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

Abstract

Provided is a secondary battery (5) including a positive electrode tab including a positive electrode current collector and a positive electrode film layer on both surfaces of the positive electrode current collector, and a negative electrode tab including a negative electrode current collector and a negative electrode film layer on both surfaces of the negative electrode current collector, the negative electrode film layer including a reaction region disposed opposite the positive electrode film layer and a non-reaction region not disposed opposite the positive electrode film layer, wherein a lithium supplement layer and a barrier layer are disposed on the non-reaction region. Also provided are a method of manufacturing the secondary battery (5), a battery module (4), a battery pack (1), and an electric device.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a secondary battery and its preparation method, battery module, battery pack and power device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its energy density, cycle performance, and safety performance.

[0003] When a battery begins charging, lithium ions from the positive electrode preferentially embed into the reaction region of the negative electrode, causing a potential drop in the reaction region and creating a voltage difference with the non-reaction region. Lithium ions in the reaction region then slowly diffuse and embed into the non-reaction region. However, these embedded lithium ions are difficult to return to the positive electrode during discharge, resulting in irreversible lithium loss from the positive electrode and deteriorating the cell's initial efficiency, cycle performance, and storage performance. Therefore, existing lithium-ion batteries still require improvement in terms of initial efficiency, cycle performance, and storage performance. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery with improved first-efficiency, cycle performance and storage performance.

[0005] To achieve the above objectives, this application provides a secondary battery, a method for preparing the same, a battery module, a battery pack, and an electrical device thereof.

[0006] The first aspect of this application provides a secondary battery, including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film on two surfaces of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film on two surfaces of the negative current collector. The negative electrode film includes a reaction region disposed opposite to the positive electrode film and a non-reaction region disposed not opposite to the positive electrode film. A lithium replenishment layer and a barrier layer are disposed on the non-reaction region.

[0007] Therefore, this application provides a lithium replenishment layer and a barrier layer on the non-reactive region of the negative electrode sheet. The lithium replenishment layer effectively prevents lithium ions in the reactive region from diffusing and embedding into the non-reactive region. At the same time, during the discharge process of the cell, lithium in the lithium replenishment layer will diffuse into the reactive region at a slow rate. The barrier layer completely isolates the non-reactive region outside the lithium replenishment layer, preventing the electrolyte from wetting it. This completely blocks the path of lithium diffusion from the reactive region and the lithium replenishment layer to the non-reactive region, thereby reducing the loss of lithium source and further improving the first efficiency, cycle performance and storage performance of the secondary battery.

[0008] In any embodiment, the lithium replenishment layer is disposed at one end of the non-reaction zone near the reaction zone, and the barrier layer is disposed starting from the lithium replenishment layer and moving away from the reaction zone. This improves lithium replenishment efficiency without affecting production capacity.

[0009] In any embodiment, the distance between the side of the lithium replenishment layer closest to the reaction zone and the reaction zone is 2 mm to 5 mm. When the distance between the side of the lithium replenishment layer closest to the reaction zone and the reaction zone is within the given range, the first-efficiency performance and cycle performance of the secondary battery can be further improved.

[0010] In any embodiment, the lithium replenishment layer comprises a substance capable of providing active lithium; optionally, it comprises one or more of lithium metal foil, lithium powder, and lithium alloy; further optionally, it comprises one or more of lithium metal foil, lithium powder, lithium silicon alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium tin alloy.

[0011] In any embodiment, the theoretical capacity C of lithium in the lithium replenishment layer Li Satisfying 20%C1≤C Li ≤120%C1, optionally 90%C1≤C Li ≤120%C1, where C1 is the capacity of the negative electrode film corresponding to the lithium replenishment layer. When the theoretical capacity C of lithium in the lithium replenishment layer... Li When given conditions are met, it is possible to improve the first-efficiency performance, cycle performance, and storage performance of secondary batteries without affecting their safety performance.

[0012] In any embodiment, the barrier layer is selected from films or coatings that cannot be wetted by the electrolyte; the film includes one or more of polypropylene, polyethylene, polyester fiber and polyvinyl chloride, optionally including one or more of cast polypropylene, uniaxially oriented polypropylene, biaxially oriented polypropylene, polyethylene, polyester fiber and polyvinyl chloride, and further optionally including polyethylene; the coating includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile and copolymers of the above substances.

[0013] In any embodiment, the thickness of the barrier layer is 6 μm-40 μm, optionally 10 μm-20 μm. When the thickness of the barrier layer is within the given range, it can ensure that the electrode does not undergo large deformation and is fully compatible with the battery cell.

[0014] In any embodiment, the film is adhesive with an adhesion force greater than 20 N / m. When the adhesion force of the film is within the given range, the film can be effectively adhered to the surface of the non-reactive area.

