Secondary battery and electric device comprising same

Abstract

The invention provides a secondary battery and an electric device comprising the same, the secondary battery comprises an electrode pole piece, the electrode pole piece comprises a current collector, a diaphragm layer arranged on at least one surface of the current collector, and a first protective layer which is arranged on the upper surface of the diaphragm layer and has a net structure; wherein the first protective layer comprises a conductive nano material. The diaphragm layer is wrapped by the conductive nano material, so that on one hand, the tensile strength and the elongation of the diaphragm layer are improved, the cracking risk of the diaphragm layer is reduced, on the other hand, the conductivity of the diaphragm layer is improved, and the cycling stability of the battery is facilitated.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application range of secondary batteries, they have been widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] Currently, secondary batteries still need to be further improved in terms of cycle stability. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a secondary battery electrode sheet with good cycle performance and an electric device containing the secondary battery.

[0005] A first aspect of the present application provides a secondary battery, including an electrode sheet, where the electrode sheet includes: a current collector; a diaphragm layer provided on at least one surface of the current collector; and a first protective layer with a network structure provided on the upper surface of the diaphragm layer; wherein, the first protective layer includes conductive nanomaterials.

[0006] By dispersing conductive nanomaterials on the diaphragm layer, effectively wrapping the diaphragm layer, a dense network structure is formed on the surface of the diaphragm layer. On the one hand, the tensile strength and elongation rate of the diaphragm layer are effectively improved, its mechanical properties are improved, thereby reducing the safety risk of induced cracking caused by too low elongation rate of the diaphragm layer. On the other hand, the conductivity of the diaphragm layer is increased. Thus, it is beneficial to the cycle stability of the battery.

[0007] In some embodiments, the conductive nanomaterials include at least one of linear conductive nanomaterials, tubular conductive nanomaterials, or sheet-like conductive nanomaterials. These types of conductive nanomaterials have controllable structures, excellent comprehensive properties, and are more cost-effective.

[0008] In some embodiments, the tubular conductive nanomaterials include at least one of single-walled nanotubes, oligomeric-walled nanotubes, and multi-walled carbon nanotubes. These materials are easy to prepare or commercially available, and are convenient to process.

[0009] In some embodiments, the sheet-like conductive nanomaterials include at least one of single-layer graphene, oligomeric-layer graphene, multi-layer graphene, or graphene nanoribbons. These materials are easy to prepare or commercially available, and are convenient to process.

[0010] In some embodiments, based on the total mass of the first protective layer, the mass percentage of the conductive nanomaterial is 28 wt% - 72 wt%. Thus, a "dense" network structure can be effectively formed to provide protection for the diaphragm layer.

[0011] In some embodiments, a second protective layer with a network structure is provided on at least one surface of the current collector, and the second protective layer includes the conductive nanomaterial; the mass percentage of the conductive nanomaterial in the second protective layer is greater than that in the first protective layer; the thickness of the second protective layer is greater than or equal to the thickness of the first protective layer. Thus, the oxide film on the surface of the current collector can be protected by the second protective layer from being damaged, the corrosion of the current collector by the electrolyte can be inhibited, the contact resistance between the diaphragm layer and the current collector can be improved, which is more conducive to improving the cycle stability of the battery. In addition, it is also beneficial to enhance the safety, life and rate performance of the battery.

[0012] In some embodiments, based on the total mass of the second protective layer, the mass percentage of the conductive nanomaterial is 28 wt% - 72 wt%.

[0013] In some embodiments, the thickness of the first protective layer is 0.5 μm to 1 μm; and / or, the thickness of the second protective layer is 1 μm to 2 μm. When the thickness of the first protective layer is within this range, while providing effective encapsulation, it can also provide a certain degree of support for the diaphragm layer, and can further effectively improve the mechanical properties of the diaphragm layer. When the thickness of the second protective layer is within this range, it can more effectively protect the oxide film on the surface of the current collector from being damaged and inhibit the corrosion of the current collector by the electrolyte.

[0014] In some embodiments, the first protective layer and / or the second protective layer further includes a binder.

[0015] In some embodiments, the aspect ratio of the linear conductive nanomaterial is 10 - 1500; and / or, the aspect ratio of the tubular conductive nanomaterial is 10 - 1500; and / or, the aspect ratio of the sheet-like conductive nanomaterial is 3.2 to 450. Thus, the strong agglomeration effect of the conductive nanomaterial or the entanglement and bonding phenomenon of the fibers are relatively low, and it is easy to disperse, which is beneficial to its uniform distribution on the surface of the diaphragm layer.

[0016] In some embodiments, the electrode tab is a positive electrode tab and / or a negative electrode tab. The first protective layer and / or the second protective layer of the present application are provided to form an effective "physical" encapsulation on the diaphragm layer. Therefore, there is no need to distinguish between the positive electrode tab and the negative electrode tab, and it can be applied to both.

