Composite negative electrode, preparation method thereof and secondary battery

Abstract

The invention relates to a composite negative electrode, a preparation method thereof and a secondary battery. The composite negative electrode comprises a metal lithium matrix and a negative electrode protection layer, the negative electrode protection layer is made of active substances, the active substances are selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups, and the thickness of the negative electrode protection layer is larger than or equal to 10 micrometers; the negative electrode protection layer is arranged on the surface of the metal lithium matrix; or, the negative electrode protection layer is arranged in the bulk phase of the metal lithium matrix, and the lithium metal matrix and the negative electrode protection layer are compounded, folded and rolled to obtain the lithium ion battery. The active substance in the composite negative electrode can be combined with metal ions in an electrolyte in the charging process of the battery, and the DCR of the whole battery is reduced, so that the nucleation particle size of lithium metal is increased, the cycle life of the lithium metal battery is prolonged, and meanwhile, the thermal safety performance of the battery is improved.

Description

Technical Field

[0001] The invention relates to the field of batteries, and in particular to a composite negative electrode and a preparation method thereof, and a secondary battery. Background Art

[0002] Lithium-ion batteries are widely used in smart phones, unmanned aerial vehicles, hybrid electric vehicles, etc., but with the development of society, traditional lithium-ion batteries can no longer meet the demand. Metallic lithium has the advantages of low potential (-3.04V vs standard hydrogen electrode) and high specific capacity (3860mAh / g), and is a very excellent negative electrode material. However, the problem of lithium dendrites exists in the process of charging the metallic lithium negative electrode, and lithium dendrites can cause two problems: (1) When lithium dendrites grow to a certain extent, they break and become dead lithium, causing battery capacity decay; (2) Lithium dendrites continue to grow and eventually pierce the diaphragm, causing a short circuit between the positive and negative electrodes, and triggering thermal runaway.

[0003] Traditional technology inhibits the growth of lithium dendrites by setting a protective layer on the surface of the metallic lithium negative electrode, but the traditional protective layer has limited effect on improving the battery cycle performance and safety performance. Summary of the invention

[0004] Based on this, it is necessary to provide a composite negative electrode and a preparation method thereof that can further improve the cycle performance and safety performance of the battery.

[0005] In addition, it is also necessary to provide a secondary battery including the composite negative electrode.

[0006] A composite negative electrode, comprising: a metal lithium matrix and a negative electrode protective layer, wherein the material of the negative electrode protective layer comprises an active substance, wherein the active substance is selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups, and the thickness of the negative electrode protective layer is ≥10 μm;

[0007] Wherein, the negative electrode protection layer is arranged on the surface of the metal lithium substrate; or,

[0008] The negative electrode protection layer is arranged in the bulk phase of the metal lithium matrix and is obtained by compounding the metal lithium matrix and the negative electrode protection layer, folding them in half, and rolling them.

[0009] In some embodiments, the thickness of the negative electrode protection layer is 10 μm to 50 μm.

[0010] In some embodiments, the active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, poly(1,4-anthraquinone), 1,4-anthraquinone, poly(1,5-anthraquinone), 1,5-anthraquinone, 9,10-anthraquinone, dianthrone, anthrone, 3,4,9,10-perylenetetracarboxamide diimide, p-benzoquinone and 1,2-naphthoquinone.

[0011] In some of the embodiments, the material of the negative electrode protective layer also includes a binder, and the binder is selected from one or more of perfluorinated resin, lithiated perfluorinated resin, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl fiber, styrene-butadiene rubber, polyimide, polyacrylic acid, polystyrene sulfonic acid, polyfluoroethylene carbonate, polypropylene carbonate, polyethylene oxide and poly(vinylidene fluoride-hexafluoropropylene).

[0012] In some embodiments, the active material accounts for 50% to 99.5% of the total mass of the negative electrode protection layer.

[0013] A method for preparing a composite negative electrode comprises the following steps:

[0014] Forming a negative electrode protection layer on the surface of the metal lithium matrix, or forming a negative electrode protection layer in the bulk phase of the metal lithium matrix by folding and rolling the metal lithium matrix and the negative electrode protection layer together;

[0015] The material of the negative electrode protection layer includes active substances, and the active substances are selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups. The thickness of the negative electrode protection layer is ≥10 μm.