[0015] In any embodiment, a spacer region is provided on the negative electrode sheet on the side of the lithium replenishment layer away from the reaction region, along the width direction of the negative electrode sheet, and the barrier layer is provided starting from the spacer region and away from the reaction region. When a spacer region is provided on the negative electrode sheet on the side of the lithium replenishment layer away from the reaction region, the first-efficiency performance, cycle performance, and storage performance of the secondary battery can be further improved.

[0016] In any embodiment, the width of the spacer region is 5 mm to 50 mm, optionally 10 mm to 15 mm. When the width of the spacer region is within the given range, it can better assist in setting the barrier layer, more effectively isolate the electrolyte, and not affect the processing of the electrode sheet.

[0017] In any embodiment, the depth of the spacer region is equal to the thickness of the negative electrode film. When the depth of the spacer region is equal to the thickness of the negative electrode film, it prevents the electrolyte from wetting the non-reactive region along the bottom negative electrode film, thereby preventing lithium ions from diffusing into the non-reactive region, and thus improving the first-efficiency, cycle performance, and storage performance of the secondary battery.

[0018] A second aspect of this application also provides a method for preparing a secondary battery, comprising the following steps: (1) Preparation of the positive electrode sheet; (2) Preparation of negative electrode sheet; (3) Preparation of the isolation membrane; (4) Preparation of electrolyte; (5) Preparation of secondary batteries; Step (2) includes the step of setting a lithium replenishment layer and a barrier layer on the negative electrode sheet; The secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film on two surfaces of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film on two surfaces of the negative current collector. The negative electrode film includes a reaction region disposed opposite to the positive electrode film and a non-reaction region disposed not opposite to the positive electrode film. A lithium replenishment layer and a barrier layer are disposed on the non-reaction region.

[0019] In any embodiment, the barrier layer is provided by a coating or adhesive process; optionally, the barrier layer is provided by an adhesive process.

[0020] A third aspect of this application provides a battery module, including a secondary battery according to the first aspect of this application or a secondary battery prepared by the method of the second aspect of this application.

[0021] A fourth aspect of this application provides a battery pack that includes the battery module of the third aspect of this application.

[0022] The fifth aspect of this application provides an electrical device, including at least one selected from the secondary battery of the first aspect of this application or a secondary battery prepared by the method of the second aspect of this application, the battery module of the third aspect of this application, or the battery pack of the fourth aspect of this application.

[0023] The battery module, battery pack, and power device of this application include the secondary battery of this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a wound-type cell of a secondary battery according to one embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the structure of a stacked cell of a secondary battery according to one embodiment of this application.

[0026] Figure 3 yes Figure 1 The diagram shown is a schematic diagram of the unfolded negative electrode of the wound cell of a secondary battery according to an embodiment of this application.

[0027] Figure 4 This is a schematic diagram of the structure of a secondary battery cell according to one embodiment of this application.

[0028] Figure 5 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0029] Figure 6 yes Figure 5 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0030] Figure 7 This is a schematic diagram of a battery module according to one embodiment of this application.

[0031] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0032] Figure 9 yes Figure 8 An exploded view of a battery pack according to one embodiment of this application is shown.

[0033] Figure 10 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0034] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0035] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0039] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0041] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0042] In wound or stacked battery cells, the negative electrode must completely cover the positive electrode. The negative electrode includes a reaction region opposite to the positive electrode and a non-reaction region not opposite to the positive electrode. When the battery starts charging, lithium ions from the positive electrode preferentially insert into the reaction region of the negative electrode. The potential of the reaction region of the negative electrode drops, creating a voltage difference with the non-reaction region. Driven by this voltage difference, lithium ions in the reaction region slowly diffuse and insert into the non-reaction region. However, lithium ions inserted into the non-reaction region are difficult to return to the positive electrode during discharge, resulting in irreversible lithium loss from the positive electrode and ultimately deteriorating the cell's initial efficiency, cycle performance, and storage performance.

[0043] This application improves the first-efficiency performance, cycle performance, and storage performance of a secondary battery by setting a lithium replenishment layer in the non-reactive region of the negative electrode sheet; and by setting a barrier layer in the non-reactive region of the negative electrode sheet, it prevents electrolyte penetration, blocks the path of lithium ions from the lithium replenishment layer and the reactive region to diffuse into the non-reactive region, improves lithium replenishment efficiency, and further improves the first-efficiency performance, cycle performance, and storage performance of the secondary battery.

[0044] [Rechargeable Battery] In one embodiment of this application, a secondary battery is provided, including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film on two surfaces of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film on two surfaces of the negative current collector. The negative electrode film includes a reaction region disposed opposite to the positive electrode film and a non-reaction region disposed not opposite to the positive electrode film. A lithium replenishment layer and a barrier layer are disposed on the non-reaction region.

