Secondary battery, battery module including the secondary battery, battery pack, and electric device

Abstract

The present application discloses a secondary battery, a battery module, a battery pack, and an electrical device including the secondary battery. The secondary battery includes: a positive electrode plate including a positive electrode film layer; a separator; a negative electrode plate including a first negative electrode film layer, the first negative electrode film layer being disposed opposite to the positive electrode film layer with the separator therebetween, and a second negative electrode film layer. The second negative electrode film layer includes a negative electrode film layer that is not disposed opposite to the positive electrode film layer. The second negative electrode film layer includes a central region and a peripheral region surrounding the central region. Wherein, a lithium source for supplementing lithium to the first negative electrode film layer is stored in at least a part of the peripheral region of the second negative electrode film layer.

Description

Technical Field

[0001] This application belongs to the technical field of secondary batteries, and particularly relates to a secondary battery, a battery module containing the secondary battery, a battery pack, and an electrical device. Background Art

[0002] Secondary batteries rely on the reciprocating insertion and extraction of active ions between the positive electrode and the negative electrode for charging and discharging. They have outstanding characteristics such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy source, secondary batteries have gradually spread from electronic products to large-scale device fields such as electric vehicles to adapt to the sustainable development strategy of the environment and energy. Thus, higher requirements are also put forward for the energy density of secondary batteries.

[0003] However, during the first charging process of a secondary battery, an SEI (solid electrolyte interface) film is inevitably formed on the surface of the negative electrode active material, resulting in irreversible consumption of active ions. As a result, the irreversible capacity loss of the secondary battery is difficult to eliminate, posing a challenge to the improvement of the energy density of secondary batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery, a battery module containing the secondary battery, a battery pack, and an electrical device, aiming to enable the secondary battery to have high energy density, good cycle performance, and storage performance.

[0005] To achieve the above-mentioned invention purpose, in the first aspect of this application, a secondary battery is provided, which includes a positive electrode tab on which a positive electrode film layer is provided; a separator; a negative electrode tab, including a first negative electrode film layer, the first negative electrode film layer being disposed opposite to the positive electrode film layer across the separator, and a second negative electrode film layer, the second negative electrode film layer including a negative electrode film layer that is not disposed opposite to the positive electrode film layer, the second negative electrode film layer including a central region and a peripheral region surrounding the central region, wherein at least a part of the peripheral region of the second negative electrode film layer stores a lithium source for supplementing lithium to the first negative electrode film layer.

[0006] In the secondary battery of this application, a lithium source for supplementing lithium to the first negative electrode film layer is stored in the peripheral region of the second negative electrode film layer of the negative electrode tab, and the region storing this lithium source can have a low electric potential. Thus, when the lithium-ion secondary battery is charged, after Li + embedded in the first negative electrode film layer, although the potential of the first negative electrode film layer decreases somewhat, the first negative electrode film layer and the second negative electrode film layer can maintain a small potential difference, thereby preventing Li +Diffuse and embed into the second negative electrode film layer. During the discharge process of the lithium-ion secondary battery, the potential of the first negative electrode film layer gradually increases. When the potential of the first negative electrode film layer is much higher than that of the second negative electrode film layer, the lithium source will form Li + , and diffuse into the first negative electrode film layer at a slow speed. Thus, the active lithium lost during the charge-discharge cycle of the lithium-ion secondary battery can be replenished, thereby significantly improving the initial Coulomb efficiency, cycle performance, and storage performance of the secondary battery. Further, the lithium source of the present application is stored in the peripheral region of the second negative electrode film layer. Compared with the central region, the distance between the peripheral region and the first negative electrode film layer is shorter. When the lithium source forms Li + under the drive of the potential difference, Li + can have a shorter diffusion path, so as to avoid loss during the diffusion process of Li + , and thus significantly improve the lithium replenishment efficiency and the utilization rate of the lithium source.

[0007] In any embodiment of the present application, the equivalent circular area diameter R of the second negative electrode film layer and the equivalent circular area diameter R1 of the peripheral region satisfy: 0.257R ≤ R1 ≤ 0.9434R. The equivalent circular area diameter of the second negative electrode film layer and the equivalent circular area diameter of the peripheral region satisfying the above conditions can allow the lithium source of the present application to have a suitable storage space, so as to supplement an appropriate amount of active lithium ions to the secondary battery through the lithium source. In addition, the equivalent circular area diameter of the second negative electrode film layer and the equivalent circular area diameter of the peripheral region satisfying the above conditions can enable Li + formed by the lithium source under the drive of the potential difference to have a suitable diffusion path, thereby improving the lithium replenishment efficiency and the utilization rate of the lithium source. Thus, the initial Coulomb efficiency, cycle performance, and storage performance of the secondary battery can be further improved.

[0008] In any embodiment of the present application, the peripheral region has a first part and a second part surrounding the first part. The equivalent circular area diameter R2 of the second part satisfies: 0 < R2 < R1. Optionally, 0 < R2 < 0.5R1, and more optionally, 0 < R2 < 0.1R1, where the lithium source is stored in the first part. The farther the lithium replenishment area is from the edge of the second negative electrode film layer, the longer the diffusion path of Li + released from the lithium source, and correspondingly, the lower the lithium replenishment efficiency. However, the edge of the second negative electrode film layer is easily affected by external forces. Therefore, the lithium source located at the edge of the second negative electrode film layer may detach from the negative electrode plate, resulting in loss of the lithium source. Dividing the peripheral region into a first part and a second part located at the edge of the second negative electrode film layer and storing the lithium source in the first part can enable the lithium source to stably exist in the second negative electrode film layer, thereby reducing the risk of lithium source loss. Thus, the efficiency of lithium replenishment for the secondary battery can be improved.

[0009] In any embodiment of the present application, the first part is annular, and the minimum distance d1 between the outer contour line of the first part and the edge of the second negative electrode film layer and the width d0 of the second negative electrode film layer satisfy: 0 < d1 ≤ d0 / 6. When the minimum distance d1 between the outer contour line of the first part and the edge of the second negative electrode film layer is within the above suitable range, while ensuring a diffusion path for the lithium source to release Li + with a suitable length, the risk of lithium source shedding can be effectively reduced. Thereby, the efficiency of lithium supplementation for the secondary battery can be improved, and thus the first Coulombic efficiency, cycle performance, and storage performance of the secondary battery can be improved.

[0010] In any embodiment of the present application, d3 ≤ d2 ≤ d0 / 6, where d2 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer in the length direction, and d3 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer in the width direction. There is a certain distance between the outer contour line of the first part and the side of the second negative electrode film layer in the length direction and the side of the second negative electrode film layer in the width direction, and this distance is within a relatively small range, while ensuring a diffusion path for the lithium source to release Li + with a suitable length, the risk of lithium source shedding can be effectively reduced. Thereby, the efficiency of lithium supplementation for the secondary battery can be improved, and thus the first Coulombic efficiency, cycle performance, and storage performance of the secondary battery can be improved.

[0011] In any embodiment of the present application, the first part is a hollow rectangle, and the first part satisfies: 0 < d4 ≤ d0 / 3, where d4 represents the width of the first part along the width direction of the second negative electrode film layer; and / or 0 < d5 ≤ l0 / 3, where d5 represents the width of the first part along the length direction of the second negative electrode film layer, and l0 represents the length of the second negative electrode film layer. The first part having a suitable width can enable the first part to have a suitable area, so as to store an appropriate amount of lithium source. The first part having a suitable width can also correspondingly allow the second part and the central region to have suitable areas. Therefore, when the lithium source is stored in the first part, it can have a suitable distance from the center of the second negative electrode film layer and / or the edge of the second negative electrode film layer. Thus, a suitable amount of active lithium can be stored in the second negative electrode film layer of the present application. This active lithium is not only not easily shed from the second negative electrode film layer, but also can diffuse through a shorter path and be embedded in the first negative electrode film layer when the secondary battery needs to supplement lithium ions. Therefore, the secondary battery of the present application can have a high first Coulombic efficiency and good cycle performance and storage performance.

