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 metal lithium composite negative electrode comprises a negative electrode active material layer, the layer comprises a metal lithium composite material with a core-shell structure, and the metal lithium composite material with the core-shell structure takes lithium-containing particles as an inner core; the inner core is provided with a lithium deposition induction layer containing a lithium-loving material as a middle layer and a lithium-phobic volume expansion reserved layer as an outermost layer. The lithium deposition induction layer can induce metal lithium to preferentially deposit and grow inwards, and the cycle performance of the composite negative electrode can be improved. The volume expansion reserved layer provides a lithium ion transmission channel and effectively relieves the volume expansion problem in the metal lithium circulation process. And the lithium deposition induction layer and the volume expansion reserved layer 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 109309205 A discloses a lithium-sulfur battery negative electrode, a preparation method thereof, and a lithium-sulfur battery. The negative electrode of the lithium-sulfur battery includes a current collector and an electrode material layer with a lithium-carbon composite material as an active material attached to the surface of the current collector, wherein the electrode material layer is composed of a micro-nanoscale metal lithium-skeleton carbon composite material, or the electrode material layer contains a micro-nanoscale lithium alloy-skeleton carbon composite material. During the charge and discharge process of the negative electrode, metal lithium is preferentially deposited on the outer surface of the skeleton carbon material, and lithium dendrites are easily formed. With the deepening of research, nano-silicon is loaded on the outer surface of the skeleton carbon, and there is a problem of uneven silicon dispersion, which has limited effect on the regulation of metal lithium deposition.

[0004] To address this problem, the present application proposes a metal lithium composite negative electrode, which effectively solves the problem of volume change and dendrite generation during the cycle of metal lithium, thereby improving the cycle life of the battery. Summary of the invention

[0005] The present invention aims to solve the above technical problems. The inventors have found that a metal lithium composite negative electrode (i.e., a negative electrode containing a lithium composite material) using a core-shell structured lithium composite material as a raw material can effectively solve the above problems. The metal lithium composite material of the core-shell structure has lithium-containing particles as the core, a lithium deposition inducing layer as the middle layer coating the lithium-containing particles, and a volume expansion reserved layer as the outermost layer. The composite negative electrode has good cycle performance and excellent processing performance.

[0006] Specifically, one aspect of the present invention provides a metal lithium composite negative electrode, the composite negative electrode includes a negative electrode active material layer, the negative electrode active material layer contains a metal lithium composite material with a core-shell structure, the metal lithium composite material with a core-shell structure has lithium-containing particles as a core, a lithium deposition inducing layer containing a lithium-philic material as an intermediate layer and a lithium-phobic volume expansion reserved layer as an outermost layer is arranged on the core, and the metal lithium composite materials with the core-shell structure are in contact with each other and form a continuous three-dimensional skeleton through the lithium-phobic volume expansion reserved layer.

[0007] In the present invention, the metal lithium composite material of the core-shell structure is a micro-nano-scale particle material, which is deformed during the preparation of the negative electrode, for example, the shape changes from a nearly spherical shape to an ellipsoidal shape, and the metal lithium composite materials of the core-shell structure are in contact with each other, wherein the lithium-phobic volume expansion layer forms a continuous, uniform and stable three-dimensional skeleton, regulates the transmission of lithium ions to the inside, and the metal lithium will not be deposited on the outermost layer, and the lithium deposition induction layer forms a uniformly dispersed deposition site, regulates the metal lithium deposition and induces the metal lithium to deposit and grow to the inside. In the metal lithium composite negative electrode, the lithium deposition induction layer and the volume expansion reserved layer cooperate with each other, and are regulated at the micro-nano scale, effectively solving the volume change and cycle dendrite generation problems, and having excellent cycle performance.

[0008] Optionally, the lithium-containing particles include metallic lithium powder and / or 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.

[0009] Optionally, the lithium alloy includes a binary alloy and / or a multi-element alloy, preferably a binary alloy and / or a ternary alloy. With the lithium alloy as the core, the metal lithium deposition can be adjusted, and at the same time, it cooperates with the lithium deposition inducing layer to further improve the stability and cycle performance of the composite negative electrode.

