Composite lithium carbon material and preparation method thereof, negative electrode and electrochemical device

Abstract

The invention discloses a composite lithium carbon material and a preparation method thereof, a negative electrode and an electrochemical device. The composite lithium carbon material includes: a hard carbon material including a plurality of hard carbon particles; the metal particle adhesion layer comprises a plurality of metal particles adhered to the surfaces of the hard carbon particles; the plurality of metal particles include silver particles, and a portion of the surface of the hard carbon particles is exposed through gaps between the plurality of metal particles; the metal particle adhesion layer is coated with the metal lithium coating layer, and part of the metal lithium coating layer makes contact with part of the surfaces, among the multiple metal particles, of the hard carbon particles. According to the composite lithium-carbon material disclosed by the embodiment of the invention, through the contained hard carbon material, the surface current density can be effectively reduced, lithium ions are promoted to be uniformly embedded into a lithium-carbon composite interface, and the problem of lithium dendrite growth of a lithium metal negative electrode is effectively relieved.

Description

Technical Field

[0001] The present application belongs to the field of lithium battery technology, and in particular relates to a composite lithium-carbon material and a preparation method thereof, a negative electrode, and an electrochemical device. Background Art

[0002] The continuous consumption of fossil fuels has led to an increase in demand for renewable energy sources such as solar and wind energy. However, due to natural conditions, solar and wind energy can only provide intermittent energy, which requires the continuous development of energy storage devices. Lithium-ion batteries are widely used in consumer electronics and electric vehicles due to their characteristics such as no memory effect and low self-discharge. However, the energy density of lithium-ion batteries has reached a bottleneck (300Wh / kg). Lithium metal batteries are an important type of battery system with a higher energy density (>400Wh / kg), which makes devices using lithium metal batteries lighter and have a longer service life. Therefore, lithium metal batteries are expected to be more widely used in portable electronic products and other fields. Secondly, lithium metal batteries have a higher voltage, which can make electronic products work better than other chemical batteries. In addition, with the continuous development of technology, rechargeable lithium metal batteries have appeared and have significantly improved in safety and electrical performance.

[0003] However, the chemical properties of lithium metal are very active, which makes the processing, storage and use of lithium metal very demanding on the environment. In addition, lithium metal anodes face problems such as increased polarization, short circuit and even thermal runaway caused by dendrite growth. The uneven distribution of current density on the electrode surface and the uneven diffusion of lithium ions at the solid electrolyte interface are one of the main reasons for the growth of lithium dendrites. Summary of the invention

[0004] The embodiment of the present application provides a method for preparing a composite lithium-carbon material, which can be used to prepare a composite lithium-carbon material; the composite lithium-carbon material can effectively reduce the surface current density, promote the uniform embedding of lithium ions into the lithium-carbon composite interface, and effectively alleviate the problem of metal lithium dendrite growth.

[0005] In a first aspect, the present application provides a composite lithium-carbon material, comprising: a hard carbon material, comprising a plurality of hard carbon particles; a metal particle attachment layer, comprising a plurality of metal particles attached to the surface of the hard carbon particles; the plurality of metal particles comprising silver particles, wherein a portion of the surface of the hard carbon particles is exposed through the gaps between the plurality of metal particles; a metal lithium coating layer, disposed on the metal particle attachment layer, wherein a portion of the metal lithium coating layer is in contact with a portion of the surface of the hard carbon particles between the plurality of metal particles.

[0006] According to an embodiment of the first aspect of the present application, the hard carbon particles are spherical.

[0007] According to an embodiment of the first aspect of the present application, the hard carbon particles have a hollow structure.

[0008] According to an embodiment of the first aspect of the present application, the average particle size of the hard carbon particles is 8 μm to 12 μm.

[0009] According to an embodiment of the first aspect of the present application, the thickness of the metal particle attachment layer on the surface of the hard carbon particles is 50nm to 300nm.

[0010] According to an embodiment of the first aspect of the present application, the thickness of the metal lithium coating layer is 0.1 μm to 5 μm.

[0011] According to an embodiment of the first aspect of the present application, the specific surface area of ​​the hard carbon particles is 0.056 m 2 / cm 3 ~0.083m 2 / cm 3 .

[0012] According to an embodiment of the first aspect of the present application, the mass ratio of the sum of the mass of the hard carbon particles and the silver particles to the mass of the metal lithium coating layer is 1:(3-5).