[0017] The second aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application.

[0018] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the cracking phenomenon in the battery cell in the prior art.

[0020] Figure 2 It is a schematic diagram of the structure of the conductive nanomaterial according to an embodiment of the present application.

[0021] Figure 3 It is a schematic diagram of the structure of the conductive nanomaterial according to an embodiment of the present application.

[0022] Figure 4 It is a schematic diagram of the structure of the conductive nanomaterial according to an embodiment of the present application.

[0023] Figure 5 It is a scanning electron microscope test (SEM) image of the first protective layer according to an embodiment of the present application.

[0024] Figure 6 It is a cross-sectional scan (CP) image of the first protective layer according to an embodiment of the present application.

[0025] Figure 7 It is a schematic diagram of the diaphragm tensile curve according to an embodiment of the present application.

[0026] Figure 8 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0027] Figure 9 is Figure 8 The exploded view of the battery cell shown in the present application according to an embodiment.

[0028] Figure 10 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0029] Figure 11 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0030] Figure 12 is Figure 11 The exploded view of the battery pack shown in the present application according to an embodiment.

[0031] Figure 13 It is a schematic diagram of an electrical device using the secondary battery as a power source according to an embodiment of the present application.

[0032] Description of the Reference Numerals:

[0033] 1 Battery pack; 2 Upper case; 3 Lower case; 4 Battery module; 5 Secondary battery; 51 Case; 52 Electrode assembly; 53 Top cover assembly Detailed implementation manners

[0034] Hereinafter, embodiments of the secondary battery and the electrical device including the same according to the present application will be specifically described with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by 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.

[0035] The "range" disclosed in the present application is 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 boundary 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 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 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, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to 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 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated 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.

[0036] It should be understood that when an element or layer is referred to as "on", "adjacent to", "connected to", or "coupled to" another element or layer, it can be directly on, adjacent to, connected to, or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as "directly on", "directly adjacent to", "directly connected to", or "directly coupled to" another element or layer, there are no intervening elements or layers.

[0037] It should be understood that although terms such as first, second, third, etc. may be used to describe various regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are only used to distinguish one region, layer, or part from another. Thus, without departing from the teachings of the present application, the first region, layer, or part discussed below may be referred to as the second region, layer, or part.

[0038] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0040] If there is no special instruction, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out in sequence, or may also include steps (b) and (a) carried out in sequence. 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 may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may also include steps (c), (a), and (b), etc.

[0041] In a wound structure battery, the swelling stress is the greatest at the corner shoulder. Due to the different maximum stresses that the substrate layer and the diaphragm layer can withstand, problems such as cracking and powder shedding of the diaphragm layer are likely to occur at the corner shoulder of the wound structure, as Figure 1 shown. This will cause safety problems and reduce the cycle life of the battery.

[0042] Regarding this problem, various solutions have been proposed in the prior art. For example, different active materials are provided in the straight region and the bent region of the wound structure to provide different stress resistances. However, for this differential coating, since the length of the bent region increases with the increase of the radius and two types of powder materials need to be switched with variable lengths back and forth, the operability is low, and the possibility of mass production and implementation is relatively low, which is not conducive to industrial production.

[0043] Based on this, the present application proposes a new type of secondary battery, which is provided with a first protective layer in the form of a mesh structure on the upper surface of the diaphragm layer to improve the tensile strength and elongation rate of the diaphragm layer, so as to alleviate the related problems caused by different stress resistances. At the same time, the present application also relates to an electrical device including this secondary battery. The present application and its preferred embodiments are described in more detail below.

[0044] Secondary battery

[0045] In the first aspect of the present application, a secondary battery is provided, which includes electrode plates. The electrode plates include: a current collector; a diaphragm layer provided on at least one surface of the current collector; and a first protective layer with a network structure provided on the upper surface of the diaphragm layer; wherein, the first protective layer includes linear conductive nanomaterials, tubular conductive nanomaterials or flaky conductive nanomaterials.

[0046] The expression "upper surface of the diaphragm layer" refers to the surface of the diaphragm layer away from the current collector. Similarly, the "lower surface of the diaphragm layer" refers to the surface of the diaphragm layer adjacent to the current collector.

[0047] In some embodiments, for example, a slurry including conductive nanomaterials can be provided on the diaphragm layer, i.e., the active material layer, through a spraying process to form a network structure on its surface, as Figures 2 to 4 schematically shown. The formed network structure is similar to a "silk fabric" structure, which can effectively wrap the diaphragm layer, thereby improving the mechanical properties of the diaphragm layer, enhancing the extensibility of the diaphragm layer, and then reducing the safety risk of cracking induced by different extensibilities of the diaphragm layer and the substrate. Moreover, even if the internal diaphragm layer breaks, the external "silk fabric" remains intact, ensuring that the broken part is not exposed to induce risks. At the same time, it can also improve the conductivity of the diaphragm layer. Thus, it helps to improve the cycle stability of the battery.

