Three-dimensional composite current collector and preparation method thereof

Abstract

The invention relates to a three-dimensional composite current collector and a preparation method thereof. The three-dimensional composite current collector comprises a three-dimensional carbide-doped carbon fiber matrix and a gradient metal layer which is deposited on one side of the bottom of the three-dimensional carbide-doped carbon fiber matrix and has metal particle concentration gradually distributed from the bottom layer to the interior of the matrix.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a three-dimensional composite current collector and a preparation method thereof. BACKGROUND

[0002] With the continuous progress of science and technology, high-energy density and high-safety energy storage systems have become the key technologies restricting the development of renewable energy utilization and electric vehicles. However, the traditional lithium ion battery is difficult to meet the requirements of the next generation of energy storage devices due to the low specific capacity of the graphite anode. In contrast, lithium metal anode is considered as a potential anode material due to its ultra-high theoretical specific capacity (3860 mAh / g) and the lowest electrochemical potential (-3.04 V vs. SHE). However, in the actual charging and discharging process, the uneven deposition / stripping behavior of lithium metal will lead to lithium dendrite growth, large volume change of the metal lithium anode and unstable solid electrolyte interface (SEI), which will lead to low coulombic efficiency, short cycle life and potential safety hazards (such as short circuit and thermal runaway), seriously restricting its commercial application.

[0003] In order to solve the above problems, researchers have modified and optimized the lithium metal anode through electrode structure design and optimization of electrolyte components, etc. to promote its commercial application. For example, using a new type of electrolyte film-forming additive to construct a high-mechanical-strength and high-ionic-conductivity SEI in situ or using a non-in situ method to prepare a high-modulus stable artificial SEI, and using a solid electrolyte to inhibit the growth of lithium dendrites. However, although these methods can obtain a stable electrolyte / anode interface, they cannot provide additional space for the deposition of lithium metal, so there is still a problem of volume change, which is not conducive to the long-term stable cycle of the battery. If the metal lithium charging and discharging cycle process can be carried out in a host structure, the metal lithium can be stably deposited / stripped, which can effectively inhibit the lithium dendrite and alleviate the problem of volume expansion.

[0004] Using a three-dimensional (3D) current collector as a host matrix for metal lithium, such as porous metal, foam carbon, hollow carbon spheres, 3D MXene, etc., not only can reduce the local current density, inhibit the growth of lithium dendrites, but also can accommodate lithium deposition, thereby ensuring the integrity of the battery. However, since many 3D current collector matrices, such as foam copper or foam nickel, carbon nanotube sponge and carbon nanofiber matrix, have poor lithium affinity, resulting in a large lithium nucleation potential, a lithium-affine layer needs to be constructed to solve this problem. More importantly, since the uniform electric field and Li +The uneven distribution of mismatch still leads to inevitable uneven lithium deposition, and the top surface is directly in contact with the high concentration of lithium flux, and the metal lithium is in a "top growth" mode, which leads to the aggregation of lithium ions on the surface of the substrate, hinders the diffusion of lithium ions to the inside of the substrate, and induces the growth of lithium dendrites, which is one of the key problems that need to be solved in the practical application of 3D current collector substrate. In addition, the large weight of the metal 3D substrate also greatly reduces the capacity based on the entire negative electrode.

[0005] Therefore, how to design a lightweight, lithiumophilic and controllable metal lithium deposition three-dimensional current collector is particularly important for preparing a composite metal lithium negative electrode with long service life and high specific capacity. SUMMARY

[0006] In view of the above technical problems, the present application aims to provide a three-dimensional composite current collector with gradient lithiumophilicity, and a preparation technology which is simple to operate and simple in process. The main purpose is to improve the lithiumophilicity of carbon fibers by metal carbide and in-situ catalyze the electrolyte to form a rich inorganic SEI film, promote the rapid transmission of lithium ions inside the current collector, avoid the aggregation of lithium ions on the top to induce the growth of lithium dendrites, and then utilize the good electronic conductivity and lithiumophilicity of the bottom metal element to reduce the nucleation overpotential, induce the "bottom-up" deposition of metal lithium, effectively inhibit the growth of lithium dendrites, and thus obtain a composite metal lithium negative electrode with high specific capacity and long service life.

[0007] In a first aspect, the present application provides a three-dimensional composite current collector, comprising: a three-dimensional carbide-doped carbon fiber substrate, and a gradient metal layer deposited on one side of the bottom of the three-dimensional carbide-doped carbon fiber substrate and gradually distributed in the substrate from the bottom layer to the inside of the substrate.

[0008] Preferably, in the three-dimensional carbide-doped carbon fiber substrate, the diameter of the carbon fiber is 200-500 nm, and the carbide includes at least one of transition metal carbide, preferably Mo2C, WC, NiC, TiC, NbC, and VC.

[0009] Preferably, the doping ratio of the carbide in the carbon fiber substrate is 0.1-10wt%, the thickness of the three-dimensional carbide-doped carbon fiber substrate is 100-300μm, the specific surface area is 10-30m 2 / g, the mass density is 0.1-1g cm -3 , the pore size range is 5-50nm, and the porosity is 70-90%.