[0013] According to an embodiment of the first aspect of the present application, the average particle size of the composite lithium-carbon material is 8 μm to 17 μm.

[0014] In a second aspect, the present application provides a method for preparing a composite lithium-carbon material, comprising:

[0015] Providing hard carbon materials;

[0016] The hard carbon material is immersed in a mixed solution of a silver ammonia solution and an aldehyde compound capable of producing a silver mirror reaction and subjected to an oscillating treatment to form a metal particle attachment layer on the surface of the hard carbon particles, thereby obtaining a silver-plated hard carbon material;

[0017] A metallic lithium coating layer is formed on the surface of the silver-plated hard carbon material to obtain a composite lithium-carbon material.

[0018] According to an embodiment of the second aspect of the present application, providing the hard carbon material includes obtaining the desired hard carbon material through commercial channels.

[0019] According to an embodiment of the second aspect of the present application, providing the hard carbon material includes: performing a water removal treatment on the hard carbon material before use.

[0020] According to an embodiment of the second aspect of the present application, the water removal treatment includes vacuum drying the hard carbon material at 60° C. to 110° C. for 48 hours to 72 hours.

[0021] According to an embodiment of the second aspect of the present application, a silver ammonia solution is prepared according to the following steps: preparing a silver nitrate aqueous solution with a mass fraction of 2wt.% to 10wt.%; adding a sodium hydroxide aqueous solution with a mass fraction of 10wt.% to 20wt.% to the silver nitrate aqueous solution until a white precipitate is visible to obtain a suspension; adding a 2wt.% to 5wt.% ammonia aqueous solution to the suspension until the white precipitate is dissolved to obtain a silver ammonia solution.

[0022] According to an embodiment of the second aspect of the present application, the aldehyde compound capable of undergoing a silver mirror reaction is selected from formic acid, formaldehyde, acetaldehyde, glyoxal, propionaldehyde, glucose, maltose, methyl formate, ethyl formate, propyl formate or a combination thereof.

[0023] According to an embodiment of the second aspect of the present application, a metallic lithium coating layer is formed on the surface of the silver-plated hard carbon material by vacuum thermal evaporation, comprising:

[0024] In a vacuum reaction chamber, metallic lithium and silver-plated hard carbon material are placed in a reaction vessel, and the silver-plated hard carbon material is placed above the reaction vessel. By heating to above 1400°C, the metallic lithium is sublimated and adheres to the surface of the silver-plated hard carbon material to form a metallic lithium coating layer.

[0025] According to an embodiment of the second aspect of the present application, the reaction container is a molybdenum crucible.

[0026] According to an embodiment of the second aspect of the present application, metallic lithium and silver-plated hard carbon material are placed in a vacuum reaction chamber in a mass ratio of (3-5):1.

[0027] According to an embodiment of the second aspect of the present application, the method for preparing a composite lithium-carbon material further includes: drying the silver-plated hard carbon material to obtain a silver-plated hard carbon material from which moisture has been removed.

[0028] According to the embodiment of the second aspect of the present application, the step of placing metallic lithium and silver-plated hard carbon material in a vacuum reaction chamber, and the step of opening the vacuum reaction chamber to take out the composite lithium-carbon material need to be carried out in an environment with a water content of less than 0.1 ppm and an oxygen value of less than 0.1 ppm.

[0029] The preparation method of the composite lithium-carbon material in the embodiment of the present application is to cause a silver mirror reaction on the surface of a hard carbon material through a silver ammonia solution and an aldehyde compound capable of undergoing a silver mirror reaction, thereby forming a metal particle attachment layer on the surface of the hard carbon particles to obtain a silver-plated hard carbon material; and forming a metal lithium coating layer on the surface of the silver-plated hard carbon material to prepare a composite lithium-carbon material.

[0030] The composite lithium-carbon material of the embodiment of the present application can effectively reduce the surface current density through the hard carbon material contained, promote the uniform embedding of lithium ions into the lithium-carbon composite interface, and effectively alleviate the problem of lithium dendrite growth at the lithium metal negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] Figure 1 It is a schematic diagram of the process of preparing the composite lithium-carbon material provided in the embodiment of the present application.

[0033] Figure 2 This is a surface atomic force microscope image of the silver metal particle attachment layer formed by the composite lithium-carbon material provided in Example 1 of the present application, wherein the unit length is 1 μm.