[0048] In some embodiments, the conductive nanomaterials include at least one of linear conductive nanomaterials, tubular conductive nanomaterials or flaky conductive nanomaterials; optionally, the linear conductive nanomaterials include carbon nanofibers; optionally, the tubular conductive nanomaterials include carbon nanotubes; optionally, the flaky conductive nanomaterials include graphene. These types of conductive nanomaterials have controllable structures, excellent comprehensive properties, and are more cost-effective. Moreover, these materials are easy to obtain, have high cost performance, and are beneficial to the cost-effectiveness of the obtained battery

[0049] In some embodiments, the carbon nanotubes include at least one of single-walled nanotubes, oligomeric-walled nanotubes, and multi-walled carbon nanotubes; optionally, the carbon nanotubes include single-walled nanotubes. These carbon nanotubes are easy to prepare or commercially available and are convenient to process. In addition, single-walled carbon nanotubes in carbon nanotubes have stronger toughness, better electrical conductivity and thermal conductivity. On the one hand, it is more conducive to improving the tensile strength and elongation rate of the diaphragm layer, improving the mechanical properties of the diaphragm layer, and thus reducing the safety risk of cracking induced by too low extensibility of the diaphragm layer; on the other hand, it is more conducive to improving the conductivity of the diaphragm layer, and thus more conducive to the cycle stability of the battery.

[0050] In some embodiments, the sheet-shaped conductive nanomaterial includes at least one of single-layer graphene, few-layer graphene, multi-layer graphene, or graphene nanoribbons; optionally, the graphene includes single-layer graphene. These materials are easy to prepare or commercially available, facilitating processing. Additionally, the single-layer graphene in the sheet-shaped conductive nanomaterial has higher mechanical strength, elasticity, and electrical conductivity. On the one hand, it is more conducive to improving the tensile strength and elongation rate of the diaphragm layer, enhancing the mechanical properties of the diaphragm layer, thereby reducing the safety risk of induced cracking caused by too low elongation rate of the diaphragm layer; on the other hand, it is more conducive to the cycle stability of the battery.

[0051] In some embodiments, based on the total mass of the first protective layer, the mass percentage of the conductive nanomaterial is 28wt% - 72wt%; optionally 40wt% - 72wt%. When the mass percentage of the conductive nanomaterial in the first protective layer is within the above range, it can be well dispersed in the slurry, effectively forming a "dense" network structure to provide protection for the diaphragm layer. The "dense network structure" refers to, for example, a network structure formed by the interweaving of carbon nanotubes, similar to "silk fabric". Within the above content range, the formed mesh holes are the most numerous and the densest.

[0052] In some embodiments, a second protective layer with a network structure is provided on at least one surface of the current collector, and the second protective layer includes the above-mentioned conductive nanomaterial; optionally, the mass percentage of the conductive nanomaterial in the second protective layer is greater than that in the first protective layer; optionally, the thickness of the second protective layer is greater than or equal to the thickness of the first protective layer.

[0053] Thus, the second protective layer can protect the oxide film on the surface of the current collector from being damaged, inhibit the corrosion of the current collector by the electrolyte, improve the contact resistance between the diaphragm layer and the current collector, and is more conducive to improving the cycle stability of the battery. In addition, it is also beneficial to enhance the safety, lifespan, and rate performance of the battery.

[0054] In this application, through the setting of the second protective layer, on the basis of providing a similar function to the first protective layer, it can also act as a bottom coating, playing the role of a bottom coating and increasing the adhesion between the current collector and the diaphragm layer.

[0055] In some embodiments, the conductive nanomaterials of both the first protective layer and the second protective layer are single-layer graphene. This can balance the elongation rate of the diaphragm layer and the contact resistance between the diaphragm layer and the current collector, and is more conducive to improving the cycle stability of the battery.

[0056] In some embodiments, based on the total mass of the second protective layer, the mass percentage of the conductive nanomaterial is 28wt% - 72wt%; optionally 50wt% - 72wt%.

[0057] In some embodiments, the thickness of the first protective layer is 0.5 μm to 1 μm. When the thickness of the first protective layer is within this range, it can provide effective encapsulation while also providing a certain degree of support to the diaphragm layer, and can further effectively improve the mechanical properties of the diaphragm layer.

[0058] In some embodiments, the thickness of the second protective layer is 1 μm to 2 μm. When the thickness of the second protective layer is within this range, it can more effectively protect the oxide film on the surface of the current collector from being damaged and inhibit the corrosion of the current collector by the electrolyte.

