Lithium metal negative plate, preparation method thereof and lithium metal battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium metal negative plate, a preparation method thereof and a lithium metal battery. The lithium metal negative plate comprises a negative current collector, an elastic composite layer and a lithium metal layer, the elastic composite layer is arranged on at least one surface of the negative electrode current collector in the thickness direction; the elastic composite layer comprises an elastic composite material, the elastic composite material comprises lithium-loving metal composite reduced graphene oxide and a polymer, and the polymer has viscoelasticity. The lithium metal negative plate can adapt to stress change caused by lithium metal deposition, and dead lithium accumulation caused by dendritic crystal fracture is reduced.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a lithium metal negative electrode sheet and a preparation method thereof, and a lithium metal battery. Background Art

[0002] Since the first commercial lithium-ion battery invented by Sony in 1991, lithium-ion batteries have been used in the mainstream market. They have been popularized in all aspects of life, from TV remote controls to new energy vehicles. However, the energy density of such lithium-ion batteries is limited to the energy density of the positive and negative electrodes, which is infinitely close to its theoretical capacity limit (~300Wh kg -1 ). Therefore, it is of great significance to develop a battery system with higher energy density to replace the current lithium-ion battery.

[0003] In recent years, due to the progress of science and technology, the development of new materials, technological innovation, and the emergence of energy and environmental protection issues, lithium metal batteries have once again aroused the interest of researchers. Lithium metal is a very active metal element, but due to its extremely small ionic radius and solvation, its standard redox potential as a negative electrode is lower than that of sodium and potassium in the same family, far exceeding the stability window of most electrolytes, including battery side reactions caused by extremely high electrochemical reaction activity, lithium dendrites caused by uneven deposition, and stress effects on the battery caused by drastic volume changes. Each problem will have a serious impact on the battery, further aggravating the deterioration of the performance of lithium metal negative electrodes and seriously hindering the application process of lithium metal batteries.

[0004] The internal structure of the battery is an important factor that affects the performance of lithium metal. The formation of dead lithium is often due to the volume expansion of lithium metal, which causes irreversible changes in the internal structure of the battery, uneven local stress distribution, and the free growth of lithium metal. Studies have shown that lithium metal can generate a pressure of 100Mpa during the deposition process inside the battery. During the charging process, lithium metal tends to grow more towards the pressure-free voids, which ultimately leads to the rapid growth of dendrite structures, causing the rapid accumulation of dead lithium during the cycle and even battery failure. Summary of the invention

[0005] In view of this, the present invention provides a lithium metal negative electrode sheet and a preparation method thereof and a lithium metal battery. The lithium metal negative electrode sheet can adapt to the stress changes caused by lithium metal deposition and reduce the accumulation of dead lithium caused by dendrite breakage.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a lithium metal negative electrode sheet, the lithium metal negative electrode sheet comprising:

[0008] (a) negative electrode current collector 1;

[0009] (b) an elastic composite layer 2, the elastic composite layer 2 is arranged on at least one surface of the negative electrode current collector 1 in the thickness direction; the elastic composite layer 2 comprises an elastic composite material, the elastic composite material comprises a lithium-philic metal composite reduced graphene oxide and a polymer, and the polymer has viscoelasticity;

[0010] (c) a lithium metal layer 3 , wherein the lithium metal layer 3 is disposed on a surface of the elastic composite layer 2 away from the negative electrode current collector 1 .

[0011] In an embodiment of the present invention, the lithium-philic metal composite reduced graphene oxide includes a lithium-philic metal and reduced graphene oxide, and the lithium-philic metal is loaded on the surface of the reduced graphene oxide.

[0012] In an embodiment of the present invention, the lithium-philic metal includes at least one of antimony, zinc, silver and tin.

[0013] In an embodiment of the present invention, the viscosity of the polymer is 20 to 35 mPas, and the elastic modulus is 50 to 80 MPa.

[0014] In an embodiment of the present invention, the polymer contains at least one of polypropylene glycol, polypropylene fiber, nylon fiber, polyester fiber, polyamide fiber, and derivatives thereof.