[0034] Figure 3 This is a surface atomic force microscope image of the silver metal particle attachment layer formed by the composite lithium-carbon material provided in Example 2 of the present application, wherein the unit length is 1 μm.

[0035] Figure 4 This is a surface atomic force microscope image of the silver metal particle attachment layer formed by the composite lithium-carbon material provided in Example 3 of the present application, wherein the unit length is 1 μm.

[0036] Figure 5 This is a cycle performance diagram of the composite lithium-carbon material provided in Example 1 of the present application after being applied to an NCM811 battery.

[0037] Figure 6 This is a coulombic efficiency diagram after the composite lithium-carbon material provided in Example 1 of the present application is applied to an NCM811 battery.

[0038] Figure 7 This is a cycle performance diagram of the NCM811 battery with metallic lithium as the negative electrode provided in Comparative Example 1.

[0039] Figure 8 This is the coulombic efficiency diagram of the NCM811 battery with metallic lithium as the negative electrode provided in Comparative Example 1. DETAILED DESCRIPTION

[0040] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0041] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0042] In order to solve the problems of the prior art, the present application provides a composite lithium-carbon material and a preparation method thereof. The preparation method of the composite lithium-carbon material provided in the present application is first introduced below.

[0043] Figure 1 A schematic diagram of the process for preparing the composite lithium-carbon material provided in an embodiment of the present application.

[0044] like Figure 1 As shown, the preparation method of the composite lithium-carbon material includes: providing a hard carbon material; immersing the hard carbon material in a mixed solution of a silver ammonia solution and an aldehyde compound capable of undergoing a silver mirror reaction and oscillating the mixture to form a metal particle attachment layer on the surface of the hard carbon particles to obtain a silver-plated hard carbon material; and forming a metal lithium coating layer on the surface of the silver-plated hard carbon material to obtain a composite lithium-carbon material.

[0045] The preparation method of the composite lithium-carbon material in the embodiment of the present application is to generate a silver mirror reaction on the surface of the hard carbon material through a silver ammonia solution and an aldehyde-containing compound, thereby forming a metal particle attachment layer on the surface of the hard carbon particles to obtain a silver-plated hard carbon material; and forming a metal lithium coating layer on the surface of the silver-plated hard carbon material to obtain a composite lithium-carbon material.

[0046] In some embodiments of the present application, the hard carbon material can be obtained through commercial channels. Optionally, the hard carbon material can be Kuraray type 2 hard carbon material, which has an average diameter of 9 μm.

[0047] In some embodiments of the present application, the specific surface area of ​​the hard carbon material is 0.056 m 2 / cm 3 ~0.083m 2 / cm 3 .

[0048] In the embodiments of the present application, the hard carbon material has disorderly stacked graphene-like layers, as well as defects and holes between the carbon layers, and thus has a large specific surface area.

[0049] In the embodiments of the present application, the defects and holes on the surface of the hard carbon material have a large specific surface area, which is conducive to the silver particles being dispersed and attached to the surface of the hard carbon material in a discrete form, forming a continuous or dispersed silver metal particle attachment layer, and in the subsequent preparation steps, it is conducive to the attachment of sublimated metal lithium to form a metal lithium coating layer with uniform thickness. And in subsequent applications, the adsorption-embedding of defects and holes on the surface promotes the embedding of lithium ions into the lithium-carbon composite interface, realizes the storage of lithium, and prevents the growth of lithium dendrites. And the hard carbon material has a large specific surface area, which can effectively reduce the surface current density. It should be noted that multiple silver particles are adjacent to part of the surface of the hard carbon particles, and a continuous metal particle attachment layer can be formed. It can be understood that the hard carbon particles can also form discontinuous, spaced and dispersed silver particles on the surface of the hard carbon particles in the silver ammonia solution, and the metal particle attachment layer is formed by the dispersed silver particles.

[0050] In some embodiments of the present application, the method for preparing the composite lithium-carbon material further includes: dehydrating the hard carbon material before use.

[0051] In some embodiments of the present application, the dehydration treatment of the hard carbon material includes vacuum drying the hard carbon material at 60° C. to 110° C. for 48 hours to 72 hours.

