Metal lithium composite negative electrode and preparation method thereof

Abstract

The invention discloses a metal lithium composite negative electrode and a preparation method thereof. The preparation method is a dry process and comprises the following steps: (1) mixing a granular metal lithium composite material with a conductive agent and a binder; (2) carrying out fibration treatment on the obtained mixture; (3) carrying out hot press molding on the fibration treatment product to obtain a metal lithium composite material layer; and (4) directly using the metal lithium composite material layer as the metal lithium composite negative electrode, or arranging the metal lithium composite material layer on at least one side of a current collector to obtain the metal lithium composite negative electrode.

Description

TECHNICAL FIELD

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

[0002] Lithium ion battery is a kind of secondary battery with lithium salt as electrolyte. In the process of charging and discharging, Li + can make multiple round trips between two poles to realize the storage and release of energy. At present, most of the commercialized lithium ion batteries use graphite or silicon-based composite materials as negative electrode materials. The capacity of such materials can reach about 200-450 mAh / g, which cannot meet the demand of high energy density. If higher energy density is required, the existing negative electrode materials must be improved or new negative electrodes must be developed.

[0003] In order to meet the demand of high energy density and long cycle in the market of electric vehicles, unmanned aerial vehicles and the like, metal lithium with abundant reserves can be selected. However, the lithium negative electrode has problems such as volume expansion and lithium dendrite in the process of charging and discharging, which seriously limits its commercial application. In addition, metal lithium is active, and the powdery metal lithium has safety hazards in the process of electrode preparation.

[0004] Therefore, there are still a series of problems to be solved in the commercial application of metal lithium negative electrode. SUMMARY

[0005] In order to solve the problems in the prior art, the present application provides a new idea for preparing a metal lithium composite negative electrode. The raw material of the composite negative electrode is a granular metal lithium composite material. The shell of the composite material is composed of single-walled carbon nanotubes and multi-walled carbon nanotubes, and a three-dimensional lithium ion transmission channel and an electronic conduction network are constructed in the negative electrode body phase. The transmission of lithium ions and electrons can be simultaneously regulated, so that the composite negative electrode can have good rate performance and can maintain good cycle life at high current. In addition, the dry process is used in the process of preparing the negative electrode, so that the above-mentioned composite material can be safely prepared into a negative electrode by a simple process, and the use of solvent (especially environmentally harmful organic solvent) is avoided.

[0006] The purpose of the present application can be achieved by the following technical solutions.

[0007] In a first aspect, the present application provides a metal lithium composite negative electrode, which comprises a metal lithium composite material layer, the metal lithium composite material layer comprising a metal lithium composite material, a conductive agent and a binder,

[0008] The metal lithium composite material comprises metal lithium powder and / or lithium alloy powder as an inner core, and the surface of the inner core is provided with an outer shell, the outer shell is composed of single-walled carbon nanotubes and multi-walled carbon nanotubes, the mass ratio of the single-walled carbon nanotubes and the multi-walled carbon nanotubes is 1:(0.1-100), and the outer shell is in contact with and cross-wound with each other to form a three-dimensional porous framework in the metal lithium composite material layer.

[0009] The conductive agent comprises a carbon-based conductive agent.

[0010] The binder comprises a perfluoroolefin polymer and / or a thermoplastic rubber.

[0011] In the present application, the composite negative electrode adopts a metal lithium composite material with a core-shell structure as raw material, the metal lithium composite material with the core-shell structure takes metal lithium powder and / or lithium alloy powder as an inner core, and the outer shell is a "mixed outer shell" composed of multi-walled carbon nanotubes and single-walled carbon nanotubes, which has a relatively "flexible" structure, and in the dry process, a stable three-dimensional porous framework is constructed in the negative electrode body phase. The outer shell constructed by the single-walled carbon nanotubes and the multi-walled carbon nanotubes with a specific mass ratio is relatively stable and has a porous structure, which can alleviate the volume expansion problem of metal lithium; moreover, the outer shell can transport lithium ions and electrons, and a three-dimensional distributed lithium ion transport channel and an electronic conductive network are constructed in the composite negative electrode, which can simultaneously regulate the transport of lithium ions and electrons, which is beneficial to the uniform stripping and deposition of metal lithium in the composite negative electrode, so that the composite negative electrode can exhibit good rate performance while maintaining good cycle life at high current when used in a lithium metal battery.