[0045] Although the mechanism is not yet clear, the applicant has unexpectedly discovered that by setting a lithium replenishment layer and a barrier layer on the non-reactive region of the negative electrode sheet, the lithium replenishment layer effectively prevents lithium ions in the reactive region from diffusing and embedding into the non-reactive region. At the same time, during the discharge process of the cell, lithium ions in the lithium replenishment layer will diffuse into the reactive region at a slow rate. The barrier layer completely isolates the non-reactive region outside the lithium replenishment layer, and the electrolyte cannot wet it, completely blocking the path of lithium ions from the reactive region and the lithium replenishment layer to diffuse into the non-reactive region, thereby reducing the loss of lithium source and further improving the first efficiency, cycle performance and storage performance of the secondary battery.

[0046] In embodiments of this application, the secondary battery further includes a separator. The positive electrode, negative electrode, and separator are fabricated into a cell using a winding or stacking process.

[0047] The two surfaces of the negative electrode are labeled as surface A and surface B, respectively. In a wound battery cell, such as... Figure 1 As shown, to ensure that the negative electrode completely covers the positive electrode, a non-reactive region is formed by one or more loops in the central area. This is defined in this application as the A-side unrolled non-reactive region. Similarly, to ensure that the negative electrode completely covers the positive electrode, there is one or more loops of non-reactive region outside the negative electrode in the terminal region. This is defined in this application as the B-side terminal non-reactive region.

[0048] like Figure 2 As shown, in a laminated cell, the outermost layer of the negative electrode is the non-reactive region.

[0049] Figure 3 for Figure 1 The diagram shows the unfolded negative electrode sheet in a wound battery cell. Figure 1 and Figure 3 As shown, a lithium replenishment layer and a barrier layer are respectively set in the empty roll non-reactive region on side A and the tail non-reactive region on side B.

[0050] The cell produced by the stacking process has no non-reactive region in the center, only in the outermost layer. In contrast, the cell produced by the winding process has non-reactive regions in both the center and the tail. The more non-reactive regions there are, the easier it is to distribute the lithium replenishment layer. Therefore, the cell can be selected as a winding cell.

[0051] Figure 4This is a schematic diagram illustrating the structural principle of a secondary battery according to one embodiment of this application. Figure 4 As shown, this application places the lithium source on the surface of the negative electrode film in the non-reaction zone before electrolyte injection to form a lithium replenishment layer. The standard electrode potential of lithium to hydrogen is -3.05V, while the standard electrode potential of non-lithium-intercalated negative electrode active materials such as graphite or silicon carbide to hydrogen is approximately 0V. Therefore, there is a voltage difference of approximately 3V between lithium and negative electrode active materials such as graphite or silicon carbide. After electrolyte injection, because the lithium source and the negative electrode film are in close contact, an electrical circuit is formed, equivalent to a direct short circuit (in this state, the lithium source is the negative electrode, and the negative electrode film is the positive electrode). Under the influence of their voltage difference, lithium in the lithium source loses electrons and becomes freely moving lithium ions, which are then intercalated into the negative electrode film to form, for example, LiC. x (x≥6) or / and Li x Si y (x>0, y>0), etc., at this time the original lithium source, LiC x or / and Li x Si y The combination forms a new, stable lithium replenishment layer. Because the potential of the lithium replenishment layer is lower, it effectively prevents lithium ions from diffusing and embedding into the non-reactive region. Simultaneously, the lithium replenishment layer remains at a relatively low potential. During cell discharge, the potential of the negative electrode reaction region gradually increases, becoming much higher than that of the non-reactive region. Driven by this potential difference, lithium from the lithium replenishment layer diffuses slowly into the reaction region, thereby improving the initial efficiency, cycle performance, and storage performance of the secondary battery.

[0052] Lithium ions in the replenishment layer not only diffuse into the reaction zone under the influence of voltage difference, but also embed into the non-reaction zone outside the replenishment layer under the influence of voltage difference. This application sets a barrier layer in the non-reaction zone to completely isolate the non-reaction zone outside the replenishment layer, preventing the electrolyte from wetting it and completely blocking the path of lithium ions from the replenishment layer and reaction zone to diffuse into the non-reaction zone, thereby reducing the loss of lithium source and further improving the first efficiency, cycle performance and storage performance of the secondary battery.

[0053] In some implementations, the lithium replenishment layer is located at the end of the non-reaction zone closer to the reaction zone, while the barrier layer is located starting from the edge of the lithium replenishment layer and moving away from the reaction zone. If the lithium replenishment layer is located away from the reaction zone and in the center of the non-reaction zone, the relative diffusion path of lithium ions will be longer, reducing the lithium replenishment efficiency. At the same time, it is inconvenient to set up the barrier layer, affecting production capacity.