[0016] In some embodiments, the step of forming the negative electrode protection layer on the surface of the metal lithium substrate comprises: laminating the negative electrode protection layer on the surface of the metal lithium substrate, and then rolling to form the negative electrode protection layer on the surface of the metal lithium substrate, and optionally, the rolling pressure is 100kPa to 800kPa; or

[0017] The step of forming the negative electrode protective layer in the bulk phase of the metallic lithium matrix includes: stacking the negative electrode protective layer on the surface of the metallic lithium matrix, then rolling to obtain a stack, then folding the stack in half and rolling, repeating the steps of folding in half and rolling to form the negative electrode protective layer in the bulk phase of the metallic lithium matrix, optionally, the pressure of each rolling is independently 100kPa to 800kPa.

[0018] In some embodiments, the step of preparing the negative electrode protective layer includes: coating a dispersion containing the active material on a substrate surface, then drying, and peeling off from the substrate surface to prepare the negative electrode protective layer.

[0019] In some embodiments, the step of preparing the negative electrode protective layer satisfies at least one of the following conditions:

[0020] (1) In the drying step, the temperature is 60°C to 90°C and the time is 24h to 72h;

[0021] (2) The solvent of the dispersion includes N-methylpyrrolidone;

[0022] (3) The active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, poly(1,4-anthraquinone), 1,4-anthraquinone, poly(1,5-anthraquinone), 1,5-anthraquinone, 9,10-anthraquinone, dianthraquinone, anthraquinone, 3,4,9,10-perylenetetracarboxamide diimide, p-benzoquinone and 1,2-naphthoquinone;

[0023] (4) The dispersion further contains a binder, and the binder is selected from one or more of perfluorinated resin, lithiated perfluorinated resin, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl fiber, styrene-butadiene rubber, polyimide, polyacrylic acid, polystyrene sulfonic acid, polyfluoroethylene carbonate, polypropylene carbonate, polyethylene oxide and poly(vinylidene fluoride-hexafluoropropylene).

[0024] A secondary battery comprises the composite negative electrode or a composite negative electrode prepared by the composite negative electrode preparation method.

[0025] The main principle of the traditional negative electrode protective layer is to physically suppress lithium dendrites through inert high Young's modulus materials or to use the lithium affinity of the protective layer to evenly distribute the local space charge to achieve uniform deposition of the metal negative electrode. However, the inventors found in experiments that only the above two methods can often only suppress the vertical growth direction of lithium dendrites, and cannot change the growth morphology of lithium dendrites. Therefore, this type of protective layer has very limited improvement on battery cycle performance and safety performance. The main reason is that the substances in the traditional negative electrode protective layer are not electrochemically active, resulting in lithium ions being blocked when passing through the negative electrode protective layer. The DCR of the battery continues to increase during the cycle process, thereby turning lithium deposition into finer dendritic growth. Based on this, the inventors proposed a composite negative electrode, including a metallic lithium matrix and a negative electrode protective layer formed on the surface or in the bulk of the metallic lithium matrix, wherein the active substance in the negative electrode protective layer is selected from one or more of quinone compounds and perylene compounds containing cyclic diones. The active substance in the negative electrode protective layer having a certain thickness can combine with the metal ions in the electrolyte during the battery charging process, thereby reducing the DCR of the overall battery, thereby increasing the particle size of lithium metal nucleation, extending the cycle life of the lithium metal battery, and improving the thermal safety performance of the battery. If the thickness of the negative electrode protective layer is less than 10 μm, the negative electrode protective layer will hardly play a role in further improving the cycle performance and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the mechanism of quinone compounds binding to metal ions in an electrolyte in some embodiments of the present invention;

[0027] Figure 2 The figure shows a comparison of the cycle life of the lithium batteries of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with the specific embodiments. Preferred embodiments of the present invention are provided in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] Unless otherwise specified or there is a contradiction, the terms or phrases used in this invention have the following meanings:

[0031] In the present invention, "first" and "second" are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0032] In the description of the present invention, “at least one” means one, two, three, etc., unless otherwise clearly and specifically defined.

