Metal lithium composite negative electrode as well as preparation method and application thereof

Abstract

The invention provides a metal lithium composite negative electrode and a preparation method and application thereof. The lithium metal composite negative electrode comprises a lithium-containing layer, the lithium-containing layer comprises a lithium-loving material and a lithium-phobic structural material which are distributed in lithium metal and / or lithium alloy, and the structural material is interwoven to form a three-dimensional skeleton structure. The lithium-loving material forms a lithium deposition inducing structure in the three-dimensional skeleton structure in a discrete and / or continuous manner, and the rest internal space of the three-dimensional skeleton structure is filled with the metal lithium and / or the lithium alloy. In the composite negative electrode, the lithium-loving material can induce metal lithium to preferentially deposit and grow inwards, so that the cycle performance of the composite material can be improved. The structural material effectively relieves the problem of volume expansion in the metal lithium circulation process. And the lithium-loving material and the structural material are matched with each other, so that the cycle life of the composite negative electrode is remarkably prolonged. In addition, the composite negative electrode is not easy to adhere in the preparation process and has good processability.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, and in particular relates to a metal lithium composite negative electrode and a preparation method and application thereof. Background Art

[0002] The theoretical specific capacity of metallic lithium is 3860mAh / g, which is 10 times that of graphite negative electrode. Its redox potential is -3.04Vvs standard hydrogen potential, which is the lowest potential among known negative electrodes. Therefore, metallic lithium negative electrode is known as the "holy grail" of battery negative electrode materials. Using metallic lithium as a battery can greatly increase the energy density of the battery. However, at present, whether using lithium ribbon or metallic lithium powder as the negative electrode active material, there are problems such as large volume change and easy generation of dendrites.

[0003] In response to the above problems, people have proposed a variety of solutions, including electrolyte additives, the construction of three-dimensional current collectors, and the regulation of metal lithium deposition. Among them, CN 110854380 A proposed a lithium-carbon composite material, a lithium battery, and a preparation method thereof, wherein the lithium-carbon composite material uses carbon paper made of carbon material as a three-dimensional conductive frame, on which there is a lithium-philic metal evaporated, and the metal lithium is composited by a hot injection method. Most of the lithium-philic metal in the lithium-carbon material is distributed on the surface of the three-dimensional conductive frame, and it is not easy to be uniformly evaporated in the bulk phase of the three-dimensional conductive frame, and the inhibition of lithium dendrite growth is limited; the metal lithium composited by the hot injection method is concentrated on the surface of the three-dimensional conductive frame, and the specific capacity of the lithium-carbon material is low.

[0004] To address this problem, the present application proposes a metal lithium composite negative electrode, which effectively solves the problem that the lithium-philic metal is only distributed on the surface and has a low specific capacity, thereby improving the battery cycle life. Summary of the invention

[0005] The present invention aims to solve the above technical problems. The inventors have found that constructing a lithium deposition-inducing structure formed by a lithiophilic material and a three-dimensional skeleton structure formed by a lithiophobic structural material in a lithium-containing layer bulk phase can effectively solve the above problems.

[0006] Specifically, one aspect of the present invention provides a metallic lithium composite negative electrode, the composite negative electrode comprising a lithium-containing layer, the lithium-containing layer comprising a lithiophilic material and a lithiophobic structural material distributed in metallic lithium and / or a lithium alloy, wherein the structural materials are interwoven to form a three-dimensional skeleton structure, the lithiophilic material forms a lithium deposition inducing structure in the three-dimensional skeleton structure in a discrete and / or continuous manner, and the remaining internal space of the three-dimensional skeleton structure is filled with the metallic lithium and / or lithium alloy.

[0007] In the present invention, the metal lithium composite negative electrode comprises a lithium-containing layer, the lithium-containing layer is mainly composed of metal lithium and / or lithium alloy, and a lithiophilic material and a structural material are distributed in the main body, the lithiophilic material forms a lithium deposition inducing structure, the structural material forms a three-dimensional skeleton structure, the metal lithium and / or lithium alloy penetrates and / or connects the lithium deposition inducing structure and the three-dimensional skeleton structure, the lithium deposition inducing structure can induce metal lithium to preferentially deposit and grow internally, inhibit the growth of metal lithium dendrites, and the three-dimensional skeleton structure of lithium phobia can reduce the current density and alleviate the problem of volume expansion of metal lithium. In the metal lithium composite negative electrode, the lithiophilic material is distributed more evenly and cooperates with the structural material, so that the composite negative electrode has a higher specific capacity and excellent cycle performance.

[0008] Optionally, the lithium-containing layer is formed by deformation and rupture of a metal lithium composite material with a core-shell structure under pressure, wherein the metal lithium composite material with a core-shell structure has lithium-containing particles (metal lithium and / or lithium alloy powder) as a core, and a lithium deposition inducing layer formed by a lithium-philic material as an intermediate layer and a volume expansion reserved layer formed by a lithium-phobic structural material as an outermost layer are arranged on the core.

