A secondary battery, a battery module, a battery pack, and an electric device

Abstract

The present application provides a secondary battery, a battery module, a battery pack, and an electrical device, including an electrode assembly. The electrode assembly includes a flat region and a bent region. Wherein, the surface of the positive active material layer in the bent region includes a functional layer, and the functional layer includes metal sulfide M x S y , 1 ≤ x ≤ 3, 1 ≤ y ≤ 3. Based on the mass of the functional layer, the mass content of the metal sulfide is 85% to 95%; the electrolyte of the secondary battery includes cyclic ester. The present application improves the problem of lithium deposition in the bent region of the secondary battery, thereby improving the safety of the secondary battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly to a secondary battery, a battery module, a battery pack, and an electric device. Background Art

[0002] Secondary batteries (such as lithium-ion batteries) have the characteristics of high specific energy, high working voltage, low self-discharge rate, small size, and light weight, and are widely used in various fields such as electric vehicles, electrical energy storage, and portable electronic devices.

[0003] For a wound-structure secondary battery, due to the structural characteristics of the wound structure, lithium deposition is more likely to occur in some areas of the battery, such as the bent parts of the electrode plates in the battery, thus affecting the service life and safety of the secondary battery. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to reduce lithium deposition in the bent part of the secondary battery and improve the safety of the secondary battery.

[0005] To achieve the above purpose, the present application provides a secondary battery, a battery module, a battery pack, and an electric device.

[0006] In a first aspect of the present application, a secondary battery is provided. The secondary battery includes an electrode assembly, and the electrode assembly includes a flat region and a bent region. Wherein, the surface of the positive active material layer in the bent region includes a functional layer, and the functional layer includes a metal sulfide M x S y , 1≤x≤3, 1≤y≤3. Based on the mass of the functional layer, the mass content of the metal sulfide is 85% to 95%; the electrolyte of the secondary battery includes a cyclic ester.

[0007] Thus, in the present application, the metal sulfide can react with the cyclic ester in the electrolyte to form a dense oxide film, preventing the lithium ions from escaping from the positive active material layer in the bent region, effectively improving the problem of lithium deposition in the bent region of the secondary battery, and thus improving the safety of the secondary battery.

[0008] In any embodiment, the areal density of the functional layer is 3mg / 1540.25mm 2 ~100mg / 1540.25mm 2 , and can be selected as 3mg / 1540.25mm 2 ~25mg / 1540.25mm 2 , which can effectively improve lithium deposition in the bent region of the secondary battery, reduce the influence of the functional layer on the capacity of the positive electrode plate, and enable the secondary battery to have both good safety performance and capacity performance.

[0009] In any embodiment, the thickness of the functional layer is 3 μm to 150 μm, preferably 5 μm to 50 μm, which can balance the sprayability of the functional layer and the gap in the bending area, and reduce the risk of the secondary battery being too wide due to excessive bending in the bending area.

[0010] In any embodiment, based on the mass of the electrolyte, the mass content of the cyclic ester is 5% to 50%, which can enable the metal sulfide in the functional layer to effectively react with the cyclic ester to form a dense oxide film, prevent the lithium ions from escaping from the positive electrode active material layer in the bending area, and effectively improve the lithium deposition problem in the bending area of the secondary battery.

[0011] In any embodiment, the cyclic ester includes at least one of ethylene carbonate and vinylene carbonate, which can react with the metal sulfide to form a dense oxide film, prevent the lithium ions from escaping from the positive electrode active material layer in the bending area, and effectively improve the lithium deposition problem in the bending area of the secondary battery.

[0012] In any embodiment, the electrode assembly includes n layers from the inside to the outside, the bending area includes n bending sub-areas where i ranges from 1 to n, and the surface of the positive electrode active material layer of at least one of the n bending sub-areas includes the functional layer, where n is greater than 2. The functional layer includes a metal sulfide that can react with the cyclic ester in the electrolyte to form a dense oxide film, effectively preventing the lithium ions from depositing on the negative electrode plate after escaping from the positive electrode active material layer, thereby improving the lithium deposition on the negative electrode plate in the bending area.