[0012] Optionally, the mass fraction of the inner core in the lithium-carbon composite material is 50% or more, preferably 70% or more, and further preferably 85% or more, based on 100% of the mass of the lithium-carbon composite material.

[0013] Optionally, the alloying elements in the lithium alloy powder include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, selenium, boron, magnesium, indium, gallium, aluminum or zinc; and preferably, the mass of the alloying elements is 1%-20%, preferably 5%-10%, based on 100% of the mass of the lithium alloy powder. When the composite negative electrode is stripped of lithium, the alloying elements do not participate in the stripping of lithium and remain in place, thereby improving the stability of the inner core; the alloying elements are lithium-affine, and can regulate the uniform deposition of metal lithium when the metal lithium is deposited.

[0014] Optionally, the length of the single-walled carbon nanotube is 0.5-100 μm, and preferably 1-50 μm. If the length of the single-walled carbon nanotube is too small, a stable framework cannot be constructed, and if the length of the single-walled carbon nanotube is too large, it is not easy to be uniformly distributed in the outer shell. The outer diameter of the single-walled carbon nanotube is 1-2 nm.

[0015] Optionally, the multi-walled carbon nanotube has a layer number of 2-15, preferably 2-10.

[0016] Optionally, the multi-walled carbon nanotube has an outer diameter of less than 30 nm, preferably 4-20 nm.

[0017] Optionally, the multi-walled carbon nanotube has a length of 0.5-50 μm.

[0018] Optionally, the length of the multi-walled carbon nanotube is less than or equal to the length of the single-walled carbon nanotube.

[0019] Optionally, the mass ratio of the single-walled carbon nanotube to the multi-walled carbon nanotube is 1:(0.5-50), preferably 1:(1-30). The mass ratio of the single-walled carbon nanotube to the multi-walled carbon nanotube can be 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:2.5, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:75, 1:90 or 1:100, etc., including but not limited to the listed point values. If the mass ratio is too large, the single-walled carbon nanotube is too much, the rigidity of the shell is weak, and the structure of the composite negative electrode is unstable; if the mass ratio is too small, the multi-walled carbon nanotube is too much, which cannot form the framework of the shell, it is difficult to form a stable shell on the surface of the core, and it is also not conducive to the construction of a stable composite negative electrode.

[0020] Optionally, the multi-walled carbon nanotube has a modification layer containing a lithium-averse element, which includes at least one of copper, nickel, titanium, chromium, vanadium, cobalt, manganese or iron,

[0021] In the prior art, the deposition of metallic lithium is focused on introducing lithium-philic deposition sites, while in the present application, the inventors found in the experimental process that the use of multi-walled carbon nanotubes containing a lithium-averse element modification layer (such as related materials sold by Beijing Deke Island Gold Technology Co., Ltd.) can also achieve the regulation of uniform deposition of metallic lithium. It is speculated that the uneven deposition of metallic lithium is caused by the uneven current density on the surface of the negative electrode. Although the lithium-averse element modification layer cannot induce the uniform deposition of metallic lithium, it has good electronic conductivity and is distributed in three dimensions, which makes the current density on the surface and in the bulk of the negative electrode more uniform, regulates the uniform stripping / deposition of metallic lithium, and at the same time solves the problems of pit formation caused by uneven stripping of metallic lithium and the growth of lithium dendrites caused by uneven deposition of metallic lithium; at the same time, the metal element skeleton is more stable, which improves the cycle performance and safety performance of the composite negative electrode.

[0022] Optionally, the mass content of the modification layer is more than 50%, preferably 60-80%, based on 100% of the mass of the multi-walled carbon nanotube.

[0023] Optionally, the conductive agent comprises at least one of Ketjen black, acetylene black, SUPER P or Cabot carbon black. The carbon-based conductive agent not only plays a role of conducting electrons, but also plays a role of relieving volume expansion of the metal lithium composite negative electrode.

[0024] Optionally, the binder comprises polytetrafluoroethylene (PTFE) and / or modified styrene-butadiene rubber (SBR), such as NaCl-modified SBR disclosed in the document Long-life Sulfide All-solid-state Battery Enabled by Substrate-Modulated Dry-Process Binder, which adjusts the size, microstructure and morphology of the original SBR by dissolving the original SBR into a p-xylene solution and then precipitating on different amounts of NaCl.