[0009] Since the lithium-containing layer is formed by deformation and rupture of a metallic lithium composite material with a core-shell structure under pressure, the lithium-phobic structural materials originally located in the outermost layer of the core-shell structure (as a volume expansion reserved layer) can contact and interweave with each other to form a three-dimensional skeleton structure, and the lithium-philic materials originally located inside the volume expansion reserved layer can also be more evenly dispersed inside the three-dimensional skeleton structure as the core-shell structure ruptures and the structural materials interweave, and may also combine with each other to form a similar layered structure.

[0010] Optionally, the alloy in the lithium alloy includes a binary alloy and / or a multi-element alloy, preferably a binary alloy and / or a ternary alloy. The lithium alloy can adjust the metal lithium deposition and cooperate with the lithium deposition induction structure to further improve the stability and cycle performance of the composite negative electrode.

[0011] Optionally, the alloying elements in the lithium alloy include any one or a combination of at least two of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, V, Cu, Fe or Ti.

[0012] Optionally, the content of alloying elements in the lithium alloy is not higher than 40%, for example, it can be 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5% or 3%, including but not limited to the listed point values. The content of alloying elements can take into account both energy density and cycle performance, and is preferably not higher than 20%.

[0013] Optionally, the thickness of the lithium-containing layer is 1-300 μm, for example, it can be 1 μm, 3 μm, 5 μm, 10 μm, 30 μm, 50 μm, 70 μm, 100 μm, 120 μm, 140 μm, 145 μm, 150 μm, 170 μm, 200 μm, 230 μm, 250 μm, 270 μm, 290 μm, 295 μm or 300 μm, including but not limited to the listed point values, preferably 5-150 μm.

[0014] Optionally, the lithiophilic material includes lithiophilic nanoparticles, micro-nano carriers loaded with lithiophilic nanoparticles, and / or micro-nano carriers doped with lithiophilic elements.

[0015] In the present invention, the lithium-philic material may include lithium-philic nanoparticles and / or lithium-philic elements. The lithium-philic nanoparticles may exist alone on the surface of metal lithium particles, or may be attached to micro-nano carriers such as carbon nanotubes, copper nanowires or graphene. The carrier provides a support point for the nanoparticles, which has a structural stability effect, and can also interact with the structural material. On the one hand, in the metal lithium composite material with a core-shell structure as a raw material, it can support the structural material layer. On the other hand, when the metal lithium composite negative electrode is formed, it is conducive to the uniform dispersion of the lithium-philic material as the structural material interweaves to form a three-dimensional skeleton structure, and maintains the structural stability of the lithium deposition induced structure.

[0016] Optionally, the lithium-philic element includes any one of nitrogen, phosphorus, sulfur, boron, fluorine or oxygen, or a combination of at least two of them.

[0017] Optionally, the lithium-philic nanoparticles include Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, ZnO, Co 3 O 4 、SnS 2 or Ni 2 Any one or a combination of at least two of P is preferably Ag and Au, Ag and Sn, Ag and Mg, Mg and In, Zn and ZnO, etc.

[0018] Optionally, the average particle size of the lithium-philic nanoparticles is 1-200nm, for example, it can be 1nm, 2nm, 4nm, 5nm, 7nm, 9nm, 10nm, 15nm, 20nm, 50nm, 70nm, 90nm, 100nm, 110nm, 120nm, 130nm, 150nm, 170nm, 190nm or 200nm, etc., including but not limited to the listed point values. If the particle size of the lithium-philic nanoparticles is too small, it is not conducive to uniform distribution. If the particle size is too large, it is not conducive to the formation of lithium deposition induced structure, preferably 10-120nm.

[0019] Optionally, the micro-nano carrier includes any one or a combination of at least two of carbon nanotubes, carbon nanofibers, graphene, copper nanowires, Ketjen black, conductive carbon black Super P, porous carbon, fullerene or conductive graphite, including but not limited to carbon nanotubes and Ketjen black, carbon nanofibers and porous carbon, graphene, conductive carbon black Super P and copper nanowires, fullerene and conductive graphite, etc.

[0020] Optionally, the lithium deposition inducing structure may have a layer structure, and the thickness of the layer is 1-500 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 50 nm, 80 nm,

[0021] 100nm, 150nm, 200nm, 250nm, 280nm, 300nm, 350nm, 400nm, 480nm, 490nm or 500nm, etc., including but not limited to the listed point values. If the thickness is too small, it will not have the effect of regulating the deposition of metallic lithium. If the thickness is too large, more inactive substances will be introduced, reducing the specific capacity of the material. Preferably, it is 10-300nm.

[0022] Optionally, the structural material layer includes one or a combination of at least two structural materials having a sheet, linear or tubular micro-nano structure (microstructure and / or nanostructure in one dimension), and the structural material includes lithium-phobic metal and / or micro-nano carbon material. The structural materials are interconnected and interwoven when forming a three-dimensional skeleton structure, so that the three-dimensional skeleton structure has a certain rigidity and porosity, which is convenient for the infiltration of electrolyte and the transmission of lithium ions.