[0012] In any embodiment of the present application, the secondary battery satisfies: 1 mm ≤ d2 ≤ 5 mm. Optionally, (l0 - 10 mm) ≤ l1 ≤ (l0 - 2 mm), where l1 represents the length of the outer contour line. Optionally, 10 mm ≤ d4 ≤ d0 / 5. Optionally, 1 mm ≤ d3 ≤ 5 mm. Optionally, (d0 - 10 mm) ≤ l2 ≤ (d0 - 2 mm), where l2 represents the width of the outer contour line. Optionally, 10 mm ≤ d5 ≤ d4. When the secondary battery satisfies at least one of the above conditions, it is beneficial for the second negative electrode film layer to provide sufficient space for storing the lithium source, and it can make the distribution position of the lithium source in the second negative electrode film layer appropriate. Thus, the lithium source is not easily detached from the second negative electrode film layer. When the secondary battery needs to supplement lithium ions, the Li provided by the lithium source + can also diffuse and embed into the first negative electrode film layer through a shorter path. Therefore, the secondary battery of the present application can have a high first Coulomb efficiency, good cycle performance, and storage performance.

[0013] Optionally, the lithium source is annularly distributed in the first part. When the lithium source is annularly distributed in the first part, it can make the second negative electrode film layer have a suitable electric potential. Thus, the Li in the first negative electrode film layer + is not easily embedded into the second negative electrode film layer, thereby further reducing the loss of active lithium. Therefore, the secondary battery of the present application can have a high first Coulomb efficiency, good cycle performance, and storage performance.

[0014] In any embodiment of the present application, the area S1 of the second negative electrode film layer storing the lithium source and the area S2 of the outer peripheral region satisfy: 10% ≤ S1 / S2 ≤ 100%, optionally 80% ≤ S1 / S2 < 100%, and more optionally 90% ≤ S1 / S2 < 100%. When the ratio of S1 to S2 is within a suitable range, it can make the amount of the lithium source stored in the second negative electrode film layer appropriate. With an appropriate amount of the lithium source, on the one hand, it can make the second negative electrode film layer have a suitable electric potential, thereby reducing the Li in the first negative electrode film layer + from escaping and embedding into the second negative electrode film layer; on the other hand, when there are sufficient active lithium ions provided, it can avoid an excess of the lithium source. Thus, it can reduce the Li lost during the cycling of the secondary battery + , improve the lithium supplement efficiency, and control the cost of lithium supplementation. Therefore, the secondary battery of the present application can have a high first Coulomb efficiency, good cycle performance, storage performance, and low cost.

[0015] In any embodiment of the present application, the lithium source includes at least one of lithium metal, lithium alloy, a composite of lithium metal and negative electrode active material, and a composite of aluminum alloy and negative electrode active material. Optionally, the lithium alloy includes at least one of silicon-lithium alloy, aluminum-lithium alloy, magnesium-lithium alloy, and tin-lithium alloy. Whether it is lithium metal foil, lithium powder, silicon-lithium alloy, aluminum-lithium alloy, magnesium-lithium alloy, tin-lithium alloy, or other forms of lithium alloy, it can be used as the lithium supplement layer and interact with the active substances in the second negative electrode film layer to form the lithium source of the present application, thereby realizing the lithium supplement for the secondary battery.

[0016] In any embodiment of the present application, the secondary battery satisfies: 20% C0 ≤ C Li ≤ 120% C0. Optionally, 90% C0 ≤ C Li ≤ 120% C0, where C0 represents the active material capacity per unit area of the second negative electrode film layer, and C Li represents the capacity per unit area of the lithium source. Under the conventional battery capacity design, when C0 and C Li meet the above conditions, the speed of lithium source releasing Li + can be in a more appropriate range, thereby taking into account the lithium supplement efficiency and the safety performance of the secondary battery.

[0017] In any embodiment of the present application, the secondary battery has a wound structure. The second negative electrode film layer includes a starting region and a finishing region along the winding direction. The secondary battery satisfies: C A ≥ C B , C A represents the capacity of the lithium source located in the starting region, and C B represents the capacity of the lithium source located in the finishing region. Compared with the second negative electrode film layer in the finishing region, the second negative electrode film layer in the starting region has a better ability to retain the electrolyte, which is more conducive to the diffusion of Li + released from the lithium source. When the total capacity of the lithium source is constant, a higher capacity of the lithium source in the starting region is beneficial to improving the lithium supplement efficiency and the utilization rate of the lithium source.

[0018] In any embodiment of the present application, the minimum distance d7 between the lithium source and the first negative electrode film layer satisfies: 0 < d7 ≤ 10 mm. When the minimum distance between the lithium source and the first negative electrode film layer is within the above appropriate range, the Li + released from the lithium source has a shorter diffusion path, thereby improving the lithium supplement efficiency and the utilization rate of the lithium source.

[0019] In any embodiment of the present application, the surface of the central region is covered with a barrier layer, and the barrier layer includes a barrier film and / or a barrier coating. Among them, the barrier film is selected from at least one of cast polypropylene film, unidirectionally stretched polypropylene film, biaxially stretched polypropylene film, polyethylene film, polyester fiber film, and polyvinyl chloride film. The barrier coating includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polystyrylamine, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile, or a copolymer of the above substances. Covering the surface of the central region with a barrier layer can reduce the risk of electrolyte infiltrating the central region. Thus, the active Li + embedded in the negative electrode film layer of the central region can be reduced, thereby further improving the lithium supplementation efficiency and the utilization rate of the lithium source, and further improving the first Coulomb efficiency, cycle performance, and storage performance of the secondary battery.

[0020] Optionally, the thickness of the barrier layer is 6 μm to 40 μm, and more optionally, the thickness of the barrier layer is 10 μm to 20 μm. When the thickness of the barrier layer is within a suitable range, it can not only have good mechanical strength and thus is not easily damaged, but also make the thickness of the negative electrode sheet within a small range, thus facilitating the processing of the negative electrode sheet.

[0021] The second aspect of the present application provides a battery module, which includes the secondary battery of the present application.

[0022] The third aspect of the present application provides a battery pack, which includes the battery module of the present application.

[0023] The fourth aspect of the present application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack of the present application.

[0024] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly described below; obviously, the following described drawings only relate to some embodiments of the present application, and for those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0026] Figure 1 is a schematic diagram of an electrode assembly included in a secondary battery in an embodiment of the secondary battery of the present application.

[0027] Figure 2 is a schematic diagram of an electrode assembly included in a secondary battery in an embodiment of the secondary battery of the present application.

[0028] Figure 3 It is a schematic diagram of the second negative electrode film layer in an embodiment of the secondary battery of the present application.

[0029] Figure 4 It is a schematic diagram of the second negative electrode film layer in an embodiment of the secondary battery of the present application.

[0030] Figure 5 It is a schematic diagram of an embodiment of the secondary battery of the present application.

[0031] Figure 6 It is an exploded schematic diagram of an embodiment of the secondary battery of the present application.

[0032] Figure 7 It is a schematic diagram of an embodiment of the battery module of the present application.

[0033] Figure 8 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0034] Figure 9 is Figure 8 An exploded schematic diagram of the embodiment of the battery pack shown.

[0035] Figure 10 It is a schematic diagram of an embodiment of the device using the secondary battery of the present application as a power source.

[0036] In the drawings, the drawings are not necessarily drawn to actual scale. Among them, the reference numerals are explained as follows: 10 electrode assembly, 11 positive electrode tab, 12 separator, 13 negative electrode tab, 13a first surface, 13b second surface, 131 negative electrode film layer provided in the starting area and / or negative electrode film layer provided in the ending area, 130 second negative electrode film layer, 1310 central area, 1320 outer peripheral area, 1321 first part, 1322 second part, 1321a outer contour line of the first part, 1321b inner contour line of the first part, 1 battery pack, 2 upper box body, 3 lower box body, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate. Detailed Embodiments

[0037] In order to make the invention purpose, technical solution and beneficial technical effects of the present application clearer, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and not for limiting the present application.

[0038] For simplicity, only some numerical ranges are explicitly disclosed in this text. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, each point or single value between the range endpoints is included within the range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or with other lower or upper limits to form a range not explicitly recited.

[0039] In the description of this text, it should be noted that unless otherwise specified, "above" and "below" include the recited number, and in "one or several", the meaning of "several" is two or more.

[0040] In the description of this text, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0041] It should be understood that relational terms such as "first", "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0042] The above summary of the invention of this application is not intended to describe every disclosed embodiment or every implementation of this application. The following description more specifically illustrates exemplary embodiments. Throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each instance, the listing is only a representative group and should not be construed as exhaustive.

