221 and the negative electrode tab 40, thereby improving the utilization rate of the internal space of the secondary battery 1000 and thus improving the energy density of the secondary battery 1000. Furthermore, the good adaptation between the negative electrode tab 40 and the first groove 221 allows the first segment 411 to be accurately disposed in the first region 2211, and the second segment 412 to be accurately disposed in the second region 2212, thereby making the electrical connection between the negative electrode tab 40 and the negative electrode sheet 20 more stable and reliable. Because the negative electrode tab 40 and the first groove 221 are more precisely matched, the negative electrode tab 40 has a more obvious effect on current guidance, which is conducive to fully improving the current distribution near the first groove 221, thereby optimizing the transport of lithium ions, reducing the excessive accumulation of lithium ions near the first groove 221, and thus reducing lithium plating.

[0057] Please refer to Figure 8 and Figure 9 The secondary battery 1000 also includes a first adhesive layer 50, which covers a first portion 41 along the third direction Z. The first portion 41 of the negative electrode tab 40 may have burrs, for example, welding burrs may be generated when the first portion 41 of the negative electrode tab 40 is welded to the negative electrode sheet 20 within the first groove 221. Cutting burrs may also be formed when the first portion 41 is cut out. In the embodiments of this application, the first adhesive layer 50 covers the first portion 41 along the third direction Z, directly separating the burrs on the negative electrode tab 40 from the separator 30. The first adhesive layer 50 has a certain thickness and flexibility, forming a physical barrier, reducing direct contact between burrs and the separator 30, thereby reducing the risk of burrs piercing the separator 30 and thus reducing the occurrence of short circuits.

[0058] Along the first direction X, the first adhesive layer 50 is divided into a fifth part 51 and a sixth part 52. Along the opposite direction X, the width of the fifth part 51 in the second direction Y is increased, allowing it to fit with the first segment 411. The width of the sixth part 52 in the second direction Y is decreased, allowing it to fit with the second segment 412. Along the third direction Z, the fifth part 51 covers the first segment 411, and the sixth part 52 covers the second segment 412. This fitting design between the first adhesive layer 50 and the negative electrode tab 40 allows the first adhesive layer 50 to adhere more tightly to the negative electrode tab 40. This effectively covers burrs while reducing space waste caused by excessive use of the first adhesive layer 50 and reducing the amount of negative electrode active material layer 22 covered by the first adhesive layer 50, thus helping to reduce the energy density loss of the secondary battery 1000.

[0059] In some embodiments, the projection of the first adhesive layer 50 along the third direction Z is located within the first groove 221, which can reduce the space occupied by the first adhesive layer 50 and improve the energy density of the secondary battery 1000. Furthermore, it can reduce the interference of the first adhesive layer 50 with the negative electrode active material layer 22, such as reducing adhesive damage to the negative electrode active material layer 22.

[0060] In some embodiments, please refer to further details. Figure 10 The secondary battery 1000 also includes a second adhesive layer 60, which is disposed on the surface of the positive electrode active material layer 12 facing the first groove 221. Along the first direction X, the second adhesive layer 60 is divided into a third portion 61 and a fourth portion 62. Along the opposite direction of the first direction X, the width of the third portion 61 in the second direction Y is increased, allowing the third portion 61 to conform to the shape of the first segment 411; the width of the fourth portion 62 in the second direction Y is decreased, allowing the shape of the fourth portion 62 to conform to the shape of the second segment 412. Along the third direction Z, the third portion 61 covers the first region 2211, and the fourth portion 62 covers the second region 2212.

[0061] In the embodiments of this application, the third portion 61 is adapted to the shape of the first region 2211, and the fourth portion 62 is adapted to the shape of the second region 2212. This facilitates precise isolation between the first groove 221 and the negative electrode active material layer 22, reducing the direct transport of lithium ions towards the first groove 221. Furthermore, the shape adapted to the first groove 221 reduces the space occupied by the second adhesive layer 60 and reduces the amount of negative electrode active material layer 22 covered by the second adhesive layer 60. It also makes it easier to guide lithium ions to distribute evenly near the first groove 221, which helps to fully utilize the negative electrode active material layer 22 and improves the energy density of the secondary battery 1000.