[0010] Optionally, the lithium alloy includes any one or a combination of at least two elements of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, V, Cu, Fe or Ti.

[0011] 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%.

[0012] Optionally, the average particle size of the lithium-containing particles 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, including but not limited to the listed point values, preferably 5-50 μm.

[0013] Optionally, the thickness of the negative electrode active material layer is 1-200 μm, for example, 1 μm,

[0014] 2μm, 5μm, 10μm, 15μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm,

[0015] 80μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm or 200μm, etc., including but not limited to the listed point values, preferably 5-100μm.

[0016] Optionally, the lithiophilic material includes lithiophilic nanoparticles, micro-nano carriers loaded with lithiophilic nanoparticles, and / or micro-nano carriers doped with lithiophilic elements.

[0017] In the present invention, the lithium deposition inducing layer may include lithium-philic nanoparticles and / or lithium-philic elements. The lithium-philic nanoparticles may exist alone on the surface of the metal lithium particles, or may be attached to micro-nano carriers such as carbon nanotubes, copper nanowires or graphene and disposed on the surface of the metal lithium particles. 。 The micro-nano carrier provides a support point for the nanoparticles, plays a role in stabilizing the structure, and also plays a supporting role for the volume expansion layer, which is beneficial to further improve the structural stability of the material.

[0018] Preferably, the mass of the micro-nano carrier loaded with lithium-philic nanoparticles and / or the micro-nano carrier doped with lithium-philic elements is less than or equal to the mass of the volume expansion layer. The thickness is regulated by mass to construct a thickness gradient, which is conducive to the deformation of the lithium deposition induction layer.

[0019] 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.

[0020] Optionally, the lithium-philic nanoparticles include any one of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, ZnO, Co3O4, SnS2 or Ni2P, or a combination of at least two of them, preferably Ag and Au, Ag and Sn, Ag and Mg, Mg and In, Zn and ZnO, etc.

[0021] 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. The particle size of the lithium-philic nanoparticles is too small, which is not conducive to uniform distribution, and the particle size is too large, which is not conducive to the formation of a lithium deposition inducing layer, preferably 10-120nm.

[0022] 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.

[0023] Optionally, the mass ratio of the lithium deposition inducing layer 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, which will reduce the energy density of the material. It is preferably 1:(5-120), and more preferably 1:(15-80).

[0024] Optionally, the thickness of the lithium deposition inducing structural layer is 1-500nm, for example, it can be 1nm, 5nm, 10nm, 15nm, 20nm, 50nm, 80nm, 100nm, 150nm, 200nm, 250nm, 280nm, 300nm, 350nm, 400nm, 480nm, 490nm or 500nm, including but not limited to the listed point values. If the thickness is too small, the effect of regulating the deposition of metallic lithium will not be achieved. If the thickness is too large, more inactive substances will be introduced, which will reduce the specific capacity of the material. It is preferably 10-300nm.

[0025] Optionally, the volume expansion reserved 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), and the structural material includes a lithium-phobic metal and / or a micro-nano carbon material. The structural materials are interconnected and interwoven when forming the volume expansion layer, so that the volume expansion layer has a certain rigidity and porosity, which is convenient for the infiltration of the electrolyte and the transmission of lithium ions.

[0026] 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 layer. 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 layer can be carbon nanotubes, graphene, or fullerene, Ketjen black, etc., and is not limited by the type of structural material.

[0027] In the present invention, lithium-phobic metal and / or carbon material is selected as the volume expansion reserved layer, which can inhibit the deposition of metallic lithium on the surface of the volume expansion reserved layer while lithium ions can be transmitted, inhibit the growth of lithium dendrites on the surface, and improve the cycle life of the composite negative electrode. At the same time, the volume expansion reserved layer has a certain rigidity and porosity, which reserves space for the volume expansion of metallic lithium.