[0025] Optionally, the mass ratio of the metal lithium composite material, the conductive agent and the binder is (90-98):(1-5):(1-5), for example, can be 90:5:5, 92:3:5, 93:5:2, 94:3:3, 95:2:3, 96:2:3, 96:2:2, 97:1.5:1.5, 97:1:2, 97:2:1, or 98:1:1, etc., preferably (94-97):(1.5-3):(1.5-3).

[0026] In a second aspect, the present application provides a method for preparing the metal lithium composite negative electrode as described above, which is a dry process and comprises the following steps:

[0027] (1) mixing a particulate metal lithium composite material with a conductive agent and a binder;

[0028] (2) performing a fiberization treatment on the obtained mixture;

[0029] (3) hot-pressing the fiberization treatment product to obtain a metal lithium composite material layer,

[0030] (4) directly using the metal lithium composite material layer as a metal lithium composite negative electrode, or arranging the metal lithium composite material layer on at least one side of a current collector to obtain a metal lithium composite negative electrode,

[0031] In the present application, the mixing in step (1) is not specifically limited, and can be shear mixing using a high-speed shearing device, ribbon mixing using a ribbon mixer, or rotary mixing using a V-type mixer, as long as the materials in step (1) can be uniformly mixed.

[0032] Optionally, the average particle size of the particulate metal lithium composite material is 1-100 μm, preferably 10-50 μm.

[0033] Optionally, the thickness of the outer shell is between 0.5 μm and 50 μm.

[0034] Optionally, in step (1), the mixing ratio of the lithium metal composite material with the conductive agent and binder is (90-98):(1-5):(1-5), for example, it can be 90:5:5, 92:3:5, 93:5:2, 94:3:3, 95:2:3, 96:2:3, 96:2:2, etc.

[0035] 97:1.5:1.5, 97:1:2, 97:2:1, or 98:1:1, etc., preferably (94-97):(1.5-3):(1.5-3).

[0036] Optionally, the fiberization process in step (2) includes air jet milling or electrostatic spraying. The gas used for air jet milling is an inert gas that does not react with the lithium metal composite material, such as argon or helium, and this invention does not specifically limit it.

[0037] Optionally, the conditions for air jet milling include a pressure of 0.1-0.5 MPa.

[0038] Optionally, the hot pressing conditions in step (3) include: a temperature of 40-120°C and a pressure of 5-50 kg, preferably a temperature of 60-100°C and a pressure of 5-30 kg.

[0039] Optionally, the thickness of the lithium metal composite material layer is 1-100 μm, preferably 5-50 μm.

[0040] Optionally, the composite negative electrode further includes a current collector, and the lithium metal composite material layer is disposed on at least one side of the current collector.

[0041] Optionally, the current collector includes at least one of pure copper foil, carbon-coated copper foil, roughened copper foil, nickel foil, copper-nickel alloy foil, stainless steel foil, carbon cloth, or carbon paper.

[0042] Optionally, the particulate lithium metal composite material can be prepared by the following method, which includes the following steps:

[0043] (1) Single-walled carbon nanotubes and multi-walled carbon nanotubes were dispersed in an organic solvent to obtain the first dispersion system;

[0044] (2) Mix lithium metal powder and / or lithium alloy powder with the first dispersion system of step (1) to obtain a second dispersion system;

[0045] (3) The second dispersion system is spray-dried to obtain the lithium metal composite material;

[0046] or after high-speed stirring at a rotation speed of 5000 rpm or above, the organic solvent is removed to obtain the metal lithium composite material.

[0047] Optionally, the organic solvent is inert to the metal lithium powder and / or lithium alloy powder, and can include any one or a combination of at least two of liquid alkanes with a carbon atom number of 4-20, liquid halogenated hydrocarbons with a carbon atom number of 4-20, toluene, xylene, solvent oil, liquid paraffin, tetrahydrofuran, N,N-dimethylformamide or silicone oil.

[0048] Compared with the prior art, the present application has the following beneficial effects:

[0049] 1. The metal lithium composite negative electrode provided by the present application uses a particulate metal lithium composite material as a raw material, takes metal lithium powder and / or lithium alloy powder as a core, and has a mixed shell composed of single-walled carbon nanotubes and multi-walled carbon nanotubes in a specific mass ratio. Compared with a single-walled carbon nanotube or multi-walled carbon nanotube shell, the shell is more stable, and a three-dimensional distributed stable porous framework is constructed in the composite negative electrode, which can effectively solve the problem of volume expansion of metal lithium.