[0033] In the present invention, "one or several" refers to any one, any two or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0034] In the present invention, the percentage concentration involved, unless otherwise specified, refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0035] The words "preferably", "more preferably", etc. in the present invention refer to embodiments of the present invention that may provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0036] When a numerical range is disclosed in the present invention, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise indicated, all ranges disclosed in the present invention should be understood to include any and all subranges included therein.

[0037] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0038] The terms "including" and "having" and any variations thereof in the embodiments of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or components that are inherent to these processes, methods, products, or devices.

[0039] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0040] Conventional technology discloses a metal phthalocyanine compound to improve the cycle performance of the battery; another conventional technology discloses a polymer layer containing porphyrin, which guides the deposition of metallic lithium through its lithiophilicity to prevent it from piercing the separator.

[0041] However, the inventors found in experiments that the above two methods can only inhibit the vertical growth direction of lithium dendrites, but cannot change the growth morphology of lithium dendrites, so this type of protective layer has very limited effect on the improvement of battery cycle performance and safety performance. The main reason is that the substances in the protective layer are not electrochemically active, which hinders lithium ions from passing through the protective layer, causing the DCR of the battery to increase continuously during the cycle, thereby turning lithium deposition into finer dendrite growth.

[0042] Based on this, the first aspect of the present invention provides a composite negative electrode, including: a metallic lithium matrix and a negative electrode protective layer, the material of the negative electrode protective layer includes an active substance, the active substance is selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups, and the thickness of the negative electrode protective layer is ≥10μm.

[0043] In some embodiments, the negative electrode protection layer is disposed on the surface of the metal lithium matrix. In other embodiments, the negative electrode protection layer is disposed in the bulk phase of the metal lithium matrix, and is obtained by folding and rolling the metal lithium matrix and the negative electrode protection layer after compounding. It can be understood that when the negative electrode protection layer is disposed in the bulk phase of the metal lithium matrix, the thickness of the negative electrode protection layer ≥ 10 μm refers to the thickness of the negative electrode protection layer before the metal lithium matrix and the negative electrode protection layer are compounded.

[0044] Among them, quinone compounds are a general term for compounds with unsaturated cyclic diketone structures (quinone-like structures) or compounds that are easily converted into such structures, including benzoquinone, phenanthrenequinone, naphthoquinone and anthraquinone. Anthraquinone compounds also include products and dimers with different reduction degrees, such as anthracene, anthracene oxide, anthrone, dianthraquinone, dianthraquinone, etc. Heterocyclic diketone refers to a heterocyclic compound with two oxo substituents (=O), and the heteroatom can be but is not limited to nitrogen, sulfur, etc.

[0045] Specifically, in some embodiments, the active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, poly(1,4-anthraquinone), 1,4-anthraquinone, poly(1,5-anthraquinone), 1,5-anthraquinone, 9,10-anthraquinone, dianthraquinone, anthrone, 3,4,9,10-perylenetetracarboxamide diimide, p-benzoquinone and 1,2-naphthoquinone. Preferably, the active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, 1,4-anthraquinone and poly(1,4-anthraquinone).

[0046] The active material in the above-mentioned negative electrode protective layer with a certain thickness can combine with the metal ions in the electrolyte during the battery charging process, reducing the DCR of the overall battery, thereby increasing the size of the lithium metal nucleation particles, extending the cycle life of the lithium metal battery, and improving the thermal safety performance of the battery. Experiments have shown that if the thickness of the negative electrode protective layer is less than 10μm, the negative electrode protective layer has little effect on the cycle performance and safety performance of the battery. In addition, the mechanical limit thickness of the industrial coating is above 10μm, and the laboratory nano-level protective layer is not mass-producible under industrial conditions. The above-mentioned negative electrode protective layer is electrochemically active within the industrial thickness range, which is of great significance to improving the safety and cycle performance of metal lithium-based batteries.

[0047] For example, quinone compounds, see Figure 1 , Schematic diagram of the mechanism by which quinone compounds bind to metal ions in the electrolyte.

