Negative electrode sheet, method for manufacturing the same, secondary battery, and power storage device

Abstract

The application relates to a negative electrode sheet, a preparation method thereof, a secondary battery and a power utilization device, and belongs to the technical field of secondary batteries. The negative electrode sheet comprises a negative electrode active material layer, at least one side of the negative electrode active material layer is provided with a protective layer, the protective layer comprises a first compound and a second compound, the first compound comprises a compound containing multiple hydrogen bonds, and the second compound comprises a compound containing an ester bond and / or a carbon-carbon double bond; the protective layer improves the lithium dendrite problem of the surface growth of a traditional negative electrode sheet, and improves the cycle performance and safety performance of a secondary battery containing the negative electrode sheet.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a negative electrode sheet, its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries possess advantages such as long cycle life, high energy density, good low-temperature performance, and no pollution, making them widely used in automobiles, mobile phones, computers, power tools, and other fields. The negative electrode material is one of the crucial raw materials for lithium-ion batteries, significantly impacting their performance. However, traditional lithium-ion battery negative electrodes develop lithium dendrites during cycling, severely compromising the battery's cycle performance and safety. Summary of the Invention

[0003] Therefore, it is necessary to provide a negative electrode sheet, its preparation method, a secondary battery, and an electrical device to improve the cycle performance and safety performance of a secondary battery containing the negative electrode sheet.

[0004] In a first aspect, this application provides a negative electrode sheet comprising a negative electrode active material layer, wherein a protective layer is disposed on at least one side of the negative electrode active material layer, the protective layer comprising a first compound and a second compound, wherein the first compound comprises a compound containing multiple hydrogen bonds, and the second compound comprises a compound containing ester bonds and / or carbon-carbon double bonds.

[0005] In some embodiments, in the protective layer, a second compound layer containing the second compound is located on both sides of a first compound layer containing the first compound.

[0006] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the protective layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector.

[0007] In some embodiments, the compound containing multiple hydrogen bonds includes one or more of polymers containing ureidopyrimidinone groups, poly(ethyl ether-thiourea), poly(hydrocarbon-thiourea), polyvinylpyrrolidone, and toluene diisocyanate.

[0008] In some embodiments, the compound containing ester bonds and / or carbon-carbon double bonds includes one or more of polystyrene sulfonic acid, lithium polystyrene sulfonate, polyacrylic acid, polylactic acid, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene.

[0009] In some embodiments, the mass ratio of the first compound to the second compound is (0.1-5):1, optionally (1.7-2.2):1.

[0010] In some embodiments, the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer is 1:(0.02-0.2), and can be optionally 1:(0.1-0.2).

[0011] A second aspect of this application provides a method for preparing the negative electrode sheet described in the first aspect of this application, comprising the following steps:

[0012] The protective layer is formed on at least one side of the negative electrode active material layer.

[0013] In some embodiments, the step of forming the protective layer on at least one side of the negative electrode active material layer includes: providing a protective slurry containing the first compound and the second compound on at least one side of the negative electrode active material layer to form the protective layer.

[0014] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the protective layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector; the step of forming the protective layer on at least one side of the negative electrode active material layer includes: disposing a protective slurry containing the first compound and the second compound on the side of the negative electrode active material layer away from the negative electrode current collector to form the protective layer.

[0015] In some embodiments, the total mass fraction of the first compound and the second compound in the protective slurry is 95%-96.8%.

[0016] In some embodiments, the preparation method of the protective slurry includes the following steps: first, mixing the first compound with a solvent, and then adding the second compound after a certain interval; optionally, the interval is 20 min to 90 min.

[0017] A third aspect of this application provides a secondary battery, including the negative electrode sheet described in the first aspect of this application or the negative electrode sheet prepared by the preparation method described in the second aspect of this application.

[0018] A fourth aspect of this application is an electrical device comprising the secondary battery described in the third aspect of this application.

[0019] Compared with traditional technologies, the above-mentioned negative electrode sheet, its preparation method, secondary battery, and power-consuming device have at least the following advantages:

[0020] (1) The compounds containing ester bonds and / or carbon-carbon double bonds in the above negative electrode sheet can significantly increase the migration of lithium ions, reduce concentration polarization, achieve uniform deposition of lithium ions, minimize the formation of lithium dendrites, thereby improving the problem of lithium dendrites growing on the surface of traditional negative electrode sheets, and improving the cycle performance and safety performance of secondary batteries containing such negative electrode sheets.