[0052] In some embodiments of the present application, the silver ammonia solution is prepared according to the following steps: preparing a silver nitrate aqueous solution with a mass fraction of 2wt.% to 10wt.%; adding a sodium hydroxide aqueous solution with a mass fraction of 10wt.% to 20wt.% to the silver nitrate aqueous solution until a white precipitate is visible to obtain a suspension; adding a 2wt.% to 5wt.% ammonia aqueous solution to the suspension until the white precipitate is dissolved to obtain a silver ammonia solution.

[0053] In some embodiments of the present application, the aldehyde compound capable of undergoing a silver mirror reaction is selected from formic acid, formaldehyde, acetaldehyde, glyoxal, propionaldehyde, glucose, maltose, methyl formate, ethyl formate, and propyl formate.

[0054] In some embodiments of the present application, the temperature of the mixture of the silver ammonia solution and the aldehyde compound capable of undergoing a silver mirror reaction is 300°C to 500°C, and the reaction time of the hard carbon material in the mixture of the silver ammonia solution and the aldehyde compound capable of undergoing a silver mirror reaction is 10 minutes to 50 minutes.

[0055] In some embodiments of the present application, a metallic lithium coating layer is formed on the surface of the silver-plated hard carbon material by vacuum thermal evaporation, including: in a vacuum reaction chamber, placing metallic lithium and the silver-plated hard carbon material into a reaction vessel, and placing the silver-plated hard carbon material above the reaction vessel, and heating the metallic lithium to above 1400°C to allow the metallic lithium to sublime and adhere to the surface of the silver-plated hard carbon material to form a metallic lithium coating layer, thereby obtaining a composite lithium-carbon material.

[0056] In some embodiments of the present application, the reaction container is a molybdenum crucible.

[0057] In some embodiments of the present application, during the process of forming the metal lithium coating layer, the evaporation rate of the lithium layer is 0.5nm / s to 0.8nm / s, and metal lithium coating layers of different thicknesses can be obtained by controlling the evaporation time. During the vacuum thermal evaporation process, the temperature of the surface of the silver-plated hard carbon material placed above the molybdenum crucible is 200℃ to 300℃, which can effectively avoid the problem of silver dissolution.

[0058] In some embodiments of the present application, metallic lithium and silver-plated hard carbon material are placed in a vacuum reaction chamber in a mass ratio of (3-5):1.

[0059] In some embodiments of the present application, the step of placing metallic lithium and silver-plated hard carbon material in a vacuum reaction chamber at a mass ratio of (3-5):1 includes: placing metallic lithium at the bottom of a reaction container in the vacuum reaction chamber, and placing the silver-plated hard carbon material at the top of the reaction container in the vacuum reaction chamber. In this way, the metallic lithium can be attached to the surface of the silver-plated hard carbon material from bottom to top during the sublimation process, forming a metallic lithium coating layer, and obtaining a composite lithium-carbon material.

[0060] In some embodiments of the present application, the step of placing metallic lithium and silver-plated hard carbon material in a vacuum reaction chamber, and the step of opening the vacuum reaction chamber to take out the composite lithium-carbon material need to be carried out in an environment with a water content of less than 0.1 ppm and an oxygen value of less than 0.1 ppm, so as to reduce the influence of water and oxygen on the composite lithium-carbon material containing a metallic lithium coating layer.

[0061] In some embodiments of the present application, the vacuum reaction chamber needs to be completely airtight to prevent the metallic lithium from contacting with air. In addition, the bottom of the reaction container in the vacuum reaction chamber is inert to the metallic lithium and is not easy to react with the metallic lithium. Optionally, the reaction container is a molybdenum crucible.

[0062] The preparation method of the composite lithium-carbon material in the embodiment of the present application is to first plate granular metallic silver on the surface of the hard carbon material using the silver mirror reaction to form a metal particle attachment layer, and then heat the metallic lithium and the silver-plated hard carbon material in a low-water, low-oxygen environment to allow the metallic lithium to sublime and adhere to the surface of the silver-plated hard carbon material. The sublimated metallic lithium forms a conductive lithium-carbon composite interface with the silver-plated hard carbon material on the surface of the cooled silver-plated hard carbon material to obtain a composite lithium-carbon material.