[0054] In some implementations, the distance between the lithium replenishment layer and the reaction zone is 2 mm to 5 mm. The lithium replenishment layer must maintain a certain distance from the reaction zone to prevent slight misalignment of the positive and negative electrode sheets during winding from causing some of the lithium replenishment layer to enter the reaction zone, leading to serious safety risks. Furthermore, the lithium in the lithium replenishment layer will diffuse in all directions after electrolyte injection. If it is too close to the reaction zone, it may cause lithium over-intercalation in the reaction zone near the lithium replenishment layer, triggering lithium plating and potentially causing a short circuit in the battery. Maintaining a distance of more than 2 mm can avoid these risks. At the same time, the distance should not be too far, as this will consume more lithium and reduce the lithium replenishment effect; a distance of less than 5 mm yields the best results.

[0055] In some embodiments, the lithium replenishment layer includes a substance capable of providing active lithium; optionally, it includes one or more of lithium metal foil, lithium powder, and lithium alloy; further optionally, it includes one or more of lithium metal foil, lithium powder, lithium silicon alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium tin alloy.

[0056] Lithium alloys have relatively low specific capacity and form metallic impurities after delithiation; elemental lithium metal has high specific capacity and produces no impurities after reaction. Lithium foil has better processing performance than lithium powder, therefore, lithium foil can be an optional lithium replenishment layer.

[0057] In some implementations, the theoretical capacity C of lithium in the lithium replenishment layer Li Satisfying 20%C1≤C Li ≤120%C1, optionally 90%C1≤C Li ≤120%C1, where C1 is the capacity of the negative electrode film corresponding to the lithium replenishment layer.

[0058] The ratio of the capacity of the lithium replenishment layer to the capacity of the corresponding negative electrode film layer below the lithium replenishment layer affects the lithium replenishment effect and cell safety. When C Li When <20%C1, V Li >V 负 (V) Li V represents the potential of the lithium replenishment layer. 负 (This refers to the lithium intercalation plateau voltage of the negative electrode), meaning the potential of the lithium replenishment layer is higher than the lithium intercalation plateau voltage of the negative electrode. Therefore, lithium in the replenishment layer cannot intercalate into the lithium intercalation region, and it cannot prevent lithium from the lithium intercalation region from diffusing into the replenishment layer. When C... Li When C1 > 120%, V Li <V 负 And (V) Li (≈0 V), at this point the potential of the lithium replenishment layer is less than the lithium intercalation plateau voltage of the negative electrode, and lithium ions will migrate to the lithium intercalation region at a relatively fastest speed, due to C Li A value much greater than C1 will result in a large amount of lithium failing to embed into the negative electrode film, eventually depositing on its surface, which will lead to V LiWhen the voltage is near 0 V for an extended period, lithium ions in the replenishment layer migrate to the lithium intercalation region at the fastest rate over a relatively long time. When the migration capacity of lithium per unit time is much greater than the capacity decay of the negative electrode, localized lithium deposition occurs in the negative electrode reaction region. Since the negative electrode consumes 6%-10% of lithium during SEI film formation, and the overall capacity of the negative electrode per unit area is 1.05-1.15 times that of the positive electrode, when C... Li A lithium concentration ≤ 120% C1 will not cause lithium deposition in the negative electrode reaction zone. Therefore, when the lithium capacity in the lithium replenishment layer satisfies 20% C1 ≤ C Li At a C1 level ≤ 120%, it can safely replenish lithium to the battery cell, while improving the initial efficiency, cycle performance, and storage performance of the secondary battery. Optionally, at a C1 level ≤ 90%, it can safely replenish lithium to the cell, while improving the initial efficiency, cycle performance, and storage performance of the secondary battery. Li ≤120%C1.

[0059] In wound battery cells, the lithium replenishment layer can be disposed in the unreacted non-reactive region on side A and / or the unreacted terminal region on side B, C. Li = C A +C B C A To determine the theoretical capacity of lithium in the lithium replenishment layer set in the unreacted non-reactive region on the A side of the battery cell, C B The theoretical lithium capacity in the lithium replenishment layer set at the end of the non-reactive region on the B side of the battery cell. (When 0% C) Li ≤C A ≤100%C Li 0%C Li ≤C B ≤100%C Li And C A and C B When not simultaneously zero, it can further improve the initial efficiency, cycle performance, and storage performance of secondary batteries. Because the center of the cell has a relatively stronger ability to retain electrolyte, it is more conducive to the diffusion of lithium ions from the lithium source, so C can be optionally selected. A >C B .

[0060] Weight of lithium replenishment layer per unit area = (Coating weight of negative electrode film × Weight ratio of negative electrode active material × Specific capacity of negative electrode active material) × (C) Li / C1) / The theoretical capacity of lithium in the lithium replenishment layer. For example, the lithium replenishment layer uses lithium foil, and the coating weight of the negative electrode film is 9.4 mg / cm³. 2 The negative electrode active material is artificial graphite, and it accounts for 96% of the weight of the negative electrode film. If C Li =100%C1, then the weight of lithium foil per unit area = (9.4 × 96% × 360) × 100% / 3860 = 0.84 mg / cm² 2The specific capacity of artificial graphite is 360 mAh / g, while the theoretical capacity of lithium metal is 3860 mAh / g. Different weights of lithium-added layers per unit area can be obtained using a rolling mill.

