Lithium metal negative electrode sheet, method of manufacturing the same, and lithium metal battery

Abstract

The application relates to the technical field of batteries, in particular to a lithium metal negative electrode sheet, a preparation method thereof and a lithium metal battery. The lithium metal negative electrode sheet comprises a negative electrode 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 metal-combined reduced graphene oxide and a polymer, and the polymer has viscoelasticity. The lithium metal negative electrode sheet can adapt to stress changes caused by lithium metal deposition and reduce dead lithium accumulation caused by dendrite fracture.

Description

TECHNICAL FIELD

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

[0002] Since the first commercial lithium-ion battery invented by Sony in 1991, the mainstream market has been using lithium-ion batteries. It has been popularized in all aspects of life, from small TV remote controls to large new energy vehicles. However, the energy density of such lithium-ion batteries has been close to its theoretical capacity limit (-300 Wh kg -1 ) due to the limitation of the energy density of the positive and negative electrodes. 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 technology, the development of new materials, the innovation of technology, and the problems of energy and environmental protection, lithium metal batteries have once again attracted the interest of researchers. Lithium metal is a very active metal element, but due to its small ionic radius and solvation, its standard oxidation-reduction potential as a negative electrode is lower than that of its homologues sodium and potassium, far exceeding the stable window of most electrolytes. The battery side reactions caused by extremely high electrochemical reactivity, lithium dendrites caused by uneven deposition, and the stress impact on the battery caused by severe volume change will all have a serious impact on the battery, further exacerbating the performance deterioration of the lithium metal negative electrode, and seriously hindering the application process of lithium metal batteries.

[0004] The internal structure of the battery is an important factor affecting the performance of lithium metal. The formation of dead lithium is often caused by the irreversible change of the internal structure of the battery due to the volume expansion of lithium metal, uneven local stress distribution, and the free growth of lithium metal. Studies have shown that lithium metal can generate a pressure of 100 MPa during deposition in the battery. During the charging process, lithium metal is more inclined to grow towards the gap without pressure, eventually leading to rapid growth of dendritic structures, resulting in rapid accumulation of dead lithium during the cycle process, and even battery failure. SUMMARY

[0005] Therefore, the present application provides a lithium metal negative electrode sheet, a preparation method thereof and a lithium metal battery. The lithium metal negative electrode sheet can adapt to the stress change caused by lithium metal deposition and reduce the accumulation of dead lithium caused by dendrite fracture.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] In a first aspect, the present application provides a lithium metal negative electrode sheet, which comprises:

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

[0009] (b) an elastic composite layer 2, the elastic composite layer 2 being arranged on at least one surface of the negative current collector 1 in a thickness direction; the elastic composite layer 2 comprising an elastic composite material, the elastic composite material comprising a lithiumophilic metal composite reduced graphene oxide and a polymer, the polymer having viscoelasticity;

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

[0011] In an embodiment of the present application, the lithiumophilic metal composite reduced graphene oxide comprises a lithiumophilic metal and a reduced graphene oxide, the lithiumophilic metal being loaded on a surface of the reduced graphene oxide.

[0012] In an embodiment of the present application, the lithiumophilic metal comprises at least one of antimony, zinc, silver and tin.

[0013] In an embodiment of the present application, the polymer has a viscosity of 20-35 mPas and an elastic modulus of 50-80 MPa.

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

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

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

[0017] In an embodiment of the present application, the elastic composite layer further comprises 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 10-40 μm.

[0021] In a second aspect, the present application provides a preparation method of the above lithium metal negative electrode sheet, comprising the following steps:

[0022] S1, mixing graphene oxide, a lithiumophilic metal salt, a reducing agent and water to obtain a mixed solution; performing a hydrothermal reaction on the mixed solution to obtain a lithiumophilic metal composite reduced graphene oxide;

[0023] S2, mixing the liphilic metal complex-reduced graphene oxide, the polymer and the first solvent, performing heating 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, 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 with an elastic composite layer;

[0025] 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.