[0062] Secondly, this application also proposes an electronic device, including a secondary battery 1000 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0063] Example 1-1 Preparation of the positive electrode sheet: The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight-average molecular weight of 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and stirred evenly under vacuum. An aluminum foil with a thickness of 8 μm and a length of 1000 mm was selected as the positive electrode current collector. The positive electrode slurry was uniformly coated on one surface of the aluminum foil and dried at 110°C to obtain a positive electrode sheet with a single-sided coating of positive active material. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material.

[0064] Preparation of negative electrode sheet: A negative electrode active material (graphite powder), silicon powder, conductive carbon black (Super P), and binder (styrene-butadiene rubber (SBR)) were mixed in a weight ratio of 87.5:10:1:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred thoroughly. A copper foil with a thickness of 5 μm and a length of 1050 mm was selected as the negative electrode current collector. The negative electrode slurry was uniformly coated onto one surface of the copper foil, leaving an uncoated area. The foil was then dried at 90°C to obtain a single-sided negative electrode sheet. This process completes the single-sided coating of the negative electrode sheet. The same steps were then repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode sheet.

[0065] Preparation of the separating membrane: A porous separator membrane was prepared by using polyethylene as a 7μm substrate layer and polyvinylidene fluoride as an adhesive layer, with an alumina ceramic layer of 2μm thickness placed on the side of the adhesive layer away from the substrate layer.

[0066] Electrolyte preparation: In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solvent. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0067] Preparation of lithium-ion secondary batteries: Laser cleaning creates a first groove of 10mm (L1) × 15mm (W1) in the aforementioned negative electrode active material layer. A nickel sheet is selected as the negative electrode tab, which is welded to the negative electrode sheet in the first groove. The structure of the negative electrode tab is as follows: Figure 5As shown, the negative electrode tab includes a first part and a second part connected together. The first part is disposed in a first groove, and the second part extends out of the negative electrode plate. The first part is divided into a first segment and a second segment. The first segment connects the second segment and the second part. Along the opposite direction of the first direction, the width of the first segment increases in the second direction, and the width of the second segment decreases in the second direction. The minimum width W of the first segment is... a1 The maximum width W of the first segment is 5mm. b1 The maximum width W of the second segment is 5.5mm. b2 =W b1 It is 5.5mm. The maximum length of the first part is L. b1 The thickness is 13mm. After welding the positive electrode tab to the positive electrode sheet, the prepared separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and wound to obtain the electrode assembly. The perforated aluminum-plastic film (150μm thick) is placed in the assembly fixture with the perforated surface facing upwards, and the electrode assembly is placed in the perforation. Then, electrolyte is injected into the perforation of the aluminum-plastic film, and the positive and negative electrode tabs are led out of the aluminum-plastic film for encapsulation, formation, and other processes to obtain a lithium-ion secondary battery.

[0068] The relevant parameters in Examples 2 to 17 and Comparative Examples 1 to 3 are shown in Table 1 below. In Example 7, the width W1 of the first groove is 10.5 mm. In Example 17, the length L1 of the first groove is 15.5 mm.

[0069] Lithium plating test method: Place the lithium-ion secondary battery in an environment with a test temperature of 25℃ for 30 minutes, and then perform step charging according to the following charging steps: (1) Charge at a constant current of 5C to 4.23V, and charge at a constant voltage of 4C; (2) Charge at a constant current of 4C to 4.3V, and charge at a constant voltage of 3C; (3) Charge at 3C constant current to 4.4V, then charge at 2C constant voltage; (4) Charge at a constant current of 2C to 4.5V, and charge at a constant voltage of 0.05C; After letting it stand for 10 minutes, proceed with the following steps to discharge: Discharge to 3V using 0.2C DC.