[0050] 2. The metal lithium composite negative electrode provided by the present application has abundant lithium ion transmission channels and electron conduction networks, and simultaneously regulates the transmission of lithium ions and the distribution of current, so that the composite negative electrode can exhibit good rate performance and maintain good cycle life under high current.

[0051] 3. The dry process is used to prepare the negative electrode. In the fiberization preparation process, the binder, the conductive agent and the particulate metal lithium composite material are connected with each other, and the shells of the particulate metal lithium composite material are cross-wound with each other, so that a more stable three-dimensional porous framework is formed, and the use of solvents (especially environmentally harmful organic solvents) is avoided.

[0052] 4. The preparation process is simple and easy to control, and is suitable for large-scale industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present application, the drawings used in the present application will be briefly introduced as follows.

[0054] Figure 1 The cycle test curves of Example 1, Example 4, Example 7 and Example 9;

[0055] Figure 2 The cycle test curves of Example 1 and Comparative Example 1-2; DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the protection scope of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application. Those skilled in the art can realize that, in addition to the improvement of materials, other any method related to the purpose of the present application can be used to replace the steps of the described method, as long as the same result is obtained, the predetermined effect is achieved, and here is not described.

[0057] Example 1

[0058] The present embodiment provides a metal lithium composite negative electrode, the thickness of the composite negative electrode is 100 μm, the raw material is a metal lithium composite material with an average particle size of 55 μm, the metal lithium composite material includes metal lithium powder and a shell arranged on the surface of the metal lithium powder, the shell includes single-walled carbon nanotubes and multi-walled carbon nanotubes with a mass ratio of 1:0.1, the thickness of the shell is 45 μm, and the mass fraction of the metal lithium powder is 50%;

[0059] The preparation method of the composite negative electrode is as follows:

[0060] (1) 10 g of single-walled carbon nanotubes (item number: 104477, outer diameter 1-2 nm, length 5-30 μm, Jiangsu Xianfeng Nanometer Material Technology Co., Ltd.) and 1 g of multi-walled carbon nanotubes (GT-400, outer diameter 20-30 nm, length 3-12 μm, Shandong Dazhan Nanometer Material Co., Ltd.) are added to 100 L of n-hexane, ultrasonically mixed, and uniformly mixed to obtain a first dispersion system;

[0061] (2) 11 g of metal lithium powder with an average particle size of 10 μm is added to the first dispersion system, mixed at a rotation speed of 7000 rpm for 20 min, filtered to remove n-hexane, and then dried at 110°C under vacuum for 24 hours to obtain a metal lithium composite material;

[0062] (3) The metal lithium composite material in step (2), Ketjen black and PTFE are mixed in a mass ratio of 19.6 g, 0.2 g and 0.2 g, then fiberized by airflow crushing under the condition of 0.3 MPa, and then formed by 30 kg pressure at 100°C to obtain the composite negative electrode.

[0063] Example 2

[0064] The embodiment provides a metal lithium composite negative electrode, the composite negative electrode has a thickness of 50 microns, raw materials are metal lithium composite materials with an average particle size of 30 microns, the metal lithium composite materials comprise metal lithium powder and a shell arranged on the surface of the metal lithium powder, the shell comprises single-walled carbon nanotubes and copper-plated multi-walled nanotubes with a mass ratio of 1:100, the thickness of the shell is 5 microns, and the mass fraction of the metal lithium powder is 95%.

[0065] The preparation method of the lithium-carbon composite material comprises the following steps:

[0066] (1) 0.1 g of single-walled carbon nanotubes (article number: 104477, outer diameter 1-2 nm, length 5-30 microns, Jiangsu Xianfeng Nanometer Material Technology Co., Ltd.) and 10 g of copper-plated multi-walled carbon nanotubes (Beijing Dekedaojin Technology Co., Ltd., CNT813, mass content of copper 60%, outer diameter 8-15 nm, length 50 microns) are added into 120 L of p-xylene, high-speed dispersion is carried out at a rotating speed of 8000 rpm, and uniform mixing is carried out to obtain a first dispersion system;