[0021] (2) In the above-mentioned negative electrode sheet, since the first compound includes a compound containing multiple hydrogen bonds and the second compound includes a compound containing ester bonds and / or carbon-carbon double bonds, the first and second compounds have weak conductivity and only conduct ions, not electrons. Lithium ions can only gain electrons from the side of the negative electrode active material layer away from the protective layer and undergo a reduction reaction to form lithium. Therefore, lithium will not be deposited on the surface of the protective layer. Even if lithium ions that have penetrated the protective layer are deposited on the negative electrode active material layer to form lithium dendrites, the protective layer can separate the lithium dendrites formed on the negative electrode active material layer from the separator, thereby further improving the cycle performance and safety performance of the secondary battery containing this negative electrode sheet.

[0022] (3) The compounds containing multiple hydrogen bonds and compounds containing ester bonds and / or carbon-carbon double bonds in the above negative electrode sheet synergistically endow the protective layer with strong self-healing and adhesion properties, which alleviates the problem of negative electrode sheet expansion caused by repeated charging and discharging. Attached Figure Description

[0023] Figure 1 This is a schematic diagram showing the changes in the lithium deposition layer on the surface of the negative electrode active material layer in the early and late stages of cycling.

[0024] Figure 2 This is a schematic diagram showing the change of the lithium deposition layer on the surface of the negative electrode active material layer in the negative electrode sheet of an embodiment of this application during the early and late stages of cycling.

[0025] Figure 3 This is a schematic diagram showing the arrangement of the first and second compounds in the protective layer according to an embodiment of this application.

[0026] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0027] Figure 5 for Figure 4 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0028] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application.

[0029] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0030] Figure 8 for Figure 7 An exploded view of a battery pack according to one embodiment of this application is shown.

[0031] Figure 9 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0034] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0035] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

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

[0038] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0039] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

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

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0043] In traditional secondary batteries, lithium dendrites are generated on the negative electrode during charge and discharge cycles. The continuous growth of lithium dendrites leads to the deterioration of the cycle performance of the secondary battery, and may even puncture the separator, causing safety problems such as thermal runaway. In view of this, this application provides a negative electrode sheet, which includes a negative electrode active material layer, and a protective layer is disposed on at least one side of the negative electrode active material layer. The protective layer includes a first compound and a second compound. The first compound includes a compound containing multiple hydrogen bonds, and the second compound includes a compound containing ester bonds and / or carbon-carbon double bonds. The compound containing ester bonds and / or carbon-carbon double bonds in the protective layer can significantly improve the migration of lithium ions, reduce concentration polarization, achieve uniform deposition of lithium ions, minimize the formation of lithium dendrites, and improve the problem of lithium dendrite growth on the surface of traditional negative electrode sheets. At the same time, the protective layer can regulate the electrons on the surface of the negative electrode sheet, inhibit the growth of lithium dendrites on the surface of the protective layer, and separate the negative electrode active material layer and the separator, stabilize the interface, and eliminate the risk of short circuits caused by lithium dendrites piercing the separator generated on the surface of the negative electrode active material layer, thereby effectively improving the cycle performance and safety performance of the secondary battery containing the negative electrode sheet.

[0044] Negative electrode sheet

[0045] One embodiment of this application provides a negative electrode sheet, including a negative electrode active material layer, and a protective layer is disposed on at least one side of the negative electrode active material layer. The protective layer includes a first compound and a second compound. The first compound includes a compound containing multiple hydrogen bonds, and the second compound includes a compound containing ester bonds and / or carbon-carbon double bonds.

[0046] like Figure 1 As shown, lithium dendrites gradually form on the surface of traditional negative electrode sheets during charge-discharge cycles. However, the compounds containing ester bonds and / or carbon-carbon double bonds in the aforementioned negative electrode sheet can significantly increase lithium-ion migration, reduce concentration polarization, achieve uniform lithium-ion deposition, and minimize lithium dendrite formation. This improves the lithium dendrite growth problem on the surface of traditional negative electrode sheets, thereby enhancing the cycle performance and safety of secondary batteries containing this negative electrode sheet.

[0047] In the aforementioned negative electrode, because the first compound includes compounds containing multiple hydrogen bonds and the second compound includes compounds containing ester bonds and / or carbon-carbon double bonds, both compounds have weak conductivity and only conduct ions, not electrons. Lithium ions can only gain electrons from the side of the negative electrode active material layer away from the protective layer, undergoing a reduction reaction to form lithium. Therefore, lithium will not deposit on the surface of the protective layer, even if lithium ions penetrate the protective layer and deposit on the negative electrode active material layer to form lithium dendrites (combined with...). Figure 2 The protective layer can also separate the lithium dendrites formed on the negative electrode active material layer from the separator, thereby further improving the cycle performance and safety performance of the secondary battery containing the negative electrode sheet.

