Negative pole piece, preparation method thereof, secondary battery and electric device

Abstract

The invention relates to a negative pole piece, a preparation method thereof, a secondary battery and an electric device, and belongs to the technical field of secondary batteries. The negative pole piece comprises a negative active material layer, at least one side of the negative 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 ester bonds and / or carbon-carbon double bonds; according to the protective layer, the problem of lithium dendrites growing on the surface of a traditional negative pole piece is solved, and the cycle performance and the safety performance of the secondary battery containing the negative pole piece are improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate, a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] Lithium-ion batteries have the advantages of long cycle life, high energy density, good low-temperature performance, and no pollution, so they are widely used in automobiles, mobile phones, computers, power tools and other fields. The negative electrode material is one of the important raw materials for lithium-ion batteries and has an important impact on the performance of lithium-ion batteries. However, the negative electrode of traditional lithium-ion batteries will produce lithium dendrites during the cycle process, which greatly reduces the cycle performance and safety performance of lithium-ion batteries. Summary of the invention

[0003] Based on this, it is necessary to provide a negative electrode plate, a preparation method thereof, a secondary battery and an electrical device to improve the cycle performance and safety performance of the secondary battery containing the negative electrode plate.

[0004] In a first aspect of the present application, a negative electrode plate is provided, comprising a negative electrode active material layer, wherein a protective layer is provided on at least one side of the negative electrode active material layer, and the protective layer comprises 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 an ester bond and / or a carbon-carbon double bond.

[0005] In some embodiments, 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.

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

[0007] In some embodiments, the compound containing multiple hydrogen bonds includes one or more of a polymer containing ureidopyrimidone groups, poly(ether-thiourea), poly(alkyl-thiourea), polyvinylpyrrolidone, and toluene diisocyanate.

[0008] In some embodiments, the compound containing an ester bond and / or a carbon-carbon double bond 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, and can be 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] The second aspect of the present application provides a method for preparing the negative electrode sheet according to the first aspect of the present 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: disposing 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 also includes a negative electrode current collector, the negative electrode active material layer is arranged on at least one side of the negative electrode current collector, and the protective layer is arranged 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: setting 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, in the protective slurry, the total mass fraction of the first compound and the second compound is 95%-96.8%.

[0016] In some embodiments, the method for preparing the protective slurry comprises the following steps: firstly mixing the first compound with a solvent, and then adding the second compound after a certain interval; optionally, the interval is 20 min-90 min.

[0017] In a third aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet described in the first aspect of the present application or the negative electrode sheet prepared by the preparation method described in the second aspect of the present application.

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

[0019] Compared with conventional technologies, the above-mentioned negative electrode sheet, preparation method thereof, secondary battery and electrical device have at least the following advantages:

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

[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 an ester bond and / or a carbon-carbon double bond, the first compound and the second compound have weak conductivity and only conduct ions but not electrons. Lithium ions can only obtain electrons from the side of the negative electrode active material layer away from the protective layer to 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 pass through 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 the negative electrode sheet.

[0022] (3) The compound containing multiple hydrogen bonds in the above-mentioned negative electrode plate synergistically gives the protective layer strong self-healing and adhesion properties, alleviating the problem of negative electrode plate expansion caused by repeated charging and discharging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the changes in the lithium deposition layer on the surface of the negative electrode active material layer in a traditional negative electrode plate at the early and late stages of the cycle.

[0024] Figure 2 Schematic diagram of the changes in the lithium deposition layer on the surface of the negative electrode active material layer in the negative electrode plate of one embodiment of the present application at the early and late stages of the cycle.

[0025] Figure 3 Schematic diagram of the arrangement of the first compound and the second compound in the protective layer according to one embodiment of the present application.

[0026] Figure 4 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

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

[0028] Figure 6 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0029] Figure 7 A schematic diagram of a battery pack according to an embodiment of the present application.