[0026] In the embodiment of the present application, in step S1, the liphilic metal salt includes at least one of antimony sulfate, zinc sulfate, silver nitrate and tin nitrate.

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

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

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

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

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

[0032] In the embodiment of the present application, in step S2, the first solvent includes at least one of acetone, ethyl ketone, benzene, ethanol, diethyl ether, dimethylbenzene and methylbenzene.

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

[0034] Preferably, the temperature of the heating stirring is 50-90℃, and the time of the heating stirring is 0.5-3h.

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

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

[0037] In a third aspect, the present application provides a lithium metal battery, which comprises the lithium metal negative electrode sheet described above, and / or the lithium metal negative electrode sheet prepared by the preparation method described above.

[0038] Compared with the prior art, the present application has the beneficial effects that:

[0039] The present application combines the polymer with viscoelasticity with the reduced graphene oxide which also has elasticity and good conductivity, to prepare an elastic composite material which can adapt to the stress change caused by lithium metal deposition, expand when lithium metal is deposited to accommodate more lithium metal, generate less solid electrolyte interface film (SEI), and shrink when lithium metal is stripped to reduce the accumulation of dead lithium caused by dendrite fracture; however, the polymer has poor conductivity, which may hinder the deposition of lithium ions in the cycle process, therefore, the present application loads lithium metal-philic atoms on the three-dimensional reduced graphene oxide to improve the conductivity of the elastic composite layer in cooperation with the reduced graphene oxide.

[0040] The present application combines the lithium metal-philic elements with the elastic material, which can make the lithium metal uniformly deposited on the negative electrode surface, further solve the problem of uneven lithium metal deposition in the cycle process of the lithium metal battery, and improve the cycle stability of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 It is a structural schematic diagram of the lithium metal negative electrode sheet.

[0042] The reference signs are as follows:

[0043] 1: negative electrode current collector;

[0044] 2: elastic composite layer;

[0045] 3: lithium metal layer. DETAILED DESCRIPTION

[0046] The present application discloses a lithium metal negative electrode sheet, a preparation method thereof and a lithium metal battery, and those skilled in the art can refer to the content herein to realize the process parameters by appropriate improvement. It is particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are all regarded as included in the present application. The method and application of the present application have been described by the preferred embodiments, and the related personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

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

[0048] In the description of the present application, the list of items connected by the term "at least one of" or other similar terms means 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; 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 can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0049] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be roughly about the ranges or values. For ranges, the endpoints are included; for values, the values are included. Ranges between, including the values, individual values, and ranges of values, can each be combined with other ranges or values to form new ranges or values. These can be inferred, from the above examples, and should be considered an explicit part of this disclosure.

[0050] If not specifically explained, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0051] If not specifically explained, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0052] If not specifically explained, the "includes" and "contains" mentioned in the present application represent open-ended and closed-ended. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

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

[0054] In a first aspect, the present application provides a lithium metal negative electrode sheet, which comprises:

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

[0056] (b) an elastic composite layer 2, the elastic composite layer 2 is arranged on at least one surface of the negative current collector 1 in the thickness direction; the elastic composite layer 2 comprises an elastic composite material, and the elastic composite material comprises a lithiumophilic metal composite reduced graphene oxide and a polymer;

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

[0058] In the embodiment of the present application, the lithiumophilic metal composite reduced graphene oxide comprises a lithiumophilic metal and reduced graphene oxide, and the lithiumophilic metal is loaded on the surface of the reduced graphene oxide. The lithiumophilic metal atoms are loaded on the three-dimensional reduced graphene oxide, and cooperates with the reduced graphene oxide to improve the conductivity of the elastic composite layer.

[0059] In the embodiment of the present application, the lithiumophilic metal comprises at least one of antimony, zinc, silver and tin.

[0060] The polymer with viscoelasticity in the present application refers to a kind of polymer material with viscoelasticity synthesized by high molecular chemistry. They are usually composed of linear, network, star-shaped and cross-linked polymers, and the most remarkable feature is that they can quickly recover shape within a certain range, while having reversible deformation and programmable deformation ability.