[0023] In the present invention, the structural material can be the same as or different from the micro-nano carrier material in the lithium deposition induction structure. For example, the structural material can be any one of copper nanowires, carbon nanotubes, carbon nanofibers or graphene, or a combination of at least two of them. The micro-nano carrier material of the lithium deposition induction structure can be carbon nanotubes, graphene, or fullerene, Ketjen black, etc., and is not limited by the type of structural material.

[0024] In the present invention, lithium-phobic metals and / or carbon materials are selected as structural materials, and while lithium ions can be transmitted, the deposition of metallic lithium on the surface of the structural material layer is suppressed, the growth of lithium dendrites on the surface is suppressed, and the cycle life of the composite negative electrode is improved. At the same time, the structural material layer has a certain rigidity and porosity, which reserves space for the volume expansion of metallic lithium.

[0025] Optionally, the lithium-phobic metal includes copper nanowires and / or nickel nanowires.

[0026] Optionally, the micro-nano carbon material includes any one or a combination of at least two of carbon nanotubes, carbon nanofibers, graphene, fullerene, Ketjen black or conductive carbon black Super P. For example, it can be carbon nanotubes and graphene, fullerene and conductive carbon black Super P, carbon nanofibers, graphene and Ketjen black.

[0027] Optionally, the thickness of the three-dimensional skeleton structure of the structural material is 100nm-5μm, for example, it can be 100nm, 105nm, 110nm, 120nm, 150nm, 200nm, 300nm, 400nm, 450nm, 500nm, 550nm, 700nm, 1μm, 3μm, 4μm, 4.5μm or 5μm, etc., including but not limited to the listed point values. If the thickness is too small, it is not easy to form a structural material layer. If the thickness is too large, there are more inactive substances, which is not conducive to improving the energy density of the material. It is preferably 10nm-3μm.

[0028] Another aspect of the present invention provides a method for preparing the above-mentioned metal lithium composite negative electrode, the method comprising:

[0029] (1) mixing an organic solvent, lithium-containing particles and a lithiophilic material, and disposing a lithium deposition inducing layer formed by the lithiophilic material on the lithium-containing particles to obtain a precursor;

[0030] (2) mixing the precursor in step (1) with the structural material, and then spray drying or stirring at a high speed of more than 6000 rpm, and disposing a volume expansion reserved layer formed by the structural material on the precursor to obtain a metal lithium composite material with a core-shell structure;

[0031] (3) The metal lithium composite material with a core-shell structure in step (2) is disposed on a substrate surface by mechanical rolling and / or twisting, so that the core-shell structure is opened to form a lithium-containing layer containing a lithiophilic material and a structural material, thereby obtaining a metal lithium composite negative electrode.

[0032] In the present invention, the metal lithium composite negative electrode uses a metal lithium composite material with a core-shell structure as a raw material. In step (3), the metal lithium composite material is arranged on the surface of a substrate to form a lithium-containing layer. During the arrangement process, the metal lithium composite material with a core-shell structure is deformed in all directions. Due to the different ductility of the lithium-containing particles, the lithium-philic material and the structural material, the core-shell structure is opened, and the lithium-containing particles are connected to form the main part of the lithium-containing layer. At the same time, the structural materials are interwoven to form a three-dimensional skeleton structure, and the lithium-philic material forms a lithium deposition inducing structure in the three-dimensional skeleton structure in a discrete and / or continuous manner. The remaining space of the three-dimensional skeleton structure is filled with the metal lithium and / or lithium alloy, thereby obtaining a stable, uniform and continuous composite negative electrode, which can be directly composited on a current collector; and the lithium deposition inducing structure and the three-dimensional skeleton structure of the structural material play an anti-sticking role, and do not adhere to the equipment used during the arrangement process, reflecting good processing performance.

[0033] In the present invention, the specific type of the substrate is not limited, and it can be a plastic film such as PP (polypropylene), PET (polyethylene terephthalate) or PI (polyimide), or it can be a commonly used electrolytic copper foil, PET composite copper foil, etc. As long as it is a substrate that can be used by technical personnel in this field, it is suitable for the present invention.

[0034] Optionally, the organic solvent in step (1) includes any one of n-hexane, cyclohexane, N-methylpyrrolidone, benzene, p-xylene, carbon tetrachloride, tetrahydrofuran, liquid paraffin or 1,2-dichloroethane, or a combination of at least two thereof.

[0035] Optionally, the lithium-containing particles in step (1) include metallic lithium powder and lithium alloy powder, and the metallic lithium particles are provided with or without a protective layer. The protective layer composition includes but is not limited to lithium fluoride, lithium carbonate, polyethylene oxide, polyethylene glycol, polysiloxane, polytrimethylene carbonate, polycarbonate, polyethylene carbonate, polypropylene carbonate, polyvinylene carbonate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, poly(vinylidene fluoride-hexafluoropropylene), polyphenylene sulfide, p-benzoquinone, and copolymers or mixtures of at least two of the above polymers.