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

[0031] Fig. 9 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0032] Description of reference numerals:

[0033] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0035] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. 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 scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

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

[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0043] The negative electrode of traditional secondary batteries will generate lithium dendrites during the charge and discharge cycle. The continuous growth of lithium dendrites will cause the cycle performance of the secondary battery to deteriorate and may even pierce the diaphragm, causing safety problems such as thermal runaway. In view of this, the present application provides a negative electrode plate, which includes a negative electrode active material layer, and a protective layer is arranged 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 increase the migration amount of lithium ions, reduce concentration polarization, achieve uniform deposition of lithium ions, minimize the formation of lithium dendrites, and improve the problem of lithium dendrites growing on the surface of traditional negative electrode plates; at the same time, the protective layer can regulate the electrons on the surface of the negative electrode plate, inhibit the growth of lithium dendrites on the surface of the protective layer, and separate the negative electrode active material layer and the diaphragm, stabilize the interface, and eliminate the risk of lithium dendrites generated on the surface of the negative electrode active material layer piercing the diaphragm to cause short circuit, thereby effectively improving the cycle performance and safety performance of the secondary battery containing the negative electrode plate.

[0044] Negative electrode

[0045] One embodiment of the present application provides a negative electrode plate, including 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 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 an ester bond and / or a carbon-carbon double bond.

[0046] like Figure 1 As shown, lithium dendrites gradually form on the surface of the conventional negative electrode during the charge and discharge cycle. In the above-mentioned negative electrode, the compound containing ester bonds and / or carbon-carbon double bonds can significantly increase the migration of lithium ions, reduce concentration polarization, achieve uniform deposition of lithium ions, and minimize the formation of lithium dendrites, thereby improving the problem of lithium dendrites growing on the surface of the conventional negative electrode, and further improving the cycle performance and safety performance of the secondary battery containing the negative electrode.

[0047] 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 compound and the second compound have weak conductivity and only conduct ions but not electrons. Lithium ions can only obtain electrons from the side of the negative electrode active material layer away from the protective layer to 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 pass through the protective layer are deposited 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 plate.

[0048] In addition, the compounds containing multiple hydrogen bonds and the compounds containing ester bonds and / or carbon-carbon double bonds synergistically give the protective layer 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 transmission capacity, but also can 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, the second compound layer containing the second compound is located on both sides of the first compound layer containing the first compound. This is conducive to further improving the lithium ion transmission capacity and further alleviating the expansion problem of the negative electrode sheet caused by repeated charge and discharge. 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, the first compound layer and the second compound layer can be distinguished using an electron scanning microscope (SEM). In addition, the first compound layer and the second compound layer can be respectively characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, which can 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 plate also 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. In the above-mentioned negative electrode plate, the conductivity of the first compound and the second compound is relatively weak, and they only conduct ions but not electrons. Lithium ions can only obtain electrons from the side of the negative electrode active material layer close to the negative electrode current collector, and a reduction reaction occurs to form lithium. Therefore, lithium will not be deposited on the surface of the protective layer, and the lithium ions that pass through the protective layer are deposited on the negative electrode active material layer to form lithium dendrites. The protective layer just separates the lithium dendrites formed on the negative electrode active material layer from the diaphragm, thereby improving the problem of lithium dendrites growing on the surface of the traditional negative electrode plate, thereby improving the cycle performance and safety performance of the secondary battery containing the negative electrode plate.

[0052] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two facing 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, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material 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 adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: metallic lithium, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional 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 further 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 further include a conductive agent, which 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 further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0058] In some embodiments, the compound containing multiple hydrogen bonds includes one or more of a polymer containing ureidopyrimidone (UPy) groups, poly(ether-thiourea), poly(alkyl-thiourea), polyvinylpyrrolidone and toluene diisocyanate. The above-mentioned types of compounds containing multiple hydrogen bonds have strong hydrogen bonding, which gives these materials excellent self-repairing ability, and can further alleviate the problem of negative electrode expansion caused by repeated charge and discharge. "Self-repair" means that after the surface of the material is damaged or broken, the mechanical properties or thermal properties can be basically restored to the state before the break through certain temperature conditions or a certain period of time.

[0059] Specifically, the structural formula of the polymer containing ureidopyrimidone (UPy) group is shown in Formula I:

[0060]

[0061] The polymer containing ureidopyrimidone (UPy) groups reacts through hydrogen bonding to form a compound of the structure shown in Formula II:

[0062]

[0063] In some embodiments, the compound containing an ester bond and / or a carbon-carbon double bond includes one or more of polystyrene sulfonic acid, lithium polystyrene sulfonate, polyacrylic acid, polylactic acid, polyvinylidene fluoride-trichloroethylene and polyvinylidene fluoride-chlorotrifluoroethylene. The above-mentioned compounds containing an ester bond and / or a carbon-carbon double bond can promote lithium ion transmission, have a strong affinity for the electrolyte, enhance the liquid retention capacity of the negative electrode plate, and have a certain degree of flexibility, thereby improving the rebound problem of the negative electrode plate during the cycle.