[0059] In some embodiments, the first protective layer and / or the second protective layer further includes a binder. Here, there is no specific limitation on the type of the binder. For example, polytetrafluoroethylene (PTFE)-type binders, polyvinylidene fluoride (PVDF)-type binders, modified PVDF-type binders, polyacrylonitrile-type binders, and polyethyleneimine-type binders, as well as 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), but not limited thereto. For example, considering easy availability, PTFE, PVDF, etc. can be selected, but not limited thereto. It will be known that a suitable binder is selected according to the type of the active material in the diaphragm layer.

[0060] In some embodiments, the first protective layer and the second protective layer are only composed of a conductive nanomaterial and a binder. This means that the sum of the weight percentages of the conductive nanomaterial and the binder is at least greater than 99.5% of the total weight of the corresponding protective layer. Therefore, in subsequent tests, the sum of the weights of the conductive nanomaterial and the binder is regarded as the weight of the protective layer.

[0061] In some embodiments, the aspect ratio of the linear conductive nanomaterial is 10 - 1500, and can be optionally 100 - 800; and / or, the aspect ratio of the tubular conductive nanomaterial is 10 - 1500, and can be optionally 100 - 800; and / or, the aspect ratio of the sheet-like conductive nanomaterial is 3.2 to 450, and can be optionally 100 - 350. When the aspect ratio or the aspect ratio of the conductive nanomaterial is within the above range, its strong agglomeration effect or the entanglement and bonding phenomenon of the fibers is relatively low, and it is easy to disperse, so that it is evenly distributed on the surface of the diaphragm layer. Furthermore, it is beneficial to make the formed protective layer thin and dense, providing effective protection to the diaphragm layer without affecting other properties of the diaphragm layer.

[0062] In some embodiments, the electrode sheet can be a positive electrode sheet or a negative electrode sheet. As described above, the first protective layer and / or the second protective layer in the present application are provided to form an effective "physical" wrapping on the diaphragm layer. Therefore, there is no need to distinguish between the positive electrode sheet and the negative electrode sheet, and both can be applied.

[0063] When it is a positive electrode sheet, the above current collector is a positive current collector, which can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can 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 can 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 polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0064] The positive electrode diaphragm layer includes active positive electrode active material, which can be a positive electrode active material for lithium ion batteries well-known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium phosphate with olivine structure, lithium transition metal oxide, 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 can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include but are not limited to lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), 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 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and at least one of its modified compounds. Examples of the olivine-structured lithium-containing phosphate may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), 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.

[0065] In addition, the above active cathode active material may also adopt a cathode active material for a sodium ion battery known in the art. For example, at least one of sodium transition metal oxides, polyanion-type compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as the cathode active material for a sodium ion battery can also be used. For example, as an alternative technical solution of this application, among sodium transition metal oxides, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO 2 , where M is one or several of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1.

[0066] As an alternative technical approach of this application, the polyanion-type compound can be a class of compounds having sodium ions, transition metal ions, and tetrahedral (YO 4 ) n- anion units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents the valence state of (YO 4 ) n- . The polyanion-type compound can also be a class of compounds having sodium ions, transition metal ions, tetrahedral (YO 4 ) n- anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (Y04 ) n- valence state; the halogen may be at least one of F, Cl, and Br. The polyanionic compound may also be a compound having sodium ions, tetrahedral (YO 4 ) n- anion units, polyhedral units (ZO y ) m+ and optionally halogen anions. Y may be at least one of P, S, and Si, n represents the valence state of (YO 4 ) n- ; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence state of (ZO y ) m+ ; the halogen may be at least one of F, Cl, and Br. Examples of the polyanionic compound are NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , NaM’PO4F (M’ is one or more of V, Fe, Mn, and Ni) and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0 ≤ y ≤ 1), etc. Prussian blue compounds may be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds are Na a Me b Me’ c (CN) 6 , where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0067] During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the list of cathode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0068] In the list of cathode materials in this application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0069] In some embodiments, the positive electrode film 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.

[0070] In some embodiments, the positive electrode film 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.

[0071] When it is a negative electrode tab, the above current collector is a negative electrode current collector, which 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 polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0072] In this case, the above negative electrode active material can be a negative electrode active material for batteries well-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 material can 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 can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0073] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder can 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).

[0074] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some embodiments, the negative electrode diaphragm layer may further optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0076] Embodiments of the present application also provide a method for preparing the above electrode tab, including the following steps: dispersing conductive nanomaterials on the upper surface of the diaphragm layer by, for example, spraying or gravure printing processes to form a first protective layer with a network structure.