[0061] In the embodiment of the present application, the polymer is a high polymer. High polymer, namely high molecular polymer, generally refers to a compound with a relative molecular mass of up to several thousand to several million. High polymers are composed of thousands of atoms connected to each other by covalent bonds, although their relative molecular mass is very large, but they are connected in a simple structural unit and repeated manner.

[0062] In the embodiment of the present application, the viscosity of the polymer is 20-35 mPas, and the elastic modulus is 50-80 Mpa. For example, the viscosity of the polymer is any value in 20 mPas, 22 mPas, 24 mPas, 26 mPas, 28 mPas, 30 mPas, 32 mPas, 34 mPas, 35 mPas or any value within the range formed by any two of the above values, and the elastic modulus is any value in 50 Mpa, 60 Mpa, 70 Mpa, 80 Mpa or any value within the range formed by any two of the above values.

[0063] In the embodiment of the present application, 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 large viscoelasticity, and is combined with reduced graphene oxide which not only has elasticity but also has good conductivity, so that the elastic composite material can adapt to the stress change caused by lithium metal deposition, expand when lithium metal is deposited to accommodate more lithium metal, generate less solid electrolyte interface film (SEI), and shrink when lithium metal is peeled off to reduce the accumulation of dead lithium caused by dendrite fracture.

[0064] The polymers of the present application can be prepared by conventional methods in the art, generally by polymerization of monomers to obtain high molecular weight polymeric materials. For example, polypropylene glycol polymers are generally obtained by condensation of propylene oxide with propylene glycol in the presence of high pressure or an acidic catalyst. For another example, see the patent application CN118638308A which discloses a method for preparing nylon fibers, comprising the following steps: S1, mixing nylon hard segment, end-capping agent and water, and then polymerizing to obtain a double-end carboxyl nylon hard segment; S2, adding the product of S1, polyether polyol, and additives into a reaction kettle, and then polymerizing to obtain a high-end carboxyl content pre-polymer nylon; S3, solid-phase polymerizing the product of S2 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] As preferred, the mass ratio of the lithiumophilic metal to the reduced graphene oxide is (1.5-4.5):(3-10). Exemplarily, the mass ratio of the lithiumophilic metal to the reduced graphene oxide is any value in the range of any two values selected from 1.5:10, 2:7, 3:5, 4:3.5, and 4.5:3. Within the range, the lithiumophilic metal composite reduced graphene oxide can have enhanced conductivity. When the proportion of the lithiumophilic metal is too small, the lithiumophilic property of the lithiumophilic metal composite reduced graphene oxide material is weakened, the lithium ion transmission capacity is reduced, and the cycle performance of the battery is deteriorated; when the proportion of the lithiumophilic metal is too large, the loading capacity of the reduced graphene oxide is exceeded.

[0066] As preferred, the mass ratio of the lithiumophilic metal composite reduced graphene oxide to the polymer is (1-1.6):(1-5). Exemplarily, the mass ratio of the lithiumophilic metal composite reduced graphene oxide to the polymer is any value in the range of any two values selected from 1:5, 1.2:4, 1.4:3, and 1.6:1. Within the range, the lithiumophilic metal composite reduced graphene oxide not only has good conductivity, but also has good elastic strength, so that the elastic composite material can adapt to the stress change caused by lithium metal deposition, expand when lithium metal is deposited to accommodate more lithium metal, generate less solid electrolyte interface film (SEI), and shrink when lithium metal is peeled off to reduce the accumulation of dead lithium caused by dendrite fracture.

[0067] In the embodiments of the present application, 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 application, the conductive agent comprises 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 application, the binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and sodium carboxymethyl cellulose (CMC-Na).

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

[0071] Preferably, the single-side thickness of the elastic composite layer is 15-30 μm. For example, the single-side thickness of the elastic composite layer is any one of 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 formed by any two of the above values. When the single-side thickness of the elastic composite layer is too small, the elastic composite material cannot well adapt to the stress change caused by the deposition of lithium metal, which may cause the accumulation of dead lithium caused by dendrite fracture; when the single-side thickness of the elastic composite layer is too large, the energy density of the battery may be reduced.