[0043] During the first charging process of a secondary battery, an SEI (solid electrolyte interface) film is inevitably formed on the surface of the negative electrode active material, resulting in irreversible consumption of active ions, and thus it is difficult to eliminate the irreversible capacity loss of the secondary battery.

[0044] To meet the requirements of lithium-ion secondary batteries in terms of high energy density, a lithium supplementation technology can be adopted to increase the active lithium content and compensate for the loss of active lithium during the first charging process of lithium-ion secondary batteries. Currently, the main and more mature technology is the negative electrode lithium supplementation process. For example, a layer of lithium metal is covered on the surface of the negative electrode sheet through lithium powder or lithium foil. This lithium can be gradually released during the manufacturing and full life cycle use of lithium-ion secondary batteries to compensate for the loss of active lithium caused by side reactions inside the lithium-ion secondary batteries, thereby greatly avoiding the capacity decline of lithium-ion secondary batteries.

[0045] In related technologies, a lithium source (such as a lithium metal layer) is mostly set on the surface of the negative electrode current collector to achieve lithium supplementation for lithium-ion secondary batteries. However, the inventors found that when the lithium source is set on the surface of the negative electrode current collector, after injecting the electrolyte into the secondary battery, the lithium in the lithium source will form Li + under the action of the potential difference, and these Li + will preferentially embed into the nearest negative electrode film layer. A large amount of Li + embedding into the negative electrode film layer in a small area may cause local Li + to be excessive and difficult to be completely embedded, thereby inducing risks such as lithium deposition on the surface of the negative electrode sheet, decline in cycle performance, and battery short circuit.

[0046] In addition, through in-depth research, the inventors also found that in a lithium-ion secondary battery, the negative electrode film layer can include a first negative electrode film layer disposed opposite to the positive electrode film layer across the separator and a second negative electrode film layer not disposed opposite to the positive electrode film layer. When the secondary battery is charged, the Li + released from the positive electrode film layer will preferentially embed into the first negative electrode film layer after passing through the separator under the drive of the potential difference. Therefore, the first negative electrode film layer can also be called the reaction zone negative electrode film layer. In addition to the first negative electrode film layer or the reaction zone negative electrode film layer, the negative electrode film layer can also include a second negative electrode film layer, that is, the negative electrode film layer not disposed opposite to the positive electrode film layer. The second negative electrode film layer can also be called the non-reaction zone negative electrode film layer. When the lithium-ion secondary battery is charged, after the Li + released from the positive electrode embeds into the reaction zone, the potential of the reaction zone drops, forming a potential difference with the non-reaction zone. At this time, the Li + in the reaction zone will slowly diffuse and embed into the non-reaction zone. The Li + embedded in the non-reaction zone is difficult to return to the positive electrode during the discharge process, which will also cause irreversible loss of active lithium, thereby reducing the first Coulomb efficiency, cycle performance, and storage performance of the lithium-ion secondary battery. Currently, there are few relevant solutions to this technical problem.

[0047] In view of this, after in-depth thinking, the inventors provided a secondary battery, a battery module, a battery pack, and an electrical device containing the secondary battery.

[0048] Secondary battery

[0049] In the first aspect of the present application, a secondary battery is provided, which includes a positive electrode sheet, a separator, and a negative electrode sheet. A positive electrode film layer is provided on the positive electrode sheet, and the negative electrode sheet includes a first negative electrode film layer and a second negative electrode film layer. Among them, the first negative electrode film layer is disposed opposite to the positive electrode film layer across the separator. The second negative electrode film layer includes a negative electrode film layer that is not disposed opposite to the positive electrode film layer. The second negative electrode film layer includes a central region and a peripheral region surrounding the central region. Among them, at least a part of the peripheral region of the second negative electrode film layer stores a lithium source for supplementing lithium to the first negative electrode film layer.

[0050] In the present application, the first negative electrode film layer can also be referred to as a reaction zone negative electrode film layer, and the second negative electrode film layer can also be referred to as a non-reaction zone negative electrode film layer. The present application does not limit the positions of the first negative electrode film layer and the second negative electrode film layer in the secondary battery, which can be determined according to the structure of the secondary battery. The present application does not limit the structure of the secondary battery.

[0051] As an example, the secondary battery of the present application may include an electrode assembly having a stacked structure. As Figure 1 shown, the electrode assembly 10 includes a positive electrode sheet 11, a separator 12, and a negative electrode sheet 13. The negative electrode sheet 13 located on the outermost side of the electrode assembly includes a first surface 13a facing the outside of the electrode assembly 10 and a second surface 13b facing the inside of the electrode assembly 10. As Figure 1 shown, the electrode assembly 10 includes two negative electrode sheets 13 located on the outermost side, and a negative electrode film layer (not shown in the figure) can be provided on one or both of the first surfaces 13a. The negative electrode film layer provided on the first surface 13a is an example of the second negative electrode film layer according to the embodiments of the present application. Negative electrode film layers are also provided on other surfaces (including the surface 13b) of the negative electrode sheet in the electrode assembly 10, which are disposed opposite to the positive electrode film layer (not shown in the figure) provided on the positive electrode sheet 11 across the separator 12. Such a negative electrode film layer is an example of the first negative electrode film layer according to the embodiments of the present application.

[0052] As another example, the secondary battery of the present application may include an electrode assembly having a wound structure. As Figure 2As shown, the electrode assembly 10 includes a positive electrode tab 11, a separator 12, and a negative electrode tab 13. The negative electrode tab 13 may be provided with a negative electrode film layer 131 in the starting region (the central hollow winding region of the electrode assembly) along the winding direction and the ending region (the outer peripheral ending region of the electrode assembly) along the winding direction. It is easy to understand that in the electrode assembly 10, the negative electrode film layer 131 provided in the starting region and / or the negative electrode film layer 131 provided in the ending region are examples of the second negative electrode film layer according to the embodiments of the present application. In other regions of the negative electrode tab 13, there may be a negative electrode film layer (not shown in the figure) disposed opposite to the positive electrode film layer (not shown in the figure) on the positive electrode tab 11. Such a negative electrode film layer is an example of the first negative electrode film layer according to the embodiments of the present application.

[0053] In the present application, the central region and the outer peripheral region have meanings well known in the art. For example, the central region may represent a region closer to the geometric center of the second negative electrode film layer relative to the outer peripheral region; the outer peripheral region may represent a region closer to the edge of the second negative electrode film layer relative to the central region. The present application does not limit the shapes of the central region and the outer peripheral region. As an example, the central region may be rectangular, square, parallelogram, circular, elliptical, polygonal, or irregular.

[0054] The lithium source of the present application may be a lithium source formed by placing a lithium supplement agent on the surface of the outer peripheral region of the second negative electrode film layer. The lithium supplement agent may be a lithium supplement agent well known in the art that can be used for the negative electrode. For example, it may include, but is not limited to, metallic lithium foil, lithium powder, lithium silicon alloy, lithium aluminum alloy, lithium magnesium alloy, lithium tin alloy, and other forms of lithium alloy. The lithium source may include a lithium-rich compound formed by the reaction of the lithium supplement agent with the negative electrode active material in the negative electrode film layer and the possibly existing unreacted lithium supplement agent. As an example, the lithium source may include the lithium supplement agent, LiC x (x≥6) formed by the reaction of the lithium supplement agent with the carbon negative electrode material, and Li y Si z (y>0) and the like. In some embodiments, lithium metal may be covered on at least part of the surface of the outer peripheral region of the second negative electrode film layer to form a lithium supplement layer, and then an electrolyte is injected into the secondary battery, so that the lithium supplement layer reacts with the negative electrode active material in the negative electrode film layer to form the lithium source of the present application. The standard electrode potential of lithium metal with respect to hydrogen is -3.05V, and the standard potential of the un-lithiated negative electrode active material (such as graphite, silicon-carbon composite material, etc.) with respect to hydrogen is about 0V. After injecting the electrolyte into the secondary battery, since the lithium metal is in direct contact with the negative electrode film layer, a circuit can be formed. At this time, it is equivalent to a direct short circuit of a battery with lithium metal as the negative electrode and the negative electrode film layer as the positive electrode. At least part of the lithium metal loses electrons and is embedded in the negative electrode film layer in the form of Li + to store the lithium source of the present application in the outer peripheral region of the second negative electrode film layer.