[0048] In addition, compounds containing multiple hydrogen bonds work synergistically with compounds containing ester bonds and / or carbon-carbon double bonds to endow the protective layer with strong self-healing and adhesion properties, alleviating the problem of negative electrode expansion caused by repeated charging and discharging. Therefore, the protective layer not only has a high lithium-ion transport capacity, but can also be firmly adhered to the surface of the negative electrode active material layer, effectively buffering the interface fluctuations caused by volume expansion.

[0049] In some embodiments, in the protective layer, a second compound layer containing the second compound is located on both sides of a first compound layer containing the first compound. This is beneficial for further improving lithium-ion transport capability and can further alleviate the problem of negative electrode expansion caused by repeated charging and discharging. Figure 3 As an example of a protective layer, a second compound layer containing a second compound is located above and below a first compound layer containing a first compound.

[0050] Optionally, scanning electron microscopy (SEM) can be used to distinguish between the first compound layer and the second compound layer. In addition, the first compound layer and the second compound layer can be characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, respectively, to jointly prove that the first compound layer contains compounds with multiple hydrogen bonds and the second compound layer contains compounds with ester bonds and / or carbon-carbon double bonds.

[0051] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, with the negative electrode active material layer disposed on at least one side of the negative electrode current collector, and a protective layer disposed on the side of the negative electrode active material layer away from the negative electrode current collector. In the aforementioned negative electrode sheet, the first and second compounds have weak conductivity and only conduct ions, not electrons. Lithium ions can only gain electrons from the side of the negative electrode active material layer closest to the negative electrode current collector, undergoing a reduction reaction to form lithium. Therefore, lithium will not deposit on the surface of the protective layer. Lithium ions that penetrate the protective layer deposit on the negative electrode active material layer, forming lithium dendrites. The protective layer effectively separates the lithium dendrites formed on the negative electrode active material layer from the separator, improving the problem of lithium dendrite growth on the surface of traditional negative electrode sheets, thereby enhancing the cycle performance and safety performance of the secondary battery containing this negative electrode sheet.

[0052] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0053] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0054] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: lithium metal, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0055] In some embodiments, the negative electrode active material layer may 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).

[0056] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0058] In some embodiments, compounds containing multiple hydrogen bonds include polymers containing ureidopyrimidinone (UPy) groups, poly(ethyl ether-thiourea), poly(hydrocarbon-thiourea), polyvinylpyrrolidone, and toluene diisocyanate, among others. These types of compounds containing multiple hydrogen bonds exhibit strong hydrogen bonding interactions, endowing these materials with excellent self-healing capabilities, which can further alleviate the problem of negative electrode expansion caused by repeated charging and discharging. "Self-healing" refers to the ability of a material to essentially restore its mechanical or thermal properties to their pre-fracture state after surface damage or breakage, under certain temperature conditions or for a certain period of time.

[0059] Specifically, the structural formula of polymers containing ureidopyrimidinone (UPy) groups is shown in Formula I:

[0060]

[0061] Polymers containing ureidopyrimidinone (UPy) groups react via hydrogen bonding to form compounds with the structure shown in Formula II:

[0062]

[0063] In some embodiments, compounds containing ester bonds and / or carbon-carbon double bonds include one or more of polystyrene sulfonic acid, lithium polystyrene sulfonate, polyacrylic acid, polylactic acid, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene. These compounds, containing ester bonds and / or carbon-carbon double bonds, can promote lithium-ion transport, have a strong affinity for electrolytes, enhance the liquid retention capacity of the negative electrode, and also possess a certain degree of flexibility, thus improving the rebound problem of the negative electrode during cycling.

[0064] In some embodiments, the mass ratio of the first compound to the second compound is (0.1-5):1. Controlling the mass ratio of the first compound to the second compound within the above range can further improve the problem of lithium dendrite growth on the surface of conventional negative electrode sheets, thereby further improving the cycle performance and safety performance of secondary batteries containing such negative electrode sheets. Specifically, the mass ratio of the first compound to the second compound includes, but is not limited to: 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, and 5:1. Further, the mass ratio of the first compound to the second compound is (1.7-2.2):1.

[0065] In some embodiments, the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer is 1:(0.02-0.2). It should be noted that if the ratio is too large, the protective layer is relatively too thin, and lithium dendrites formed on the negative electrode active material layer may penetrate the protective layer, resulting in minimal improvement in the cycle performance and safety of the secondary battery. Conversely, if the ratio is too small, the protective layer is relatively too thick, reducing the proportion of negative electrode active material in the negative electrode active material layer (assuming the same battery weight), which is detrimental to the capacity utilization of the secondary battery. For example, the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer can be 1:0.02, 1:0.04, 1:0.06, 1:0.08, 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18, or 1:0.2. Optionally, the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer can be 1:(0.1-0.2).