[0077] In some embodiments, the method of the present application further includes: dispersing conductive nanomaterials on the lower surface of the diaphragm layer by, for example, spraying or gravure printing processes to form a second protective layer with a network structure. In some embodiments, the second protective layer can be first set on the current collector by gravure printing, and then the diaphragm layer is set, and then the first protective layer is set.

[0078] The preparation method of the present application is simple in operation, has high practicability, and is suitable for large-scale production.

[0079] In some embodiments, the above term "secondary battery" refers to a battery cell, a battery module or a battery pack. The following will be described separately.

[0080] Generally, a battery cell includes the above-mentioned electrode tabs (including a positive electrode tab and a negative electrode tab) of the first aspect, as well as an electrolyte and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode tab and the negative electrode tab. The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab. The separator is disposed between the positive electrode tab and the negative electrode tab, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0081] [Electrolyte]

[0082] The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab. The present application has no specific limitation on the type of electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel or all-solid state.

[0083] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0084] In some embodiments, the electrolyte salt can 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 bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0085] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene 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.

[0086] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0087] [Separator membrane]

[0088] In some embodiments, the battery cell 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.

[0089] 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.

[0090] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane may be made into an electrode assembly by a winding process or a stacking process.

[0091] In some embodiments, the battery cell may include an outer package. The outer package may be used to encapsulate the above electrode assembly and electrolyte.

[0092] In some embodiments, the outer package of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic, and examples of the plastic may include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0093] The present application does not particularly limit the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 8 is a battery cell 5 with a square structure as an example.

[0094] In some embodiments, referring to Figure 9, the outer package may include a housing 51 and a top cover assembly 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 top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0095] In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells 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.

[0096] Figure 10 is a battery module 4 as an example. Refer to Figure 10 , in the battery module 4, a plurality of battery cells 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 battery cells 5 can be fixed by fasteners.

[0097] Optionally, the battery module 4 can further include a housing having a receiving space, and a plurality of battery cells 5 are received in the receiving space.

[0098] 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.

[0099] Figure 11 and Figure 12 is a battery pack 1 as an example. Refer to Figure 11 and Figure 12 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 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.

[0100] The second aspect of the present application also provides an electrical device.

[0101] The electrical device includes the secondary battery provided by the present application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may 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.

[0102] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0103] Figure 13 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a 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 a battery module can be adopted.

[0104] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a battery cell can be adopted as the power source.

[0105] Embodiment

[0106] Hereinafter, 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 of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0107] Embodiment 1

[0108] Mix LiFePO 4 with conductive carbon black and polyvinylidene fluoride in a weight ratio of 96:2.5:1.5, add an appropriate amount of NMP as a solvent, and stir evenly to obtain a positive electrode slurry.

[0109] Then coat the positive electrode slurry on both surfaces of the aluminum foil, dry and cold press to form a positive electrode film layer.

[0110] Weigh 2 g of conductive nanomaterial single-walled carbon nanotubes (tube diameter 20 nm, length 1.5 μm), 2 g of PVDF binder, and 96 g of N-methylpyrrolidone (NMP), add them to an ultrasonic disperser, and after dispersing evenly, obtain a first protective layer slurry. Apply it to the positive electrode film layer formed in the previous step by spraying with a thickness of 2 μm to form a first protective layer. The thickness of the first protective layer is 1 μm. After drying, a positive electrode plate is obtained, wherein the mass ratio of single-walled carbon nanotubes in the first protective layer is 50%.

[0111] Pole piece performance test

[0112] Morphology test

[0113] The electrode sheet of Example 1 was subjected to scanning electron microscopy (SEM) and cross-section scanning (CP). Exemplarily, Figure 5 The scanning electron microscopy test image of Example 1 is shown, Figure 6 The cross-section scanning image of Example 1 is shown. It can be seen that the carbon nanotubes are evenly spread on the surface of the diaphragm layer, and the carbon nanotubes are intertwined with each other. The intertwined state between the carbon nanotubes effectively forms a "physical" package for the diaphragm layer, which is beneficial to improving the tensile and extensibility of the diaphragm layer. Figure 6 It is confirmed that the thickness of the carbon nanotube protective layer is about 2 μm.

[0114] Tensile strength

[0115] A gradually increasing tensile load was applied in the length direction of the standard rubber strip of the electrode sheet until it was deformed until it broke. The maximum tensile stress required when the electrode sheet broke was the tensile strength. The change in the tensile strength of the electrode sheet was expressed by the elongation at break.

[0116] Five electrode sheets were cut longitudinally and transversely respectively as required.

[0117] For each electrode sheet, the thicknesses of 3 points were measured within the marked line, and the arithmetic mean value was taken. The longitudinal axis of the electrode sheet was aligned with the center line connecting the upper and lower clamps of the testing machine, and the tightness was appropriate;

[0118] Tensile was carried out at a specified speed of 100 mm / min;

[0119] After the electrode sheet broke, the load and the elongation of the marked line spacing were read. If the electrode sheet broke outside the marked line, a new electrode sheet was taken for re-experiment.