[0015] Preferably, the mass ratio of the lithium-philic metal to the reduced graphene oxide is (1.5-4.5):(3-10).

[0016] Preferably, the mass ratio of the lithium-philic metal composite reduced graphene oxide to the polymer is (1 to 1.6):(1 to 5).

[0017] In an embodiment of the present invention, the elastic composite layer further includes a conductive agent and a binder.

[0018] Preferably, the mass ratio of the elastic composite material, the conductive agent and the binder is (90-95):(3-5):(2-5).

[0019] Preferably, the single-side thickness of the elastic composite layer is 15-30 μm.

[0020] Preferably, the single-side thickness of the lithium metal layer is 10 to 40 μm.

[0021] In a second aspect, the present invention provides a method for preparing the above-mentioned lithium metal negative electrode sheet, comprising the following steps:

[0022] S1, mixing graphene oxide, a lithium-philic metal salt, a reducing agent and water to obtain a mixed solution; subjecting the mixed solution to a hydrothermal reaction to obtain a lithium-philic metal composite reduced graphene oxide;

[0023] S2, mixing the lithium-philic metal composite reduced graphene oxide, the polymer and the first solvent, heating and stirring, solid-liquid separation, and drying to obtain an elastic composite material;

[0024] S3, mixing the elastic composite material, the conductive agent, the binder and the second solvent to obtain a slurry, and coating the slurry on at least one surface of the negative electrode current collector in the thickness direction to obtain a negative electrode current collector composited with an elastic composite layer;

[0025] S4, placing lithium metal on the surface of the elastic composite layer away from the negative electrode current collector to obtain a lithium metal negative electrode sheet.

[0026] In an embodiment of the present invention, in step S1, the lithium-philic metal salt includes at least one of antimony sulfate, zinc sulfate, silver nitrate, and tin nitrate.

[0027] Preferably, the concentration of the lithium-philic metal salt in the mixed solution is 0.5 to 2 mol / L.

[0028] Preferably, the mass ratio of graphene oxide to lithium-philic metal salt is (0.3-0.8): (0.3-1).

[0029] In an embodiment of the present invention, the reducing agent includes at least one of L-ascorbic acid, hydrazine hydrate, and hydroxylamine.

[0030] Preferably, the mass ratio of graphene oxide to reducing agent is (1-10):(0.5-5).

[0031] Preferably, the temperature of the hydrothermal reaction is 100-200° C., and the time of the hydrothermal reaction is 10-20 h.

[0032] In an embodiment of the present invention, in step S2, the first solvent includes at least one of acetone, ethylketone, benzene, ethanol, ethyl ether, xylene, and toluene.

[0033] Preferably, in g / mL, the ratio of the lithium-philic metal composite reduced graphene oxide to the solvent is (1-10):(5-15).

[0034] Preferably, the heating and stirring temperature is 50 to 90° C., and the heating and stirring time is 0.5 to 3 h.

[0035] In an embodiment of the present invention, in step S3, the second solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0036] In an embodiment of the present invention, in step S4, lithium metal is disposed on the surface of the elastic composite layer away from the negative electrode current collector by magnetron sputtering.

[0037] In a third aspect, the present invention provides a lithium metal battery, which includes the above-mentioned lithium metal negative electrode sheet, and / or the lithium metal negative electrode sheet prepared by the above-mentioned preparation method.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention combines a viscoelastic polymer with reduced graphene oxide which is also elastic and has good conductivity to prepare an elastic composite material. The elastic composite material can adapt to the stress changes caused by lithium metal deposition, ensure that it expands when lithium metal is deposited, accommodate more lithium metal, generate less solid electrolyte interface film (SEI), and shrink itself as the internal stress of the battery changes when lithium metal is stripped, reducing the accumulation of dead lithium caused by dendrite breakage. However, due to the poor conductivity of the polymer, the deposition of lithium ions may be hindered during the cycle process. Therefore, the present invention loads lithium-philic metal atoms on the three-dimensional reduced graphene oxide, and cooperates with the reduced graphene oxide to improve the conductivity of the elastic composite layer.