[0048] In some embodiments, the thickness of the negative electrode protective layer is 10 μm to 50 μm. For example, the thickness of the negative electrode protective layer may be, but is not limited to, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, or a range consisting of any two of these values. Experiments have shown that when the material of the negative electrode protective layer remains unchanged, the thickness is greater than 50 μm, and the DCR increases significantly, but the thicker protective layer thickness will affect the uniformity of lithium deposition, thereby reducing the life and safety of the battery, but the negative electrode protective layer that does not contain active substances or other materials can still improve the cycle performance and safety performance of the battery. Therefore, in this embodiment, preferably, the thickness of the negative electrode protective layer is 10 μm to 50 μm.

[0049] In some embodiments, the material of the negative electrode protective layer also includes a binder. Specifically, the binder is selected from one or more of perfluorinated resin (Nafion), lithiated perfluorinated resin (Li-Nafion), polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl fiber, styrene-butadiene rubber, polyimide, polyacrylic acid, polystyrene sulfonic acid, polyfluoroethylene carbonate, polypropylene carbonate, polyethylene oxide and poly (vinylidene fluoride-hexafluoropropylene). Adding a binder to the negative electrode protective layer can improve the mechanical properties of the negative electrode protective layer, and it is not easy to tear when preparing the negative electrode protective layer.

[0050] In some embodiments, the active material accounts for 50% to 99.5% of the total mass of the negative electrode protective layer. For example, the quinone compound accounts for 50%, 55%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 99.5% of the total mass of the negative electrode protective layer, or a range consisting of any two of these values. Preferably, the active material accounts for 50% to 90% of the total mass of the negative electrode protective layer.

[0051] The above-mentioned composite negative electrode includes a metallic lithium matrix and a negative electrode protective layer. The electrochemical substances in the negative electrode protective layer can combine with metal ions in the electrolyte during the battery charging process, thereby reducing the DCR of the overall battery, thereby increasing the particle size of lithium metal nucleation, extending the cycle life of the lithium metal battery, and improving the thermal safety performance of the battery.

[0052] A second aspect of the present invention provides a method for preparing a composite negative electrode, comprising the following steps:

[0053] Forming a negative electrode protection layer on the surface of the metal lithium matrix, or forming a negative electrode protection layer in the bulk phase of the metal lithium matrix by folding and rolling the metal lithium matrix and the negative electrode protection layer together;

[0054] The material of the negative electrode protection layer includes active substances, and the active substances are selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups. The thickness of the negative electrode protection layer is ≥10 μm.

[0055] In some embodiments, the thickness of the negative electrode protective layer is 10 μm to 50 μm. For example, the thickness of the negative electrode protective layer can be, but is not limited to, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, or a range consisting of any two of these values.

[0056] In some embodiments, the active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, poly(1,4-anthraquinone), 1,4-anthraquinone, poly(1,5-anthraquinone), 1,5-anthraquinone, 9,10-anthraquinone, dianthraquinone, anthrone, 3,4,9,10-perylenetetracarboxamide diimide, p-benzoquinone and 1,2-naphthoquinone. Preferably, the active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, 1,4-anthraquinone and poly(1,4-anthraquinone).

[0057] In some of the embodiments, the dispersion also contains a binder. Specifically, the binder is selected from one or more of perfluorinated resin (Nafion), lithiated perfluorinated resin (Li-Nafion), polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl fiber, styrene-butadiene rubber, polyimide, polyacrylic acid, polystyrene sulfonic acid, polyfluoroethylene carbonate, polypropylene carbonate, polyethylene oxide and poly (vinylidene fluoride-hexafluoropropylene). Adding a binder to the negative electrode protective layer can improve the mechanical properties of the negative electrode protective layer, and it is not easy to tear when preparing the negative electrode protective layer.

[0058] In some embodiments, the active material accounts for 50% to 99.5% of the total mass of the active material and the binder. For example, the active material accounts for 50%, 55%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 99.5% or a range consisting of any two of these values.

[0059] In some of the embodiments, the step of preparing the negative electrode protective layer includes: coating a dispersion containing active materials on the surface of a substrate, and then drying and peeling the dispersion from the surface of the substrate to prepare the negative electrode protective layer.