[0028] Optionally, the lithium-phobic metal includes copper nanowires and / or nickel nanowires.

[0029] Optionally, 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. For example, it may be carbon nanotubes and graphene, fullerene and conductive carbon black Super P, carbon nanofibers, graphene and Ketjen black.

[0030] Optionally, the mass ratio of the volume expansion reserved layer to the lithium-containing particles 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. It is preferably 1:(12-40).

[0031] Optionally, the volume expansion reserved layer has a thickness of 2nm-5μm, for example, it can be 2nm, 5nm, 10nm, 20nm, 50nm, 100nm, 300nm, 500nm, 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 volume expansion reserved 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.

[0032] Another aspect of the present invention provides a method for preparing the above-mentioned metal lithium composite negative electrode, the method comprising:

[0033] (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;

[0034] (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;

[0035] (3) The core-shell lithium metal composite material in step (2) is disposed on at least one side of the current collector, wherein the disposition method includes any one of mechanical rolling, twisting or coating, or a combination of at least two of them.

[0036] In the present invention, the metal lithium composite negative electrode uses a metal lithium composite material with a core-shell structure as an active material. In the process of setting the metal lithium composite material on the surface of the current collector in step (3), the composite material uses lithium-containing particles as the core, is easy to shape, and can form a stable, uniform and continuous negative electrode; and the lithium deposition induction layer and volume expansion reserved layer of the composite material play an anti-sticking role, and does not adhere to the equipment used during the setting process, showing good processing performance.

[0037] In the present invention, the specific type of the current collector is not limited, and it can be ordinary copper foil, PET composite copper foil, foam copper, carbon-coated copper foil, punched copper foil, nickel foil, etc., mainly current collectors used by technicians in this field are all suitable for the present invention.

[0038] 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.

[0039] 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.

[0040] Optionally, the lithium-containing particles in step (1) include pure metallic lithium particles and / or lithium alloy powder.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Optionally, the lithium-philic nanoparticles include any one of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, ZnO, Co3O4, SnS2 or Ni2P, or a combination of at least two of them, preferably Ag and Au, Ag and Sn, Ag and Mg, Mg and In, Zn and ZnO, etc.

[0045] 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;

[0046] Optionally, the mass ratio of the lithium-philic material to the metallic lithium particles in step (1) 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, which will reduce the energy density of the material. It is preferably 1:(5-120), and more preferably 1:(15-80).

[0047] 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.

[0048] Optionally, the mass ratio of the structural material to the metallic lithium 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).

[0049] Optionally, the spray drying conditions in step (2) include: an air inlet temperature of 180-240°C, such as 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 215°C or 220°C, etc., preferably 200-220°C; an air outlet temperature of 90-110°C, such as 90°C, 95°C, 100°C, 105°C or 110°C, etc., preferably 100-110°C; an atomization pressure of 0.1-0.5Mpa, such as 0.2Mpa, 0.25Mpa, 0.3Mpa, 0.35Mpa or 0.4Mpa, etc., preferably 0.2-

[0050] 0.4Mpa.

[0051] 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.

[0052] Optionally, the pressure of the mechanical rolling in step (3) is 1-10 MPa, for example, it can be 1 MPa, 1.2 MPa, 1.5 MPa, 2 MPa, 2.3 MPa, 2.5 MPa, 3 MPa, 4 MPa, 5 MPa, 5.5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 9.5 MPa or 10 MPa, etc., preferably 2-6 MPa.

[0053] Optionally, the twisting pressure in step (3) is 0.1-10 MPa, for example, it can be 0.1 MPa, 0.3 MPa, 0.5 MPa, 1 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 7 MPa, 9 MPa or 10 MPa, etc., preferably 0.5-5 MPa, and more preferably 3-5 MPa.

[0054] 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.