[0013] In any embodiment, the first bending sub-area is located in the first layer of the electrode assembly, and the coating range L1 of the functional layer of the first bending sub-area satisfies: The second bending sub-area is located in the second layer of the electrode assembly, and the coating range L2 of the functional layer of the second bending sub-area satisfies: The nth bending sub-area is located in the nth layer of the electrode assembly, and the coating range L n satisfies: where X is the circumference of the first circle of the electrode assembly; Y is a first constant, 3 ≤ Y ≤ 100; N1 is a first coefficient, 0 mm ≤ N1 ≤ 0.5 mm; r = the thickness of the positive electrode active material layer + 2 × the thickness of the separator + the thickness of the negative electrode active material layer. This application determines the coating range of the functional layer of the bending sub-area based on the relationship between the bending sub-area and the number of layers of the electrode assembly, which can make the coating position of the functional layer more accurate and is beneficial to further improving the lithium deposition problem in the bending area.

[0014] In any embodiment, the metal sulfide includes at least one of CuS, Cu₂S, MoS, MoS₂, MoS₃, NiS, and Ni₃S₂, and can react with the cyclic ester to form a dense oxide film, preventing the lithium ions from escaping from the positive electrode active material layer in the bending region, and effectively improving the problem of lithium deposition in the bending region of the secondary battery.

[0015] In any embodiment, the secondary battery is a lithium nickel cobalt manganese oxide system secondary battery, a lithium manganese oxide system secondary battery, or a lithium iron phosphate system secondary battery. For secondary batteries of different electrochemical systems, the present application can effectively improve the problem of lithium deposition in the bending region.

[0016] The second aspect of the present application provides a battery module, including the secondary battery of the first aspect of the present application.

[0017] The third aspect of the present application provides a battery pack, including the battery module of the second aspect of the present application.

[0018] The fourth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the first aspect of the present application, the battery module of the second aspect of the present application, or the battery pack of the third aspect of the present application.

[0019] Advantages of the present application:

[0020] A secondary battery, a battery module, a battery pack, and an electrical device provided by the present application. The secondary battery includes an electrode assembly. The surface of the positive electrode active material layer in the bending region of the electrode assembly includes a functional layer, and the functional layer includes a metal sulfide M x S y , and the metal sulfide can react with the cyclic ester in the electrolyte to form a dense oxide film, thereby preventing the lithium ions from escaping from the positive electrode active material layer, effectively improving the problem of lithium deposition in the bending region of the secondary battery, and thus improving the safety of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of an electrode assembly according to an embodiment of the present application.

[0022] Figure 2 is Figure 1 an enlarged structural diagram of the structure of part A shown.

[0023] Figure 3 is a schematic structural diagram of an electrode assembly according to another embodiment of the present application.

[0024] Figure 4 is a schematic structural diagram of a positive electrode tab according to another embodiment of the present application.

[0025] Figure 5 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0026] Figure 6 is Figure 5 An exploded view of a secondary battery according to an embodiment of the present application as shown.

[0027] Figure 7 A schematic diagram of a battery module according to an embodiment of the present application.

[0028] Figure 8 A schematic diagram of a battery pack according to an embodiment of the present application.

[0029] Figure 9 is Figure 8 An exploded view of a battery pack according to an embodiment of the present application as shown.

[0030] Figure 10 A schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0031] Description of reference numerals:

[0032] 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; 11 Functional layer; 12 Positive electrode plate; 13 Negative electrode plate; 121 Positive current collector; 122 Positive active material layer; 123 Positive electrode tab. Detailed implementation manners

[0033] Hereinafter, embodiments of the secondary battery, battery module, battery pack, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0034] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0036] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0037] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0038] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0039] 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, 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).

[0040] In the process of researching secondary batteries, the applicant found that for wound-structure secondary batteries, due to their structural characteristics, some areas in the battery are more prone to lithium deposition. A wound-structure secondary battery generally includes a flat region and a bent region. The part of the electrode tab located in the flat region is usually flat, and the part of the electrode tab located in the bent region is usually curved. The part of the electrode tab located in the flat region is more likely to undergo lithium deposition than the part of the electrode tab located in the bent region.

[0041] Related technologies improve the interfacial performance of the bent region of a secondary battery by keeping a relatively high positive and negative electrode capacity ratio in the region where the inner ring of the positive electrode wraps the negative electrode in the secondary battery. However, this method requires different gram capacities of active materials to be matched in different regions of the secondary battery. On the one hand, different gram capacities of active materials need to be prepared during the manufacturing process of the secondary battery. On the other hand, active materials with different gram capacities need to be separately coated on different regions of the secondary battery to form active material layers with different gram capacities, which increases the manufacturing cost of the secondary battery.