[0072] Preferably, the single-side thickness of the lithium metal layer is 10-40 μm. For example, the single-side thickness of the lithium metal layer is any one of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or any value within the range formed by any two of the above values. When the thickness of the lithium metal layer is too small, the supply of lithium may be insufficient; when the thickness of the lithium metal layer is too large, the energy density of the battery may be reduced.

[0073] In a second aspect, the present application provides a preparation method of the above lithium metal negative electrode sheet, comprising the following steps:

[0074] S1, mixing graphene oxide, a lithiumophilic metal salt, a reducing agent, and water to obtain a mixed solution; performing hydrothermal reaction on the mixed solution to obtain lithiumophilic metal composite reduced graphene oxide;

[0075] S2, mixing the lithiumophilic metal composite reduced graphene oxide, a polymer, and a first solvent, performing 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 with an elastic composite layer;

[0077] 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.

[0078] In the embodiments of the present application, in step S1, the lithiumophilic metal salt includes at least one of antimony sulfate, zinc sulfate, silver nitrate, and tin nitrate.

[0079] Preferably, the concentration of the lithiumophilic metal salt in the mixed solution is 0.5-2 mol / L. For example, the concentration of the lithiumophilic metal salt in the mixed solution is any one of 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 formed by any two of the above values.

[0080] Preferably, the mass ratio of graphene oxide to lithiumophilic metal salt is (0.3-0.8):(0.3-1). For example, the mass ratio of graphene oxide to lithiumophilic metal salt is any one of 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 formed by any two of the above values.

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

[0082] Preferably, the mass ratio of graphene oxide to reducing agent is (1-10):(0.5-5). For example, the mass ratio of graphene oxide to reducing agent is any one of 1:5, 3:5, 5:3, 7:2, 9:1, 10:0.5, or any value within the range formed by 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 10-20 h. For example, the temperature of the hydrothermal reaction is any one of 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, or any value within the range formed by any two of the above values, and the time of the hydrothermal reaction is any one of 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, or any value within the range formed by any two of the above values.

[0084] In the embodiments of the present application, in step S1, after the hydrothermal reaction, a first cleaning step and a first drying step are further included.

[0085] In the embodiment of the present application, the first cleaning in step S1 is that the lower layer slurry is washed with ethanol and water respectively for 2-5 times.

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

[0087] In the embodiment of the present application, in step S2, the first solvent includes at least one of acetone, ethyl ketone, benzene, ethanol, diethyl ether, dimethylbenzene, and toluene.

[0088] Preferably, the ratio of the amount of the lithiumophilic metal composite reduced graphene oxide to the solvent is (1-10):(5-15) in g / mL. For example, the ratio of the amount of the lithiumophilic metal composite reduced graphene oxide to the solvent is any one of 1:15, 3:13, 5:11, 7:9, 9:7, 2:1 or any value within the range formed by any two of the above values.

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

[0090] In the embodiment of the present application, in step S2, after the heating and stirring, the second cleaning and the second drying are further included.

[0091] In the embodiment of the present application, the second cleaning in step S2 is that the lower layer slurry is washed with water and ethanol respectively for 4-8 times.

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

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

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

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

[0096] In the embodiments of the application, the battery structure includes, but is not limited to, a button cell, a soft package battery, a cylindrical battery, and the like.

[0097] The positive plate, the separator, and the electrolyte in the battery are not particularly limited in the application, and can be selected by a person skilled in the art according to actual needs, as long as the purpose of the application can be achieved.

[0098] The reagents, instruments, and materials used in the application can be obtained through commercial channels.