[0055] Optionally, the coating in step (3) includes the following process:

[0056] A non-polar solvent, a conductive agent and a binder are mixed to prepare a conductive slurry, and then a metal lithium composite material is added to mix to prepare a negative electrode slurry, which is coated on a current collector and baked to obtain a negative electrode sheet;

[0057] The non-polar solvent includes any one or a combination of at least two of liquid alkanes with 5 to 10 carbon atoms, liquid cycloalkanes with 5 to 15 carbon atoms, benzene, p-xylene or petroleum ether, preferably any one or a combination of at least two of p-xylene, cyclohexane, n-hexane or heptane;

[0058] The conductive agent includes any one of acetylene black, Ketjen black, conductive graphite, Cabot black or Super P, or a combination of at least two thereof;

[0059] The binder includes any one or a combination of at least two of styrene-butadiene rubber, polyisobutylene, styrene-butadiene-styrene block copolymer or styrene-ethylene-butylene-styrene block copolymer.

[0060] The mass ratio of the conductive agent, the binder and the metal lithium composite material is (1-5): (1-5):

[0061] (90-98), for example, it can be 1:1:98, 1:3:96, 2:2:96, 2:5:93, 3:2:95, 3:3:94, 4:5:91, 5:5:90, etc., preferably (2-3): (2-3): (94-96).

[0062] Another aspect of the present invention provides a lithium battery, wherein the lithium battery comprises the metal lithium composite negative electrode as described in the first aspect.

[0063] The present invention has at least one of the following beneficial technical effects:

[0064] 1. The lithium metal composite negative electrode has a high content of lithium metal (containing the core of lithium particles), which can provide high energy density.

[0065] 2. The metal lithium composite negative electrode includes uniformly dispersed deposition sites that can effectively transmit lithium ions and electrons, and contains lithium-philic materials that 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 supports the volume expansion reserved layer, which is beneficial to the stability of the composite negative electrode structure.

[0066] 3. The volume expansion reserved layer in the metal lithium composite negative electrode has certain rigidity, porosity and lithium repellency, which can play the role of a three-dimensional protective skeleton and reserve 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 layer and the volume expansion reserved layer effectively extend the cycle life of the composite negative electrode.

[0067] 4. The metal lithium composite material particles with a core-shell structure are easy to shape and can 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.

[0068] 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

[0069] Figure 1is the SEM image of the precursor in Example 2;

[0070] Figure 2 This is a SEM image of the metal lithium composite material with a core-shell structure in Example 2;

[0071] Figure 3 is a SEM image of the composite negative electrode in Example 2;

[0072] Figure 4 The battery cycle test curves of Example 2 and Comparative Examples 1, 2 and 3 are shown. DETAILED DESCRIPTION

[0073] 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.

[0074] Example 1

[0075] This embodiment provides a metal lithium composite negative electrode, the composite negative electrode includes a core-shell structure metal lithium composite material, the composite material includes a metal lithium particle core, the metal lithium particle is pure metal lithium, the core is provided with tin powder with an average particle size of 100nm as a lithium deposition induction layer, and the lithium deposition induction layer is provided with graphene as a volume expansion reserved layer. The thickness of the negative electrode active layer formed by the core-shell structure metal lithium composite material in the composite negative electrode is 5μm.

[0076] The method for preparing the composite negative electrode comprises the following steps:

[0077] (1) 0.008 g of tin powder with an average particle size of 100 nm (purchased from Beijing Dekedao Gold) 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-tin powder on the metal lithium particles to obtain a precursor;

[0078] (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;

[0079] (3) The core-shell structure lithium metal composite material, acetylene black and polyisobutylene in step (2) are mixed in a mass ratio of 96:2:2, with n-hexane as the solvent, to prepare a negative electrode slurry with a solid content of 40%, which is then coated on the surface of a 6 μm copper foil, dried, and compacted to control the thickness of the active material layer to 5 μm, thereby obtaining the composite negative electrode.