[0042] Based on this, the applicant found through in-depth research that by providing a functional layer on the surface of the positive electrode active material layer in the bent region of the electrode assembly, the functional layer includes a metal sulfide that can react with the cyclic ester in the electrolyte to form a dense oxide film, thereby effectively preventing the deposition of lithium ions released from the positive electrode active material layer onto the negative electrode tab, achieving the effect of improving lithium deposition on the negative electrode tab in the bent region, and there is no need to separately coat active materials with different gram capacities on different regions of the secondary battery to form active material layers with different gram capacities, which is beneficial to reducing the manufacturing cost of the secondary battery.

[0043] In order to reduce the risk of lithium deposition at the bent part of the secondary battery and improve the safety of the secondary battery, in view of this, the present application provides a secondary battery, a battery module, a battery pack, and an electrical device.

[0044] In one embodiment of the present application, the present application provides a secondary battery, including an electrode assembly, as Figure 1 shown, the electrode assembly includes a flat region and a bent region, wherein the surface of the positive electrode active material layer in the bent region includes a functional layer 11, and the functional layer 11 includes a metal sulfide M x S y, where 1 ≤ x ≤ 3 and 1 ≤ y ≤ 3, based on the quality of the functional layer 11, the mass content of the metal sulfide is 85% - 95%; the electrolyte of the secondary battery includes cyclic esters.

[0045] The flat area of the present application may refer to the area where the electrode plate in the electrode assembly is in a flat shape; the bent area of the present application may refer to the area where the electrode plate in the electrode assembly is in a bent shape; the functional layer may refer to a functional coating including a metal sulfide; the metal sulfide may refer to a metal sulfide conforming to the general formula M x S y (1 ≤ x ≤ 3, 1 ≤ y ≤ 3), where M represents a metal and S represents a sulfur element.

[0046] Although the mechanism is not yet clear, the applicant unexpectedly found that: for the electrode assembly of the present application, when the surface of the positive electrode active material layer in the bent area includes a functional layer, it can improve the problem of lithium deposition in the bent area of the secondary battery. This may be because the metal sulfide in the functional layer can react with the cyclic ester in the electrolyte to form a dense metal sulfide oxide film, thereby effectively preventing the lithium ions from depositing on the negative electrode plate after escaping from the positive electrode active material layer, thus improving lithium deposition in the bent area, especially lithium deposition on the negative electrode plate in the bent area. In addition to blocking the lithium ion transmission by forming a film, the functional layer of the present application also has the ability to consume lithium in the early stage, making the capacity of the negative electrode plate larger than that of the positive electrode plate and improving lithium deposition on the negative electrode plate in the bent area during the cycling process. This may be because the metal sulfide in the functional layer can react with Li + to consume the lithium ions in the positive electrode active material layer synchronously, so that the capacity of the negative electrode plate is larger than that of the positive electrode plate.

[0047] Reference Figure 1 , the electrode assembly of the present application includes a positive electrode plate 12 and a negative electrode plate 13. Figure 2 For Figure 1 the enlarged structural schematic diagram of the structure of part A shown, reference Figure 2 , the positive electrode plate 12 includes a positive electrode current collector 121 and a positive electrode active material layer 122, and the functional layer 11 is disposed on the surface of the positive electrode active material layer 122. It can be understood that the negative electrode plate 13 may also include a negative electrode current collector and a negative electrode active material layer.

[0048] Since the functional layer of the present application includes the metal sulfide M x S y, the electrolyte includes cyclic esters, and the metal sulfide can react with the cyclic esters in the electrolyte to form a dense oxide film, preventing the lithium ions from escaping from the positive electrode active material layer in the bent area, effectively improving the problem of lithium deposition in the bent area of the secondary battery, and thus improving the safety of the secondary battery. Compared with the current solutions for improving the interfacial performance of the bent area of the secondary battery, the present application does not require coating active materials with different specific capacities on different areas of the secondary battery to form active material layers with different specific capacities, which is beneficial to reducing the manufacturing cost of the secondary battery.