[0036] Optionally, step (1) further comprises heat treating the precursor, wherein the heat treatment temperature is above the temperature at which the metal lithium and the lithiophilic material react to form an alloy. That is, the heat treatment temperature is not lower than the temperature corresponding to the phase transition in the phase diagram of the alloy formed by the metal lithium and the lithiophilic material. The heat treatment causes the lithiophilic material to be in-situ alloyed with the lithium-containing core, resulting in good structural stability, and further optimizing the cycle performance of the composite negative electrode.

[0037] Optionally, the average particle size of the lithium-containing particles in step (1) is 1-100 μm, for example, it can be 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 95 μm or 100 μm, etc., preferably 5-50 μm.

[0038] Optionally, the lithiophilic material in step (1) includes lithiophilic nanoparticles, micro-nano carriers loaded with lithiophilic nanoparticles and / or micro-nano carriers doped with lithiophilic elements, preferably micro-nano carriers loaded with lithiophilic nanoparticles and / or micro-nano carriers doped with lithiophilic elements.

[0039] Optionally, the lithium-philic element includes any one of nitrogen, phosphorus, sulfur, boron, fluorine or oxygen, or a combination of at least two of them.

[0040] Optionally, the lithium-philic nanoparticles include Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, ZnO, Co 3 O 4 、SnS 2 or Ni 2 Any one or a combination of at least two of P is preferably Ag and Au, Ag and Sn, Ag and Mg, Mg and In, Zn and ZnO, etc.

[0041] Optionally, the average particle size of the lithium-philic nanoparticles is 10-200 nm, for example, 1 nm, 2 nm, 4 nm, 5 nm, 7 nm, 9 nm, 10 nm, 15 nm, 20 nm, 50 nm, 70 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 150 nm, 170 nm, 190 nm or 200 nm, etc., preferably 20-120 nm;

[0042] Optionally, in step (1), the mass ratio of the lithiophilic material to the lithium-containing particles is 1:(1-150), for example, it can be 1:1, 1:2, 1:4, 1:7, 1:10, 1:12, 1:15, 1:18, 1:20, 1:30, 1:50, 1:60, 1:70, 1:90, 1:100, 1:110, 1:130 or 1:150, etc. If the mass ratio is too small, it will not have the effect of regulating the deposition of metallic lithium. If the mass ratio is too large, more inactive substances will be introduced, thereby reducing the energy density of the material. It is preferably 1:(5-120), and more preferably 1:(15-80).

[0043] Optionally, the shape of the structural material in step (2) includes one or a combination of at least two of sheet-like, linear or tubular micro-nanostructured structural materials, and the structural material includes lithium-phobic metals and / or micro-nanocarbon materials (microstructures and / or nanostructures). For example, the structural material can be any one or a combination of at least two of copper nanowires, carbon nanotubes, carbon nanofibers or graphene. The micro-nanocarrier material of the lithium deposition induction layer can be carbon nanotubes, graphene, or fullerene, conductive carbon black Super P, etc., and is not limited by the type of structural material.

[0044] Optionally, the mass ratio of the structural material to the lithium-containing particles in step (2) is 1:(1-50), for example, it can be 1:1, 1:2, 1:4, 1:7, 1:10, 1:12, 1:15, 1:18, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45 or 1:50, etc. If the mass ratio is too small, it is not easy to form a volume expansion reserved layer; if the mass ratio is too large, there are more inactive substances, which is not conducive to improving the energy density of the material. Preferably, it is 1:(12-40).

[0045] Optionally, the spray drying conditions in step (2) include: an inlet air temperature of 180-240°C, for example, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 215°C or 220°C, etc., preferably 200-220°C; an outlet air temperature of 90-110°C, for example, 90°C, 95°C, 100°C, 105°C or 110°C, etc., preferably 100-110°C; an atomization pressure of 0.1-0.5Mpa, for example, 0.2Mpa, 0.25Mpa, 0.3Mpa, 0.35Mpa or 0.4Mpa, etc., preferably 0.2-0.4Mpa.

[0046] Optionally, the speed of the high-speed stirring in step (2) is 6000-15000 rpm, and the time is 0.5-5 min. For example, the speed can be 6000 rpm, 6500 rpm, 7000 rpm, 75000 rpm, 8000 rpm, 8500 rpm, 9000 rpm, 10000 rpm, 11000 rpm, 11500 rpm, 12000 rpm, 12500 rpm, 13000 rpm, 14000 rpm, 14500 rpm or 15000 rpm, and the time can be 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min or 5 min, etc., preferably the speed is 8000-12000 rpm, and the time is 1-3 min.