[0120] According to the above test method, the tensile strength of the electrode sheets was tested respectively using a Zhongzhi testing tensile machine (model LXG2-LLCS-0009).

[0121] Secondary battery performance test

[0122] Preparation of secondary battery (full battery)

[0123] Negative electrode sheet: Graphite, conductive carbon black, and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:2.5:1.5, and an appropriate amount of deionized water was added and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the copper foil, dried and cold-pressed to form a negative electrode sheet.

[0124] Electrolyte: In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a mass ratio of 35:65, a lithium salt LiPF 6 is added and mixed evenly to obtain an electrolyte, where the molar concentration of LiPF 6 in the electrolyte is 1 mol / L.

[0125] The positive electrode plate, a 12-μm-thick polypropylene porous membrane as the separator, and the negative electrode plate are stacked in sequence, with the separator placed in the middle of the positive and negative electrodes to play a separating role, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer package, injected with the above-prepared electrolyte and sealed, and a lithium-ion secondary battery is obtained through processes such as formation, degassing, and edge trimming.

[0126] Battery performance test

[0127] At 25 °C, the battery corresponding to Example 1 is charged at a constant current of 1 / 3C to 4.3V, then charged at a constant voltage of 4.3V until the current is 0.05C. After standing for 5 minutes, the voltage V1 is recorded. Then it is discharged at 1 / 3C for 30s, and the voltage V2 is recorded. Then the direct current internal resistance DCR of the secondary battery = 3*(V2 - V1) / C.

[0128] Example 2

[0129] The positive electrode plate is prepared in the same method as in Example 1 and assembled into a secondary battery. The only difference is that when preparing the first protective layer, 2 g of carbon fiber (diameter 40 nm, length 15 μm) is used as the conductive nanomaterial in the first protective layer slurry.

[0130] Example 3

[0131] The positive electrode plate is prepared in the same method as in Example 1 and assembled into a secondary battery. The only difference is that when preparing the first protective layer, 2 g of single-layer graphene (length 12 μm, width 0.2 μm) is used as the conductive nanomaterial in the first protective layer slurry.

[0132] Example 4

[0133] The positive electrode plate is prepared in the same method as in Example 1 and assembled into a secondary battery. The only difference is that when preparing the first protective layer, 5 g of single-layer graphene (length 12 μm, width 0.2 μm) is used as the conductive nanomaterial in the first protective layer slurry.

[0134] Example 5

[0135] The positive electrode plate is prepared in the same method as in Example 1 and assembled into a secondary battery. The only difference is that when preparing the first protective layer, 5 g of PVDF binder is used in the first protective layer slurry.

[0136] Example 6

[0137] The positive electrode sheet was prepared in the same manner as in Example 1 and assembled into a secondary battery, except that when preparing the first protective layer, 2 g of multi-layer graphene (length 20 μm, width 0.35 μm) was used in the first protective layer slurry.

[0138] Example 7

[0139] The positive electrode sheet was prepared in the same manner as in Example 1 and assembled into a secondary battery, except that the thickness of the prepared first protective layer was 0.5 μm.

[0140] Comparative Example 1

[0141] The positive electrode sheet was prepared in the same manner as in Example 1 and assembled into a secondary battery, except that the first protective layer was not prepared.

[0142] Comparative Example 2

[0143] The positive electrode sheet was prepared in the same manner as in Example 1 and assembled into a secondary battery, except that when preparing the first protective layer, the first protective layer slurry was composed of only 2 g of PVDF binder and 98 g of solvent NMP.

[0144] Figures 2 to 4 The schematic diagrams of the conductive nanomaterials in Examples 1 to 3 are shown respectively, among which, Figures 2 to 4 the left figures in are all cross-sectional views, Figures 2 to 4 the right figures in are all top views or bottom views. It can be seen that the conductive nanomaterials in the present application can form a network structure similar to a "silk fabric" structure.

[0145] The tensile strength test results of Examples 1 to 7, Comparative Examples 1 and 2 are shown in Table 1 below, and the test results of the secondary batteries prepared in Examples 1 to 7, Comparative Examples 1 and 2 are shown in Table 2 below.

[0146] Table 1.

[0147]

[0148]

[0149] Table 2.

[0150]

[0151] Referring to the relevant data in Table 1, the tensile curves of Example 1 and Comparative Example 1 were plotted, as Figure 7 shown.