[0049] In some embodiments, the areal density of the functional layer is 3 mg / 1540.25 mm 2 ~100 mg / 1540.25 mm 2 , and can be optionally 3 mg / 1540.25 mm 2 ~25 mg / 1540.25 mm. By controlling the areal density of the functional layer within the above range, the lithium deposition in the bent area of the secondary battery can be effectively improved, the influence of the functional layer on the capacity of the positive electrode plate can be reduced, and the secondary battery can have both good safety performance and capacity performance.

[0050] In some embodiments, the thickness of the functional layer is 3 μm to 150 μm, and can be optionally 5 μm to 50 μm. By controlling the thickness of the functional layer within the above range, the problem of poor sprayability caused by too thin functional layer can be improved, and at the same time, the problem of too large gap in the bent area caused by too thick functional layer can be improved, which can balance the sprayability of the functional layer and the gap in the bent area, and reduce the risk of the secondary battery being too wide due to excessive bending degree in the bent area.

[0051] In some embodiments, based on the mass of the electrolyte, the mass content of the cyclic ester is 5% to 50%. By controlling the mass content of the cyclic ester within the above range, the metal sulfide in the functional layer can effectively react with the cyclic ester to form a dense oxide film, preventing the lithium ions from escaping from the positive electrode active material layer in the bent area, and effectively improving the problem of lithium deposition in the bent area of the secondary battery.

[0052] In some embodiments, the electrode assembly includes n circles from the inside to the outside, the bent area includes n bent sub-areas where i ranges from 1 to n, and the surface of the positive electrode active material layer in at least one of the n bent sub-areas includes a functional layer.

[0053] Exemplarily, please refer to Figure 3 the shown electrode assembly, which sequentially includes six layers of structures, namely the first layer, the second layer, the third layer, the fourth layer, the fifth layer and the sixth layer from the inside to the outside. It can also be seen from Figure 3 that there are two bent parts in each layer. Based on the structural characteristics of the wound electrode assembly, one of the bent parts belongs to the positive electrode plate (such as Figure 3(the bent part on the left side in the first layer shown), and the other bent part belongs to the negative electrode tab (such as Figure 3 (the bent part on the right side in the first layer shown). The bent sub-region mentioned in this application refers to the bent part in each layer of the positive electrode tab. It can be seen that Figure 3 the electrode assembly in [reference] has a total of 6 bent sub-regions. Among the above 6 bent sub-regions, the surface of the positive active material layer in at least one bent sub-region includes the functional layer 11. As an example, Figure 3 shows that the surfaces of the positive active material layers in 6 bent sub-regions all include the functional layer 11. Of course, it can also be that the surfaces of the positive active material layers in 2, 3, 4, or 5 bent sub-regions all include the functional layer 11, which is all reasonable. In addition, referring to Figure 4 , the positive electrode tab 12 can also be welded with at least one positive electrode ear 123 respectively. In this application, by including a functional layer on the surface of the positive active material layer in at least one of the n bent sub-regions, and the functional layer includes a metal sulfide that can react with the cyclic ester in the electrolyte to form a dense oxide film, it effectively prevents the lithium ions from depositing on the negative electrode tab after escaping from the positive active material layer, thereby improving the lithium deposition on the negative electrode tab in the bent region.

[0054] This application can determine the coating range of the functional layer of the bent sub-region based on the relationship between the bent sub-region and the number of layers of the electrode assembly. In some embodiments, referring to Figure 3 , the first bent sub-region is located in the first layer of the electrode assembly, and the coating range L1 of the functional layer of the first bent sub-region satisfies:

[0055] The second bent sub-region is located in the second layer of the electrode assembly, and the coating range L2 of the functional layer of the second bent sub-region satisfies:

[0056] The nth bent sub-region is located in the nth layer of the electrode assembly, and the coating range L n of the functional layer of the nth bent sub-region satisfies: wherein, X is the perimeter of the first circle of the electrode assembly; Y is the first constant, 3 ≤ Y ≤ 100; N1 is the first coefficient, 0mm ≤ N1 ≤ 0.5mm; r = the thickness of the positive active material layer + 2 × the thickness of the separator + the thickness of the negative active material layer.