[0063] On the other hand, the present application also provides a composite lithium-carbon material, including: a hard carbon material, including multiple hard carbon particles; a metal particle attachment layer, including multiple metal particles attached to the surface of the hard carbon particles; the multiple metal particles include silver particles, wherein part of the surface of the hard carbon particles is exposed through the gaps between the multiple metal particles; a metal lithium coating layer, coated on the metal particle attachment layer, wherein part of the metal lithium coating layer is in contact with part of the surface of the hard carbon particles between the multiple metal particles.

[0064] The composite lithium-carbon material of the embodiment of the present application can effectively reduce the surface current density through the hard carbon material, promote the uniform embedding of lithium ions into the lithium-carbon composite interface, and effectively alleviate the problem of lithium dendrite growth at the lithium metal negative electrode.

[0065] In the embodiment of the present application, the hard carbon material has a large specific surface area and is combined with silver particles and metallic lithium, so that the surface current can be evenly distributed on the negative electrode, avoiding the problem of uneven surface current density distribution. It also allows lithium ions to be evenly embedded and extracted on the surface of the negative electrode material, preventing the formation of lithium dendrites.

[0066] In the embodiments of the present application, the hard carbon material includes a plurality of hard carbon particles, which means that the hard carbon material contains more than two hard carbon particles. For example, the hard carbon material may include 20-50, 30-200, 50-500, 100-1000, 200-2000 hard carbon particles.

[0067] In some embodiments of the present application, the hard carbon particles have a hollow structure.

[0068] In some embodiments of the present application, the average particle size of the hard carbon particles is 8 μm to 12 μm.

[0069] In the embodiments of the present application, the shapes of the hard carbon particles in the hard carbon material include but are not limited to square, ellipsoidal, and spherical. It is understood that the hard carbon material may be irregular in shape after being crushed from a block material.

[0070] In some embodiments of the present application, the hard carbon particles are spherical.

[0071] In some embodiments of the present application, the specific surface area of ​​the hard carbon particles is 0.056 m 2 / cm3 ~0.083m 2 / cm 3 .

[0072] In some embodiments of the present application, the thickness of the metal particle attachment layer attached to the surface of the hard carbon particles is 50 nm to 300 nm.

[0073] In the embodiment of the present application, silver particles are attached to the surface of the hard carbon material to increase the contact area between the metal lithium and the hard carbon material and enhance the conductivity of the hard carbon material, so that the surface of the negative electrode coated with the composite lithium-carbon material has a more uniform current density.

[0074] In some embodiments of the present application, the thickness of the metal lithium coating layer is 0.1 μm to 5 μm.

[0075] In some embodiments of the present application, the mass ratio of the sum of the mass of the hard carbon particles and the silver particles to the mass of the metal lithium coating layer is 1:(3-5). Optionally, the mass ratio of the sum of the mass of the hard carbon particles and the silver particles to the mass of the metal lithium coating layer is 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.8, 1:4, 1:4.1, 1:4.3, 1:4.5, 1:4.7, 1:4.8, 1:4.9.

[0076] In some embodiments of the present application, the average particle size of the composite lithium-carbon material is 8 μm to 17 μm.

[0077] Test Section

[0078] Preparation of composite lithium-carbon materials

[0079] The composite lithium-carbon material is prepared according to the preparation method of the composite lithium-carbon material of the present application.

[0080] The following are some of the materials and equipment requirements and their available sources for the examples and comparative examples:

[0081] Hard carbon material, model: Kuraray 2, purchased from Kuraray Company, the average diameter of hard carbon particles is 9 μm;

[0082] The vacuum thermal evaporation coating apparatus was purchased from Tianjin Coreto Technology Co., Ltd., model EDM-300.

[0083] Embodiment 1 A method for preparing a composite lithium-carbon material comprises:

[0084] S1, providing a hard carbon material including a plurality of hard carbon particles, and performing a water removal treatment on the hard carbon material at 110° C. for 12 hours;

[0085] S2, immersing the dehydrated hard carbon material in a mixture of a silver ammonia solution and acetaldehyde for oscillation treatment, comprising:

[0086] S20, adding acetaldehyde to the silver ammonia solution, immersing the hard carbon material in a mixture of the silver ammonia solution and acetaldehyde at 350° C., controlling the reaction time to be 5 minutes, forming a nano silver particle attachment layer on the surface of the hard carbon particles, and obtaining a silver-plated hard carbon material; wherein the silver ammonia solution is prepared according to the following steps:

[0087] S201, preparing a silver nitrate aqueous solution with a mass fraction of 2 wt.%;