[0061] In some embodiments, the barrier layer is selected from films or coatings that cannot be wetted by the electrolyte; the film includes one or more of polypropylene, polyethylene, polyester fiber and polyvinyl chloride, optionally including one or more of cast polypropylene, uniaxially oriented polypropylene, biaxially oriented polypropylene, polyethylene, polyester fiber and polyvinyl chloride, and further optionally including polyethylene; the coating includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile and copolymers of the above substances.

[0062] Because polyethylene (PE) film has advantages such as being odorless, non-toxic, stable within a temperature range of -90℃ to 100℃, resistant to acids and alkalis, resistant to organic solvents, having low water absorption, and excellent electrical insulation properties, it can optionally include PE film.

[0063] In some embodiments, the polyester fiber includes polyethylene terephthalate and polybutylene terephthalate.

[0064] In some embodiments, the thickness of the barrier layer is 6 μm-40 μm, and optionally 10 μm-20 μm.

[0065] In the embodiments of this application, it is necessary to control the thickness of the barrier layer. If the barrier layer is too thin, it is easily damaged; if it is too thick, it will cause greater deformation of the electrode. When the thickness of the barrier layer is within a given range, it can be ensured that the electrode does not undergo large deformation and is fully compatible with the battery cell.

[0066] In some embodiments, the film is adhesive with an adhesive force greater than 20 N / m, optionally greater than 200 N / m, and further optionally greater than 400 N / m.

[0067] In the embodiments of this application, the film has a certain degree of adhesion. If the adhesive force is too weak, the film cannot be tightly bonded to the negative electrode film layer on the negative electrode sheet, and it is easily torn. The adhesive force of the film is greater than 20 N / m, which can effectively adhere it to the surface of the non-reactive area. Optionally, the adhesive force of the film is greater than the cohesive force between particles in the negative electrode film layer. As long as the electrolyte can be isolated, either single-sided or double-sided adhesive films can meet the requirements of this application. Since the thickness of double-sided adhesive films is relatively increased compared to single-sided adhesive films, this will lead to greater deformation of the electrode sheet. Therefore, the film can optionally be a single-sided adhesive film.

[0068] In some embodiments, a spacer region is provided on the negative electrode sheet on the side of the lithium replenishment layer away from the reaction region, along the width direction of the negative electrode sheet, and a barrier layer is provided starting from the spacer region and away from the reaction region. More specifically, the barrier layer is provided on the bottom surface of the spacer region, the side of the spacer region near the non-reaction region, and on the non-reaction region away from the reaction region.

[0069] By setting a spacer region on the side of the lithium replenishment layer away from the reaction zone on the negative electrode sheet, the electrolyte can be prevented from wetting the non-reaction zone after liquid injection, thereby preventing lithium ions from the lithium replenishment layer and reaction zone from diffusing into the non-reaction zone, and further improving the first efficiency, cycle performance and storage performance of the secondary battery.

[0070] In some implementations, the width of the spacing zone is 5 mm to 50 mm, and optionally 10 mm to 15 mm.

[0071] Excessively wide spacer zones negatively impact electrode processing performance, particularly during cold pressing, leading to uneven electrode compaction. Conversely, excessively narrow spacer zones hinder subsequent non-reactive area lamination, resulting in loose lamination and electrolyte seepage from the bottom. When the spacer zone width falls within a specified range, it better facilitates the setting of the barrier layer, more effectively isolating the electrolyte without affecting electrode processing.

[0072] In some implementations, the depth of the spacer region is equal to the thickness of the negative electrode film.

[0073] If the depth of the spacer region is less than the thickness of the negative electrode film, meaning there is a negative electrode film at the bottom of the spacer region, then after electrolyte injection, the electrolyte will seep along the bottom negative electrode film into the non-reactive region, failing to prevent lithium ions from the lithium replenishment layer and the reactive region from diffusing into the non-reactive region. Therefore, the depth of the spacer region should be equal to the thickness of the negative electrode film, meaning the bottom of the spacer region is the current collector of the negative electrode sheet.

[0074] In one embodiment of this application, a method for preparing a secondary battery is provided, comprising the following steps: (1) Preparation of the positive electrode sheet; (2) Preparation of negative electrode sheet; (3) Preparation of the isolation membrane; (4) Preparation of electrolyte; (5) Preparation of secondary batteries; Step (2) includes the step of setting a lithium replenishment layer and a barrier layer on the negative electrode sheet; The secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film on two surfaces of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film on two surfaces of the negative current collector. The negative electrode film includes a reaction region disposed opposite to the positive electrode film and a non-reaction region disposed opposite to the positive electrode film. A lithium replenishment layer and a barrier layer are disposed on the non-reaction region.