[0040] The present invention combines lithium-philic metal elements with elastic materials, so that lithium metal can be evenly deposited on the surface of the negative electrode, further solving the problem of uneven lithium metal deposition during the cycle of the lithium metal battery and improving the cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of the lithium metal negative electrode sheet.

[0042] The reference numerals are as follows:

[0043] 1: negative electrode current collector;

[0044] 2: Elastic composite layer;

[0045] 3: Lithium metal layer. DETAILED DESCRIPTION

[0046] The present invention discloses a lithium metal negative electrode sheet and a preparation method thereof and a lithium metal battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the same. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all deemed to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0047] In the description of the present invention, it should be noted that the terms "first", "second", etc. are only used for descriptive purposes, and do not indicate or imply relative importance.

[0048] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0049] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0050] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] 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.

[0052] 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.

[0053] Specifically, the present invention adopts the following technical solutions:

[0054] In a first aspect, the present invention provides a lithium metal negative electrode sheet, the lithium metal negative electrode sheet comprising:

[0055] (a) negative electrode current collector 1;

[0056] (b) an elastic composite layer 2, the elastic composite layer 2 being disposed on at least one surface in the thickness direction of the negative electrode current collector 1; the elastic composite layer 2 comprising an elastic composite material, the elastic composite material comprising a lithium-philic metal composite reduced graphene oxide and a polymer;

[0057] (c) a lithium metal layer 3 , wherein the lithium metal layer 3 is disposed on a surface of the elastic composite layer 2 away from the negative electrode current collector 1 .

[0058] In an embodiment of the present invention, the lithium-philic metal composite reduced graphene oxide includes a lithium-philic metal and reduced graphene oxide, and the lithium-philic metal is loaded on the surface of the reduced graphene oxide. The lithium-philic metal atoms are loaded on the three-dimensional reduced graphene oxide, and cooperate with the reduced graphene oxide to improve the conductive properties of the elastic composite layer.

[0059] In an embodiment of the present invention, the lithium-philic metal includes at least one of antimony, zinc, silver and tin.

[0060] The viscoelastic polymers of the present invention refer to a class of polymer materials with viscoelasticity obtained by macromolecular chemical synthesis. They are usually composed of linear, network, star and cross-linked polymers, and their most notable feature is that they can quickly restore their shape within a certain range, and have reversible deformation and programmable deformation capabilities.

[0061] In the embodiment of the present invention, the polymer is a high polymer. A high polymer is a macromolecular polymer, generally referring to a compound with a relative molecular mass of several thousand to several million. A high polymer is composed of hundreds of thousands of atoms connected to each other by covalent bonds. Although their relative molecular mass is large, they are all connected in a simple structural unit and repeated manner.

[0062] In an embodiment of the present invention, the viscosity of the polymer is 20 to 35 mPas, and the elastic modulus is 50 to 80 MPa. Exemplarily, the viscosity of the polymer is any value among 20 mPas, 22 mPas, 24 mPas, 26 mPas, 28 mPas, 30 mPas, 32 mPas, 34 mPas, 35 mPas, or any value within the range of any two of the above values, and the elastic modulus is any value among 50 MPa, 60 MPa, 70 MPa, 80 MPa, or any value within the range of any two of the above values.

[0063] In an embodiment of the present invention, the polymer contains at least one of polypropylene glycol, polypropylene fiber, nylon fiber, polyester fiber, polyamide fiber, and derivatives of the above substances. The polymer has a large viscoelasticity, and combined with the reduced graphene oxide which is not only elastic but also has good conductivity, the elastic composite material can adapt to the stress changes caused by lithium metal deposition, while ensuring that it expands when lithium metal is deposited, accommodating more lithium metal, generating less solid electrolyte interface film (SEI), and when lithium metal is stripped, it can shrink with the change of internal stress of the battery, reducing the accumulation of dead lithium caused by dendrite breakage.