[0088] S202, adding a sodium hydroxide aqueous solution with a mass fraction of 10 wt.% to the silver nitrate aqueous solution and shaking the test tube until a white precipitate is seen to obtain a suspension;

[0089] S203, adding 2 wt.% dilute ammonia solution dropwise to the suspension until the white precipitate is just dissolved, to obtain a silver ammonia solution;

[0090] S3, drying the silver-plated hard carbon material, including: taking out the silver-plated hard carbon material and drying it until the water content is less than 0.1 ppm, to obtain a dried silver-plated hard carbon material;

[0091] S4. Forming a metallic lithium coating layer on the surface of the dried silver-plated hard carbon material by vacuum thermal evaporation, comprising:

[0092] S401. In an environment where the water content and the oxygen content are both less than 0.1 ppm, placing metallic lithium in a molybdenum crucible in a vacuum reaction chamber, placing a silver-plated hard carbon material directly above the molybdenum crucible, and heating the metallic lithium to 1400° C. to allow the metallic lithium to sublime and adhere to the surface of the silver-plated hard carbon material to form a metallic lithium coating layer;

[0093] S402, in an environment where the water content and oxygen content are both less than 0.1 ppm, open the vacuum reaction chamber to obtain Figure 2 The composite lithium-carbon material shown.

[0094] Embodiment 2 A method for preparing a composite lithium-carbon material comprises:

[0095] S1, providing a hard carbon material including a plurality of hard carbon particles, and performing a water removal treatment on the hard carbon material at 110° C. for 12 hours;

[0096] S2, immersing the dehydrated hard carbon material in a mixture of a silver ammonia solution and acetaldehyde for oscillation treatment, comprising:

[0097] S20, adding acetaldehyde to the silver ammonia solution, immersing the hard carbon material in a mixture of the silver ammonia solution and acetaldehyde at 300° C., controlling the reaction time to be 5 minutes, forming a nano silver particle attachment layer on the surface of the hard carbon particles, and obtaining a silver-plated hard carbon material;

[0098] Wherein, the silver ammonia solution is prepared according to the following steps:

[0099] S201, preparing a silver nitrate aqueous solution with a mass fraction of 10wt.%;

[0100] S202, adding a sodium hydroxide aqueous solution with a mass fraction of 20 wt.% to the silver nitrate aqueous solution and shaking the test tube until a white precipitate is seen to obtain a suspension;

[0101] S203, add 5 wt.% dilute ammonia solution dropwise to the suspension until the white precipitate is just dissolved to obtain a silver ammonia solution.

[0102] S3, drying the silver-plated hard carbon material, including: taking out the silver-plated hard carbon material and drying it until the water content is less than 0.1 ppm, to obtain a dried silver-plated hard carbon material;

[0103] S4. Forming a metallic lithium coating layer on the surface of the dried silver-plated hard carbon material by vacuum thermal evaporation, comprising:

[0104] S401. In an environment where the water content and the oxygen content are both less than 0.1 ppm, placing metallic lithium in a molybdenum crucible in a vacuum reaction chamber, placing a silver-plated hard carbon material directly above the molybdenum crucible, wherein the mass ratio of the metallic lithium to the dry silver-plated hard carbon material is 4:1, and heating to 1400° C. to allow the metallic lithium to sublime and adhere to the surface of the silver-plated hard carbon material to form a metallic lithium coating layer;

[0105] S402, in an environment where the water content and oxygen content are both less than 0.1 ppm, open the vacuum reaction chamber to obtain Figure 3 The composite lithium-carbon material shown.

[0106] Embodiment 3 A method for preparing a composite lithium-carbon material comprises:

[0107] S1, providing a hard carbon material including a plurality of hard carbon particles, and performing a water removal treatment on the hard carbon material at 110° C. for 12 hours;

[0108] S2, immersing the hard carbon material in a mixture of silver ammonia solution and acetaldehyde for oscillation treatment, comprising:

[0109] S20, adding acetaldehyde to the silver ammonia solution, immersing the hard carbon material in a mixture of the silver ammonia solution and acetaldehyde at 300° C., controlling the reaction time to be 5 minutes, forming a nano silver particle attachment layer on the surface of the hard carbon particles, and obtaining a silver-plated hard carbon material;

[0110] Wherein, the silver ammonia solution is prepared according to the following steps:

[0111] S201, preparing a silver nitrate aqueous solution with a mass fraction of 5 wt.%;

[0112] S202, adding a sodium hydroxide aqueous solution with a mass fraction of 15 wt.% to the silver nitrate aqueous solution and shaking the test tube until a white precipitate is seen to obtain a suspension;

[0113] S203, add 3 wt.% dilute ammonia solution dropwise to the suspension until the white precipitate is just dissolved to obtain a silver ammonia solution.