[0047] Optionally, the pressure of the mechanical rolling in step (3) is 10-100 MPa, for example, it can be 10 MPa, 12 MPa, 15 MPa, 20 MPa, 23 MPa, 25 MPa, 30 MPa, 40 MPa, 50 MPa, 55 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 95 MPa or 100 MPa, etc., preferably 20-60 MPa.

[0048] Optionally, the twisting pressure in step (3) is 1-10 GPa, for example, it can be 1 GPa, 3 GPa, 5 GPa, 7 GPa, 9 GPa or 10 GPa, etc., preferably 3-5 GPa.

[0049] Optionally, the number of twisting turns in step (3) is 1-20 turns, for example, it can be 1 turn, 2 turns, 3 turns, 5 turns, 8 turns, 10 turns, 12 turns, 15 turns, 17 turns or 20 turns, preferably 5-10 turns.

[0050] In the present invention, the type of current collector is not specifically limited, and it can be ordinary copper foil, PET (polyethylene terephthalate) composite copper foil, foam copper, carbon-coated copper foil, perforated copper foil, nickel foil and other current collectors. As long as they are commonly used by technicians in this field, they are suitable for the present invention.

[0051] Another aspect of the present invention provides an energy storage device, the energy storage device comprising the metal lithium composite negative electrode as described in the first aspect above. The energy storage device comprises a lithium primary battery, a lithium secondary battery or a lithium ion supercapacitor.

[0052] The present invention has at least one of the following beneficial technical effects:

[0053] 1. The metal lithium content in the metal lithium composite negative electrode is high, which can provide a high specific capacity.

[0054] 2. The metal lithium composite negative electrode includes a uniformly dispersed and stable lithium deposition inducing structure, which can effectively transmit lithium ions and electrons. The lithium-philic materials contained therein can effectively adjust the deposition position and uniformity of metal lithium, inhibit the growth of lithium dendrites, and regulate the internal deposition of metal lithium into the composite negative electrode. At the same time, it plays a supporting role for the structural material layer, which is beneficial to the stability of the composite negative electrode structure.

[0055] 3. The three-dimensional skeleton structure formed by the structural materials in the metal lithium composite negative electrode has certain rigidity, porosity and lithium repellency, which plays a supporting role and reserves space for metal lithium deposition and volume change at the same time; the ingenious design and mutual coordination of the lithium-philic-lithium-repellent structure of the lithium deposition-inducing material and the structural material effectively prolongs the cycle life of the composite negative electrode.

[0056] 4. The preparation method provided by the present invention adopts a metal lithium composite material with a core-shell structure as a raw material, and utilizes the different ductility of lithium-containing particles, lithium-philic materials and structural materials to form a uniform and stable negative electrode. The composite material is not easy to adhere to the equipment, so that the composite negative electrode has good processing performance.

[0057] 5. The preparation method provided by the present invention has a simple and easy process, can be adjusted to prepare composite negative electrodes with different proportions, and is easy for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is the SEM image of the precursor in Example 2;

[0059] Figure 2 This is a SEM image of the metal lithium composite material with a core-shell structure in Example 2;

[0060] Figure 3 This is the SEM image of the composite negative electrode in Example 2. DETAILED DESCRIPTION

[0061] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] Example 1

[0063] The present embodiment provides a metal lithium composite negative electrode, which includes a metal lithium layer with a thickness of 5 μm, in which a structural material layer with a thickness of 100 nm formed by graphene and a lithium deposition inducing layer with a thickness of 10 nm formed by nano-gold powder are distributed, and the lithium deposition inducing layer is interspersed in the structural material layer.

[0064] The method for preparing the composite negative electrode comprises the following steps:

[0065] (1) 0.01 g of nano-gold powder with an average particle size of 15 nm (purchased from Beijing Zhongke Keyou Technology Co., Ltd.) was dispersed in p-xylene, 1.2 g of metal lithium particles with an average particle size of 5 μm were added, and mechanical stirring was performed to arrange the lithium deposition induction layer formed by the nano-gold powder on the metal lithium particles to obtain a precursor;

[0066] (2) mixing the precursor in step (1) with 0.8 g of a graphene dispersion having a mass fraction of 3%, stirring at a rotation speed of 8000 rpm for 1 min, separating the solid, and obtaining a metal lithium composite material with a core-shell structure;

[0067] (3) The core-shell structure lithium metal composite material in step (2) is placed on a 6 μm copper foil surface by mechanical rolling at a pressure of 10 MPa, and the thickness of the lithium metal layer is controlled to be 5 μm to obtain the composite negative electrode.

[0068] Example 2

[0069] The present embodiment provides a metal lithium composite negative electrode, which includes a metal lithium layer with a thickness of 150 μm, in which a structural material layer with a thickness of 3 μm formed by single-walled carbon nanotubes and a lithium deposition inducing layer with a thickness of 300 nm formed by nano silver powder are distributed, and the lithium deposition inducing layer is interspersed in the structural material layer.