[0099] The application will be further described below in combination with examples:

[0100] Example 1

[0101] The preparation method of the lithium metal negative plate in this example is as follows:

[0102] (1) Preparation method of the composite precursor material: 5 g of graphene oxide was weighed, ultrasonically treated for 1 h, then 1.5 g of L-ascorbic acid was added, and then 0.8 mol / L 15 mL of antimony sulfate solution (containing 6.38 g of pure antimony sulfate) was added. After stirring for 30 min, the slurry was transferred to a hydrothermal reaction kettle for hydrothermal reaction at 150℃ for 12 h. After the reaction was completed, the lower layer of the slurry was washed with ethanol and water for 3 times respectively, and then dried in a drying oven at 60℃ for 12 h to obtain the composite precursor material.

[0103] (2) 5 g of the composite precursor material and 5 g of polypropylene glycol material were taken, and then 10 mL of acetone solution was added. After heating and stirring in a water bath at 70℃ for 2 h, the upper liquid was poured out after cooling, and then the lower slurry was washed with water and ethanol alternately for 6 times. After washing, the slurry was dried in a drying oven at 60℃ 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) according to a mass ratio of 90:5:5, and an appropriate amount of solvent NMP was added. After grinding uniformly, the slurry was scraped and coated on a copper foil and dried. The thickness of the elastic composite layer was 20 μm.

[0105] (4) Lithium metal was sputtered on the surface of the elastic composite material by using a magnetron sputtering method to prepare a composite negative material. The thickness of the sputtered lithium was 30 μm. The structure of the lithium metal negative plate is shown in Figure 1 .

[0106] Example 2

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

[0108] Example 3:

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

[0110] Example 4:

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

[0112] Example 5:

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

[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] Preparation of batteries and cycle performance test

[0119] The lithium metal negative electrode sheets prepared in the examples and comparative examples are combined with NCM613 positive electrode sheets to form card batteries, and the batteries are subjected to electrochemical performance tests.

[0120] The electrochemical performance test includes:

[0121] (1) Gram capacity 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 static for 5 min, then charged to 4.35V at 0.1C constant current, static for 5 min, then discharged to 2.8V at 0.1C constant current, static for 5 min, and the discharge capacity of the first cycle at 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 at 0.1C constant current, static for 5 min, then discharged to 2.8V at 0.1C constant current, static for 5 min, and the discharge capacity at this time is recorded as the initial capacity of the battery, and the process is repeated twice and static for 30 min to complete the formation process; charged to 4.35V at 0.33C constant current, then constant voltage charged to current≤0.05C, static for 5 min, then discharged to 2.8V at 0.5C constant current, static for 5 min, and the process is repeated until the cycle number reaches 80% of the initial capacity of the battery, and the cycle number is recorded.

[0123] Table 1 is the specific capacity and cycle performance test results of lithium metal batteries.

[0124] Table 1

[0125] Group Capacity (mAh / g) Cycling 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] From the above test results, it can be seen that by constructing the elastic composite layer, embodiments 1-5 of the present application can realize uniform deposition and stripping of lithium metal inside it, and the material undergoes reversible expansion and contraction during deposition and stripping. Antimony is a lithiumophilic element, which can induce uniform deposition of lithium metal on the negative electrode, slow down the stress unevenness caused by lithium metal deposition and stripping, and the added graphene material not only provides active sites for lithiumophilic elements, but also enhances the conductivity of the negative electrode side and improves ion kinetics. Reduced graphene oxide is a very excellent elastic material, and polypropylene glycol material is also a very good elastic organic material, but the content of polypropylene glycol material added will affect the conductivity of the material, therefore, appropriate amount of polypropylene glycol material can greatly relieve the stress generated during the deposition and stripping process of lithium metal battery, and thus improve the cycle performance of lithium metal battery.

[0127] Comparative Example 1 cannot well adapt to the stress change caused by lithium metal deposition due to the absence of polypropylene glycol material, and cannot effectively shrink with the change of the internal stress of the battery during lithium metal stripping, resulting in accumulation of dead lithium caused by dendrite fracture, which leads to poor cycle performance of lithium metal battery.