[0114] S3, drying the silver-plated hard carbon material, including: taking out the silver-plated hard carbon material and drying it until the water content is less than 0.1 ppm, to obtain a dried silver-plated hard carbon material;

[0115] S4. Forming a lithium coating layer on the surface of the dried silver-plated hard carbon material by vacuum thermal evaporation, comprising:

[0116] S401. In an environment where the water content and the oxygen content are both less than 0.1 ppm, metallic lithium is placed in a molybdenum crucible in a vacuum reaction chamber, a silver-plated hard carbon material is placed directly above the molybdenum crucible, the mass ratio of metallic lithium to the dry silver-plated hard carbon material is 5:1, and the metallic lithium is sublimated by heating to 1400° C. and adhered to the surface of the silver-plated hard carbon material to form a metallic lithium coating layer;

[0117] S402, in an environment where the water content and oxygen content are both less than 0.1 ppm, open the high temperature reactor to obtain Figure 4 The composite lithium-carbon material shown.

[0118] Preparation results

[0119] The concentration of the silver ammonia solution in Example 1 is relatively small, and the preparation is as follows Figure 2 In the atomic force micrograph of the silver metal particle attachment layer formed by the composite lithium-carbon material shown, the morphology of the composite lithium-carbon material is slightly different, and the particle size of the silver particles in the composite lithium-carbon material of Example 1 is uniform, and the average particle size of the silver particles is 100nm to 150nm.

[0120] The concentration of the silver ammonia solution in Example 2 is relatively large, and the preparation is as follows Figure 3 In the atomic force micrograph of the silver metal particle attachment layer formed by the composite lithium-carbon material shown, the morphology of the composite lithium-carbon material varies greatly, and some are flat disc-shaped or flat spherical. The particle size of the silver particles in the composite lithium-carbon material of Example 2 varies greatly, and the average particle size of the silver particles is 100nm to 300nm.

[0121] The concentration of the silver ammonia solution of Example 3 is greater than that of the silver ammonia solution of Example 1, and is smaller than that of the silver ammonia solution of Example 2, and the following is prepared: Figure 4In the atomic force micrograph of the silver metal particle attachment layer formed by the composite lithium-carbon material shown, the morphology of the silver particles in the composite lithium-carbon material is not much different. The particle size of the silver particles in the composite lithium-carbon material of Example 3 is relatively uniform, and the average particle size of the silver particles is 100nm to 170nm.

[0122] The composite lithium-carbon materials prepared in Examples 1-3 were used to make negative electrodes, wherein the negative electrode was made of the composite lithium-carbon material as the negative electrode plate; NCM811 was used as the positive electrode, and the battery was assembled with 1 mol / L LiPF6 / FEC:DMC (volume ratio 1:4) electrolyte, and the battery cycle performance was tested.

[0123] Comparative Example 1

[0124] A lithium metal battery is provided, wherein a metal lithium sheet is used as a negative electrode, NCM811 is used as a positive electrode, and an electrolyte of 1 mol / L LiPF6 / FEC:DMC (volume ratio 1:4) is used for battery assembly, and a battery cycle performance test is performed.

[0125] The electrochemical performance of the lithium metal batteries of Example 1-3 and Comparative Example 1 was tested, and the charge and discharge cycle test was performed under the conditions of 3V to 4.3V voltage and 0.2A current. The test results are as follows: Figure 5 , Figure 6 , Figure 7 , Figure 8 From the comparison, it can be concluded that after the composite lithium-carbon material prepared in Example 1 is applied to the NCM811 battery, its coulombic efficiency after 200 cycles is still maintained at 99.81%, and the capacity retention rate after 200 cycles is still 99.12%; under the same cycle conditions, the coulombic efficiency of the NCM811 battery of Comparative Example 1 after 200 cycles is only 98.12%, and the capacity retention rate after 200 cycles is significantly reduced to 76.22%.