[0057] Among them, the first turn of the electrode assembly refers to the winding structure between the starting end and the ending end, where the ending end is the point after one week along the winding direction starting from the starting end of the wound electrode assembly. The first constant can be set by designers based on the winding equipment model and the designed width of the electrode tab. As long as the coating of the functional layer of the present application can be achieved and the purpose of the present application can be achieved. For example, if the winding equipment model is Xiandao 250 and the width of the electrode tab material roll is 50 mm to 400 mm, the range of the first constant is 3 ≤ Y ≤ 100. The first coefficient belongs to the measurement fluctuation and can be a predetermined fluctuation range. r is determined based on the thickness of the positive electrode active material layer, the thickness of the separator, and the thickness of the negative electrode active material layer.

[0058] The present application determines the coating range of the functional layer of the bending sub-region based on the relationship between the bending sub-region and the number of layers of the electrode assembly, which can make the coating position of the functional layer more accurate and is beneficial to further improving the lithium deposition problem in the bending region.

[0059] The present application has no special restrictions on metal sulfides, as long as the purpose of the present application can be achieved. In one embodiment, the metal sulfide includes at least one of CuS, Cu2S, MoS, MoS2, MoS3, NiS, and Ni3S2, which can react with the cyclic ester to form a dense oxide film, prevent the lithium ions in the positive electrode active material layer in the bending region from escaping, and effectively improve the lithium deposition problem in the bending region of the secondary battery.

[0060] The present application has no special restrictions on cyclic esters, and they can be cyclic esters used in electrolytes, as long as the purpose of the present application can be achieved. In one embodiment, the cyclic ester includes at least one of ethylene carbonate and vinylene carbonate, which can react with the metal sulfide to form a dense oxide film, prevent the lithium ions in the positive electrode active material layer in the bending region from escaping, and effectively improve the lithium deposition problem in the bending region of the secondary battery.

[0061] The present application has no special restrictions on the electrochemical system of the secondary battery, as long as the purpose of the present application can be achieved. In one embodiment, the secondary battery is a lithium nickel cobalt manganese oxide system secondary battery, a lithium manganese oxide system secondary battery, or a lithium iron phosphate system secondary battery. For secondary batteries with different electrochemical systems, the present application can effectively improve the lithium deposition problem in the bending region.

[0062] The present application has no special restrictions on the preparation method of the functional layer. For example, the slurry spraying method or the slurry coating method can be used, as long as the purpose of the present application can be achieved. In one example, the functional layer is prepared by the following steps:

[0063] Preparation of the functional layer slurry:

[0064] Mix metal sulfide, acetylene black, and conductive carbon black in a mass ratio of 90:5:2 and grind them evenly to obtain a mixture. Then, add a binder solution to the mixture (where the mass ratio of the mixture to the binder in the binder solution is 97:3), and then add N-methylpyrrolidone (NMP) as a solvent to formulate a slurry with a solid content of 40 wt%, and stir evenly to obtain the functional layer slurry. The binder in the binder solution of this application may include sodium carboxymethyl cellulose, and the mass percentage content of the binder in the binder solution is 2% - 4%.

[0065] Preparation of the functional layer:

[0066] In the die-cutting process of the positive electrode plate, according to the position of the bending area in the designed positive electrode plate (the coating range of the functional layer can be determined based on the relationship between the bending sub-area and the number of electrode assembly layers), spray the obtained functional layer slurry on the corresponding position on the surface of the positive electrode active material layer through a spraying device (such as a Wagner spraying instrument from Germany). During the die-cutting and tape-running process of the positive electrode plate, NMP volatilizes to obtain the functional layer.

[0067] In addition, the secondary battery, battery module, battery pack, and electrical device of this application will be described below with appropriate reference to the drawings.

[0068] In one embodiment of this application, a secondary battery is provided.

[0069] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short-circuiting between the positive and negative electrodes, and at the same time allows ions to pass through.

[0070] [Positive electrode plate]

[0071] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0072] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0073] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries known in the art. By way of example, the positive electrode active material may include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05at least one of O2) and its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0075] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0076] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0078] [Negative electrode plate]

[0079] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0080] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0081] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. 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 materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0083] In some embodiments, the negative electrode active material layer may also optionally include a binder. The binder 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).

[0084] In some embodiments, the negative electrode active material layer may also 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.

[0085] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0086] In some embodiments, the negative electrode plate can be prepared in the following manner: the components for preparing the negative electrode plate described above, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0087] [Electrolyte]

[0088] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The present application has no specific limitation on the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid.

[0089] In some embodiments, the electrolyte uses an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

[0090] 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0091] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluorinated ethylene 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.