[0064] The polymer of the present invention can be prepared by conventional methods in the art, generally by polymerizing monomers to obtain high molecular polymer materials. For example, polypropylene glycol polymers are mainly obtained by condensing propylene oxide and propylene glycol under high pressure or in the presence of an acidic catalyst. For another example, referring to the invention patent with publication number CN118638308A, a method for preparing nylon fibers is disclosed, comprising the following steps: S1, after mixing a nylon hard segment, an end-capping agent and water, polymerizing to obtain a double-terminated carboxyl nylon hard segment; S2, adding the S1 product, polyether polyol, and an auxiliary agent to a reactor, polymerizing to obtain a high-end carboxyl content prepolymerized nylon; S3, solid-phase polymerizing the S2 product in a double-cone vacuum drum; the end-capping agent in S1 is one or more of adipic acid, suberic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and hexadecanedioic acid, preferably one or more of adipic acid, sebacic acid, and dodecanedioic acid.

[0065] Preferably, the mass ratio of the lithium-philic metal to the reduced graphene oxide is (1.5-4.5):(3-10). Exemplarily, the mass ratio of the lithium-philic metal to the reduced graphene oxide is any value among 1.5:10, 2:7, 3:5, 4:3.5, 4.5:3 or any value within the range of values ​​composed of any two of the above values. Within this range, the conductivity of the lithium-philic metal composite reduced graphene oxide can be enhanced. When the proportion of the lithium-philic metal is too small, the lithium-philic performance of the lithium-philic metal composite reduced graphene oxide material is weakened, and the lithium ion transmission capacity decreases, resulting in poor cycle performance of the battery; when the proportion of the lithium-philic metal is too large, it will exceed the load capacity of the reduced graphene oxide.

[0066] Preferably, the mass ratio of the lithium-philic metal composite reduced graphene oxide to the polymer is (1 to 1.6): (1 to 5). Exemplarily, the mass ratio of the lithium-philic metal composite reduced graphene oxide to the polymer is any value in 1:5, 1.2:4, 1.4:3, 1.6:1 or any value in the range of values ​​composed of any two of the above values. Within this range, not only does the lithium-philic metal composite reduced graphene oxide have good electrical conductivity, but also has good elastic strength, so that the elastic composite material can adapt to the stress changes caused by lithium metal deposition, while ensuring that it expands when lithium metal is deposited, accommodating more lithium metal, generating less solid electrolyte interface film (SEI), and when the lithium metal is stripped, it can shrink as the internal stress of the battery changes, reducing the accumulation of dead lithium caused by dendrite breakage.

[0067] In the embodiment of the present invention, the elastic composite layer further comprises a conductive agent and a binder. The addition of the conductive agent can further enhance the conductivity of the elastic composite layer, and the addition of the binder can make the elastic composite layer have good processing performance.

[0068] In an embodiment of the present invention, the conductive agent includes at least one of conductive carbon black (SP), acetylene black, graphene, conductive graphite, conductive carbon tube, and conductive carbon fiber.

[0069] In an embodiment of the present invention, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and sodium carboxymethyl cellulose (CMC-Na).

[0070] Preferably, the mass ratio of the elastic composite material, the conductive agent and the binder is (90-95):(3-5):(2-5). Exemplarily, the mass ratio of the elastic composite material, the conductive agent and the binder is any value among 90:5:5, 91:4.5:4.5, 92:4:4, 94:3:3, 95:3:2 or any value within the range consisting of any two of the above values.

[0071] Preferably, the thickness of the elastic composite layer on one side is 15 to 30 μm. Exemplarily, the thickness of the elastic composite layer on one side is any value among 15 μm, 17 μm, 19 μm, 20 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, 30 μm or any value within the range of any two of the above values. When the thickness of the elastic composite layer on one side is too small, the elastic composite material cannot adapt well to the stress changes caused by the deposition of lithium metal, which will cause the accumulation of dead lithium caused by dendrite fracture; when the thickness of the elastic composite layer on one side is too large, the energy density of the battery will be reduced.