[0070] The above charging and discharging process constitutes one cycle. After repeating 100 cycles, with the lithium-ion secondary battery fully charged (maximum design voltage 4.5V), the secondary battery is disassembled to obtain the positive electrode, separator, and negative electrode. If the lithium deposition area near the first groove is found to be greater than or equal to 2mm², then... 2 If the number of lithium-ion batteries tested is X, then the lithium plating rate is X / 20.

[0071] Table 1

[0072] According to Table 1 above, and in conjunction with Examples 1 to 17 and Comparative Examples 1 to 3, it can be seen that when W is used... a1 ≥W2, and W b2 >W2 effectively reduces the risk of lithium plating. Along the opposite direction of the first direction X, the width of the first segment is increased in the second direction. This causes the cross-sectional area of ​​the conduction path to gradually increase as the current travels between the first segment and the negative electrode. This guides the current to diffuse away from the edge of the negative electrode active material layer, promoting a more uniform current distribution near the first groove and reducing current concentration at the edge of the negative electrode active material layer, thereby reducing lithium plating. The width of the second segment is decreased in the second direction Y. This prevents the current from becoming too dispersed due to the larger cross-sectional area of ​​the path during continued conduction, reducing current accumulation on the side of the first groove away from the first edge, further reducing the risk of lithium plating.

[0073] In conjunction with Examples 1 to 7, in Example 1, the maximum width W of the second segment b2 Smaller, that is, the maximum width W of the first segment b1 If smaller, then W1-W b1 When the current is relatively large, it is easy for uneven current dispersion to occur in the remaining space of the first groove when the current is conducted from the first section to the negative electrode. This can easily lead to excessively high or low local current density, which in turn affects the uniform intercalation of lithium ions into the negative electrode active material layer, increasing the risk of lithium plating. Furthermore, it can cause waste of the active material layer, resulting in a loss of energy density in the secondary battery. In Example 7, W b2 The larger size necessitates a larger first groove to accommodate the second section, which easily leads to waste of the active material layer, resulting in energy density loss in the secondary battery. Furthermore, the failure rate is similar to that of Example 6. Considering both increasing energy density and reducing lithium plating, in the embodiments of this application, a depth of 6mm ≤ W is selected. b2 ≤10mm, W b1 =W b2 That is, the maximum width of the first segment can be selected as 6mm≤W b1 ≤10mm. Regarding the minimum width difference between the first groove and the first segment, in the embodiments of this application, in conjunction with embodiments 2 to 6, 0mm ≤ W1-W can be selected. b1 ≤4mm.

[0074] In Examples 4 and 5, the lithium plating rate is relatively low. Furthermore, compared to Example 6, Examples 4 and 5 have a certain gap between the negative electrode tab and the first groove, facilitating the connection between the negative electrode tab and the negative electrode sheet. In Example 6, however, the maximum width of the first section is larger, which may cause interference with the negative electrode active material layer during installation, potentially damaging the negative electrode active material layer. In the embodiments of this application, preferably 8mm ≤ W b1 ≤9mm, and 8mm≤W b2 ≤9mm. Regarding the minimum width difference between the first groove and the first segment, in the embodiments of this application, in conjunction with embodiments 4 and 5, it can be selected as 1mm ≤ W1-W. b1 ≤2mm.

[0075] Referring to Examples 12 to 17, in Example 12, the maximum length L of the first part is... b1 If smaller, then L1-L b1 The larger size of the first groove, which is relatively longer than the first portion, may cause excessive current dispersion during transmission. This can lead to irregular distribution of lithium ions within the excess space of the first groove, resulting in uneven embedding of lithium ions in the negative electrode active material layer and easily triggering lithium plating. In Example 17, L b1 The first portion is relatively large, requiring a larger first groove to accommodate its size, resulting in a significant waste of the negative electrode active material layer and a loss in the energy density of the secondary battery. Furthermore, the failure rate is similar to that of Example 16. In the embodiments of this application, the maximum length of the first portion can be selected to be 12mm ≤ L. b1 ≤15mm. Regarding the length difference between the first groove and the first portion, in the embodiments of this application, preferably 0mm≤L1-L b1 ≤3mm.