[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 to be within the above range can further improve the problem of lithium dendrites growing on the surface of the traditional negative electrode sheet, thereby further improving the cycle performance and safety performance of the secondary battery containing the negative electrode sheet. 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, 5:1. Furthermore, 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 when the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer is too large, the thickness of the protective layer is relatively too thin, and the lithium dendrites formed on the negative electrode active material layer may pass through the protective layer, so that the cycle performance and safety performance of the secondary battery are not significantly improved; when the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer is too small, the thickness of the protective layer is relatively too thick, and the proportion of the negative electrode active material in the negative electrode active material layer is reduced (when the battery weight is the same), which is not conducive to the capacity of the secondary battery. As an 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, 1:0.2. Optionally, the ratio of the thickness of the negative electrode active material layer to the thickness of the protective layer may be 1:(0.1-0.2).

[0066] Another embodiment of the present 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] Thereby, the protective layer can be prepared simply.

[0069] In some embodiments, 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 at least one side of the negative electrode active material layer to form the protective layer.

[0070] In some embodiments, the negative electrode sheet also includes a negative electrode current collector, the negative electrode active material layer is arranged on at least one side of the negative electrode current collector, and the protective layer is arranged 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: setting 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, in the protective slurry, the total mass fraction of the first compound and the second compound is 95%-96.8%. As an example, in the protective slurry, the total mass fraction of the first compound and the second compound can be 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, 96.8%.

[0072] In some embodiments, the preparation method of the protective slurry includes the following steps: first mixing the first compound with the solvent, and then adding the second compound after a period of time. In the above preparation method, first mixing the first compound with the solvent can cause the first compound to react through hydrogen bonding to form a first compound layer containing the first compound, and then adding the second compound after a period of time, so that the second compound layer in the prepared protective layer is located on both sides of the first compound layer. In this way, it is beneficial to further improve the lithium ion transmission capacity, and at the same time, it can further alleviate the expansion problem of the negative electrode plate caused by repeated charging and discharging. Optionally, the interval time is 20min-90min. As an example, the interval time can be 20min, 30min, 40min, 50min, 55min, 60min, 70min, 80min or 90min, etc.

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

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

[0075] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0076] Positive electrode

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

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

[0079] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material 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 adopt a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 may include, but are not limited to, lithium cobalt oxides (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 (Also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and its modified compounds, etc. Examples of lithium phosphates containing olivine structures may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, a composite material of lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0081] In some embodiments, the positive electrode active material layer may further 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 fluorine-containing acrylate resin.

[0082] In some embodiments, the positive electrode active material layer may further 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.

[0083] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0084] Negative electrode

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

[0086] Electrolytes

[0087] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

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

[0089] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0090] In some embodiments, the solvent can 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, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

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

[0092] Isolation film

[0093] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

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

[0095] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0096] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0097] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 4 The secondary battery 5 is a square structure as an example.

[0099] In some embodiments, reference Figure 5 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

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

[0101] Figure 6 4 is an example of a battery module. Figure 6 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

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

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

[0104] Figure 7 and Figure 8 1 is a battery pack 1 as an example. Figure 7 and Figure 8 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 cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0105] In addition, the present application also provides an electrical device, which includes at least one of the secondary batteries, battery modules, or battery packs provided in the present application. The secondary batteries, battery modules, or battery packs can be used as power sources for electrical devices, and can also be used as energy storage units for electrical devices. Electrical devices may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these. Among them, mobile devices may be, for example, mobile phones, laptop computers, 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 these.

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

[0107] Fig. 9The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0108] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0109] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0110] Example 1

[0111] (1) Preparation of negative electrode sheet

[0112] (1.1) The negative electrode active material graphite, the conductive agent carbon black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are dissolved in a solvent deionized water at a weight ratio of 97.2:0.8:0.8:1.2, and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and a negative electrode active material layer is obtained after cold pressing. The single-side thickness of the negative electrode active material layer is 100 μm, and the compaction density of the negative electrode active material layer is 1.62 g / cm 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 hydroxymethyl cellulose (CMC) are dissolved in a solvent deionized water at a weight ratio of 64.13:32.07:1.8:0.8:1.2, mixed evenly and prepared into a protective slurry, and the protective slurry is coated on the negative electrode active material layer, and the single-side thickness of the protective layer is 15 μm.