[0080] Example 2

[0081] This embodiment provides a metal lithium composite negative electrode, the metal lithium composite negative electrode includes a core-shell structure metal lithium composite material, the composite material includes a metal lithium particle core, the metal lithium particle is a metal lithium particle containing a protective layer of LiF, a single-walled carbon nanotube with a silver powder having an average particle size of 20nm is deposited on the core as a lithium deposition induction layer, and a single-walled carbon nanotube is disposed on the lithium deposition induction layer as a volume expansion reserved layer. The thickness of the negative electrode active layer formed by the core-shell structure metal lithium composite material in the composite negative electrode is 80μm.

[0082] The method for preparing the composite negative electrode comprises the following steps:

[0083] (1) 0.015 g of silver powder with an average particle size of 20 nm (purchased from Xidian Laboratory) 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 with an average particle size of 50 μm 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 be clearly seen 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, and the single-walled carbon nanotubes are sparsely distributed to form a thinner layer;

[0084] (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 air inlet temperature of 200° C., an air outlet 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; the single-walled carbon nanotubes as the reserved layer for volume expansion are thicker;

[0085] (3) Mechanically rolling the core-shell structure composite material in step (2) onto a 6 μm copper foil surface at a rolling pressure of 2 MPa to obtain the composite negative electrode.

[0086] Figure 3 This is a SEM image of the composite negative electrode. It can be clearly seen from the image that the composite negative electrode includes a metal lithium composite material with a core-shell structure, and the metal lithium composite materials with the core-shell structure are in contact with each other and form a continuous three-dimensional skeleton through a lithium-phobic volume expansion reserved layer.

[0087] Example 3

[0088] This embodiment provides a metal lithium composite negative electrode, the composite negative electrode includes a core-shell structure metal lithium composite material, the composite material includes a lithium-boron alloy core, the boron content is 20%, the core is provided with zinc oxide with an average particle size of 200nm as a lithium deposition induction layer, and the lithium deposition induction layer is provided with copper nanowires as a volume expansion reserved layer. The thickness of the composite negative electrode is 180μm.

[0089] The method for preparing the composite negative electrode comprises the following steps:

[0090] (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, 1.2 g of lithium-boron alloy particles with an average particle size of 100 μm were added, and high-speed stirring was performed at a rate of 15000 rpm to set a lithium deposition induction layer formed by nano-cobalt oxide on the metal lithium particles to obtain a precursor;

[0091] (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;

[0092] (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 MPa, and then the film material is mechanically rolled onto the surface of the carbon-coated copper foil to obtain the composite negative electrode.

[0093] Example 4

[0094] 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.

[0095] Example 5

[0096] Compared with Example 2, the only difference is that the mass of the silver powder is replaced with 1.5 g, and the other conditions remain unchanged.

[0097] Example 6

[0098] Compared with Example 2, the only difference is that the mass of silver powder is replaced with 0.005 g, and the other conditions remain unchanged.

[0099] Example 7

[0100] Compared with Example 2, the only difference is that the silver powder is replaced by a mixture of tin powder (average particle size 50 nm, purchased from Xidian Laboratory) and silver powder, the mass ratio of the two is 1:1, and the other conditions remain unchanged.

[0101] Example 8

[0102] Compared with Example 2, the only difference is that the mass of the single-walled carbon nanotube dispersion in step (2) is replaced with 0.05 g, and the other conditions remain unchanged.

[0103] Example 9

[0104] Compared with Example 2, the only difference is that the mass of the single-walled carbon nanotube dispersion in step (2) is replaced with 50 g, and the other conditions remain unchanged.

[0105] Example 10

[0106] 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.

[0107] Embodiment 11

[0108] Compared with Example 10, the only difference is that the silver content is replaced with 45%, and the other conditions are the same.

[0109] Example 12

[0110] Compared with Example 3, the only difference is that the lithium-boron alloy is replaced by lithium-indium alloy, and the other conditions are the same.

[0111] Comparative Example 1

[0112] Compared with Example 2, the only difference is that in the composite negative electrode provided in this comparative example, the metal lithium core is a metal lithium particle containing a protective layer of LiF, with an average particle size of 45 μm and no intermediate layer and outermost layer.