[0128] Comparative Example 2 has poor conductivity of the elastic composite layer due to the absence of antimony sulfate solution and the reduced graphene oxide not loaded with lithiumophilic elements, and the lithium metal cannot be uniformly deposited on the surface of the negative electrode, resulting in poor cycle performance of the lithium metal battery.

[0129] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered within the scope of protection of the present application.

Claims

1. A lithium metal negative electrode sheet, characterized by, The lithium metal negative electrode sheet comprises: (a) a negative current collector (1); (b) an elastic composite layer (2) provided on at least one surface of the negative current collector (1) in the thickness direction; the elastic composite layer (2) comprises an elastic composite material, the elastic composite material comprises lithiumophilic metal composite reduced graphene oxide and a polymer, the polymer has viscoelasticity; the lithiumophilic metal is loaded on the surface of the reduced graphene oxide; the polymer contains at least one of polypropylene glycol, polypropylene fiber, nylon fiber, polyester fiber and polyamide fiber; the mass ratio of the lithiumophilic metal to the reduced graphene oxide is (1.5-4.5):(3-10); the mass ratio of the lithiumophilic metal composite reduced graphene oxide to the polymer is (1-1.6):(1-5); the single-sided thickness of the elastic composite layer is 15-30 μm; (c) a lithium metal layer (3) provided on the surface of the elastic composite layer (2) away from the negative current collector (1).

2. The lithium metal negative electrode sheet of claim 1, wherein, The lithiumophilic metal comprises at least one of antimony, zinc, silver and tin; And / or, the viscosity of the polymer is 20-35 mPas, and the elastic modulus is 50-80 Mpa.

3. The lithium metal negative electrode sheet of claim 1, wherein, The elastic composite layer further comprises 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).

4. The lithium metal negative electrode sheet of claim 1, wherein, The single-sided thickness of the lithium metal layer is 10-40 μm.

5. The method of producing the lithium metal negative electrode sheet according to any one of claims 1 to 4, characterized by, The method comprises the following steps: S1. Mixing graphene oxide, lithiumophilic metal salt, reducing agent and water to obtain a mixed solution; performing hydrothermal reaction on the mixed solution to obtain lithiumophilic metal composite reduced graphene oxide; S2. Mixing the lithiumophilic metal composite reduced graphene oxide, a polymer and a first solvent, performing heating and stirring, solid-liquid separation and drying to obtain an elastic composite material; S3. Mixing the elastic composite material, a conductive agent, a binder and a second solvent to obtain slurry, coating the slurry on at least one surface of the negative current collector in the thickness direction to obtain a negative current collector with an elastic composite layer; S4. Providing lithium metal on the surface of the elastic composite layer away from the negative current collector to obtain a lithium metal negative electrode sheet.

6. The production method according to claim 5, wherein In the step S1, the lithiumophilic metal salt comprises at least one of antimony sulfate, zinc sulfate, silver nitrate and tin nitrate; And / or, the concentration of the lithiumophilic metal salt in the mixed solution is 0.5-2 mol / L; And / or, the mass ratio of the graphene oxide to the lithiumophilic metal salt is (0.3-0.8):(0.3-1); And / or, the reducing agent comprises 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℃, and the time of the hydrothermal reaction is 10-20 h.

7. The preparation method according to claim 5, characterized in that, In the step S2, the first solvent comprises at least one of acetone, ethyl ketone, benzene, ethanol, diethyl ether, dimethylbenzene and methylbenzene. And / or, the ratio of the amount of the lithium-philic metal to the solvent is (1-10):(5-15) in g / mL; And / or, the temperature of the heating and stirring is 50-90 ℃, and the time of the heating and stirring is 0.5-3 h. In the step S3, the second solvent comprises at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

8. The preparation method according to claim 5, characterized in that, In the step S4, lithium metal is disposed on the surface of the elastic composite layer away from the negative current collector by a magnetron sputtering method.

9. A lithium metal battery, characterized in that, The lithium metal battery comprises the lithium metal negative electrode sheet according to any one of claims 1-4, and / or the lithium metal negative electrode sheet prepared by the preparation method according to any one of claims 5-8.

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