[0126] The use of the composite lithium-carbon material of the embodiment of the present application can effectively improve the coulombic efficiency and cycle stability of the battery, so that the capacity retention rate of the battery after 200 cycles is maintained at more than 98%.

[0127] The above is only a specific implementation method of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A composite lithium-carbon material, It is characterized in that include: a hard carbon material, comprising a plurality of hard carbon particles; a metal particle attachment layer, comprising a plurality of metal particles attached to the surface of the hard carbon particles; the plurality of metal particles comprising silver particles, wherein a portion of the surface of the hard carbon particles is exposed through gaps between the plurality of metal particles; The metal lithium coating layer is disposed to coat the metal particle attachment layer, wherein a portion of the metal lithium coating layer is in contact with a portion of the surface of the hard carbon particles between the plurality of metal particles.

2. The composite lithium-carbon material according to claim 1, It is characterized in that The hard carbon particles have a hollow structure; The hard carbon particles are spherical.

3. The composite lithium-carbon material according to claim 1, It is characterized in that The average particle size of the hard carbon particles is 8 μm to 12 μm; and / or, The specific surface area of ​​the hard carbon particles is 0.056 m 2 / cm 3 ~0.083m 2 / cm 3 and / or, The thickness of the metal particle adhesion layer is 50nm to 300nm; and / or The thickness of the metal lithium coating layer is 0.1 μm to 5 μm.

4. The composite lithium-carbon material according to claim 1, It is characterized in that The mass ratio of the sum of the mass of the hard carbon particles and the silver particles to the mass of the metal lithium coating layer is 1:(3-5).

5. The composite lithium-carbon material according to claim 1, It is characterized in that The average particle size of the composite lithium-carbon material is 8 μm to 17 μm.

6. A method for preparing the composite lithium-carbon material according to any one of claims 1 to 5, It is characterized in that include: providing the hard carbon material; The hard carbon material is immersed in a mixed solution of a silver ammonia solution and an aldehyde compound capable of generating a silver mirror reaction and subjected to an oscillating treatment to form a metal particle attachment layer on the surface of the hard carbon particles, thereby obtaining a silver-plated hard carbon material; A layer of the metal lithium coating layer is formed on the surface of the silver-plated hard carbon material to obtain a composite lithium-carbon material.

7. The preparation method according to claim 6, It is characterized in that The silver ammonia solution is prepared according to the following steps: Prepare a silver nitrate aqueous solution with a mass fraction of 2wt.% to 10wt.%; Adding 10 wt.% to 20 wt.% of sodium hydroxide aqueous solution to the silver nitrate aqueous solution until a white precipitate is visible to obtain a suspension; Adding 2 wt.% to 5 wt.% of an aqueous ammonia solution to the suspension until the white precipitate is dissolved to obtain a silver ammonia solution; and / or The aldehyde compound capable of undergoing a silver mirror reaction is selected from formic acid, formaldehyde, acetaldehyde, glyoxal, propionaldehyde, glucose, maltose, methyl formate, ethyl formate, propyl formate or a combination thereof.

8. The preparation method according to claim 6, It is characterized in that The temperature of the mixed solution of the silver ammonia solution and the aldehyde compound capable of undergoing a silver mirror reaction is 300° C. to 500° C., and the reaction time of the hard carbon material in the mixed solution of the silver ammonia solution and the aldehyde compound capable of undergoing a silver mirror reaction is 10 minutes to 50 minutes.

9. The preparation method according to claim 6, It is characterized in that The step of forming a metal lithium coating layer on the surface of the silver-plated hard carbon material by vacuum thermal evaporation comprises: In a vacuum reaction chamber, the metallic lithium and the silver-plated hard carbon material are placed in a reaction container, and the silver-plated hard carbon material is placed above the reaction container, and the metallic lithium is sublimated and attached to the surface of the silver-plated hard carbon material by heating to above 1400°C.

10. The preparation method according to claim 9, It is characterized in that The metallic lithium and the silver-plated hard carbon material are placed in the vacuum reaction chamber in a mass ratio of (3-5):

1.

11. A negative electrode, It is characterized in that It comprises a current collector and a composite lithium-carbon material as described in any one of claims 1 to 5 coated on at least one side surface of the current collector.

12. An electrochemical device, It is characterized in that Comprising the negative electrode as claimed in claim 11.

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