[0072] Preferably, the thickness of the lithium metal layer on one side is 10 to 40 μm. Exemplarily, the thickness of the lithium metal layer on one side is any value among 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or any value within the range of any two of the above values. When the thickness of the lithium metal layer is too small, it will lead to insufficient supply of lithium; when the thickness of the lithium metal layer is too large, it will lead to a decrease in the energy density of the battery.

[0073] In a second aspect, the present invention provides a method for preparing the above-mentioned lithium metal negative electrode sheet, comprising the following steps:

[0074] S1, mixing graphene oxide, a lithium-philic metal salt, a reducing agent and water to obtain a mixed solution; subjecting the mixed solution to a hydrothermal reaction to obtain a lithium-philic metal composite reduced graphene oxide;

[0075] S2, mixing the lithium-philic metal composite reduced graphene oxide, the polymer and the first solvent, heating and stirring, solid-liquid separation, and drying to obtain an elastic composite material;

[0076] S3, mixing the elastic composite material, the conductive agent, the binder and the second solvent to obtain a slurry, and coating the slurry on at least one surface of the negative electrode current collector in the thickness direction to obtain a negative electrode current collector composited with an elastic composite layer;

[0077] S4, placing lithium metal on the surface of the elastic composite layer away from the negative electrode current collector to obtain a lithium metal negative electrode sheet.

[0078] In an embodiment of the present invention, in step S1, the lithium-philic metal salt includes at least one of antimony sulfate, zinc sulfate, silver nitrate, and tin nitrate.

[0079] Preferably, the concentration of the lithium-philic metal salt in the mixed solution is 0.5 to 2 mol / L. Exemplarily, the concentration of the lithium-philic metal salt in the mixed solution is any value among 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 1.9 mol / L, 2 mol / L, or any value within the range of any two of the above values.

[0080] Preferably, the mass ratio of graphene oxide to the lithium-philic metal salt is (0.3-0.8):(0.3-1). Exemplarily, the mass ratio of graphene oxide to the lithium-philic metal salt is any value among 0.3:1, 0.4:0.9, 0.5:0.8, 0.7:0.5, 0.8:0.3, or any value within the range of any two of the above values.

[0081] In an embodiment of the present invention, the reducing agent includes at least one of L-ascorbic acid, hydrazine hydrate, and hydroxylamine.

[0082] Preferably, the mass ratio of graphene oxide to the reducing agent is (1-10):(0.5-5). Exemplarily, the mass ratio of graphene oxide to the reducing agent is any value among 1:5, 3:5, 5:3, 7:2, 9:1, 10:0.5 or any value within the range of any two of the above values.

[0083] Preferably, the temperature of the hydrothermal reaction is 100-200°C, and the time of the hydrothermal reaction is 10-20h. Exemplarily, the temperature of the hydrothermal reaction is any value in 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, or any value in the range of any two of the above values, and the time of the hydrothermal reaction is any value in 10h, 12h, 14h, 16h, 18h, 20h, or any value in the range of any two of the above values.

[0084] In the embodiment of the present invention, in step S1, after the hydrothermal reaction, the steps of first washing and first drying are also included.

[0085] In the embodiment of the present invention, the first cleaning in step S1 is: taking the lower layer of slurry and washing it with ethanol and water respectively for 2 to 5 times.

[0086] In an embodiment of the present invention, the temperature of the first drying in step S1 is 50-100° C., and the time of the first drying is 10-20 hours.

[0087] In an embodiment of the present invention, in step S2, the first solvent includes at least one of acetone, ethylketone, benzene, ethanol, ethyl ether, xylene, and toluene.

[0088] Preferably, in g / mL, the ratio of the lithium-philic metal composite reduced graphene oxide to the solvent is (1-10):(5-15). Exemplarily, the ratio of the lithium-philic metal composite reduced graphene oxide to the solvent is any value among 1:15, 3:13, 5:11, 7:9, 9:7, 2:1, or any value within the range of any two of the above values.