[0152] The above results show that, compared with Comparative Example 1 (the positive electrode sheet without a protective layer), by providing the first protective layer on the diaphragm layer, the tensile strength (e.g., about 17% to 53%) and elongation (about 10% to 31%) of the positive electrode sheet are significantly improved. This may be because the conductive nanomaterials in the first protective layer can form a "silk fabric"-like network structure, which can effectively wrap the diaphragm layer, thereby enhancing the mechanical properties of the diaphragm layer and improving the extensibility of the diaphragm layer.

[0153] By comparing Example 1 and Example 7, it can be seen that the thickness of the first protective layer has little effect on the tensile strength and elongation of the positive electrode sheet. Therefore, there is no obvious difference in the cycle performance and internal resistance between Example 1 and Example 7.

[0154] For the polymer protective layer (see Comparative Example 2 for example), although it also enhances the tensile strength and elongation of the electrode sheet to a certain extent, the presence of this polymer layer will greatly increase the DC internal resistance of the battery and deteriorate the battery performance.

[0155] As can be seen from Table 2 above, compared with Comparative Example 1, although the initial DC internal resistance is slightly higher, when comparing the internal resistance after 500 cycles, it can be seen that the internal resistance increase rate of Examples 1 to 7 is lower. Without wishing to be bound by theory, this may be because the presence of the first protective layer in the present application makes the contact between active particles closer during the battery cycling process, the swelling is reduced, and thus the internal resistance increase rate is smaller. As described above, although for Comparative Example 2, the internal resistance increase rate is also comparable to that of Examples 1 to 7, however, its initial DC internal resistance value limits its use.

[0156] Moreover, Examples 1 to 7 exhibit excellent properties in terms of capacity retention rate after 500 cycles compared with Comparative Examples 1 and 2.

[0157] Example 8

[0158] Weigh 2 g of single-walled carbon nanotubes (tube diameter 20 nm, length 1.5 μm), 2 g of PVDF binder, and 96 g of solvent NMP, add them to an ultrasonic disperser, and after uniform dispersion, obtain the second protective layer slurry. Then, uniformly coat it onto the aluminum foil through gravure printing technology to form the second protective layer with a thickness of 2 μm.

[0159] Mix LiFePO 4 with conductive carbon black and polyvinylidene fluoride in a weight ratio of 96:2.5:1.5, add an appropriate amount of NMP as a solvent, and stir evenly to obtain the positive electrode slurry. Coat the positive electrode slurry on the surface of the protective layer obtained in the previous step, dry and cold press to form the diaphragm layer.

[0160] Then, the same protective layer slurry is applied to the formed positive electrode sheet layer by spraying to form a first protective layer with a thickness of 0.5 μm, and after drying, a positive electrode plate is obtained.

[0161] Example 9

[0162] The negative electrode plate is prepared by the same method as in Example 8 and assembled into a secondary battery, except that the thickness of the first protective layer is 0.5 μm and the thickness of the second protective layer is 1 μm.

[0163] The tensile strength test results of Examples 7, 8, and 9 are shown in Table 3 below, and the test results of the secondary batteries prepared in Examples 7, 8, and 9 are shown in Table 3 below.

[0164] Table 3.

[0165]

[0166] Table 4.

[0167]

[0168] As can be seen from Table 3 above, after adding the second protective layer on the basis of Example 7, the tensile strength and elongation rate of the positive electrode plate have been improved to a certain extent. As can be seen from Table 4 above, after adding the second protective layer on the basis of Example 7, although the initial DC internal resistance is slightly higher, it can be seen from the internal resistance after 500 cycles that the internal resistance increase rate has decreased. Without wishing to be bound by theory, this may be because the presence of the second protective layer in the present application can protect the oxide film on the surface of the current collector from being damaged, inhibit the corrosion of the current collector by the electrolyte, and improve the contact resistance between the sheet layer and the current collector.

[0169] Comparing Example 8 and Example 9, it can be seen that the thickness of the second protective layer has little effect on the tensile strength and elongation rate of the positive electrode plate. Therefore, there is no obvious difference in the cycle performance and internal resistance between Example 8 and Example 9.

[0170] Example 10

[0171] Graphite is mixed with conductive carbon black and styrene-butadiene rubber (SBR) in a weight ratio of 96:2.5:1.5, and an appropriate amount of deionized water is added and stirred evenly to obtain a negative electrode slurry.

[0172] The negative electrode slurry is coated on both surfaces of the copper foil, dried and cold-pressed to form a negative electrode sheet layer.

[0173] Weigh 2 g of single-layer graphene (length 12 μm, width 0.4 μm), 2 g of SBR binder, and 96 g of solvent NMP. Add them to an ultrasonic disperser. After uniform dispersion, a protective layer slurry is obtained. Apply it to the negative electrode film layer formed in the previous step by spraying with a thickness of 2 μm to form a first protective layer. The thickness of the first protective layer is 0.8 μm. After drying, a negative electrode plate is obtained.