[0060] Specifically, the solvent of the dispersion containing the active substance includes, but is not limited to, N-methylpyrrolidone. The substrate may be, but is not limited to, a PTFE (polytetrafluoroethylene) substrate.

[0061] In some embodiments, in the drying step, the temperature is 60° C. to 90° C. and the time is 24 h to 72 h. Furthermore, the drying step adopts a vacuum drying method.

[0062] In some embodiments, the negative electrode protection layer is peeled off from the substrate surface by tearing off the film.

[0063] In some embodiments, the step of forming a negative electrode protection layer on the surface of the metal lithium substrate includes: laminating the negative electrode protection layer on the surface of the metal lithium substrate, and then rolling to form the negative electrode protection layer on the surface of the metal lithium substrate.

[0064] Optionally, the roller pressure is 100 kPa to 800 kPa. For example, the roller pressure may be, but is not limited to, 100 kPa, 150 kPa, 200 kPa, 250 kPa, 300 kPa, 350 kPa, 400 kPa, 450 kPa, 500 kPa, 550 kPa, 600 kPa, 650 kPa, 700 kPa, 750 kPa, 800 kPa, or a range consisting of any two of these values.

[0065] In some other embodiments, the step of forming the negative electrode protection layer in the bulk phase of the metal lithium matrix includes: laminating the negative electrode protection layer on the surface of the metal lithium matrix, then rolling to obtain a laminate, then folding the laminate in half, rolling, and repeating the steps of folding in half and rolling to form the negative electrode protection layer in the bulk phase of the metal lithium matrix. Optionally, the pressure of each rolling is independently 100kPa to 800kPa.

[0066] Through the above steps, a negative electrode protection layer can be formed on the surface or in the bulk of the metallic lithium matrix.

[0067] The preparation process of the above-mentioned composite negative electrode is simple and easy to industrialize. In addition, the active material in the above-mentioned composite negative electrode can combine with the metal ions in the electrolyte during the battery charging process to reduce the DCR of the overall battery, thereby increasing the particle size of lithium metal nucleation, extending the cycle life of the lithium metal battery, and improving the thermal safety performance of the battery.

[0068] A third aspect of the present invention provides a secondary battery, comprising the above-mentioned composite negative electrode or a composite negative electrode prepared by the above-mentioned method for preparing the composite negative electrode.

[0069] Specifically, the secondary battery is a lithium metal battery.

[0070] The active material in the above-mentioned secondary battery can combine with the metal ions in the electrolyte during the battery charging process, reducing the DCR of the entire battery, thereby increasing the particle size of lithium metal nuclei, extending the cycle life of the battery, and improving the thermal safety performance of the battery.

[0071] In order to make the purpose and advantages of the present invention clearer, the composite negative electrode of the present invention and its effects are further described in detail in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and shall not be used to limit the present invention. The following embodiments do not include other components except inevitable impurities unless otherwise specified. The drugs and instruments used in the embodiments are conventionally selected in the art unless otherwise specified. The experimental methods for which specific conditions are not specified in the embodiments are implemented according to conventional conditions, such as the conditions described in the literature and books or the methods recommended by the manufacturer.

[0072] Example 1

[0073] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0074] (1) 10 mg of polyvinylidene fluoride and 90 mg of pyrene-4,5,9,10-tetraketone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0075] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0076] Example 2

[0077] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0078] (1) 10 mg of polyvinylidene fluoride and 90 mg of poly(1,4-anthraquinone) were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 50 μm to obtain a negative electrode protective layer.

[0079] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0080] Example 3

[0081] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0082] (1) 10 mg of polyvinylidene fluoride and 90 mg of 1,4-anthraquinone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0083] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0084] Example 4

[0085] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0086] (1) 10 mg of polyvinylidene fluoride and 90 mg of pyrene-4,5,9,10-tetraketone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 200 μm to obtain a negative electrode protective layer.

[0087] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0088] Example 5

[0089] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0090] (1) 10 mg of polyvinylidene fluoride and 90 mg of poly(1,4-anthraquinone) were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 200 μm to obtain a negative electrode protective layer.