[0089] Preferably, the temperature of heating and stirring is 50-90°C, and the time of heating and stirring is 0.5-3h. Exemplarily, the temperature of heating and stirring is any value among 50°C, 60°C, 70°C, 80°C, 90°C, or any value within the range of any two of the above values, and the time of heating and stirring is any value among 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, or any value within the range of any two of the above values.

[0090] In an embodiment of the present invention, in step S2, after heating and stirring, the steps of second washing and second drying are also included.

[0091] In the embodiment of the present invention, the second cleaning in step S2 is: taking the lower layer of slurry and washing it with water and ethanol for 4 to 8 times respectively.

[0092] In an embodiment of the present invention, the temperature of the second drying in step S2 is 50-100° C., and the time of the second drying is 10-20 hours.

[0093] In an embodiment of the present invention, in step S3, the second solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0094] In an embodiment of the present invention, in step S4, lithium metal is disposed on the surface of the elastic composite layer away from the negative electrode current collector by magnetron sputtering.

[0095] In a third aspect, the present invention provides a lithium metal battery, which includes the above-mentioned lithium metal negative electrode sheet, and / or the lithium metal negative electrode sheet prepared by the above-mentioned preparation method.

[0096] In the embodiment of the present invention, the battery structure includes but is not limited to button batteries, soft-pack batteries, cylindrical batteries, etc.

[0097] The present application has no particular restrictions on the positive electrode sheet, separator, and electrolyte in the battery, and those skilled in the art can select them according to actual needs as long as the purpose of the present application can be achieved.

[0098] The reagents, instruments or materials used in the present invention can be obtained through commercial channels.

[0099] The present invention will be further described below in conjunction with embodiments:

[0100] Embodiment 1:

[0101] The preparation method of the lithium metal negative electrode sheet of this embodiment is as follows:

[0102] (1) Preparation method of composite precursor material: Weigh 5 g of graphene oxide, add 1.5 g of L-ascorbic acid after ultrasonic treatment for 1 h, then add 15 mL of 0.8 mol / L antimony sulfate solution (containing 6.38 g of pure antimony sulfate), stir for 30 min, transfer to a hydrothermal reactor for a hydrothermal reaction at 150 ° C for 12 h, remove the lower slurry after the reaction is completed, wash it with ethanol and water for 3 times respectively, and dry it in a drying oven at 60 ° C for 12 h to obtain a composite precursor material;

[0103] (2) 5 g of the composite precursor material and the polypropylene glycol material were taken, and then 10 mL of acetone solution was added, heated and stirred in a 70°C water bath for 2 h, and then cooled. After cooling, the upper layer of liquid was poured out and the lower layer of slurry was washed with water and ethanol alternately for 6 times. After washing, it was dried in a drying oven at 60°C for 12 h to obtain an elastic composite material;

[0104] (3) 5 g of the dried elastic composite material was mixed with conductive carbon black (SP) and polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5, an appropriate amount of solvent NMP was added, and after grinding evenly, the slurry was scraped onto a copper foil and dried, and the thickness of the elastic composite layer was 20 μm;

[0105] (4) The magnetron sputtering method is used to sputter lithium metal onto the surface of the elastic composite material to prepare a composite negative electrode material. The thickness of the sputtered lithium is 30 μm. The structural schematic diagram of the lithium metal negative electrode sheet is shown in FIG. Figure 1 shown.

[0106] Embodiment 2:

[0107] The only difference between this embodiment and embodiment 1 is that the content of the polypropylene glycol material is changed to 3 g in step (2).

[0108] Embodiment 3:

[0109] The only difference between this embodiment and embodiment 1 is that the content of the polypropylene glycol material in step (2) is changed to 10 g.

[0110] Embodiment 4:

[0111] The only difference between this embodiment and embodiment 1 is that the polypropylene glycol material is replaced by polypropylene fiber in step (2).

[0112] Embodiment 5:

[0113] The only difference between this embodiment and embodiment 1 is that the polypropylene glycol material is replaced by nylon fiber in step (2).