[0092] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high-temperature or low-temperature performance, etc.

[0093] [Separator membrane]

[0094] In some embodiments, the secondary battery further includes a separator membrane. The present application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0095] In some embodiments, the material of the separator membrane may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0096] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator membrane may be made into a secondary battery by a winding process.

[0097] In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the above secondary battery and electrolyte.

[0098] In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic, and examples of the plastic may include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0099] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 5 is a secondary battery 5 with a square structure as an example.

[0100] In some embodiments, referring to Figure 6 , the outer package 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 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator may be formed into an electrode assembly 52 through a winding 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 included in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0101] In some embodiments, the secondary batteries can be assembled into a battery module. The number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0102] Figure 7 is a battery module 4 as an example. Referring to Figure 7 , in the battery module 4, a plurality of 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 way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0103] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of secondary batteries 5 are received in the receiving space.

[0104] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0105] Figure 8 and Figure 9 is a battery pack 1 as an example. Referring to Figure 8 and Figure 9 , the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0106] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0107] As the electrical device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0108] Figure 10 Here is an example of an electrical device. The electrical device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high-power and high-energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be adopted.

[0109] Another example of the device can be a mobile phone, tablet computer, laptop computer, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0110] Embodiment

[0111] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technical or conditions noted in the embodiments, the technologies or conditions described in the literature in the field or according to the product specifications are followed. For reagents or instruments without the producer noted, they are all conventional products that can be obtained through commercial purchase.

[0112] Embodiment 1

[0113] <Preparation of the positive electrode plate>

[0114] Mix the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent conductive carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 96:2:2, then add N-methylpyrrolidone (NMP) as a solvent, and stir under a vacuum mixer until the system becomes homogeneous to obtain a positive electrode slurry with a solid content of 60 wt%. Uniformly coat the positive electrode slurry on one surface of an aluminum foil with a thickness of 12 μm, dry it at 120 °C, and obtain a positive electrode plate roll with a positive electrode active material layer thickness of 100 μm after cold pressing.

[0115] <Preparation of the functional layer slurry>

[0116] Mix copper sulfide (CuS), acetylene black, and conductive carbon black in a mass ratio of 90:5:2 and grind them evenly to obtain a mixture. Then, add a binder solution to the mixture, where the mass ratio of the mixture to the binder in the binder solution is 97:3. Next, add N-methylpyrrolidone (NMP) as a solvent to formulate a slurry with a solid content of 40 wt%, and stir it evenly to obtain the functional layer slurry. Among them, the binder solution is a sodium carboxymethyl cellulose solution, and the mass percentage of sodium carboxymethyl cellulose in the binder solution is 3%.

[0117] <Preparation of the functional layer>

[0118] Unroll the obtained positive electrode sheet roll. In the die-cutting process of the positive electrode sheet, after the positive electrode sheet is die-cut and the positive electrode tab is welded, according to the position of the bending area in the designed positive electrode sheet (the coating range of the functional layer is determined based on the relationship between the bending sub-region and the number of electrode assembly layers), spray the obtained functional layer slurry on the corresponding position on the surface of the positive electrode active material layer through a spraying device (Wagner spraying instrument from Germany), so that the surface of the positive electrode active material layer in each bending sub-region has a functional layer during the subsequent winding process. During the die-cutting and tape-running process of the positive electrode sheet, NMP volatilizes to form a functional layer, and a positive electrode sheet with a functional layer as shown in Figure 4 is obtained. The surface density of the functional layer is 10 mg / 1540.25 mm 2 , and the thickness is 20 μm.

[0119] <Preparation of the separator>

[0120] Use a polyethylene (PE) porous polymer film with a thickness of 15 μm as the separator.

[0121] <Preparation of the electrolyte>

[0122] In an environment with a water content of less than 10 ppm, mix dimethyl carbonate (DMC), vinylene carbonate (VC), and ethylene carbonate (EC) in a non-aqueous organic solvent in a mass ratio of 76:4:20. Then, add lithium hexafluorophosphate (LiPF6) to the non-aqueous organic solvent and dissolve and mix it evenly. Among them, the mass fraction of LiPF6 in the electrolyte is 12.5 wt%.