[0076] In Examples 14 and 15, the lithium plating rate is further reduced. Furthermore, compared to Example 16, in Examples 14 and 15, there is a certain gap between the negative electrode tab and the first groove, which facilitates the connection between the negative electrode tab and the negative electrode sheet. In Example 16, this gap may cause interference between the negative electrode tab and the negative electrode active material layer, potentially damaging the negative electrode active material layer. Therefore, in the embodiments of this application, a thickness of 13mm ≤ L is preferred. b1 ≤14mm. Regarding the length difference between the first groove and the first portion, in the embodiments of this application, it is preferred that 1mm ≤ L1-L. b1 ≤2mm.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A secondary battery, comprising a positive electrode, a separator, a negative electrode, and a negative electrode tab, wherein the separator is stacked between the positive electrode and the negative electrode, the negative electrode includes a negative active material layer facing the positive electrode, the positive electrode includes a positive active material layer facing the negative active material layer, and the negative active material layer is provided with a first groove; the negative electrode tab includes a first portion and a second portion connected together, the first portion being disposed in the first groove, and the second portion extending out of the negative electrode, characterized in that: Along a first direction, the first part is divided into a first segment and a second segment, the first direction being the direction in which the negative electrode sheet points to the second part; the first segment is connected between the second segment and the second part; along the opposite direction of the first direction, the width of the first segment is increased in the second direction, and the width of the second segment is decreased in the second direction; Along the second direction, the minimum width of the first segment is W. a1 The maximum width of the second segment is W. b2 The width of the second part is W2, W a1 ≥W2, W b2 >W2; The third direction is the thickness direction of the negative electrode sheet, and the first direction, the second direction, and the third direction are all perpendicular to each other.

2. The secondary battery according to claim 1, characterized in that, Along the second direction, the width of the first groove is W1, and the maximum width of the first segment is W. b1 ,0mm≤W1-W b1 ≤4mm.

3. The secondary battery according to claim 2, characterized in that, 1mm≤W1-W b1 ≤2mm。 4. The secondary battery according to claim 2, characterized in that, 6mm≤W b1 ≤10mm。 5. The secondary battery according to claim 4, characterized in that, 8mm≤W b1 ≤9mm。 6. The secondary battery according to claim 1, characterized in that, Along the first direction, the maximum length of the first portion is L. b1 The length of the first groove is L1, where 0mm ≤ L1 - L b1 ≤3mm.

7. The secondary battery according to claim 6, characterized in that, 1mm≤L1-L b1 ≤2mm。 8. The secondary battery according to claim 6, characterized in that, 12mm≤L b1 ≤15mm。 9. The secondary battery according to claim 8, characterized in that, 13mm≤L b1 ≤14mm。 10. The secondary battery according to claim 1, characterized in that, Viewed along the third direction, the first groove is divided into a first region and a second region along the first direction; along the opposite direction of the first direction, the width of the first region in the second direction is increased, and the width of the second region in the second direction is decreased. The first segment is set in the first region, and the second segment is set in the second region.

11. The secondary battery according to claim 10, characterized in that, The secondary battery further includes a second adhesive layer, which is disposed on the surface of the positive electrode active material layer facing the first groove. Along the first direction, the second adhesive layer is divided into a third part and a fourth part; along the opposite direction of the first direction, the width of the third part in the second direction is increased, and the width of the fourth part in the second direction is decreased. Along the third direction, the third portion covers the first region, and the fourth portion covers the second region.

12. The secondary battery according to claim 1, characterized in that, The secondary battery further includes a first adhesive layer, which covers the first portion along the third direction.

13. The secondary battery according to claim 12, characterized in that, Along the first direction, the first adhesive layer is divided into a fifth part and a sixth part; along the opposite direction of the first direction, the width of the fifth part in the second direction is increased, and the width of the sixth part in the second direction is decreased. Along the third direction, the fifth part covers the first segment, and the sixth part covers the second segment.

14. The secondary battery according to claim 12 or 13, characterized in that, Along the third direction, the projection of the first adhesive layer is located within the first groove.

15. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 14.

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