[0010] Preferably, the metal in the gradient metal layer includes at least one of Au, Ag, Sn, and Pt, and the particle size of the metal particles is 5-100nm; preferably, the thickness of the gradient metal layer is 1-20μm, and the total mass of the metal in the gradient metal layer is 5-10% of the mass of the three-dimensional composite current collector.

[0011] In a second aspect, the present application provides a preparation method of the three-dimensional composite current collector, the preparation method comprising the following steps: (1) forming a three-dimensional carbide precursor doped carbon fiber precursor composite by electrospinning, hydrothermal method, or solvothermal method through a precursor solution containing carbide precursor and carbon fiber precursor; (2) performing carbonization reduction on the three-dimensional carbide precursor doped carbon fiber precursor composite to convert the carbide precursor into carbide and carbonize the carbon fiber precursor into carbon fiber, thereby obtaining a three-dimensional carbide doped carbon fiber matrix; (3) depositing a gradient metal layer on the bottom of the three-dimensional carbide doped carbon fiber matrix by magnetron sputtering, thereby obtaining the three-dimensional composite current collector.

[0012] Preferably, in step (1), the carbide precursor comprises a transition metal organic complex or a mixture of a transition metal-containing salt and an organic component, the transition metal organic complex comprises molybdenum acetylacetone, nickel acetylacetone, tungsten acetylacetone, titanium acetylacetone, niobium oxalate, vanadium triacetylacetone, the transition metal-containing salt can comprise ammonium molybdate, ammonium tungstate, ammonium fluorotitanate, ammonium niobate, ammonium vanadate, the organic component can comprise glucose, urea, the carbon fiber precursor comprises at least one of an organic precursor, carbon cloth fiber, and biomass carbon material, the organic precursor is preferably polyacrylonitrile, and the solvent of the precursor solution comprises N,N-dimethylformamide (DMF). In the precursor solution, the mass ratio of the carbon fiber precursor to the carbide precursor is 1-1.5:0.2-0.8.

[0013] Preferably, in step (1), the parameters of the electrospinning include a spinning voltage of 10-20 kV, a flow rate of 0.2-1.0 mL / h, a distance between the injector needle and the collector of 15-20 cm, a rotation speed of the receiver roller of 400-800 rpm, and a time of 12-36 h.

[0014] Preferably, in step (2), the three-dimensional carbide precursor doped carbon fiber precursor composite formed by electrospinning is further subjected to low-temperature pre-oxidation before carbonization reduction, the temperature of the low-temperature pre-oxidation is 200-250℃, the temperature rising rate is 1-2℃ / min, and the pre-oxidation time is 2-5 h.

[0015] Preferably, in step (2), the carbonization reduction is performed in an Ar / H2 mixed atmosphere, the temperature is 600-850℃, the temperature rising rate is 2-3℃ / min, and the time is 2-3 h.

[0016] Preferably, in step (3), the time of the magnetron sputtering is 60-360 s, and the current intensity is 6-8 mA.

[0017] Advantages (1) The carbide-doped carbon-based current collector with gradient lithium affinity prepared in the present application can regulate the deposition of lithium ions from bottom to top due to the gradient of lithium affinity and electronic conductivity in the upper and lower layers of the current collector, fully utilize the internal space of the current collector, and alleviate the growth of lithium dendrites. (2) The transition metal carbide-doped carbon nanofiber current collector with large specific surface area and low mass density obtained by electrospinning and high-temperature carbonization technology in the present application can provide sufficient deposition space for metal lithium and improve the overall energy density of the battery. (3) The doped transition metal carbide can not only improve the strength of the fiber and increase the mechanical properties of the current collector, but also improve the lithium affinity of the current collector itself, and catalyze the decomposition of lithium salt anions to generate an SEI film rich in inorganic matter, promote the rapid transport of lithium ions in the current collector, and avoid the accumulation of lithium ions at the top to induce the growth of lithium dendrites. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Preparation process schematic diagram of the three-dimensional composite current collector exemplified by the present application; Figure 2 Scanning electron microscope image of the three-dimensional composite current collector prepared in Example 1 of the present application; Figure 3 Scanning electron microscope images of the upper / lower layers of the three-dimensional composite current collector prepared in Example 1 of the present application after plating lithium; Figure 4 Cycle performance diagram of the symmetric battery prepared from the three-dimensional composite current collector prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0019] The present application is further illustrated by the following embodiments, which should be understood as merely illustrative of the present application, rather than limiting the present application.

[0020] First, the present application provides a three-dimensional composite current collector. The three-dimensional composite current collector can include a three-dimensional carbide-doped carbon fiber substrate and a gradient metal layer deposited on one side of the bottom of the three-dimensional carbide-doped carbon fiber substrate and gradually distributed with metal particles from the bottom layer to the inside of the substrate.