[0114] Comparative Example 1:

[0115] The only difference between this comparative example and Example 1 is that no polypropylene glycol material is added in step (2).

[0116] Comparative Example 2:

[0117] The only difference between this comparative example and Example 1 is that no antimony sulfate solution is added in step (1).

[0118] Battery preparation and cycle performance testing

[0119] The lithium metal negative electrode sheets prepared in the examples and comparative examples and the NCM613 positive electrode sheets were used to form card batteries, and the electrochemical performance of the batteries was tested.

[0120] Electrochemical performance tests include:

[0121] (1) Gram capacity test: The test temperature is 25°C, and the test voltage range is 2.8-4.35V. After the battery is connected to the charging cabinet, it is first left to stand for 5 minutes, and then charged to 4.35V with a constant current of 0.1C. After standing for 5 minutes, it is discharged to 2.8V with a constant current of 0.1C. After standing for 5 minutes, the discharge capacity of the first cycle of 0.1C is recorded as the gram capacity.

[0122] (2) Cycle performance test: The test temperature is 25°C, the test voltage range is 2.8-4.35V, the battery is connected to the charging cabinet, first charged to 4.35V with a constant current of 0.1C, let it stand for 5 minutes, then discharged to 2.8V with a constant current of 0.1C and let it stand for 5 minutes, the discharge capacity at this time is recorded as the initial capacity of the battery, this step is repeated twice and then let it stand for 30 minutes to complete the formation step; charge to 4.35V with a constant current of 0.33C, then charge at a constant voltage to a current ≤0.05C, let it stand for 5 minutes, then discharge to 2.8V with a constant current of 0.5C and let it stand for 5 minutes, repeat this step until the battery reaches 80% of the initial capacity, and record the number of cycles.

[0123] Table 1 shows the gram capacity of lithium metal batteries and the battery cycle performance test results.

[0124] Table 1

[0125] Group Gram capacity (mAh / g) Cycle performance (cycle) Example 1 185 285 Example 2 177 256 Example 3 170 192 Example 4 161 150 Example 5 160 130 Comparative Example 1 160 125 Comparative Example 2 151 134

[0126] It can be seen from the above test results that embodiments 1-5 of the present invention can realize uniform deposition and stripping of lithium metal inside the elastic composite layer by constructing the elastic composite layer, and the material undergoes reversible expansion and contraction changes during the deposition and stripping process. Antimony is a lithium-philic element, which can induce uniform deposition of lithium metal at the negative electrode, and alleviate the uneven stress caused by the deposition and stripping of lithium metal. The added graphene material can not only provide active sites for the lithium-philic elements, but also enhance the conductivity of the negative electrode side and improve ion dynamics. Reduced graphene oxide is a very excellent elastic material, and polypropylene glycol material is also an organic material with very good elasticity, but the content of polypropylene glycol material added will affect the conductivity of the material. Therefore, an appropriate amount of polypropylene glycol material added can greatly alleviate the stress generated by the lithium metal battery during the deposition and stripping process, thereby improving the cycle performance of the lithium metal battery.

[0127] Since comparative example 1 does not add polypropylene glycol material, it cannot adapt well to the stress changes caused by lithium metal deposition. When the lithium metal is stripped, it cannot effectively shrink with the changes in the internal stress of the battery. The dendrite breakage causes dead lithium accumulation, resulting in poor cycle performance of the lithium metal battery.

[0128] In Comparative Example 2, since no antimony sulfate solution was added, the reduced graphene oxide was not loaded with lithium-philic elements, the conductivity of the elastic composite layer was poor, and the lithium metal could not be evenly deposited on the negative electrode surface, resulting in poor cycle performance of the lithium metal battery.

[0129] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lithium metal negative electrode sheet, characterized in that: The lithium metal negative electrode sheet comprises: (a) negative electrode current collector (1); (b) an elastic composite layer (2), the elastic composite layer (2) being arranged on at least one surface of the negative electrode current collector (1) in the thickness direction; the elastic composite layer (2) comprising an elastic composite material, the elastic composite material comprising a lithium-philic metal composite reduced graphene oxide and a polymer, the polymer having viscoelasticity; (c) a lithium metal layer (3), wherein the lithium metal layer (3) is arranged on a surface of the elastic composite layer (2) away from the negative electrode current collector (1).