[0067] (2) 20.2 g of metal lithium powder with an average particle size of 25 microns is added into the first dispersion system, mechanical stirring is carried out at a rotating speed of 3000 rpm for 90 min, spray drying is carried out, the inlet air temperature is 220 DEG C, the outlet air temperature is 90 DEG C, the atomization pressure is 1.2 Mpa, the sample feeding amount is 200 mL / min, and a metal lithium composite material is obtained;

[0068] (3) the metal lithium composite material in step (2), Cabot carbon black and PTFE are mixed according to a mass ratio of 9 g, 0.5 g and 0.5 g, then the mixture is sprayed on both sides of the current collector by electrostatic spraying, and the composite negative electrode is obtained by forming at a pressure of 5 kg at 60 DEG C.

[0069] Example 3

[0070] Compared with example 1, the only difference is that the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is replaced by 1:0.5, and the remaining conditions are the same.

[0071] Example 4

[0072] Compared with example 1, the only difference is that the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is replaced by 1:30, and the remaining conditions are the same.

[0073] Example 5

[0074] Compared with example 1, the only difference is that the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is replaced by 1:50, and the remaining conditions are the same.

[0075] Example 6

[0076] Compared with Example 1, the only difference is that the multi-walled carbon nanotubes are replaced with nickel-plated multi-walled carbon nanotubes (Beike Nano, HQNANO-CNTs-009-6A, with a nickel content of more than 60%, an outer diameter of 8-15 nm, and a length of 50 μm), while all other conditions are the same.

[0077] Example 7

[0078] Compared with Example 1, the only difference is that lithium metal powder is replaced with lithium boron alloy powder, and the mass fraction of boron is 5%, while all other conditions are the same.

[0079] Example 8

[0080] Compared with Example 1, the only difference is that the mass of lithium metal composite material, Ketjen black and PTFE is replaced with 18.8g, 0.6g and 0.6g respectively, while the other conditions remain unchanged.

[0081] Example 9

[0082] Compared with Example 1, the only difference is that the mass of lithium metal composite material, Ketjen black and PTFE is replaced with 19.4g, 0.3g and 0.3g respectively, while the other conditions remain unchanged.

[0083] Comparative Example 1

[0084] Compared with Example 1, the only difference is that the negative electrode thickness is 50 μm and the raw material is lithium metal powder with an average particle size of 30 μm (without a shell), while all other conditions are the same.

[0085] Comparative Example 2

[0086] Compared with Example 1, the only difference is that the composite negative electrode has a thickness of 50 μm, and the raw materials are lithium metal powder with an average particle size of 30 μm and single-walled carbon nanotubes disposed on the surface of the lithium metal powder.

[0087] Comparative Example 3

[0088] Compared with Example 1, the only difference is that the composite negative electrode has a thickness of 50 μm, and the raw materials are lithium metal powder with an average particle size of 30 μm and multi-walled carbon nanotubes disposed on the surface of the lithium metal powder.

[0089] Comparative Example 4

[0090] Compared with Example 1, the only difference is that the composite anode has a thickness of 100 μm and the raw material is a physical mixture of lithium metal powder, single-walled carbon nanotubes and multi-walled carbon nanotubes with an average particle size of 10 μm (not the core-shell structure of the raw material in the composite anode of the present invention).

[0091] Comparative Example 5

[0092] Compared with Example 1, the only difference is that the composite negative electrode consists only of lithium metal composite material and does not include Ketjen Black and PTFE.

[0093] Comparative Example 6

[0094] Compared with Example 1, the only difference is that the composite negative electrode includes lithium metal composite material and Ketjen black, but does not include PTFE.

[0095] Comparative Example 7

[0096] Compared with Example 1, the only difference is that the composite negative electrode includes lithium metal composite material and PTFE, but does not include Ketjen Black.

[0097] Comparative Example 8

[0098] Compared with Example 1, the only difference is that the preparation method of the composite negative electrode does not involve a fiberization step, and the mixture is directly molded at 100°C under 30kg pressure.

[0099] Comparative Example 9

[0100] Compared with Example 1, the only difference is that the composite negative electrode is formed at 20°C under 2kg pressure in the preparation method.