[0113] Comparative Example 2

[0114] Compared with Example 2, the only difference is that the composite negative electrode provided in this comparative example includes a metallic lithium composite material, the composite material includes a metallic lithium particle core, the metallic lithium particle is a metallic lithium particle containing a protective layer of LiF, and the average particle size is 45 μm, and the core is provided with single-walled carbon nanotubes with silver powder having an average particle size of 20 nm deposited thereon as a lithium deposition inducing layer, and does not include a volume expansion reserved layer formed by the single-walled carbon nanotubes.

[0115] Comparative Example 3

[0116] Compared with Example 2, the only difference is that the composite negative electrode provided in this comparative example includes a metal lithium composite material with a core-shell structure, the composite material includes a metal lithium particle core, the metal lithium particle is a metal lithium particle containing a protective layer of LiF, and the average particle size is 45 μm, and a volume expansion reserved layer formed by single-walled carbon nanotubes is arranged on the core, and a lithium deposition induction layer of single-walled carbon nanotubes with an average particle size of 20 nm silver powder is not included.

[0117] Material performance testing:

[0118] The composite negative electrode provided in Examples 1-12 and Comparative Examples 1-3 was prepared into a negative electrode sheet and LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) positive electrode assembled full battery CR2025, the electrolyte is 1mol / LLiPF6 EC (ethylene carbonate) / DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) (volume ratio is 1:1:1), added with 10wt% FEC (fluoroethylene carbonate) and 2wt% VC (vinylene carbonate) electrolyte. The cycle performance was tested under the conditions of voltage range of 2.7-4.3V, 0.2C charging and 0.3C discharging. The test ended when the discharge specific capacity was 80% of the initial discharge specific capacity. The test results are shown in Table 1.

[0119] Table 1

[0120] Stable cycle times Example 1 150 Example 2 210 Example 3 243 Example 4 225 Example 5 134 Example 6 138 Example 7 212 Example 8 126 Example 9 152 Example 10 255 Embodiment 11 146 Example 12 245 Comparative Example 1 92 Comparative Example 2 120 Comparative Example 3 113

[0121] From Table 1, we can see the following points:

[0122] (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.

[0123] (2) In combination with Example 2 and Examples 5-6, the silver powder constituting the lithium deposition inducing layer cannot effectively improve the cycle performance of the composite negative electrode if the content is too little or too much.

[0124] (3) In combination with Example 2 and Examples 8-9, the single-walled carbon nanotubes constituting the volume expansion layer cannot significantly improve the cycle life of the composite negative electrode if the content is too little or too much.

[0125] (4) In combination with Example 3 and Examples 10-12, the lithium alloy as the core of the core-shell structure lithium metal composite material has the performance of regulating the deposition of lithium metal, and the cycle performance is better than that of lithium metal powder. It cooperates with the lithium deposition inducing layer and the volume expansion layer, so that the composite negative electrode has good cycle performance; however, the excessively high content of alloy elements (Example 11) is not conducive to improving the energy density of the battery, and is not conducive to uniform dispersion, and the improvement of the cycle performance is limited.

[0126] (5) Combining Example 2 with Comparative Examples 1-3, the cycle performance of the composite negative electrode prepared in Example 2 is better than that of the negative electrode in Comparative Examples 1-3. 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 deposition and volume change of metal lithium at the micro-nano scale; Combining the cycle test curves of Example 2 and Comparative Examples 1-3 (such as Figure 4 As shown in the figure, in Comparative Example 1, the surface of the metal lithium powder is not modified, and dendrites are easily generated during the deposition of metal lithium; in Comparative Example 2, it may be because there is no reserved layer for volume expansion, and 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 there is no lithium deposition induction layer, and as the cycle proceeds, the deposition of metal lithium cannot be effectively regulated.