[0075] In some implementations, the barrier layer is provided by coating or adhesive processes; alternatively, the barrier layer is provided by adhesive processes.

[0076] A barrier layer to prevent electrolyte wetting is crucial and can be installed using either coating or adhesive bonding processes. Since coating involves equipment mixing, coating, and baking, making the process more complex than adhesive bonding, the barrier layer can optionally be installed using adhesive bonding.

[0077] The lithium replenishment layer can be set through processes such as lamination, rolling, and coating.

[0078] In some embodiments, the method further includes setting a spacer region on the side of the lithium replenishment layer away from the reaction zone on the negative electrode sheet, along the width direction of the negative electrode sheet, and the spacer region is set by solvent cleaning, polishing or intermittent coating.

[0079] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0080] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0081] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0082] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0083] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0084] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0085] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0086] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0088] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0089] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0090] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0091] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0092] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0093] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0095] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0096] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0097] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0098] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0099] In some embodiments, the solvent may be selected from at least one of ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0100] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0101] [Isolation membrane] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0102] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0103] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly (cell) using a winding or stacking process.

[0104] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0105] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0106] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 This is an example of a square-structured secondary battery 5.

[0107] In some implementations, refer to Figure 6 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0108] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0109] Figure 7 This is battery module 4, used as an example. (See reference...) Figure 7 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0110] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0111] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0112] Figure 8 and Figure 9 This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0113] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0114] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0115] Figure 10This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0116] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0117] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0118] Example 1 (1) Preparation of positive electrode sheet Lithium iron phosphate (LiFePO4), acetylene black (Acetylene black), and polyvinylidene fluoride (PVDF) (a binder) were mixed at a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto both surfaces of a 12 μm thick aluminum foil used as a positive electrode current collector. The foil was dried at 115 °C for 15 min and cold-pressed to obtain a positive electrode film with a single-sided thickness of 84 μm. The film was then slit to obtain positive electrode sheets with a length of 605 mm and a width of 88 mm. The coating weight was 20 mg / cm². 2 The compacted density is 2.4 g / cm³. 3 .

[0119] (2) Preparation of negative electrode sheet Artificial graphite (negative electrode active material), acetylene black (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and SBR (binder) were mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of an 8 μm thick copper foil current collector. After drying at 115℃ for 15 min, it was cold-pressed to obtain a negative electrode film with a single-sided thickness of 61 μm. The film was then slit to obtain negative electrode sheets with a length of 735 mm and a width of 93 mm. The coating weight of the negative electrode sheets was 9.4 mg / cm². 2 The compacted density is 1.55 g / cm³. 3 Lithium foil of the same specification is applied to the unreacted region and the unreacted region at the end of the negative electrode sheet, wherein the theoretical capacity C of lithium in the lithium foil is... LiThe capacity C1 of the corresponding negative electrode film below satisfies C Li = 100%C1, the distance between the lithium foil and the reaction zone is 3 mm. Starting from the lithium replenishment layer and away from the reaction zone, a single-sided adhesive polyethylene film is pasted as a barrier layer. The adhesive strength of the polyethylene film is 470 N / m and the thickness is 20 μm.

[0120] (3) Preparation of electrolyte Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0121] (4) Preparation of the separating membrane A polyethylene film with a thickness of 12 μm was selected as the separator.

[0122] (5) Preparation of secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte at an injection coefficient of 4.2 g / Ah. After vacuum sealing, settling, formation, and shaping, a secondary battery with a capacity of about 3 Ah is obtained.

[0123] Example 2 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, lithium-aluminum alloy is applied to the empty non-reactive region and the tail non-reactive region of the negative electrode sheet, and its delithiation capacity is 1980 mAh / g.

[0124] Examples 3-6 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, the distance between the side of the lithium foil closest to the reaction zone and the reaction zone is 0 mm, 2 mm, 5 mm and 6 mm, respectively.

[0125] Examples 7-11 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, lithium foil of the same specification is applied to both the empty and closed non-reactive regions of the negative electrode sheet, wherein the theoretical capacity C of lithium in the lithium foil is... Li The capacity C1 of the corresponding negative electrode film below satisfies C Li =10%C1、C Li =20%C1、C Li =90%C1、C Li =120%C1 and C Li=130%C1.

[0126] Examples 12-13 The preparation of the secondary battery was generally the same as in Example 1, except that the thickness of the polyethylene film was 6 μm and 40 μm, respectively.

[0127] Examples 14-15 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, the single-sided adhesive polyethylene film is replaced with single-sided adhesive polyethylene terephthalate film and polyvinyl chloride film, respectively.

[0128] Example 16 The preparation of the secondary battery is generally the same as in Example 1, except that polytetrafluoroethylene is coated as a barrier layer with a thickness of 20 μm in the non-reactive area of ​​the negative electrode sheet.

[0129] Example 17 The preparation of the secondary battery is generally the same as in Example 1, except that polymethyl methacrylate is coated as a barrier layer with a thickness of 20 μm in the non-reactive area of ​​the negative electrode sheet.