[0114] (2) Preparation of positive electrode sheet

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

[0116] (3) Preparation of electrolyte

[0117] In an argon atmosphere glove box, the organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) were mixed evenly in a volume ratio of 36:29:35, and 1 M LiPF 6 The lithium salt is dissolved in an organic solvent and stirred evenly to obtain an electrolyte.

[0118] (4) Isolation film

[0119] Polypropylene film is selected as the isolation film.

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

[0121] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell, the tabs are welded to the bare cell, and the bare cell is placed in an aluminum shell, and baked at 100°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then goes through the processes of static, hot and cold pressing, formation, shaping, capacity testing, etc. 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. Cycle capacity retention rate test

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

[0129] 2. Electrode rebound rate test

[0130] The fully charged negative electrode plate after 500 cycles was disassembled and the plate thickness was measured. The plate rebound rate = (fully charged plate thickness - fresh plate thickness) / fresh plate 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] It can be seen from Table 1 and Table 2 that the protective layer of the negative electrode plates of Examples 1-19 contains both compounds with multiple hydrogen bonds and compounds with ester bonds and / or carbon-carbon double bonds, while the negative electrode plates of Comparative Examples 1-3 are not provided with a protective layer, or the protective layer thereof contains only one of the above two compounds. The capacity retention rate of the battery of Example 1-19 is higher than that of the battery of Comparative Examples 1-3, and its plate rebound ratio is lower than that of the plate rebound ratio of Comparative Examples 1-3, indicating that the protective layer of Examples 1-19 contains compounds with multiple hydrogen bonds and compounds with ester bonds and / or carbon-carbon double bonds. The use of the compounds improves the cycle performance and safety performance of the battery, and alleviates the expansion problem of the negative electrode plate caused by repeated charge and discharge.

[0140] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims, and the description and drawings may be used to interpret the contents of the claims.

Claims

1. A negative electrode plate, characterized in that: It includes a negative electrode active material layer, at least one side of which is provided with a protective 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 an ester bond and / or a carbon-carbon double bond.

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 plate 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. The protective layer is disposed on a 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 negative electrode plate includes at least one of the following features: (1a) the compound containing multiple hydrogen bonds comprises one or more of a polymer containing ureidopyrimidone groups, poly(ether-thiourea), poly(alkyl-thiourea), polyvinylpyrrolidone and toluene diisocyanate; (1b) The compound containing an ester bond and / or a carbon-carbon double bond includes one or more of polystyrene sulfonic acid, lithium polystyrene sulfonate, polyacrylic acid, polylactic acid, polyvinylidene fluoride-trichloroethylene and polyvinylidene fluoride-chlorotrifluoroethylene.

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 (0.1-5):1, and can be optionally (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), and can be optionally 1:(0.1-0.2).

7. The method for preparing a negative electrode sheet according to any one of claims 1 to 6, characterized in that: The steps include: The protective layer is formed on at least one side of the negative electrode active material layer.

8. The preparation method according to claim 7, characterized in that: 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 at least one side of the negative electrode active material layer to form the protective layer; Optionally, the negative electrode sheet further comprises a negative electrode current collector, the negative electrode active material layer is arranged on at least one side of the negative electrode current collector, and the protective layer is arranged on a 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 comprises: arranging a protective slurry containing the first compound and the second compound on a side of the negative electrode active material layer away from the negative electrode current collector to form the protective layer; Optionally, in the protective slurry, the total mass fraction of the first compound and the second compound is 95%-96.8%; Optionally, the method for preparing the protective slurry comprises the following steps: firstly mixing the first compound with a solvent, and then adding the second compound after a certain interval; further optionally, the interval time is 20 min-90 min.

9. A secondary battery, characterized in that: It comprises the negative electrode sheet described in any one of claims 1 to 6 or the negative electrode sheet prepared by the preparation method described in any one of claims 7 to 8.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to claim 9.

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