[0066] Another embodiment of this application provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0067] A protective layer is formed on at least one side of the negative electrode active material layer.

[0068] Therefore, the protective layer can be easily prepared.

[0069] In some embodiments, the step of forming a protective layer on at least one side of the negative electrode active material layer includes: providing a protective slurry containing a first compound and a second compound on at least one side of the negative electrode active material layer to form a protective layer.

[0070] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, a negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and a protective layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector; the step of forming a protective layer on at least one side of the negative electrode active material layer includes: disposing a protective slurry containing a first compound and a second compound on the side of the negative electrode active material layer away from the negative electrode current collector to form a protective layer.

[0071] In some embodiments, the total mass fraction of the first compound and the second compound in the protective slurry is 95%-96.8%. As an example, the total mass fraction of the first compound and the second compound in the protective slurry can be 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, or 96.8%.

[0072] In some embodiments, the preparation method of the protective slurry includes the following steps: first, mixing a first compound with a solvent, and then adding a second compound after a certain interval. In the above preparation method, mixing the first compound with the solvent first promotes the first compound to react through hydrogen bonding to form a first compound layer containing the first compound. Adding the second compound after a certain interval ensures that the second compound layer is located on both sides of the first compound layer in the prepared protective layer. This is beneficial for further improving lithium-ion transport capability and can further alleviate the problem of negative electrode expansion caused by repeated charging and discharging. Optionally, the interval time is 20 min to 90 min. As an example, the interval time can be 20 min, 30 min, 40 min, 50 min, 55 min, 60 min, 70 min, 80 min, or 90 min, etc.

[0073] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0074] In one embodiment of this application, a secondary battery is provided.

[0075] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0076] Positive electrode sheet

[0077] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0078] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0079] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0081] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0082] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0083] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0084] Negative electrode sheet

[0085] The above-mentioned negative electrode sheet is used.

[0086] electrolytes

[0087] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0088] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0089] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0090] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0091] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0092] Separating membrane

[0093] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0094] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0096] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0097] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 This is an example of a square-structured secondary battery 5.

[0099] In some implementations, refer to Figure 5 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0100] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0101] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0102] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0103] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0104] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0105] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0106] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0107] Figure 9 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. 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 used.

[0108] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0109] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0110] Example 1

[0111] (1) Preparation of negative electrode sheet

[0112] (1.1) A negative electrode slurry was prepared by dissolving graphite (anode active material), carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) in deionized water at a weight ratio of 97.2:0.8:0.8:1.2 and mixing them evenly. The negative electrode slurry was then coated onto both surfaces of the copper foil (anode current collector), and the negative electrode active material layer was obtained after cold pressing. The thickness of the negative electrode active material layer on one side was 100 μm, and the compaction density of the negative electrode active material layer was 1.62 g / cm³. 3 ;

[0113] (1.2) The first compound UPy (manufacturer: McLean, purity ≥99%), the second compound lithium polystyrene sulfonate, the binder styrene-butadiene rubber (SBR), the conductive carbon SP, and the thickener sodium carboxymethyl cellulose (CMC) were dissolved in deionized water in a weight ratio of 64.13:32.07:1.8:0.8:1.2 and mixed evenly to prepare a protective slurry. The protective slurry was coated on the negative electrode active material layer, and the thickness of the protective layer on one side was 15 μm.

[0114] (2) Preparation of positive electrode sheet

[0115] A composite lithium manganese oxide positive electrode active material, COF-derived carbon porous conductive agent, polyvinylidene fluoride (PVDF) binder, and N-methylpyrrolidone (NMP) were mixed evenly in a weight ratio of 95.81:1.5:1.55:1.14 to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector, and then cold-pressed to obtain a positive electrode sheet. The thickness of the positive electrode active material layer on one side was 130 μm, and the compaction density of the positive electrode active material layer was 3.4 g / cm³. 3 ;

[0116] (3) Preparation of electrolyte

[0117] In an argon-atmospheric glove box, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed evenly at a volume ratio of 36:29:35. 1M LiPF6 lithium salt was added and dissolved in the organic solvent, and the mixture was stirred evenly to obtain the electrolyte.

[0118] (4) Separating membrane

[0119] Polypropylene film was selected as the separator.

[0120] (5) Preparation of lithium-ion batteries

[0121] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 100°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a lithium-ion battery.