[0130] Example 18 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, an interval region is set on the side of the lithium replenishment layer away from the reaction zone along the width direction of the negative electrode sheet. The interval region is formed by removing the negative electrode film layer by polishing and grinding. Its width is 15 mm and its depth is equal to the thickness of the negative electrode film layer, i.e., 61 μm. The barrier layer is set from the interval region away from the reaction zone.

[0131] Examples 19-20 The preparation of the secondary battery is generally the same as in Example 18, except that the width of the spacer region is 5 mm and 50 mm, respectively.

[0132] Example 21 The preparation of the secondary battery is generally the same as in Example 18, except that the depth of the spacer region is 20 μm, that is, the negative electrode film layer of the spacer region is not completely removed.

[0133] Comparative Example 1 The preparation of the secondary battery is generally the same as in Example 1, except that a barrier layer is not set in the non-reaction area during the preparation of the negative electrode sheet.

[0134] Comparative Example 2 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, the lithium replenishment layer is not set in the non-reactive region, and the barrier layer is set on the entire non-reactive region.

[0135] Comparative Example 3 The preparation of the secondary battery is generally the same as in Example 1, except that in the preparation of the negative electrode sheet, the lithium replenishment layer and the barrier layer are not set in the non-reaction area.

[0136] Secondary battery performance test 1. The capacity measured by charging at 0.02C for 10 h at 45℃ is marked as C0. Then, the capacity measured by charging at 0.33C to 3.65 V at 25℃ and maintaining a constant voltage of 3.65 V to 0.05C is marked as C1. Finally, the capacity measured by discharging at 0.33C to 2.5 V is marked as D0. D0 / (C0+C1)×100% is the first-cycle coulombic efficiency (first-cycle efficiency) of the secondary battery.

[0137] 2. Storage performance of secondary batteries The secondary battery was stored at 100% SOC (State of Charge) at 45℃. Data was collected every 15 days for the first 60 days, and every 30 days thereafter until the capacity decayed to 80%. The number of days of storage was recorded.

[0138] 3. Cycle performance of secondary batteries: At 45°C, the secondary battery is charged at a 1C rate to 3.65 V, kept constant at 3.65 V to 0.05C, and discharged at a 1C rate to 2.5 V. The above steps are repeated to perform a full charge and discharge cycle test until the capacity of the secondary battery decays to 80% of the initial capacity, and the number of cycles is recorded.

[0139] The secondary batteries obtained in the above embodiments and comparative examples were tested according to the above process, and the specific values ​​are shown in Table 1.

[0140] Table 1

[0141] As shown in Table 1, the number of cycles for the secondary batteries in all the above embodiments when the capacity retention rate is 80% is higher than that of the secondary batteries in the comparative example.

[0142] Comparing Example 1 with Comparative Examples 1 to 3, by providing a lithium replenishment layer and a barrier layer in the non-reactive region of the negative electrode sheet, the initial efficiency, storage performance and cycle performance of the secondary battery can be significantly improved.

[0143] Comparing Examples 1 and 3 to 6, when the distance between the side of the lithium replenishment layer closest to the reaction zone and the reaction zone is 2 mm-5 mm, the initial efficiency, storage days at 80% capacity, and cycle count at 80% capacity retention of the secondary battery can be further improved. Although the initial efficiency of the secondary battery is good when the distance between the side of the lithium replenishment layer closest to the reaction zone is 0 mm, if the side of the lithium replenishment layer closest to the reaction zone is completely close to the edge of the reaction zone, lithium plating may occur in the reaction zone, thus affecting cell safety. Therefore, the distance between the side of the lithium replenishment layer closest to the reaction zone should be greater than 0 mm.

[0144] Comparing Examples 1 and 7 to 11, when the theoretical capacity C of lithium in the lithium replenishment layer... Li The capacity C1 of the negative electrode film corresponding to the lithium replenishment layer satisfies 20%C1≤C Li ≤120%C1 can further improve the initial efficiency, storage performance, and cycle performance of secondary batteries. Although C Li At 130% C1, the secondary battery exhibits good initial efficiency, storage performance, and cycle performance. However, if C... Li A concentration >120% C1 may cause localized lithium deposition in the negative electrode reaction region; therefore, the C1 content must be satisfied. Li ≤120%C1.

[0145] By comparing Examples 1 and 18 to 21, it is found that when a spacer region is provided on the side of the lithium replenishment layer away from the reaction region on the negative electrode sheet, the first efficiency, storage performance and cycle performance of the secondary battery can be further improved.

[0146] Comparing Examples 18 and 21, when the depth of the spacer region is equal to the thickness of the negative electrode film, the initial efficiency, storage performance, and cycle performance of the secondary battery can be further improved.