2. The lithium metal negative electrode sheet according to claim 1, characterized in that: The lithium-philic metal is supported on the surface of the reduced graphene oxide; and / or, the lithium-philic metal comprises at least one of antimony, zinc, silver and tin; and / or, the viscosity of the polymer is 20 to 35 mPas and the elastic modulus is 50 to 80 Mpa; And / or, the polymer contains at least one of polypropylene glycol, polypropylene fiber, nylon fiber, polyester fiber, polyamide fiber, and derivatives thereof.

3. The lithium metal negative electrode sheet according to claim 1, characterized in that: The mass ratio of the lithium-philic metal to the reduced graphene oxide is (1.5-4.5):(3-10); The mass ratio of the lithium-philic metal composite reduced graphene oxide to the polymer is (1 to 1.6):(1 to 5).

4. The lithium metal negative electrode sheet according to claim 1, characterized in that: The elastic composite layer also includes a conductive agent and a binder; The mass ratio of the elastic composite material, the conductive agent and the binder is (90-95):(3-5):(2-5).

5. The lithium metal negative electrode sheet according to claim 1, characterized in that: The thickness of one side of the elastic composite layer is 15 to 30 μm; And / or, the single-side thickness of the lithium metal layer is 10 to 40 μm.

6. The method for preparing the lithium metal negative electrode sheet according to any one of claims 1 to 5, characterized in that: The steps include: S1, mixing graphene oxide, a lithium-philic metal salt, a reducing agent and water to obtain a mixed solution; subjecting the mixed solution to a hydrothermal reaction to obtain a lithium-philic metal composite reduced graphene oxide; S2, mixing the lithium-philic metal composite reduced graphene oxide, the polymer and the first solvent, heating and stirring, solid-liquid separation, and drying to obtain an elastic composite material; S3, mixing the elastic composite material, the conductive agent, the binder and the second solvent to obtain a slurry, and coating the slurry on at least one surface of the negative electrode current collector in the thickness direction to obtain a negative electrode current collector composited with an elastic composite layer; S4, disposing lithium metal on the surface of the elastic composite layer away from the negative electrode current collector to obtain a lithium metal negative electrode sheet.

7. The preparation method according to claim 6, characterized in that: In the step S1, the lithium-philic metal salt includes at least one of antimony sulfate, zinc sulfate, silver nitrate, and tin nitrate; and / or, the concentration of the lithium-philic metal salt in the mixed solution is 0.5 to 2 mol / L; And / or, the mass ratio of the graphene oxide to the lithium-philic metal salt is (0.3-0.8): (0.3-1); And / or, the reducing agent includes at least one of L-ascorbic acid, hydrazine hydrate, and hydroxylamine; And / or, the mass ratio of the graphene oxide to the reducing agent is (1-10):(0.5-5); And / or, the temperature of the hydrothermal reaction is 100-200° C., and the time of the hydrothermal reaction is 10-20 h.

8. The preparation method according to claim 6, characterized in that: In step S2, the first solvent includes at least one of acetone, ethylketone, benzene, ethanol, ether, xylene, and toluene; and / or, in g / mL, the ratio of the lithium-philic metal composite reduced graphene oxide to the solvent is (1 to 10):(5 to 15); And / or, the heating and stirring temperature is 50 to 90° C., and the heating and stirring time is 0.5 to 3 hours; In step S3, the second solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

9. The preparation method according to claim 6, characterized in that: In the step S4, lithium metal is disposed on the surface of the elastic composite layer away from the negative electrode current collector by magnetron sputtering.

10. A lithium metal battery, characterized in that: The lithium metal battery comprises the lithium metal negative electrode sheet as described in any one of claims 1 to 5, and / or the lithium metal negative electrode sheet prepared by the preparation method as described in any one of claims 6 to 9.

Images