[0055] Although the mechanism is not yet clear, the inventors unexpectedly found that a lithium source for supplementing lithium to the first negative electrode film layer is stored in the outer peripheral region of the second negative electrode film layer, which can effectively improve the first Coulomb efficiency, storage performance and cycling performance of the secondary battery.

[0056] Without intending to be limited by any theory or explanation, a lithium source for supplementing lithium to the first negative electrode film layer is stored in the outer peripheral region of the second negative electrode film layer of the present application, and the region storing the lithium source can have a low electric potential. Thus, when the lithium ion secondary battery is charged, the Li + after being inserted into the first negative electrode film layer, although the potential of the first negative electrode film layer decreases, the potential difference between the first negative electrode film layer and the second negative electrode film layer can be kept small, so as to prevent Li + from diffusing and being inserted into the second negative electrode film layer. During the discharge process of the lithium ion secondary battery, the potential of the first negative electrode film layer gradually increases. When the potential of the first negative electrode film layer is much higher than that of the second negative electrode film layer, the lithium source will form Li + under the driving of the potential difference between the first negative electrode film layer and the second negative electrode film layer, and diffuse to the first negative electrode film layer at a slow speed. Thus, the active lithium lost in the charge and discharge cycles of the lithium ion secondary battery can be supplemented, thereby significantly improving the first Coulomb efficiency, cycling performance and storage performance of the secondary battery. Further, the lithium source of the present application is stored in the outer peripheral region of the second negative electrode film layer. Compared with the central region, the distance between the outer peripheral region and the first negative electrode film layer is shorter. When the lithium source forms Li + under the driving of the potential difference, Li + can have a shorter diffusion path, so as to avoid the loss of Li + during the diffusion process, and further significantly improve the lithium supplement efficiency and the utilization rate of the lithium source.

[0057] In some embodiments, the equivalent circular area diameter R of the second negative electrode film layer and the equivalent circular area diameter R1 of the outer peripheral region may satisfy: 0.257R ≤ R1 ≤ 0.9434R, 0.3R ≤ R1 ≤ 0.85R, 0.35R ≤ R1 ≤ 0.8R, 0.4R ≤ R1 ≤ 0.75R, 0.45R ≤ R1 ≤ 0.7R, 0.5R ≤ R1 ≤ 0.65R or 0.55R ≤ R1 ≤ 0.6R.

[0058] In the present application, the equivalent circular area diameter can represent the diameter of a circle corresponding to an area equal to the defined region. For example, the equivalent circular area diameter of the second negative electrode film layer represents: the diameter of a circle corresponding to an area equal to that of the second negative electrode film layer; the equivalent circular area diameter of the outer peripheral region represents: the diameter of a circle corresponding to an area equal to that of the outer peripheral region.

[0059] Without intending to be limited by any theory or explanation, the equivalent circular area diameter of the second negative electrode film layer and the equivalent circular area diameter of the peripheral region meet the above conditions, which can allow the lithium source of the present application to have a suitable storage space, so that the lithium source can be used to supplement the secondary battery with an appropriate amount of active lithium ions. In addition, the equivalent circular area diameter of the second negative electrode film layer and the equivalent circular area diameter of the peripheral region meet the above conditions, which can allow the lithium source to form Li under the drive of the potential difference. + With a suitable diffusion path, the efficiency of lithium replenishment and the utilization rate of lithium sources can be improved, thereby further improving the initial coulombic efficiency, cycle performance and storage performance of the secondary battery.

[0060] In some embodiments, the peripheral region has a first portion and a second portion surrounding the first portion, and the equivalent circular area diameter R2 of the second portion may satisfy: 0<R2<R1, optionally, 0<R2<0.5R1, and more optionally, 0<R2<0.1R1, wherein the lithium source is stored in the first portion.

[0061] The present application does not limit the shapes of the first part and the second part. As an example, the first part can be a circular ring, an elliptical ring, a hollow rectangle or other ring or an irregular shape. At least a part of the first part stores a lithium source for replenishing lithium to the first negative electrode film layer.

[0062] Without intending to be bound by any theory or explanation, the inventors found that the farther the lithium replenishment area is from the edge of the second negative electrode film layer, the more Li + The longer the diffusion path, the lower the lithium replenishment efficiency accordingly. However, the edge of the second negative electrode film layer is susceptible to external forces, so the lithium source located at the edge of the second negative electrode film layer may detach from the negative electrode plate, resulting in the loss of lithium source. Dividing the peripheral area into a first part and a second part located at the edge of the second negative electrode film layer, so that the lithium source is stored in the first part, can make the lithium source stably exist in the second negative electrode film layer, thereby reducing the risk of lithium source loss. In this way, the efficiency of lithium replenishment for secondary batteries can be improved.

[0063] In some embodiments, the first portion is annular, and a minimum distance d1 between an outer contour line of the first portion and an edge of the second negative electrode film layer and a width d0 of the second negative electrode film layer may satisfy: 0<d1≤d0 / 6.

[0064] In this embodiment, the ring shape is not limited, and it may specifically include a figure surrounded by a closed outer contour line and a closed inner contour line. As an example, the first part may be a ring shape such as a circular ring, an elliptical ring, a hollow rectangle, or an irregular shape.

[0065] Figure 3In one embodiment of the secondary battery of the present application, it is a schematic diagram of the second negative electrode film layer. The exemplary second negative electrode film layer 130 includes a central region 1310 and a peripheral region 1320. Among them, the peripheral region 1320 is composed of a first part 1321 and a second part 1322 in an elliptical ring shape. The first part 1321 is enclosed by an outer contour line 1321a and an inner contour line 1321b. At least a part of the first part 1321 stores a lithium source for supplementing lithium to the first negative electrode film layer. The minimum distance d1 between the outer contour line 1321a of the first part and the edge of the second negative electrode film layer can be as Figure 3 shown in

[0066] Figure 4 In another embodiment of the secondary battery of the present application, it is a schematic diagram of the second negative electrode film layer. The exemplary second negative electrode film layer 130 includes a central region 1310 and a peripheral region 1320. Among them, the peripheral region 1320 is composed of a first part 1321 and a second part 1322 in a hollow rectangle shape. The first part 1321 is enclosed by an outer contour line 1321a and an inner contour line 1321b. At least a part of the first part 1321 stores a lithium source for supplementing lithium to the first negative electrode film layer. The minimum distance d1 between the outer contour line 1321a of the first part and the edge of the second negative electrode film layer 130 can be as Figure 4 shown in

[0067] Without being limited to any theory or explanation, when the minimum distance d1 between the outer contour line of the first part and the edge of the second negative electrode film layer is within the above suitable range, it can ensure that the Li + with a suitable length of diffusion path for the lithium source to escape, while effectively reducing the risk of lithium source shedding. Thereby, the efficiency of lithium supplementation for the secondary battery can be improved, and thus the first Coulomb efficiency, cycle performance, and storage performance of the secondary battery can be improved.

[0068] In some embodiments, the secondary battery may satisfy: d3 ≤ d2 ≤ d0 / 6, where d2 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer in the length direction, and d3 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer in the width direction.

[0069] In some embodiments, as Figure 4 shown, d2 represents the minimum distance between the outer contour line 1321a and the side of the second negative electrode film layer 130 in the length direction, and d3 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer 130 in the width direction. Among them, d3 ≤ d2 ≤ d0 / 6, and at this time, d3 = d1.

[0070] Without being bound by any theory or explanation, there is a certain distance between the outer contour line of the first part and the edges in the length direction and the width direction of the second negative electrode film layer, and this distance is within a relatively small range, which can ensure the Li + while having a diffusion path with a suitable length, effectively reducing the risk of lithium source shedding. Thereby, the efficiency of lithium supplementation for the secondary battery can be improved, and thus the first Coulombic efficiency, cycle performance, and storage performance of the secondary battery can be improved.

[0071] In some embodiments, as Figure 4 shown, the first part 1321 is a hollow rectangle, and the first part 1321 can satisfy: 0 < d4 ≤ d0 / 3, and / or 0 < d5 ≤ l0 / 3. Where d4 represents the width of the first part 1321 in the width direction of the second negative electrode film layer 130; d5 represents the width of the first part 1321 in the length direction of the second negative electrode film layer 130, and l0 represents the length of the second negative electrode film layer 130.