[0127] 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, characterized in that: The composite negative electrode comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises a metal lithium composite material with a core-shell structure, wherein the metal lithium composite material with a core-shell structure has lithium-containing particles as a core, and a lithium deposition inducing layer containing a lithiophilic material as an intermediate layer and a lithium-phobic volume expansion reserved layer as an outermost layer are arranged on the core, and the metal lithium composite materials with a core-shell structure are in contact with each other and form a continuous three-dimensional skeleton through the lithium-phobic volume expansion reserved layer.

2. The metal lithium composite negative electrode according to claim 1, characterized in that: The lithium-containing particles include metallic lithium powder and / or lithium alloy powder; Preferably, the lithium alloy comprises a binary alloy and / or a multi-element alloy, preferably a binary alloy and / or a ternary alloy; Preferably, the lithium alloy includes any one or a combination of at least two elements selected from Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, V, Cu, Fe or Ti; Preferably, the mass content of alloying elements in the lithium alloy is not higher than 40%, preferably not higher than 20%; Preferably, the average particle size of the lithium-containing particles is 1-100 μm, preferably 5-50 μm; Preferably, the thickness of the negative electrode active material layer is 1-200 μm, preferably 5-100 μm.

3. The metal lithium composite negative electrode according to claim 1 or 2, 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 any one or a combination of at least two of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, ZnO, Co3O4, SnS2 or Ni2P; Preferably, the average particle size of the lithium-philic nanoparticles is 1-200 nm, preferably 10-120 nm; Preferably, the micro-nano carrier comprises 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; Preferably, the mass ratio of the lithium deposition inducing layer to the lithium-containing particles is 1:(1-150), more preferably 1:(5-120), and further preferably 1:(15-80).

4. The metal lithium composite negative electrode according to any one of claims 1 to 3, characterized in that: The volume expansion reserved layer comprises one or a combination of at least two structural materials having a sheet-like, linear or tubular micro-nano structure, wherein 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 any one of carbon nanotubes, carbon nanofibers, graphene, fullerene, Ketjen black or conductive carbon black Super P, or a combination of at least two thereof; Preferably, the mass ratio of the volume expansion reserved layer to the lithium-containing particles is 1:(1-50), preferably 1:(10-40).

5. The metal lithium composite negative electrode according to any one of claims 1 to 4, characterized in that: The metal lithium composite negative electrode further includes a current collector, and the negative electrode active material 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, 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 core-shell structured lithium metal composite material in step (2) is prepared into a film material or disposed on at least one side surface of a current collector by any one of mechanical rolling, twisting or coating or a combination of at least two of them.

7. The method according to claim 6, 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, 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, characterized in that: The pressure of the mechanical rolling in step (3) is 1-10Mpa, preferably 2-6Mpa; Preferably, the twisting pressure in step (3) is 0.1-10 MPa, preferably 0.5-5 MPa; Preferably, the number of turns of twisting in step (3) is 1-20 turns, preferably 5-10 turns; Preferably, the coating in step (3) comprises the following process: A non-polar solvent, a conductive agent and a binder are mixed to prepare a conductive slurry, and then a metal lithium composite material is added to mix to prepare a negative electrode slurry, which is coated on a current collector and baked to obtain a negative electrode sheet; The non-polar solvent includes any one or a combination of at least two of liquid alkanes with 5 to 10 carbon atoms, liquid cycloalkanes with 5 to 15 carbon atoms, benzene, p-xylene or petroleum ether, preferably any one or a combination of at least two of p-xylene, cyclohexane, n-hexane or heptane; The conductive agent includes any one of acetylene black, Ketjen black, conductive graphite, Cabot black or Super P, or a combination of at least two thereof; The binder includes any one or a combination of at least two of styrene-butadiene rubber, polyisobutylene, styrene-butadiene-styrene block copolymer or styrene-ethylene-butylene-styrene block copolymer. The mass ratio of the conductive agent, the binder and the metal lithium composite material is (1-5): (1-5): (90-98), preferably (2-3): (2-3): (94-96).

10. A lithium battery, characterized in that: The lithium battery comprises the metal lithium composite negative electrode as described in any one of claims 1 to 5.

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