[0101] Negative electrode performance test:

[0102] The negative electrodes of Examples 1-9 and Comparative Examples 1-9 were subjected to an areal loading of 40 mg / cm³. 2 LiNi 0.9 Co 0.05 Mn 0.05 O2 (NCM90) positive electrode assembly soft-pack battery with ether electrolyte. Cycle performance was tested at 0.5C / 1C. The test was stopped when the battery capacity decayed to 80% of the initial capacity or a short circuit occurred. The test results are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from Table 1:

[0107] (1) Comparing Examples 1 and 3-5, it can be seen that the cycle performance of the lithium metal composite anode in Examples 3-5 is better than that in Example 1. This is because the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes in Examples 3-5 is more suitable (within the preferred range of the present invention), and the constructed composite anode structure has good stability, which is conducive to the performance of cycle performance; combined with Figure 1It can be seen that the composite negative electrode in Example 4 began to show capacity decay after 40 cycles, while the composite negative electrode in Example 1 began to show capacity decay after 20 cycles, and its cycle stability was worse than that of Example 4.

[0108] (2) Comparing Example 1 and Example 6, it can be seen that the cycle performance of the lithium metal composite anode in Example 6 is better than that in Example 1. This is because nickel-plated multi-walled carbon nanotubes are used in Example 6. Although the lithium-phobic element modification layer cannot induce uniform deposition of lithium metal, it has good electronic conductivity and is distributed in three dimensions, which makes the current density on the surface and bulk phase of the anode more uniform, regulates the uniform stripping / deposition of lithium metal, and solves the problems of pitting caused by uneven stripping of lithium metal and the generation and growth of lithium dendrites by uneven deposition of lithium metal. At the same time, the metal element skeleton is more stable, which improves the cycle performance of the composite anode.

[0109] (3) Comparing Examples 1 and 7, it can be seen that the cycle performance of the lithium metal composite anode in Example 7 is better than that in Example 1. This is because the lithium-containing core used in Example 7 is lithium-boron alloy powder, which contains active lithium and a porous lithium-boron phase. The lithium-boron phase not only alleviates the volume expansion of lithium metal but also induces lithium metal deposition. Figure 1 It can be seen that the capacity decay of the composite negative electrode in Example 7 started from about 60 cycles, which was later and slower than the capacity decay of the composite negative electrode in Example 1.

[0110] (4) Comparing Examples 1 and 8-9, it can be seen that the cycle performance of the lithium metal composite anode in Examples 8-9 is better than that in Example 1. This is because the mass ratio of lithium metal composite material, Ketjen Black, and PTFE in Examples 8-9 is more suitable, resulting in a more stable composite anode, which is beneficial to the performance of the composite anode; combined with Figure 1 It can be seen that the composite negative electrode in Example 9 exhibits capacity decay around 70 cycles, which is later than the composite negative electrode in Example 1.

[0111] (5) Comparing Example 1 and Comparative Examples 1-4, it can be seen that the cycle performance of the lithium metal composite anode in Example 1 is better than that in Comparative Examples 1-4. This is because the lithium metal material forming the composite anode in Comparative Examples 1-4 did not form the structure of the lithium metal composite material in this invention, and its effect on alleviating the problem of lithium metal volume expansion and regulating the uniform deposition of lithium metal was worse than that in Example 1; combined with Figure 2 It can be seen that the composite negative electrode in Example 1 has the best cycle performance, the composite negative electrode in Comparative Example 2 has the second best performance, and the negative electrode in Comparative Example 1 has the worst performance.

[0112] (6) Comparing Example 1 and Comparative Example 5-7, it can be seen that the cycle performance of the lithium metal composite anode in Example 1 is better than that in Comparative Example 5-7. This is because when preparing the composite anode in Comparative Example 5-7, the lithium metal composite material, conductive agent and binder were not included at the same time. During the charging and discharging process, the structure of the lithium metal composite anode is prone to collapse.

[0113] (7) Comparing Example 1 and Comparative Examples 8-9, it can be seen that the cycle performance of the lithium metal composite anode in Example 1 is better than that in Comparative Examples 8-9. This is because the preparation process used in Comparative Examples 8-9 is different from that in Example 1. The connection effect between the lithium metal composite material, the conductive agent and the PTFE particles is poor. The shell of the particulate lithium metal composite material cannot be formed or the three-dimensional porous structure formed is unstable. The structural stability of the prepared composite anode is poor.