[0072] In some embodiments, the first part can be a hollow rectangle, and the geometric centers of the outer contour line and the inner contour line of the first part may not coincide. At this time, the first part has two unequal widths d 41 and d 42 in the width direction of the second negative electrode film layer, d 41 and d 42 can both satisfy being greater than 0 and less than or equal to d0 / 3; the first part has two unequal widths d 51 and d 52 in the length direction of the second negative electrode film layer, d 51 and d 52 can both satisfy being greater than 0 and less than or equal to l0 / 3.

[0073] Without being bound by any theory or explanation, the first part has a suitable width, which can enable the first part to have a suitable area, so as to store an appropriate amount of lithium source. The first part having a suitable width can also correspondingly allow the second part and the central region to have suitable areas. Therefore, when the lithium source is stored in the first part, it can have a suitable distance from the center and / or the edge of the second negative electrode film layer. Thus, a suitable amount of active lithium can be stored in the second negative electrode film layer of the present application. This active lithium is not only not easily shed from the second negative electrode film layer, but when the secondary battery needs to supplement lithium ions, this active lithium can also diffuse through a shorter path and be embedded in the first negative electrode film layer. Therefore, the secondary battery of the present application can have a high first Coulombic efficiency and good cycle performance and storage performance.

[0074] In some embodiments, the secondary battery can satisfy: 1 mm ≤ d2 ≤ 5 mm.

[0075] Optionally, (l0 - 10 mm) ≤ l1 ≤ (l0 - 2 mm), where l1 represents the length of the outer contour line.

[0076] Optionally, 10 mm ≤ d4 ≤ d0 / 5.

[0077] Optionally, 1 mm ≤ d3 ≤ 5 mm.

[0078] Optionally, (d0 - 10 mm) ≤ l2 ≤ (d0 - 2 mm), where l2 represents the width of the outer contour line.

[0079] Optionally, 10 mm ≤ d5 ≤ d4.

[0080] When the secondary battery satisfies at least one of the above conditions, it is beneficial for the second negative electrode film layer to provide sufficient space for storing the lithium source, and it can make the distribution position of the lithium source in the second negative electrode film layer appropriate. Thus, the lithium source is not easily detached from the second negative electrode film layer. When the secondary battery needs to supplement lithium ions, the Li provided by the lithium source + can also diffuse and embed into the first negative electrode film layer through a shorter path. Therefore, the secondary battery of the present application can have a high initial Coulomb efficiency, good cycle performance, and storage performance.

[0081] Optionally, the lithium source is annularly distributed in the first part.

[0082] Without intending to be limited by any theory or explanation, when the lithium source is annularly distributed in the first part, the second negative electrode film layer can have a suitable electric potential. Thus, Li in the first negative electrode film layer + is not easily embedded into the second negative electrode film layer, thereby further reducing the loss of active lithium. Therefore, the secondary battery of the present application can have a high initial Coulomb efficiency, good cycle performance, and storage performance.

[0083] In some embodiments, the area S1 of the second negative electrode film layer storing the lithium source and the area S2 of the outer peripheral region may satisfy: 10% ≤ S1 / S2 ≤ 100%. Optionally, 80% ≤ S1 / S2 < 100%, and more optionally, 90% ≤ S1 / S2 < 100%.

[0084] Without intending to be limited by any theory or explanation, when the ratio of S1 to S2 is within the above suitable range, the amount of the lithium source stored in the second negative electrode film layer can be appropriate. With an appropriate amount of the lithium source, on the one hand, the second negative electrode film layer can have a suitable electric potential, thereby reducing the Li in the first negative electrode film layer + from escaping and embedding into the second negative electrode film layer; on the other hand, when there are sufficient active lithium ions, it can avoid an excess of the lithium source. Thus, the loss of Li during the cycling of the secondary battery can be reduced.+ , improve the lithium supplement efficiency and control the cost of lithium supplement. Therefore, the secondary battery of the present application can have a high first Coulomb efficiency, good cycling performance and storage performance, and low cost.

[0085] In some embodiments, the lithium source may include at least one of lithium metal, lithium alloy, a composite of lithium metal and negative electrode active material, and a composite of aluminum alloy and negative electrode active material, and may be optionally lithium metal and / or a composite of lithium metal and negative electrode active material. Optionally, the lithium alloy includes at least one of silicon-lithium alloy, aluminum-lithium alloy, magnesium-lithium alloy, and tin-lithium alloy.

[0086] Without being bound by any theory or explanation, the inventors have found that: whether it is lithium metal foil, lithium powder, silicon-lithium alloy, aluminum-lithium alloy, magnesium-lithium alloy, tin-lithium alloy or other forms of lithium alloy, it can be used as the lithium supplement layer and interact with the active substances in the second negative electrode film layer to form the lithium source of the present application. Among them, lithium metal (including lithium metal foil, lithium powder, etc.) has a high specific capacity and no impurities are generated after reacting with the negative electrode active material. Therefore, the lithium source formed by lithium metal can have a higher lithium supplement efficiency. Further, the lithium metal foil has good processing performance. By attaching the lithium metal foil to the surface of the second negative electrode film layer and making the lithium metal foil react with the negative electrode active material to form a lithium source, while improving the lithium supplement efficiency, the secondary battery of the present application can have high productivity.

[0087] In some embodiments, the secondary battery may satisfy: 20% C0 ≤ C Li ≤ 120% C0, where C0 represents the active material capacity per unit area of the second negative electrode film layer, and C Li represents the capacity per unit area of the lithium source. Optionally, 90% C0 ≤ C Li ≤ 120% C0,

[0088] In the present application, the active material capacity C0 per unit area of the second negative electrode film layer can be expressed as: the capacity of the negative electrode active material in the second negative electrode film layer per unit area. Generally, C0 can be equal to the active material capacity per unit area of the first negative electrode film layer. The capacity C Li per unit area of the lithium source can be expressed as: the capacity of the lithium source contained in the second negative electrode film layer per unit area storing the lithium source.

[0089] The inventors unexpectedly found that when C0 and C Li meet the above conditions, the secondary battery can have both a high first Coulomb efficiency, good cycling performance, good storage performance and good safety performance. Without being bound by any theory or explanation, when C LiWhen it is relatively small, the region storing the lithium source has a relatively high electric potential. During the discharge of the secondary battery, the first film layer needs to reach a relatively high electric potential to form a sufficient potential difference with the second negative electrode film layer to drive the lithium source to release Li + , and diffuse toward the first negative electrode film layer at a slow speed. When C Li is relatively large, the region storing the lithium source has a relatively low electric potential, which is extremely easy to form a sufficient potential difference with the second negative electrode film layer, and causes the lithium source to quickly release Li + . When the release speed of Li + is too fast, it may cause Li + to be difficult to be embedded into the first negative electrode film layer in time, thus causing the risk of local lithium deposition on the negative electrode plate. Under the conventional battery capacity design, when C0 and C Li meet the above conditions, it can make the release speed of the lithium source to release Li + within a more appropriate range, so as to balance the lithium supplement efficiency and the safety performance of the secondary battery.

[0090] In some embodiments, the secondary battery has a wound structure, the second negative electrode film layer includes a starting region and an ending region along the winding direction, and the secondary battery can satisfy: C A ≥C B , where C A represents the capacity of the lithium source located in the starting region, and C B represents the capacity of the lithium source located in the ending region.

[0091] Not intending to be limited by any theory or explanation, the inventors found that compared with the second negative electrode film layer in the ending region, the second negative electrode film layer in the starting region has better ability to retain the electrolyte, thus being more conducive to the diffusion of Li + released from the lithium source. When the total capacity of the lithium source is certain, a higher lithium source capacity in the starting region is beneficial to improving the lithium supplement efficiency and the utilization rate of the lithium source.

[0092] In some embodiments, the minimum distance d7 between the lithium source and the first negative electrode film layer can satisfy: 0 < d7 ≤ 10 mm.

[0093] Not intending to be limited by any theory or explanation, when the minimum distance between the lithium source and the first negative electrode film layer is within the above appropriate range, it can make Li + released from the lithium source have a shorter diffusion path, thus improving the lithium supplement efficiency and the utilization rate of the lithium source.

[0094] In some embodiments, the surface of the central region is covered with a barrier layer, and the barrier layer includes a barrier film and / or a barrier coating. The present application does not limit the material of the barrier film, as long as it can prevent the electrolyte from contacting the central region. It can be a film with single-sided adhesion or double-sided adhesion, preferably a film with single-sided adhesion. Optionally, the adhesion force between at least one surface of the barrier film and the surface of the central region can be greater than 20 N / m. More optionally, the adhesion force between the barrier film and the surface of the central region is greater than the cohesive force of the second negative electrode film layer.