[0070] The method for preparing the composite negative electrode comprises the following steps:

[0071] (1) 0.015 g of silver powder with an average particle size of 20 nm (purchased from Aladdin) and 0.005 g of single-walled carbon nanotube dispersion (purchased from Okoshiel) were dispersed in n-hexane, 1.2 g of metal lithium particles containing a LiF protective layer were added, and high-speed stirring was performed at a rate of 10,000 rpm, and a lithium deposition induction layer formed by the single-walled carbon nanotubes deposited with nano-silver powder was arranged on the metal lithium particles to obtain a precursor; Figure 1 The SEM characterization result of the precursor can clearly show that the lithium deposition induction layer formed by the single-walled carbon nanotubes deposited with nano-silver powder is arranged on the metal lithium particles;

[0072] (2) mixing the precursor in step (1) with 1.6 g of a single-walled carbon nanotube dispersion (purchased from Auxiliary), wherein the mass fraction of the single-walled carbon nanotubes in the dispersion is 3%, and then spray drying the mixture with an inlet air temperature of 220° C., an outlet air temperature of 100° C., and an atomization pressure of 0.3 MPa to obtain a composite material with a core-shell structure; Figure 2 and Figure 1 By comparison, it can be seen that the single-walled carbon nanotubes are wrapped around the surface of the precursor to form a core-shell structure;

[0073] (3) Mechanically rolling the core-shell structure composite material in step (2) onto a 6 μm copper foil surface at a rolling pressure of 30 MPa to obtain the composite negative electrode.

[0074] Figure 3 This is the SEM characterization result of the composite negative electrode. It can be clearly seen from the figure that: the surface of the composite negative electrode is uniform, because the metal lithium composite material particles with a core-shell structure are easy to form; the surface of the composite negative electrode is continuous and uniform, showing a state of metal lithium belts, from which it can be known that after the metal lithium powder is deformed, it penetrates and / or connects the lithium deposition inducing layer and the structural material layer, and connects with each other to form a negative electrode.

[0075] Example 3

[0076] The present embodiment provides a metallic lithium composite negative electrode, which includes a lithium-boron alloy layer with a thickness of 300 μm, in which a structural material layer with a thickness of 5 μm formed by copper nanowires and a lithium deposition inducing layer with a thickness of 200 nm formed by zinc oxide are distributed, and the lithium deposition inducing layer is interspersed in the structural material layer.

[0077] The preparation method of the composite negative electrode comprises the following steps:

[0078] (1) 1.2 g of zinc oxide with an average particle size of 200 nm (purchased from Yijin New Materials) was dispersed in n-hexane, and 1.2 g of lithium-boron alloy particles with an average particle size of 100 μm was added, wherein the boron mass content of the lithium-boron alloy was 20%, and the mixture was stirred at a high speed of 15000 rpm to arrange a lithium deposition induction layer formed by nano-cobalt oxide on the metal lithium particles to obtain a precursor;

[0079] (2) mixing the precursor in step (1) with 80 g of a copper nanowire dispersion (purchased from Aladdin), wherein the mass fraction of the copper nanowires in the dispersion is 1.5%, and then spray drying the mixture at an air inlet temperature of 240° C., an air outlet temperature of 90° C., and an atomization pressure of 0.5 MPa to obtain a composite material with a core-shell structure;

[0080] (3) The core-shell composite material in step (2) is twisted into a film material, the number of twists is 10, the twisting pressure is 5 GPa, and then the film material is mechanically rolled onto the surface of the carbon-coated copper foil to obtain the composite negative electrode.

[0081] Example 4

[0082] Compared with Example 2, the only difference is that the precursor obtained in step (1) is heated to 200° C. and kept warm for 30 minutes for in-situ alloying, and the alloyed precursor is subjected to the operations in steps (2) and (3), and the other conditions are the same.

[0083] Example 5

[0084] Compared with Example 2, the only difference is that the mass of the nano silver powder in step (1) is replaced with 0.005 g, and the other conditions remain unchanged.

[0085] Example 6

[0086] Compared with Example 2, the only difference is that the mass of nano silver powder in step (1) is replaced with 1.5 g, and the other conditions remain unchanged.

[0087] Example 7

[0088] Compared with Example 2, the only difference is that the mass of the single-walled carbon nanotubes in step (2) is replaced with 0.02 g, and the other conditions remain unchanged.

[0089] Example 8

[0090] Compared with Example 2, the only difference is that the mass of the single-walled carbon nanotubes in step (2) is replaced with 45 g, and the other conditions remain unchanged.

[0091] Example 9

[0092] Compared with Example 3, the only difference is that the lithium-boron alloy is replaced by a lithium-silver alloy, and the other conditions are the same.

[0093] Example 10

[0094] Compared with Example 3, the only difference is that the lithium-boron alloy is replaced by lithium-indium-chromium alloy, and the other conditions are the same.