[0122] Example 2-19

[0123] It is basically the same as Example 1, except that the parameters described in Table 1 are different.

[0124] Comparative Examples 1-3

[0125] It is basically the same as Example 1, except that the parameters described in Table 1 are different.

[0126] Performance testing

[0127] 1. Cyclic capacity retention test

[0128] The prepared lithium-ion battery was charged at 45℃ with a constant current of 1 / 3C to 4.4V, then charged with a constant voltage of 4.4V to a current of 0.05C, rested for 5 minutes, and then discharged at 1 / 3C to 2.5V. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The capacity retention rate of the battery after each cycle was Pn = Cn / C0 * 100%. In this test, the first cycle corresponds to n = 1, the second cycle to n = 2, ..., the 500th cycle to n = 500.

[0129] 2. Electrode rebound rate test

[0130] Disassemble the fully charged negative electrode sheet that has undergone 500 cycles, measure the electrode sheet thickness, and calculate the electrode sheet rebound rate as (fully charged electrode sheet thickness - fresh electrode sheet thickness) / fresh electrode sheet thickness.

[0131] In Table 2, H1 represents the thickness of the protective layer on one side, and H2 represents the thickness of the negative electrode active material layer on one side.

[0132] Table 1

[0133]

[0134]

[0135]

[0136] Table 2

[0137]

[0138]

[0139] As shown in Tables 1 and 2, the protective layers of the negative electrode sheets in Examples 1-19 contain compounds with multiple hydrogen bonds and compounds containing ester bonds and / or carbon-carbon double bonds. In contrast, the negative electrode sheets in Comparative Examples 1-3 do not have a protective layer, or their protective layers contain only one of the two types of compounds mentioned above. The capacity retention rate of the batteries in Examples 1-19 is higher than that of the batteries in Comparative Examples 1-3, and their electrode rebound ratio is lower than that of the electrodes in Comparative Examples 1-3. This indicates that the combination of compounds with multiple hydrogen bonds and compounds containing ester bonds and / or carbon-carbon double bonds in the protective layers of Examples 1-19 improves the cycle performance and safety performance of the batteries, while alleviating the problem of negative electrode sheet expansion caused by repeated charging and discharging.

[0140] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0141] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode active material layer, and a protective layer is provided on at least one side of the negative electrode active material layer. The protective layer includes a first compound and a second compound. The first compound is one or more of a polymer containing a ureidopyrimidinone group, poly(ethyl ether-thiourea), poly(hydrocarbon-thiourea), polyvinylpyrrolidone, and toluene diisocyanate. The second compound is one or more of polystyrene sulfonic acid, lithium polystyrene sulfonate, polyacrylic acid, polylactic acid, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene. In the protective layer, the total mass fraction of the first compound and the second compound is 95%-96.8%.

2. The negative electrode sheet according to claim 1, characterized in that, In the protective layer, the second compound layer containing the second compound is located on both sides of the first compound layer containing the first compound.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The negative electrode sheet further includes a negative electrode current collector, the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the protective layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector.

4. The negative electrode sheet according to claim 1 or 2, characterized in that, The mass ratio of the first compound to the second compound is (0.1-5):

1.

5. The negative electrode sheet according to claim 1 or 2, characterized in that, The mass ratio of the first compound to the second compound is (1.7-2.2):

1.

6. The negative electrode sheet according to claim 1 or 2, characterized in that, The ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer is 1:(0.02-0.2).

7. The negative electrode sheet according to claim 1 or 2, characterized in that, The ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer is 1:(0.1-0.2).

8. The method for preparing the negative electrode sheet according to any one of claims 1-7, characterized in that, Includes the following steps: The protective layer is formed on at least one side of the negative electrode active material layer.

9. The preparation method according to claim 8, characterized in that, The step of forming the protective layer on at least one side of the negative electrode active material layer includes: providing a protective slurry containing the first compound and the second compound on at least one side of the negative electrode active material layer to form the protective layer.

10. The preparation method according to claim 8 or 9, characterized in that, The negative electrode sheet further includes a negative electrode current collector, the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the protective layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector; the step of forming the protective layer on at least one side of the negative electrode active material layer includes: disposing a protective slurry containing the first compound and the second compound on the side of the negative electrode active material layer away from the negative electrode current collector to form the protective layer.

11. The preparation method according to claim 9, characterized in that, The preparation method of the protective slurry includes the following steps: first, the first compound is mixed with a solvent, and then the second compound is added after a certain period of time.

12. The preparation method according to claim 11, characterized in that, The interval is 20 min to 90 min.

13. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-7 or the negative electrode sheet prepared by the preparation method described in any one of claims 8-12.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 13.

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