[0095] Optionally, the barrier film is selected from at least one of cast polypropylene film, unidirectionally stretched polypropylene film, biaxially stretched polypropylene film, polyethylene film, polyester fiber film, and polyvinyl chloride film. The barrier coating includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polybenzyl acrylamide, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile, or a copolymer of the above substances.

[0096] Without intending to be limited by any theory or explanation, covering the surface of the central region with a barrier layer can reduce the risk of electrolyte infiltration into the central region. Thereby, it can reduce the active Li + embedded in the negative electrode film layer of the central region, thereby further improving the lithium supplementation efficiency and the utilization rate of the lithium source, and further improving the first Coulombic efficiency, cycle performance, and storage performance of the secondary battery.

[0097] Optionally, the thickness of the barrier layer is 6 μm to 40 μm. More optionally, the thickness of the barrier layer is 10 μm to 20 μm.

[0098] When the thickness of the barrier layer is within a suitable range, it can have good mechanical strength and thus is not easily damaged, and can also keep the thickness of the negative electrode sheet within a small range, which is convenient for the processing of the negative electrode sheet.

[0099] In the present application, the length and width of the negative electrode film layer have the meanings well-known in the art. For example, when the secondary battery includes an electrode assembly with a wound structure, the length of the negative electrode film layer can represent the length of the negative electrode film layer along the winding direction of the electrode assembly, and the width of the negative electrode film layer can represent the length perpendicular to the winding direction of the negative electrode film layer. When the secondary battery includes an electrode assembly with a stacked structure, the length of the negative electrode film layer can represent the length of the longer side of the negative electrode film layer, and the width of the negative electrode film layer can represent the length of the shorter side of the negative electrode film layer.

[0100] In the present application, C0 can be obtained by performing a capacity test on the second negative electrode film layer that does not store a lithium source. As an example, one side of the negative electrode film layer is scrubbed to expose the empty substrate, the electrode sheet containing one side of the negative electrode film layer is punched into small round pieces with an area of S, the capacity C of the small round pieces containing the negative electrode film layer is measured by using a coin-type lithium half-cell, and through the publicFormula C0 = C / S calculates the negative electrode film layer capacity C0 per unit area.

[0101] In the present application, C Li can be calculated by methods well-known in the art. As an example, when the lithium source is formed by a lithium metal foil attached to the outer peripheral region of the second negative electrode film layer, the capacity C1 of the lithium foil can be calculated based on the weight and theoretical gram capacity of the lithium foil, and then the area S' of the lithium foil is measured to calculate C Li . C Li can be calculated by the following formula: C Li = C1 / S'.

[0102] In the secondary battery of the present application, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on either one or both of the two opposite surfaces of the negative electrode current collector.

[0103] As previously referred to Figure 1 and Figure 2 described, in the embodiments of the present application, the negative electrode film layer includes the first negative electrode film layer and the second negative electrode film layer described in the present application.

[0104] The type of the negative electrode active material is not specifically limited, and negative electrode active materials well-known in the art for secondary batteries can be used. As an example, the negative electrode active material may include one or more of graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials may include one or more of elemental tin, tin oxides, and tin alloy materials. The present application is not limited to these materials, and other conventionally well-known materials that can be used as negative electrode active materials for secondary batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0105] In some embodiments, the negative electrode active material includes one or several of artificial graphite, natural graphite, and silicon-based materials. Selecting the negative electrode active material from the above-mentioned types of materials can enable the second negative electrode film layer to have a suitable potential, thereby improving the lithium supplementation efficiency and the utilization rate of the lithium source.

[0106] The type of the negative electrode current collector is not specifically limited and can be selected according to actual needs. For example, the negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, the negative electrode current collector can be a copper foil. The composite current collector can include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material can be selected from one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material substrate can be selected from one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0107] In the secondary battery of the present application, the negative electrode film layer is usually formed by coating a negative electrode paste on the negative electrode current collector and then drying and cold pressing. The negative electrode paste is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or water, but is not limited thereto. As an example, the conductive agent can include one or several of superconducting carbon, carbon black (such as acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder can include one or several of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives are, for example, thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0108] In addition, in the secondary battery of the present application, the negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in the present application may further include a conductive bottom coating (such as composed of a conductive agent and an adhesive) disposed between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode sheet described in the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0109] In the secondary battery of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0110] The type of the positive electrode active material is not specifically limited, and the positive electrode active materials known in the art for secondary batteries can be used. For example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of the lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as the positive electrode active material of the secondary battery can also be used.

[0111] The type of the negative electrode current collector is not specifically limited and can be selected according to actual needs. For example, the positive electrode current collector may be a metal foil or a composite current collector (a composite current collector can be formed by disposing a metal material on a polymer substrate). As an example, the positive electrode current collector may be an aluminum foil.

[0112] In the secondary battery of the present application, the positive electrode film layer generally includes a positive electrode active material, an optional binder, and an optional conductive agent, and is usually formed by coating a positive electrode slurry and drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, the optional conductive agent, the binder, etc. in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP).

[0113] As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0114] As an example, the conductive agent for the positive electrode film layer may include one or more of superconducting carbon, carbon black (e.g., acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] The type of the electrolyte in the secondary battery of the present application is not specifically limited and can be selected according to needs. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution).

[0116] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0117] In some embodiments, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluoro(dioxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

[0118] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0119] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may further include additives capable of improving certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature performance of the battery, and the like.

[0120] In secondary batteries using the electrolyte and some secondary batteries using solid electrolytes, a separator is further included. The separator is disposed between the positive electrode plate and the negative electrode plate and functions to isolate them. The present application does not particularly limit the type of the separator, and any well-known porous structure separator having good chemical stability and mechanical stability can be selected. In some embodiments, the material of the separator may be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film. When the separator is a multi-layer composite thin film, the materials of each layer may be the same or different.

[0121] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be made into an electrode assembly by a winding process or a stacking process.

[0122] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0123] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0124] This application places no particular restrictions on the shape of the secondary battery, which can be cylindrical, square, or any other arbitrary shape. As Figure 5 shown, it is a secondary battery 5 with a square structure as an example.

[0125] In some embodiments, referring to Figure 6 , the outer packaging may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or several, which can be adjusted according to requirements.

[0126] Battery module and battery pack

[0127] The secondary battery according to the present application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0128] Figure 7 shown, it is a schematic diagram of a battery module 4 as an example. As Figure 7 shown, in the battery module 4, multiple secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple secondary batteries 5 can be fixed by fasteners.

[0129] Optionally, the battery module 4 can further include an outer shell having a receiving space, and multiple secondary batteries 5 are received in the receiving space.

[0130] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0131] Figure 8 and Figure 9 shown, it is a schematic diagram of a battery pack 1 as an example. As Figure 8 and Figure 9As shown, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0132] Electric device

[0133] The present application also provides an electric device, which includes at least one of the secondary battery, battery module or battery pack of the present application. The secondary battery, battery module or battery pack can be used as the power source of the electric device or as the energy storage unit of the electric device. The electric device may be, but is not limited to, a mobile device (such as a mobile phone, laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0134] Figure 10 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the device for high power and high energy density, a battery pack or battery module including the secondary battery of the present application can be adopted.

[0135] Another example of an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. This electric device usually requires thin and light, and a secondary battery can be used as the power source.

[0136] Example

[0137] The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0138] Examples 1 to 12

[0139] Preparation of positive electrode sheet

[0140] The cathode active material lithium iron phosphate, the conductive agent acetylene black, and the binder PVDF are mixed in a mass ratio of 96:2:2, and the solvent NMP is added, and the mixture is stirred in a vacuum mixer until the system becomes homogeneous to obtain a cathode slurry;

[0141] The positive electrode paste is evenly coated on the positive electrode current collector aluminum foil, and then through drying, cold pressing and slitting, the positive electrode plate is obtained.