[0174] Assemble a secondary battery using the positive electrode plate prepared in Comparative Example 1 and the negative electrode plate of Example 8 according to the above method for preparing a secondary battery (full cell).

[0175] Example 11

[0176] Prepare a negative electrode plate in the same manner as in Example 10 and assemble it into a secondary battery, with the only difference being that 2 g of single-walled carbon nanotubes (diameter 15 nm, length 1.5 μm) are used in the first protective layer slurry.

[0177] Comparative Example 3

[0178] Prepare a negative electrode plate in the same manner as in Example 10 and assemble it into a secondary battery, except that the first protective layer is not applied.

[0179] The tensile strength test results of Example 10 and 11 and Comparative Example 3 are shown in Table 5 below. The test results of the secondary batteries prepared in Example 10 and 11 and Comparative Example 3 are shown in Table 6 below.

[0180] Table 5.

[0181]

[0182] Table 6.

[0183]

[0184] As can be seen from Table 5 above, compared with Comparative Example 3 (negative electrode plate without a protective layer), Example 10 and Example 11 also confirm that by setting the first protective layer of the present application on the negative electrode film layer, the tensile strength and elongation rate of the negative electrode plate can be significantly improved. This may be because the conductive nanomaterials in the first protective layer can form a "silk fabric" - like network structure, which can effectively wrap the film layer, thereby enhancing the mechanical properties of the film layer and improving the ductility of the film layer.

[0185] As can be seen from Table 6 above, although the initial DC internal resistance is slightly higher than that of Comparative Example 3, the internal resistance after 500 cycles shows that the internal resistance increase rate of Examples 10 and 11 is lower. Without wishing to be limited by theory, this may be because the presence of the first protective layer of the present application makes the contact between the active particles closer during the battery cycle, reduces expansion, and thus reduces the increase rate of internal resistance. In addition, Examples 10 and 11 also have a certain improvement in the capacity retention rate after 500 cycles compared to Comparative Example 3.

[0186] In summary, in the present application, by providing a first protective layer and / or a second protective layer having a mesh structure on the membrane layer, effective wrapping is produced, thereby improving the mechanical properties (such as tensile strength and elongation) and electrical properties (such as conductivity) of the membrane layer; thereby improving the internal resistance increase rate and cycle capacity retention rate of the secondary battery containing it.

[0187] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising an electrode tab, characterized in that, the electrode tab comprises: a current collector; a diaphragm layer provided on at least one surface of the current collector; and a first protective layer having a network structure provided on the upper surface of the diaphragm layer; wherein the first protective layer comprises a conductive nanomaterial.

2. The secondary battery according to claim 1, characterized in that, the conductive nanomaterial comprises at least one of a linear conductive nanomaterial, a tubular conductive nanomaterial or a flaky conductive nanomaterial.

3. The secondary battery according to claim 2, characterized in that, the tubular conductive nanomaterial comprises at least one of a single-walled nanotube, an oligomeric-walled nanotube, a multi-walled carbon nanotube.

4. The secondary battery according to claim 2, characterized in that, the flaky conductive nanomaterial comprises at least one of a single-layer graphene, an oligomeric-layer graphene, a multi-layer graphene or a graphene nanoribbon.

5. The secondary battery according to claim 1, characterized in that, based on the total mass of the first protective layer, the mass ratio of the conductive nanomaterial is 28 wt% - 72 wt%.

6. The secondary battery according to any one of claims 1-5, characterized in that, a second protective layer having a network structure is provided on at least one surface of the current collector, and the second protective layer comprises the conductive nanomaterial; the mass ratio of the conductive nanomaterial in the second protective layer is greater than the mass ratio of the conductive nanomaterial in the first protective layer; the thickness of the second protective layer is greater than or equal to the thickness of the first protective layer.

7. The secondary battery according to claim 6, characterized in that, based on the total mass of the second protective layer, the mass ratio of the conductive nanomaterial is 28 wt% - 72 wt%.

8. The secondary battery according to claim 6, characterized in that, the thickness of the first protective layer is 0.5 μm to 1 μm; and / or, the thickness of the second protective layer is 1 μm to 2 μm.

9. The secondary battery according to claim 6, characterized in that, the first protective layer and / or the second protective layer further comprises a binder.

10. The secondary battery according to claim 2, characterized in that, the aspect ratio of the linear conductive nanomaterial is 10 - 1500; and / or, the aspect ratio of the tubular conductive nanomaterial is 10 - 1500; and / or, the aspect ratio of the flaky conductive nanomaterial is 3.2 to 450.

11. The secondary battery according to any one of claims 1 to 5, characterized in that, the electrode tab is a positive electrode tab and / or a negative electrode tab.

12. An electrical device, characterized in that, comprises the secondary battery according to any one of claims 1-11.

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