[0123] <Preparation of the negative electrode sheet>

[0124] Mix artificial graphite as the negative electrode active material, conductive carbon black, and sodium polyacrylate in a mass ratio of 95:2:3, add deionized water as a solvent, and stir under a vacuum mixer until the system becomes homogeneous to obtain a negative electrode slurry with a solid content of 50 wt%. Uniformly coat the negative electrode slurry on one surface of a copper foil with a thickness of 8 μm, dry it at 110 °C, and obtain a negative electrode sheet with a negative electrode active material layer thickness of 70 μm after cold pressing. Obtain the negative electrode sheet through processes such as tab forming and slitting.

[0125] <Preparation of secondary battery>

[0126] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle between the positive electrode sheet and the negative electrode sheet to play a role in isolation. Wind the above components to obtain an electrode assembly, place the electrode assembly in an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the prepared electrolyte, and obtain a secondary battery through processes such as vacuum packaging, standing, formation, and shaping.

[0127] Examples 2 to 3

[0128] Except that in <Preparation of functional layer slurry>, as shown in Table 1, adjust the content of metal sulfide in the functional layer slurry to change the content of metal sulfide in the functional layer, the rest is the same as in Example 1.

[0129] Examples 4 to 7

[0130] Except that in <Preparation of functional layer slurry>, as shown in Table 1, adjust the type of metal sulfide, the rest is the same as in Example 1.

[0131] Examples 8 to 12

[0132] Except that in <Preparation of functional layer>, as shown in Table 2, adjust the areal density and thickness of the functional layer, the rest is the same as in Example 1.

[0133] Examples 13 to 16

[0134] Except that in <Preparation of electrolyte>, as shown in Table 3, adjust the ratio of organic solvents in the electrolyte to change the content of cyclic ester in the electrolyte, the rest is the same as in Example 1.

[0135] Comparative Example 1

[0136] Except that in <Preparation of positive electrode sheet>, do not spray the functional layer slurry on the surface of the positive electrode active material layer, that is, the bending area of the secondary battery does not have a functional layer, the rest is the same as in Example 1.

[0137] The relevant parameters of the secondary batteries of the above Examples 1 to 7 and Comparative Example 1 are shown in Table 1 below.

[0138] Table 1

[0139] Types of metal sulfides Content of metal sulfides (%) Example 1 CuS 90 Example 2 CuS 85 Example 3 CuS 95 Example 4 <![CDATA[Cu2S]]> 90 Example 5 MoS 90 Example 6 <![CDATA[Ni3S2]]> 90 Example 7 <![CDATA[MoS3]]> 90 Comparative Example 1 / /

[0140] In Table 1, " / " indicates that the relevant preparation parameters are not included.

[0141] The relevant parameters of the secondary batteries in the above Examples 8 to 12 are shown in Table 2 below.

[0142] Table 2

[0143]

[0144]

[0145] The relevant parameters of the secondary batteries in the above Examples 13 to 16 are shown in Table 3 below.

[0146] Table 3

[0147]

[0148] In addition, the secondary batteries obtained in the above Examples 1 to 16 and Comparative Example 1 were respectively subjected to the following performance tests.

[0149] Lithium deposition test of secondary battery:

[0150] Select the secondary batteries of Examples 1 to 18 and Comparative Example 1 for charge-discharge cycle testing. After 100 charge-discharge cycles, fully charge the secondary battery after the last charge-discharge cycle again, and then disassemble the secondary battery to observe whether a lithium deposition interface appears on the negative electrode sheet in the bent area of the secondary battery. If a lithium deposition interface appears, it indicates that lithium deposition has occurred in the secondary battery; if no lithium deposition interface appears, it indicates that no lithium deposition has occurred in the secondary battery. The test results are shown in Table 4.

[0151] Table 4

[0152]

[0153] According to the above results, it can be seen that in Examples 1 to 16, no lithium deposition or only slight lithium deposition occurred on the negative electrode sheet in the bent area of the secondary battery, indicating that the functional layer of the present application can effectively improve the lithium deposition problem in the bent area of the secondary battery, thereby improving the safety of the secondary battery. When the content of the active substance in the functional layer is small, the amount of the positive active material participating in the reaction is too small, and slight lithium deposition will occur; when the content of the cyclic ester in the electrolyte is small, the amount of the metal sulfide participating in the reaction is too small, and slight lithium deposition will occur.

[0154] In contrast, lithium deposition occurred on the negative electrode sheet in the bent area of the secondary battery in Comparative Example 1, and it is difficult to improve the safety of the secondary battery.