[0095] Comparative Example 1

[0096] Compared with Example 2, the only difference is that the negative electrode provided in this comparative example is formed by pressing metal lithium particles containing a protective layer of LiF, without a lithium deposition inducing layer and a structural material layer, and the other conditions are the same.

[0097] Comparative Example 2

[0098] Compared with Example 2, the only difference is that the composite negative electrode provided in this comparative example includes a metal lithium layer with a thickness of 150 μm, in which a lithium deposition inducing layer with a thickness of 300 nm formed by nano-silver powder is distributed, and does not include a structural material layer, and the other conditions are the same.

[0099] Comparative Example 3

[0100] Compared with Example 2, the only difference is that the metal lithium composite negative electrode provided in this comparative example includes a metal lithium layer with a thickness of 150 μm, in which a structural material layer with a thickness of 3 μm formed by single-walled carbon nanotubes is distributed, and does not include a lithium deposition inducing layer. The other conditions are the same.

[0101] Comparative Example 4

[0102] Compared with Example 2, the only difference is that the composite negative electrode provided in this comparative example includes a metal lithium composite negative electrode with a core-shell structure, and the rolling pressure in step (3) is 2 MPa.

[0103] Material performance testing:

[0104] The negative electrodes provided in Examples 1-10 and Comparative Examples 1-4 were prepared into negative electrode sheets and LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) positive electrode assembly full battery CR2025, electrolyte is 1mol / LLiPF 6 EC (ethylene carbonate) / DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) (volume ratio of 1:1:1), 10wt% FEC (fluoroethylene carbonate) and 2wt% VC (vinylene carbonate) electrolyte were added. The cycle performance was tested under the conditions of voltage range of 2.7-4.3V, 0.2C charge and 0.3C discharge. The test was terminated when the discharge specific capacity was 80% of the initial discharge specific capacity. The test results are shown in Table 1.

[0105] Table 1

[0106]

[0107] From Table 1, we can see the following points:

[0108] (1) In combination with Example 2 and Example 4, the precursor undergoes in-situ alloying after heat treatment, which can further optimize the cycle performance of the composite negative electrode.

[0109] (2) Combining Example 2 and Examples 5-6, the composite negative electrode of Example 2 can take into account both specific capacity and cycle performance. The lithium deposition induction layer of the silver powder layer in Example 5 is thinner. Although the specific capacity is higher than that of Example 2, the cycle performance is worse than that of Example 2. The negative electrode in Example 6 has a good cycle life, but a low specific capacity.

[0110] (3) Combining Example 2 and Examples 7-8, the composite negative electrode of Example 2 can take into account both specific capacity and cycle performance. The thickness of the structural material layer composed of single-walled carbon nanotubes in Example 7 is thinner than that in Example 2. Although the specific capacity is higher than that in Example 2, the cycle performance is worse than that in Example 2. The negative electrode in Example 8 has a good cycle life, but a low specific capacity.

[0111] (4) In combination with Example 3 and Examples 9-10, the lithium alloy as the lithium-containing layer has the ability to regulate the deposition of metallic lithium, and its cycle performance is better than that of metallic lithium powder. It cooperates with the lithium deposition inducing layer and the structural material layer, so that the composite negative electrode has good cycle performance.

[0112] (5) Combining Example 2 and Comparative Examples 1-4, the cycle performance of the composite negative electrode prepared in Example 2 is better than that of the negative electrodes in Comparative Examples 1-4. This is because the composite negative electrode in Example 2 uses a metal lithium composite material with a micro-nano core-shell structure as a raw material, and regulates the structure of the composite negative electrode at the micro-nano scale, so that it has both excellent cycle performance and specific capacity; the composite negative electrode in Comparative Example 1 is pressed from metal lithium powder, and the surface is not modified, so dendrites are easily generated during the deposition of metal lithium; in Comparative Example 2, although the silver powder on the surface of the composite negative electrode can regulate the deposition of metal lithium, because it has no structural material layer to regulate the current density and alleviate the volume change, the silver powder on the surface of the composite negative electrode regulates the metal lithium to preferentially deposit on the outer surface, and lithium dendrites are formed as the cycle proceeds. In Comparative Example 3, it may be because it has no lithium deposition inducing layer, and as the cycle proceeds, the deposition of metal lithium cannot be regulated. In the preparation method in Comparative Example 4, the rolling pressure is small, and the metal lithium composite negative electrode with a core-shell structure maintains the core-shell structure, but the contact between the particles may be poor, resulting in poor specific capacity and cycle performance compared with Example 2.

[0113] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A metal lithium composite negative electrode, It is characterized in that The composite negative electrode includes a lithium-containing layer, wherein the lithium-containing layer contains a lithiophilic material and a lithium-phobic structural material distributed in metallic lithium and / or a lithium alloy, wherein the structural materials are interwoven to form a three-dimensional skeleton structure, the lithiophilic material forms a lithium deposition-inducing structure in the three-dimensional skeleton structure in a discrete and / or continuous manner, and the remaining internal space of the three-dimensional skeleton structure is filled with the metallic lithium and / or lithium alloy.