[0114] The above are merely preferred embodiments of the present invention and not examples. All modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A lithium metal composite anode, characterized in that, The lithium metal composite anode comprises a lithium metal composite material layer, which includes a lithium metal composite material, a conductive agent, and a binder. The lithium metal composite material includes lithium metal powder and / or lithium alloy powder as the core, and the core surface is provided with a shell. The shell is composed of single-walled carbon nanotubes and multi-walled carbon nanotubes, and the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 1:(0.1-100). The shells are in contact with each other and are intertwined to form a three-dimensional porous skeleton in the lithium metal composite material layer. The conductive agent includes a carbonaceous conductive agent; and The adhesive comprises perfluoroolefin polymers and / or thermoplastic rubbers.

2. The lithium metal composite anode according to claim 1, characterized in that, Based on the mass of the lithium-carbon composite material as 100%, the mass fraction of the core in the lithium-carbon composite material is 50% or more, preferably 70% or more, and more preferably 85% or more. Preferably, the alloying element in the lithium alloy powder includes at least one selected from tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, selenium, boron, magnesium, indium, gallium, aluminum, or zinc; preferably, the alloying element accounts for 1%-20% of the mass of the lithium alloy powder, and more preferably 5%-10%. Preferably, the length of the single-walled carbon nanotube is 0.5 μm to 100 μm, and more preferably 1-50 μm; Preferably, the multi-walled carbon nanotubes have 2 or more layers and 15 or less layers, and more preferably 2-10 layers. Preferably, the outer diameter of the multi-walled carbon nanotube is less than 30 nm, and more preferably 4-20 nm; Preferably, the length of the multi-walled carbon nanotubes is 0.5-50 μm; Preferably, the length of the multi-walled carbon nanotube is less than or equal to the length of the single-walled carbon nanotube; Preferably, the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is 1:(0.5-50), and more preferably 1:(1-30).

3. The lithium metal composite anode according to claim 1 or 2, characterized in that, The multi-walled carbon nanotubes have a modification layer containing a lithium-repellent element, which includes at least one of copper, nickel, titanium, chromium, vanadium, cobalt, manganese, or iron. Preferably, based on the mass of the multi-walled carbon nanotubes as 100%, the mass content of the modification layer is above 50%, preferably 60-80%.

4. The lithium metal composite anode according to any one of claims 1-3, characterized in that, The conductive agent includes at least one of Ketjen Black, acetylene black, SUPER P or Cabot carbon black. The adhesive includes polytetrafluoroethylene (PTFE) and / or modified styrene-butadiene rubber (SBR).

5. The lithium metal composite anode according to any one of claims 1-4, characterized in that, The mass ratio of the lithium metal composite material to the conductive agent and the binder is (90-98):(1-5):(1-5), preferably (94-97):(1.5-3):(1.5-3).

6. A method for preparing a lithium metal composite anode according to any one of claims 1-5, characterized in that, The method is a dry process, including the following steps: (1) Mix the granular lithium metal composite material with a conductive agent and a binder; (2) The resulting mixture is subjected to fibrosis treatment; (3) The fiberized product is hot-pressed to obtain a lithium metal composite material layer; (4) The lithium metal composite material layer is directly used as a lithium metal composite negative electrode, or the lithium metal composite material layer is disposed on at least one side of the current collector to obtain a lithium metal composite negative electrode.

7. The method according to claim 6, characterized in that, The average particle size of the particulate lithium metal composite material in step (1) is 1-100 μm, preferably 10-50 μm; the thickness of the shell is between 0.5 μm and 50 μm.

8. The method according to claim 6 or 7, characterized in that, The fiberization process in step (2) includes air jet milling or electrostatic spraying. Preferably, the conditions for air jet milling include: an inert gas flow that does not react with metallic lithium, at a pressure of 0.1-0.5 MPa.

9. The method according to any one of claims 6-8, characterized in that, The conditions for hot pressing in step (3) include: temperature of 40-120℃ and pressure of 5-50kg, preferably temperature of 60-100℃ and pressure of 5-30kg.

10. The method according to any one of claims 6-9, characterized in that, The thickness of the lithium metal composite material layer is 1-100 μm, preferably 5-50 μm; Preferably, the current collector in step (4) includes at least one of pure copper foil, carbon-coated copper foil, roughened copper foil, nickel foil, copper-nickel alloy foil, stainless steel foil, carbon cloth, or carbon paper.

Images