[0155] As can be seen from Examples 2 to 7, by coordinately regulating the type and content of metal sulfide within the scope of this application, the metal sulfide can react with the cyclic ester in the electrolyte to form a dense oxide film, thereby preventing the lithium ions from escaping from the positive electrode active material layer, effectively improving the problem of lithium precipitation in the bending area of the secondary battery, and enhancing the safety of the secondary battery.

[0156] As can be seen from Examples 1, 8 to 12, by coordinately regulating the areal density and thickness of the functional layer, the problem of lithium precipitation in the bending area of the secondary battery can be improved, and the safety of the secondary battery can be enhanced. When the thickness of the functional layer is further regulated within the range of 5 μm to 50 μm, it is beneficial to improve the swelling performance of the secondary battery, which may be because the functional layer with this thickness range has lower stress in the bending area, and the risk of the secondary battery swelling and deforming due to excessive stress can be reduced.

[0157] As can be seen from Examples 1, 13 to 15, and 16, by regulating the type and content of the cyclic ester in the electrolyte, the problem of lithium precipitation in the bending area of the secondary battery can be further improved, and the safety of the secondary battery can be enhanced.

[0158] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes an electrode assembly, and the electrode assembly includes a flat region and a bent region, wherein The surface of the positive active material layer in the bending region includes a functional layer, and the functional layer includes metal sulfide M x S y , where 1 ≤ x ≤ 3 and 1 ≤ y ≤ 3. Here, M is Cu, Mo, or Ni, and based on the mass of the functional layer, the mass content of the metal sulfide is 85% - 95%; the electrolyte of the secondary battery includes a cyclic ester.

2. The secondary battery according to claim 1, characterized in that, The areal density of the functional layer is 3 mg / 1540.25 mm 2 ~100 mg / 1540.25 mm 2 .

3. The secondary battery according to claim 2, characterized in that, The areal density of the functional layer is 3 mg / 1540.25 mm 2 to 25 mg / 1540.25 mm 2 .

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The thickness of the functional layer is 3 μm to 150 μm.

5. The secondary battery according to claim 4, characterized in that, The thickness of the functional layer is 5 μm to 50 μm.

6. The secondary battery according to any one of claims 1 to 3, characterized in that, Based on the mass of the electrolyte, the mass content of the cyclic ester is 5% to 50%.

7. The secondary battery according to any one of claims 1 to 3, characterized in that, The cyclic ester includes at least one of ethylene carbonate and vinylene carbonate.

8. The secondary battery according to any one of claims 1 to 3, characterized in that, The electrode assembly includes n layers from the inside to the outside, the bent region includes n bent sub-regions where i ranges from 1 to n, and the surface of the positive electrode active material layer in at least one of the n bent sub-regions includes the functional layer, and n is greater than 2.

9. The secondary battery according to claim 8, wherein, The first bent sub-region is located in the first layer of the electrode assembly, and the coating range L1 of the functional layer of the first bent sub-region satisfies: The second bent sub-region is located in the second layer of the electrode assembly, and the coating range L2 of the functional layer of the second bent sub-region satisfies: The nth bent sub-region is located in the nth layer of the electrode assembly, and the coating range L of the functional layer of the nth bent sub-region n satisfies: Wherein, X is the perimeter of the first turn of the electrode assembly; Y is a first constant, 3 ≤ Y ≤ 100; N1 is a first coefficient, 0 mm ≤ N1 ≤ 0.5 mm; r = the thickness of the positive electrode active material layer + 2 × the thickness of the separator + the thickness of the negative electrode active material layer.

10. The secondary battery according to any one of claims 1-3, characterized in that, The metal sulfide includes at least one of CuS, Cu2S, MoS, MoS2, MoS3, NiS, and Ni3S2.

11. The secondary battery according to any one of claims 1 to 3, characterized in that, The secondary battery is a lithium nickel cobalt manganese oxide system secondary battery, a lithium manganate system secondary battery, or a lithium iron phosphate system secondary battery.

12. A battery module, characterized in that, It includes the secondary battery according to claim 11.

13. A battery pack, characterized in that, It includes the battery module according to claim 12.

14. An electrical device, characterized in that, It includes at least one selected from the secondary battery according to claim 11, the battery module according to claim 12, or the battery pack according to claim 13.

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