[0091] (2) Covering the negative electrode protection layer on the metal lithium negative electrode and rolling at 200 kPa to obtain a composite negative electrode.

[0092] Example 6

[0093] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0094] (1) 50 mg of polyvinylidene fluoride and 50 mg of pyrene-4,5,9,10-tetraketone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0095] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0096] Example 7

[0097] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0098] (1) 10 mg of polyvinylidene fluoride and 90 mg of anthrone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0099] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0100] Example 8

[0101] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0102] (1) 10 mg of polyvinylidene fluoride and 90 mg of 3,4,9,10-perylenetetracarboxylic acid diimide were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0103] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0104] Example 9

[0105] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0106] (1) 10 mg of polyvinylidene fluoride and 90 mg of p-benzoquinone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0107] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0108] Example 10

[0109] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0110] (1) 10 mg of polyvinylidene fluoride and 90 mg of 1,2-naphthoquinone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0111] (2) Covering the negative electrode protection layer on the metal lithium negative electrode, and rolling at 200 kPa to obtain the composite negative electrode of this embodiment.

[0112] Embodiment 11

[0113] This embodiment provides a composite negative electrode, and the preparation process is as follows:

[0114] (1) 10 mg of polyvinylidene fluoride and 90 mg of pyrene-4,5,9,10-tetraketone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0115] (2) Cover the negative electrode protection layer on the metal lithium negative electrode and roll it at 200 kPa to obtain a laminate, then fold the laminate in half and roll it at 200 kPa. Repeat the folding and rolling steps 5 times in total to disperse the negative electrode protection layer in the metal lithium negative electrode phase to obtain the composite negative electrode of this embodiment.

[0116] Comparative Example 1

[0117] This comparative example provides a composite negative electrode, and the preparation process is as follows:

[0118] (1) 100 mg of polyvinylidene fluoride was dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0119] (2) A negative electrode protective layer containing only polyvinylidene fluoride is covered on the metal lithium negative electrode, and rolling is performed at 200 kPa to obtain a composite negative electrode.

[0120] Comparative Example 2

[0121] This comparative example provides a composite negative electrode, and the preparation process is as follows:

[0122] (1) 10 mg of polyvinylidene fluoride and 90 mg of pyrene-4,5,9,10-tetraketone were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 3 μm to obtain a negative electrode protective layer.

[0123] (2) Covering the negative electrode protection layer on the metal lithium negative electrode and rolling at 200 kPa to obtain a composite negative electrode.

[0124] Comparative Example 3

[0125] This comparative example provides a composite negative electrode, and the preparation process is as follows:

[0126] (1) 10 mg of polyvinylidene fluoride and 90 mg of porphyrin were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 30 μm to obtain a negative electrode protective layer.

[0127] (2) Covering the negative electrode protective layer containing porphyrin on the metal lithium negative electrode, and rolling at 200 kPa to obtain a composite negative electrode.

[0128] Comparative Example 4

[0129] This comparative example provides a composite negative electrode, and the preparation process is as follows:

[0130] (1) 10 mg of polyvinylidene fluoride and 90 mg of copper phthalocyanine were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 200 μm to obtain a negative electrode protective layer.

[0131] (2) Covering the negative electrode protection layer on the metal lithium negative electrode and rolling at 200 kPa to obtain a composite negative electrode.

[0132] Comparative Example 5

[0133] This comparative example provides a composite negative electrode, and the preparation process is as follows:

[0134] (1) 10 mg of polyvinylidene fluoride and 90 mg of copper phthalocyanine were dissolved in NMP, uniformly dispersed and coated on a PTFE substrate with a thickness of 3 μm to obtain a negative electrode protective layer.

[0135] (2) Covering the negative electrode protection layer on the metal lithium negative electrode and rolling at 200 kPa to obtain a composite negative electrode.