[0142] Preparation of negative electrode sheet

[0143] The negative electrode active material, conductive agent acetylene black, thickening agent CMC, and binder SBR are mixed according to a mass ratio of 96.4:1:1.2:1.4, and deionized water as a solvent is added. Under the action of a vacuum mixer, it is stirred until the system becomes homogeneous to obtain the negative electrode paste;

[0144] The negative electrode paste is evenly coated on the negative electrode current collector copper foil, and then through drying, cold pressing and slitting, the negative electrode plate is obtained.

[0145] Preparation of electrolyte

[0146] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to a volume ratio of 1:1:1 to obtain an organic solvent; the fully dried lithium salt LiPF6 is dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0147] Preparation of separator

[0148] A polyethylene film is used as the separator.

[0149] Preparation of secondary battery

[0150] The above-mentioned positive electrode plate, separator, and negative electrode plate are stacked in sequence, and the separator is placed between the positive and negative electrode plates to play a role in isolation. Through processing, a stacked electrode assembly is obtained; the stacked electrode assembly is placed in an outer packaging shell, dried, and then the electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0151] Among them, before injecting the electrolyte, a lithium supplement agent is applied to the surface of the outer peripheral region of the second negative electrode film layer of the negative electrode plate, so as to form a second negative electrode film layer as shown in Figure 4 . In Example 8, the lithium supplement agent is discontinuously applied to the outer peripheral region to form a non-continuous distribution of lithium sources. In the remaining examples, the lithium supplement agent is continuously applied to the outer peripheral region to form a continuous distribution of lithium sources.

[0152] In Examples 1 to 12, the lithium supplement d0 = 100 mm, l0 = 150 mm, the negative electrode active material, lithium supplement agent, R1 / R, R2 / R1, d2, d3, d4, d5, l1, l2, S1 / S2, C Li / C0 are respectively shown in Table 1-1.

[0153] Examples 13 to 18

[0154] According to the preparation processes of Examples 1 to 12, prepare the positive electrode sheet, negative electrode sheet, electrolyte, and separator of Examples 13 to 18;

[0155] Stack the above positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator positioned between the positive and negative electrode sheets to play a separating role, and obtain a wound electrode assembly through winding; Place the wound electrode assembly in an outer packaging case, inject the electrolyte after drying, and obtain a secondary battery through processes such as vacuum packaging, standing, forming, and shaping.

[0156] Among them, before injecting the electrolyte, apply a lithium supplement agent on the outer peripheral region of the second negative electrode film layer (denoted as the A side) located in the starting region, and / or on the surface of the outer peripheral region of the second negative electrode film layer (denoted as the B side) located in the ending region, so as to form the second negative electrode film layer as shown in Figure 4 on the A side and / or B side respectively after injecting the electrolyte.

[0157] Examples 19 to 20

[0158] Based on the preparation processes of Examples 13 to 18, prepare the positive electrode sheet, negative electrode sheet, electrolyte, separator, and secondary battery of Examples 19 to 20.

[0159] Among them, a polyethylene separator with a thickness of 20 μm is applied on the central region of the A side in Example 19, and a polytetrafluoroethylene coating with a thickness of 20 μm is applied on the central region of the A side in Example 20.

[0160] In Examples 13 to 20, d0 of the A side = 100 mm, l0 of the A side = 150 mm, d0 of the B side = 100 mm, and l0 of the B side = 165 mm. R1 / R, R2 / R1, d2, d3, d4, d5, l1, l2, S1 / S2, C Li / C0 of the A side and R1 / R, R2 / R1, d2, d3, d4, d5, l1, l2, S1 / S2, C Li / C0 of the B side are respectively shown in Table 1.

[0161] In Examples 13 to 20, based on the total capacity of the lithium source, the capacity ratio C A of the lithium source stored on the A side, the capacity ratio C B of the lithium source stored on the B side, the negative electrode active material, the lithium supplement agent, and d7 are respectively shown in Table 1-2.

[0162] Comparative Examples 1 to 2

[0163] Based on the preparation processes of Examples 1 to 12, the positive electrode sheet, negative electrode sheet, electrolyte, separator, and secondary battery of Comparative Examples 1 to 2 were prepared according to Table 1-1. Among them, no lithium supplement agent was applied to the surface of the outer peripheral region of the second negative electrode film layer in Comparative Examples 1 to 2.

[0164] Comparative Examples 3 to 4

[0165] Based on the preparation processes of Examples 13 to 18, the positive electrode sheet, negative electrode sheet, electrolyte, separator, and secondary battery of Comparative Examples 3 to 4 were prepared according to Table 1-2. Among them, no lithium supplement agent was applied to the surface of the outer peripheral region of the second negative electrode film layer in Comparative Examples 3 to 4.

[0166]

[0167]

[0168] Test part

[0169] 1) First Coulombic efficiency test of the secondary battery

[0170] The capacity measured by charging at a rate of 0.02C for 10 h at 45°C was marked as C0. Then, it was charged at a rate of 0.33C to 3.65V at 25°C, and the capacity measured by constant voltage charging at 3.65V to 0.05C was marked as C1. Finally, the capacity measured by discharging at a rate of 0.33C to 2.5V was marked as D0. The first Coulombic efficiency of the secondary battery = D0 / (C0 + C1) × 100%.

[0171] 2) Storage performance test of the secondary battery

[0172] The following steps were performed at 25°C:

[0173] Let it stand for 5 minutes; discharge at a rate of 0.33D0 to 2.5V; let it stand for 5 minutes; charge at a rate of 0.33D0 to 3.65V, and charge at a constant voltage of 3.65V to 0.05D0; let it stand for 5 minutes; discharge at a rate of 0.33D0 to 2.5V and record the capacity at this time as C dn , n represents the number of days of storage; let it stand for 5 minutes; charge at a rate of 0.33D0 to 3.65V; charge at a constant voltage of 3.65V to 0.05D0 (fully charged state); transfer the secondary battery to a storage environment at 45°C.

[0174] Data was collected once every 30 days of storage at 25°C according to the above steps, and the last data was collected after 180 days of storage. The reversible capacity retention rate of the secondary battery = C d180 / C d0 *100%.

[0175] 3) Cycle performance test of the secondary battery

[0176] Perform the following steps at 25 °C:

[0177] Let it stand for 5 minutes; discharge to 2.5 V at 0.33D0; let it stand for 5 minutes; charge to 3.65 V at 0.33D0, and perform constant voltage charging at 3.65 V until 0.05C; let it stand for 5 minutes; discharge to 2.5 V at 0.33C, and record the capacity at this time as C’0.

[0178] After letting the secondary battery stand for 5 minutes, transfer it to an environment of 45 °C, and perform charge and discharge cycles according to the following steps: let it stand for 20 minutes, charge to 3.65 V at 1D0, and perform constant voltage charging at 3.65 V until 0.05D0; let it stand for 5 minutes; discharge to 2.5 V at 1D0; let it stand for 5 minutes. Record the discharge capacity C of each cycle m , where m represents the number of cycles, until C m / C’0 * 100 = 80%, record the value of m at this time as the cycle life of the secondary battery:

[0179] The test results of Examples 1 to 20 and Comparative Examples 1 to 4 are shown in Table 2 respectively.

[0180] Table 2-1

[0181]

[0182] Table 2-2

[0183]

[0184] Table 2-3

[0185] Serial number Initial Coulomb efficiency Reversible capacity retention rate Cycle life / cycle Example 13 91.50％ 90.40％ 2151 Example 14 92.10％ 91.00％ 2314 Example 15 92.00％ 90.90％ 2306 Example 17 91.70％ 90.10％ 2153 Example 18 92.00％ 90.60％ 2274 Example 19 92.10％ 91.30％ 2418 Example 20 92.00％ 91.10％ 2369 Comparative example 3 91.20％ 89.10％ 2012

[0186] Table 2-4

[0187] Serial number Initial Coulomb efficiency Reversible capacity retention rate Cycle life / cycle Example 16 88.40％ 86.80％ 851 Comparative example 4 87.30％ 84.70％ 709

[0188] As can be seen from Table 1 and Table 2, setting a lithium source in the outer peripheral region of the second negative electrode film layer of the negative electrode tab can significantly improve the first Coulomb efficiency of the secondary battery, and enable the secondary battery to maintain a high reversible capacity retention rate and a long cycle life.