2. The metal lithium composite negative electrode according to claim 1, It is characterized in that The lithium alloy comprises a binary alloy and / or a multi-element alloy, preferably a binary alloy and / or a ternary alloy; Preferably, the alloying elements in the lithium alloy include any one or a combination of at least two of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, V, Cu, Fe or Ti; Preferably, the mass content of the alloying element is not higher than 40%, preferably not higher than 20%; Preferably, the thickness of the lithium-containing layer is 1-300 μm, preferably 5-150 μm.

3. The metal lithium composite negative electrode according to claim 1 or 2, It is characterized in that The structural material comprises one or a combination of at least two of structural materials having a sheet-like, linear or tubular micro-nano structure, and the structural material comprises a lithium-phobic metal and / or a micro-nano carbon material; Preferably, the lithium-phobic metal comprises copper nanowires and / or nickel nanowires; Preferably, the micro-nano carbon material includes carbon nanotubes, carbon nanofibers, graphene 、 Any one of fullerene, Ketjen black or conductive carbon black Super P, or a combination of at least two thereof; Preferably, the thickness of the three-dimensional skeleton structure formed by the structural material is 100 nm-5 μm, preferably 500 nm-3 μm.

4. The metal lithium composite negative electrode according to any one of claims 1 to 3, It is characterized in that The lithium-philic material includes lithium-philic nanoparticles, micro-nano carriers loaded with lithium-philic nanoparticles and / or micro-nano carriers doped with lithium-philic elements; Preferably, the lithium-philic element includes any one of nitrogen, phosphorus, sulfur, boron, fluorine or oxygen, or a combination of at least two thereof; Preferably, the lithium-philic nanoparticles include Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, ZnO, Co 3 O 4 、SnS 2 or Ni 2 Any one or a combination of at least two of P; Preferably, the average particle size of the lithium-philic nanoparticles is 1-200 nm, preferably 10-120 nm; Preferably, the micro-nano carrier includes carbon nanotubes, carbon nanofibers, graphene, copper nanowires 、 Any one of Ketjen black, conductive carbon black Super P, porous carbon, fullerene or conductive graphite, or a combination of at least two thereof; Preferably, when the lithiophilic material forms a lithium deposition inducing structure in a continuous manner, the thickness of the layer structure of the lithium deposition inducing structure is 1-500 nm, preferably 10-300 nm.

5. The metal lithium composite negative electrode according to any one of claims 1 to 4, It is characterized in that The metal lithium composite negative electrode further includes a current collector, and the lithium-containing layer is attached to at least one surface of the current collector.

6. A method for preparing a metal lithium composite negative electrode according to any one of claims 1 to 5, It is characterized in that The method comprises: (1) mixing an organic solvent, lithium-containing particles and a lithiophilic material, and disposing a lithium deposition inducing layer formed by the lithiophilic material on the lithium-containing particles to obtain a precursor; (2) mixing the precursor in step (1) with the structural material, and then spray drying or stirring at a high speed of more than 6000 rpm, and disposing a volume expansion reserved layer formed by the structural material on the precursor to obtain a metal lithium composite material with a core-shell structure; (3) The metal lithium composite material with a core-shell structure in step (2) is disposed on a substrate surface by mechanical rolling and / or twisting, so that the core-shell structure is opened to form a lithium-containing layer containing a lithiophilic material and a structural material, thereby obtaining a metal lithium composite negative electrode.

7. The method according to claim 6, It is characterized in that The organic solvent in step (1) comprises any one or a combination of at least two of liquid alkanes having 5 to 15 carbon atoms, liquid cycloalkanes having 5 to 15 carbon atoms, N-methylpyrrolidone, benzene, p-xylene, carbon tetrachloride, tetrahydrofuran, liquid paraffin or 1,2-dichloroethane; Preferably, step (1) further comprises subjecting the precursor to heat treatment, wherein the temperature of the heat treatment is above the temperature at which the metallic lithium and the lithiophilic material undergo an alloying reaction.

8. The method according to claim 6 or 7, It is characterized in that The rotation speed of step (2) is 6000-15000 rpm, and the time is 0.5-5 min; Preferably, the rotation speed is 8000-12000 rpm, and the time is 1-3 min.

9. The method according to any one of claims 6 to 8, It is characterized in that The pressure of the mechanical rolling in step (3) is 10-100 MPa, preferably 20-60 MPa; Preferably, the twisting pressure in step (3) is 1-10 GPa, preferably 3-5 GPa; Preferably, the number of twisting turns in step (3) is 1-20 turns, preferably 5-10 turns.

10. An energy storage device, It is characterized in that The energy storage device comprises a metal lithium composite negative electrode as described in any one of claims 1 to 5; Preferably, the energy storage device comprises a lithium primary battery, a lithium secondary battery or a lithium ion supercapacitor.

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