[0136] The following is the test part:

[0137] (1) Lithium-lithium symmetrical battery test method: Li / Li battery assembly test is performed in the order of negative electrode shell, spring, gasket, lithium sheet, diaphragm, lithium sheet, and positive electrode shell. 30-60 μL of electrolyte is added to each battery to wet the diaphragm, and the battery is finally packaged. The battery is charged at 1 mA / cm 2 The deposition was carried out for 3 hours at a current density of 1 mA / cm 2 Lithium was stripped at a current density of 3000 nm for 3 hours and cycled until failure.

[0138] (2) DSC test method: Remove the lithium sheet from the lithium-lithium symmetrical battery that has been cycled 100 times, cut out a 4 mg lithium metal disc (thickness 500 μm) and place it in a ceramic crucible, add 10 μL of electrolyte and seal it. Place the crucible in the DSC instrument, set the thermal scan temperature range from 50°C to 300°C, and scan to obtain the heat release value.

[0139] (3) Discharge DCR impedance test: At room temperature (25°C), discharge the fully charged lithium-ion battery to 50% SOC capacity at 0.5C, let it stand for 10 minutes, record the voltage V1 at this time, and discharge it for 10 seconds at a current of I=2C, and record the voltage V2 after 10 seconds. The discharge DCR value is calculated using the formula DCR=(V1-V2) / I.

[0140] Table 1 Experimental data of each embodiment and comparative example

[0141]

[0142]

[0143] From the comparison between Comparative Example 1 and Example 1, it can be concluded that, at a thickness of more than 10 μm, adding active quinone compounds to replace a portion of the binder can effectively reduce the DCR value of the protective film, while extending the cycle life and thermal peak temperature of the battery.

[0144] From the comparison between Example 5 and Example 2, it can be concluded that when the material of the negative electrode protection layer remains unchanged, the thickness is greater than 50 μm, and the DCR increases significantly. The thicker thickness of the negative electrode protection layer will affect the uniformity of lithium deposition, thereby reducing the life and safety of the battery to a certain extent.

[0145] From the comparison between Comparative Example 3 and Example 3, it can be concluded that electrochemically inert substances such as porphyrin will increase the DCR during the battery cycle, thereby reducing the life and safety of the battery.

[0146] From the comparison between Comparative Example 4 and Example 4, it can be concluded that the negative electrode protective layer contains electrochemically inert substances such as copper phthalocyanine, and the thickness of the negative electrode protective layer is relatively thick, which has a great impact on the DCR of the cycle process and reduces the life and safety of the battery.

[0147] From the comparison between Comparative Example 5 and Comparative Example 2, it can be seen that when the thickness of the negative electrode protective layer is less than 10 μm, the negative electrode protective layer containing quinone compounds has little improvement on the cycle performance and safety performance of the battery, which is equivalent to the performance of the negative electrode protective layer containing electrochemically inert substances such as copper phthalocyanine.

[0148] It can be seen from Examples 1 to 3 and Examples 7 to 10 that the above-mentioned electrochemically active substances can improve the cycle performance and safety performance of the battery. It can be seen from Example 11 that forming the negative electrode protective layer in the bulk phase of the metal lithium matrix can also improve the cycle performance and safety performance of the battery.

[0149] See also Figure 2 , the cycle life of the lithium battery of Example 1 and Comparative Example 1 is compared. As can be seen from the figure, the negative electrode protective layer of the electrochemically active quinone molecular material added in Example 1 effectively improves the cycle life of the lithium metal symmetric battery and inhibits the growth of lithium dendrites and the formation of dead lithium.

[0150] 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.

[0151] The above-described embodiments only express several implementation methods of the present invention, which is convenient for understanding the technical solutions of the present invention in detail, but it cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several modifications and improvements can be made, which all belong to the protection scope of the present invention. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided by the present invention are all within the protection scope of the claims attached to the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the contents of the attached claims, and the description and drawings can be used to interpret the contents of the claims.

Claims

1. A composite negative electrode, characterized in that: include: A metal lithium matrix and a negative electrode protective layer, wherein the material of the negative electrode protective layer includes an active substance, wherein the active substance is selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups, and the thickness of the negative electrode protective layer is ≥10 μm; Wherein, the negative electrode protection layer is arranged on the surface of the metal lithium substrate; or, The negative electrode protection layer is arranged in the bulk phase of the metal lithium matrix and is obtained by compounding the metal lithium matrix and the negative electrode protection layer, folding them in half, and rolling them.