[0189] Specifically, as can be seen from Table 1-1, Table 2-1, and 2-2, compared with Comparative Examples 1 and 2, in Examples 1 to 12, a lithium source is provided in the outer peripheral region of the second negative electrode film layer of the secondary battery having a laminated structure. The first Coulombic efficiency of the secondary battery can be increased by more than 0.3%, the reversible capacity retention rate can be increased by more than 0.7%, and the cycle life can be increased by more than 79 cycles. It can be seen that providing a lithium source in the outer peripheral region of the second negative electrode film layer can achieve efficient lithium supplementation for the secondary battery, thereby effectively improving the first Coulombic efficiency and long-term cycling performance of the secondary battery. As can be seen from Examples 1 to 7, when a lithium source is provided in the outer peripheral region of the second negative electrode film layer, the area of the lithium source is appropriate and the lithium source maintains a suitable distance from the edge of the second negative electrode film layer, which can improve the lithium supplementation efficiency and the utilization rate of the lithium source. As can be seen from Example 8, compared with a non-continuously distributed lithium source, a continuously distributed lithium source can have a higher lithium supplementation efficiency and lithium source utilization rate. As can be seen from Examples 9 and 10, when the lithium source is stored in the outer peripheral region of the second negative electrode film layer and C Li / C0 is in the range of 20% to 120%, the first Coulombic efficiency and long-term cycling performance of the secondary battery can be effectively improved. In particular, when C Li / C0 is in the range of 90% to 120%, the improvement of the first Coulombic efficiency and long-term cycling performance of the secondary battery is more obvious. As can be seen from Example 12, a lithium source formed of a lithium alloy can also have a high lithium supplementation efficiency. However, relatively speaking, a lithium source formed of lithium metal has greater advantages in lithium supplementation.

[0190] As can be seen from Table 1-2, Table 2-3, and 2-4, compared with Comparative Examples 3 and 4, in Examples 13 to 20, a lithium source is provided in the outer peripheral region of the second negative electrode film layer of the secondary battery having a wound structure. The first Coulombic efficiency of the secondary battery can be increased by more than 0.3%, the reversible capacity retention rate can be increased by more than 1%, and the cycle life can be increased by more than 139 cycles. It can be seen that providing a lithium source in the outer peripheral region of the second negative electrode film layer can achieve efficient lithium supplementation for the secondary battery, thereby effectively improving the first Coulombic efficiency and long-term cycling performance of the secondary battery. As can be seen from Examples 13 to 15, when a lithium source is provided in the outer peripheral region of the second negative electrode film layer, the area of the lithium source is appropriate and the lithium source maintains a suitable distance from the edge of the second negative electrode film layer, which can improve the lithium supplementation efficiency and the utilization rate of the lithium source. As can be seen from Examples 17 and 18, when the secondary battery has a wound structure, compared with providing a lithium source in the winding end region, providing a lithium source in the winding start region can have a higher lithium supplementation efficiency. In addition, as can be seen from Examples 19 and 20, providing a barrier layer in the central region of the second negative electrode film layer can effectively reduce the infiltration of the electrolyte into the negative electrode film layer in the central region, thereby improving the first Coulombic efficiency, reversible capacity retention rate, and cycle life of the secondary battery.

[0191] As described above, this is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A secondary battery, comprising: a positive electrode plate including a positive electrode film layer; a separator; a negative electrode plate including a first negative electrode film layer which is disposed opposite to the positive electrode film layer with the separator therebetween, the first negative electrode film layer being a reaction zone negative electrode film layer, and a second negative electrode film layer which includes a negative electrode film layer not disposed opposite to the positive electrode film layer, the second negative electrode film layer being a non-reaction zone negative electrode film layer; the second negative electrode film layer includes a central region and a peripheral region surrounding the central region, wherein at least a part of the peripheral region of the second negative electrode film layer stores a lithium source for supplementing lithium to the first negative electrode film layer, and the lithium source is stored only in the second negative electrode film layer.

2. The secondary battery according to claim 1, wherein, The equivalent circular area diameter R of the second negative electrode film layer and the equivalent circular area diameter R1 of the peripheral region satisfy: 0.257R ≤ R1 ≤ 0.9434R.

3. The secondary battery according to claim 2, wherein, The peripheral region has a first part and a second part surrounding the first part, and the equivalent circular area diameter R2 of the second part satisfies: 0 < R2 < R1, wherein the lithium source is stored in the first part.

4. The secondary battery according to claim 3, wherein, 0 < R2 < 0.5R1.

5. The secondary battery according to claim 4, 0 < R2 < 0.1R1.

6. The secondary battery according to claim 3, wherein, The first part is annular, and the minimum distance d1 between the outer contour line of the first part and the edge of the second negative electrode film layer and the width d0 of the second negative electrode film layer satisfy: 0 < d1 ≤ d0 / 6.

7. The secondary battery according to claim 6 satisfies: d3 ≤ d2 ≤ d0 / 6, where d2 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer in the length direction, and d3 represents the minimum distance between the outer contour line and the side of the second negative electrode film layer in the width direction.

8. The secondary battery according to claim 7, wherein, The first part is a hollow rectangle, and the first part satisfies: 0 < d4 ≤ d0 / 3, where d4 represents the width of the first part in the width direction of the second negative electrode film layer; and / or 0 < d5 ≤ l0 / 3, where d5 represents the width of the first part in the length direction of the second negative electrode film layer, and l0 represents the length of the second negative electrode film layer.

9. The secondary battery according to claim 8, wherein The secondary battery satisfies at least one of the following: (1) 1 mm ≤ d2 ≤ 5 mm; (2) (l0 - 10 mm) ≤ l1 ≤ (l0 - 2 mm), where l1 represents the length of the outer contour line; (3) 10 mm ≤ d4 ≤ d0 / 5; (4) 1 mm ≤ d3 ≤ 5 mm; (5) (d0 - 10 mm) ≤ l2 ≤ (d0 - 2 mm), where l2 represents the width of the outer contour line; (6) 10 mm ≤ d5 ≤ d4; (7) The lithium source is annularly distributed in the first part.

10. The secondary battery according to claim 1, wherein, The area S1 of the second negative electrode film layer storing the lithium source and the area S2 of the peripheral region satisfy: 10% ≤ S1 / S2 ≤ 100%.

11. The secondary battery according to claim 10, wherein, 80% ≤ S1 / S2 < 100%.

12. The secondary battery according to claim 11, wherein, 90% ≤ S1 / S2 < 100%.

13. The secondary battery according to claim 1, wherein, The lithium source includes at least one of lithium metal, lithium alloy, and a composite of lithium metal and a negative electrode active material.

14. The secondary battery according to claim 13, wherein the lithium alloy includes at least one of silicon-lithium alloy, aluminum-lithium alloy, magnesium-lithium alloy, and tin-lithium alloy.

15. The secondary battery according to claim 1, wherein, The secondary battery satisfies: 20% C0 ≤ C Li ≤ 120% C0, where C0 represents the active material capacity per unit area of the second negative electrode film layer, and C Li represents the capacity per unit area of the lithium source.

16. The secondary battery according to claim 15, wherein, 90% C0 ≤ C Li ≤ 120% C0.

17. The secondary battery according to claim 1, wherein, The secondary battery has a wound structure, and the second negative electrode film layer includes a starting region and an ending region along the winding direction. The secondary battery satisfies: C A ≥C B , C A represents the capacity of the lithium source located in the starting region, and C B represents the capacity of the lithium source located in the ending region.

18. The secondary battery according to claim 17, wherein, The minimum distance d7 between the lithium source and the first negative electrode film layer satisfies: 0 < d7 ≤ 10 mm.

19. The secondary battery according to claim 1, wherein, The surface of the central region is covered with a barrier layer, and the barrier layer includes a barrier film and / or a barrier coating, where the barrier film is selected from at least one of a cast polypropylene film, a uniaxially stretched polypropylene film, a biaxially stretched polypropylene film, a polyethylene film, a polyester fiber film, and a polyvinyl chloride film; the barrier coating includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polybenzyl acrylamide, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile, or a copolymer of the above substances.

20. The secondary battery according to claim 19, wherein, The thickness of the barrier layer is 6 μm to 40 μm.

21. The secondary battery according to claim 20, wherein, The thickness of the barrier layer is 10 μm to 20 μm.

22. A battery module, comprising the secondary battery according to any one of claims 1-21.

23. A battery pack, comprising the battery module according to claim 22.

24. An electrical device, comprising at least one of the secondary battery according to any one of claims 1-21, the battery module according to claim 22, or the battery pack according to claim 23.

Images