[0147] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, comprising a positive electrode and a negative electrode, wherein the positive electrode includes a positive current collector and a positive electrode film on two surfaces of the positive current collector, and the negative electrode includes a negative current collector and a negative electrode film on two surfaces of the negative current collector, wherein the negative electrode film includes a reaction region disposed opposite to the positive electrode film and a non-reaction region disposed not opposite to the positive electrode film, wherein... A lithium replenishment layer and a barrier layer are provided on the non-reactive region; The lithium replenishment layer is disposed at one end of the non-reaction zone near the reaction zone, and the barrier layer is disposed starting from the lithium replenishment layer and away from the reaction zone; the barrier layer is selected from thin films or coatings that cannot be wetted by electrolyte. The film comprises one or more of polypropylene, polyethylene, polyester fiber, and polyvinyl chloride; The coating comprises one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile, and copolymers of the above substances. The barrier layer blocks the path of lithium ions from the lithium replenishment layer and the reaction zone to the non-reaction zone.

2. The secondary battery according to claim 1, wherein, The distance between the side of the lithium replenishment layer closest to the reaction zone and the reaction zone is 2 mm-5 mm.

3. The secondary battery according to claim 1, wherein, The lithium replenishment layer includes a substance capable of providing active lithium.

4. The secondary battery according to claim 3, wherein, The lithium replenishment layer includes one or more of lithium foil, lithium powder, and lithium alloy.

5. The secondary battery according to claim 4, wherein, The lithium alloy includes one or more of the following: silicon-lithium alloy, aluminum-lithium alloy, magnesium-lithium alloy, and tin-lithium alloy.

6. The secondary battery according to claim 1, wherein, The theoretical capacity C of lithium in the lithium replenishment layer Li Satisfying 20%C1≤C Li ≤120%C1, where C1 is the capacity of the negative electrode film corresponding to the lithium replenishment layer.

7. The secondary battery according to claim 6, wherein, The theoretical capacity C of lithium in the lithium replenishment layer Li Satisfying 90%C1≤C Li ≤120%C1.

8. The secondary battery according to claim 1, wherein, The polypropylene includes one or more of cast polypropylene, uniaxially oriented polypropylene, and biaxially oriented polypropylene.

9. The secondary battery according to claim 1, wherein, The film comprises polyethylene.

10. The secondary battery according to claim 1, wherein, The thickness of the barrier layer is 6 μm-40 μm.

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

12. The secondary battery according to claim 1, wherein, The film is adhesive with an adhesion force greater than 20 N / m.

13. The secondary battery according to claim 1, wherein, An interval region is provided on the negative electrode sheet on the side of the lithium replenishment layer away from the reaction region, along the width direction of the negative electrode sheet, and the barrier layer is provided starting from the interval region and away from the reaction region.

14. The secondary battery according to claim 13, wherein, The width of the interval is 5 mm to 50 mm.

15. The secondary battery according to claim 14, wherein, The width of the interval is 10 mm to 15 mm.

16. The secondary battery according to claim 13, wherein, The depth of the spacer region is equal to the thickness of the negative electrode film.

17. A method for preparing a secondary battery, comprising the following steps: (1) Preparation of the positive electrode sheet; (2) Preparation of negative electrode sheet; (3) Preparation of the isolation membrane; (4) Preparation of electrolyte; (5) Preparation of secondary batteries; Step (2) includes the step of setting a lithium replenishment layer and a barrier layer on the negative electrode sheet; The secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film on two surfaces of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film on two surfaces of the negative current collector. The negative electrode film includes a reaction region disposed opposite to the positive electrode film and a non-reaction region disposed not opposite to the positive electrode film. A lithium replenishment layer and a barrier layer are disposed on the non-reaction region. The lithium replenishment layer is disposed at one end of the non-reaction zone near the reaction zone, and the barrier layer is disposed starting from the lithium replenishment layer and away from the reaction zone; the barrier layer is selected from thin films or coatings that cannot be wetted by electrolyte. The film comprises one or more of polypropylene, polyethylene, polyester fiber, and polyvinyl chloride; The coating comprises one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyamide, polyimide, polymethyl methacrylate, polyurethane, polystyrene, polyacrylic acid, polyacrylamide, polyacrylonitrile, and copolymers of the above substances. The barrier layer blocks the path of lithium ions from the lithium replenishment layer and the reaction zone to the non-reaction zone.

18. The method according to claim 17, wherein, The barrier layer is applied by coating or pasting processes.

19. The method according to claim 18, wherein, The barrier layer is set by an adhesive bonding process.

20. A battery module, wherein, The secondary battery includes any one of claims 1 to 16 or a secondary battery prepared by any one of claims 17 to 19.

21. A battery pack, wherein, Includes the battery module as described in claim 20.

22. An electrical appliance, wherein, It includes at least one selected from the secondary battery of any one of claims 1 to 16, the secondary battery prepared by the method of any one of claims 17 to 19, the battery module of claim 20, or the battery pack of claim 21.

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