2. The composite negative electrode according to claim 1, characterized in that The thickness of the negative electrode protection layer is 10 μm to 50 μm.

3. The composite negative electrode according to claim 1 or 2, characterized in that: The active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, poly(1,4-anthraquinone), 1,4-anthraquinone, poly(1,5-anthraquinone), 1,5-anthraquinone, 9,10-anthraquinone, dianthraquinone, anthraquinone, 3,4,9,10-perylenetetracarboxamide diimide, p-benzoquinone and 1,2-naphthoquinone.

4. The composite negative electrode according to claim 1 or 2, characterized in that: The material of the negative electrode protective layer also includes a binder, and the binder is selected from one or more of perfluorinated resin, lithiated perfluorinated resin, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl fiber, styrene-butadiene rubber, polyimide, polyacrylic acid, polystyrene sulfonic acid, polyfluoroethylene carbonate, polypropylene carbonate, polyethylene oxide and poly(vinylidene fluoride-hexafluoropropylene).

5. The composite negative electrode according to claim 4, characterized in that: The active material accounts for 50% to 99.5% of the total mass of the negative electrode protection layer.

6. A method for preparing a composite negative electrode, characterized in that: The steps include: Forming a negative electrode protection layer on the surface of the metal lithium matrix, or forming a negative electrode protection layer in the bulk phase of the metal lithium matrix by folding and rolling the metal lithium matrix and the negative electrode protection layer together; The material of the negative electrode protection layer includes active substances, and the active substances are selected from one or more of quinone compounds and perylene compounds containing heterocyclic diketone groups. The thickness of the negative electrode protection layer is ≥10 μm.

7. The method for preparing a composite negative electrode according to claim 6, characterized in that: The step of forming the negative electrode protection layer on the surface of the metal lithium substrate comprises: laminating the negative electrode protection layer on the surface of the metal lithium substrate, and then rolling to form the negative electrode protection layer on the surface of the metal lithium substrate, and optionally, the rolling pressure is 100kPa to 800kPa; or The step of forming the negative electrode protective layer in the bulk phase of the metallic lithium matrix includes: stacking the negative electrode protective layer on the surface of the metallic lithium matrix, then rolling to obtain a stack, then folding the stack in half and rolling, repeating the steps of folding in half and rolling to form the negative electrode protective layer in the bulk phase of the metallic lithium matrix, optionally, the pressure of each rolling is independently 100kPa to 800kPa.

8. The method for preparing a composite negative electrode according to claim 6 or 7, characterized in that: The step of preparing the negative electrode protective layer comprises: coating the dispersion containing the active material on the surface of the substrate, then drying, and peeling off from the surface of the substrate to prepare the negative electrode protective layer.

9. The method for preparing a composite negative electrode according to claim 8, characterized in that: The step of preparing the negative electrode protective layer satisfies at least one of the following conditions: (1) In the drying step, the temperature is 60°C to 90°C and the time is 24h to 72h; (2) The solvent of the dispersion includes N-methylpyrrolidone; (3) The active substance is selected from one or more of pyrene-4,5,9,10-tetraketone, poly(1,4-anthraquinone), 1,4-anthraquinone, poly(1,5-anthraquinone), 1,5-anthraquinone, 9,10-anthraquinone, dianthraquinone, anthraquinone, 3,4,9,10-perylenetetracarboxamide diimide, p-benzoquinone and 1,2-naphthoquinone; (4) The dispersion further contains a binder, and the binder is selected from one or more of perfluorinated resin, lithiated perfluorinated resin, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl fiber, styrene-butadiene rubber, polyimide, polyacrylic acid, polystyrene sulfonic acid, polyfluoroethylene carbonate, polypropylene carbonate, polyethylene oxide and poly(vinylidene fluoride-hexafluoropropylene).

10. A secondary battery, characterized in that: The invention comprises the composite negative electrode according to any one of claims 1 to 5 or a composite negative electrode prepared by the method for preparing the composite negative electrode according to any one of claims 6 to 9.

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