[0021] In some embodiments, the diameter of the carbon fiber in the three-dimensional carbide-doped carbon fiber substrate can be 200-500 nm; the carbide can include a transition metal carbide, preferably at least one of Mo2C, WC, NiC, TiC, NbC, and VC.

[0022] In some embodiments, the doping ratio of the carbide in the carbon fiber matrix can be 0.1-10wt%; the thickness of the three-dimensional carbide-doped carbon fiber matrix can be 100-300μm, the specific surface area can be 10-30m 2 / g, the mass density can be 0.1-1g cm -3 , the pore size range can be 5-50nm, and the porosity can be 70-90%.

[0023] Wherein, the doping ratio of the carbide in the carbon fiber matrix is too large, which leads to the mass density of the current collector being too large; and the doping ratio is too small, which leads to the carbide being unable to be uniformly dispersed, and the lithium affinity of the current collector being difficult to be greatly improved. The thickness of the matrix is too large, which leads to the volume of the current collector being too large, affecting the lithium ion transmission process; and the thickness of the matrix is too small, which cannot provide deposition space for lithium ions. The specific surface area is too large, which leads to the side reaction being intensified and the accumulation of dead lithium; and the specific surface area is too small, which leads to the local current density being too large, and easily causing lithium dendrite growth.

[0024] The carbide doped in the matrix of the composite current collector provided by the application has lithium affinity and catalytic properties, which can ensure the uniform distribution of lithium ions in the thickness direction, and can catalyze the decomposition of lithium salt anions to form an inorganic-rich SEI film on the surface of the carbon fiber, promote the rapid transmission of lithium ions in the current collector, avoid the aggregation of lithium ions at the top to induce lithium dendrite growth, and also enhance the strength of the carbon fiber. In addition, the carbon fiber matrix doped with carbide has a high specific surface area and a low mass density, which can effectively improve the energy density of the battery as a whole.

[0025] The deposited metal elements used in the application have lithium affinity and electronic conductivity. In some embodiments, the metal in the gradient metal layer can include at least one of Au, Ag, Sn, and Pt, and the particle size of the metal particles can be 5-100nm; preferably, the thickness of the gradient metal layer can be 1-20μm, and the total mass of the metal in the gradient metal layer can be 5-10% of the mass of the three-dimensional composite current collector.

[0026] The bottom gradient deposited metal in the composite current collector provided by the application has lithium affinity and electronic conductivity, which can reduce the nucleation overpotential, regulate the "from bottom to top" deposition of lithium ions, make the lithium ion deposition process away from the separator, and inhibit the growth of lithium dendrites. The application adopts a single-sided sputtering metal layer, and due to the porosity of the current collector itself, the metal ions present a concentration gradient from the sputtering layer to the inside. Too large metal content will lead to an increase in the mass density of the current collector, a decrease in the energy density of the battery, and affect the uniformity of the gradient distribution, and uneven deposition; and too small metal content cannot effectively ensure the "from bottom to top" deposition mode during the deposition process.

[0027] The three-dimensional composite current collector provided by this invention has different gradient lithiophilicity and electronic conductivity at its top and bottom. In some embodiments, the surface conductivity of the three-dimensional composite current collector can be 50-100 S / cm, and the bottom surface conductivity can be 500-1000 S / cm.

[0028] It should be noted that in lithium batteries, different capacity cathode materials require matching with lithium metal of appropriate specific capacity, i.e., the so-called N / P ratio. If the active lithium content in the cathode is too high (i.e., N / P is too low), it not only easily leads to lithium dendrite formation or even "dead lithium," resulting in reduced safety and lifespan, but also hinders the improvement of battery energy density. Conversely, if the active lithium content in the cathode is too low (i.e., N / P is too high), it is detrimental to the performance of the cathode material and affects battery energy density. Therefore, those skilled in the art have long been committed to developing ultrathin lithium metal anodes or ultrathin lithium composite anodes. This invention provides a current collector that serves as the host for lithium metal. The amount of active lithium metal deposited can be quantitatively controlled through electrodeposition, thereby allowing for the customization of composite lithium anodes (i.e., current collector + deposited lithium metal composition) with specific thickness and specific capacity according to the active lithium required by different cathode materials. This maximizes the performance of the cathode material without compromising battery safety due to excessive active lithium. Furthermore, this current collector with gradient lithium affinity can induce lithium deposition within the current collector, preventing lithium dendrite formation and mitigating volume expansion during deposition, thus extending the lifespan of the lithium metal anode.

[0029] In conventional technical solutions, the current collector is often a metal strip network structure, attached to one side of the lithium metal composite sheet. Since the battery consists of multiple positive and negative electrodes, current collectors, and electrolytes stacked on a planar basis, the current collector of a negative electrode is attached to the lithium metal composite sheet from both sides, which is beneficial for lithium-ion deposition or migration on both sides of the lithium metal composite sheet. Its main function is to provide electron conduction, and its network structure helps to increase the utilization area per unit mass of the negative electrode composite sheet, that is, to improve the electron and ion conduction efficiency per unit mass of the composite negative electrode sheet. However, the lithium metal composite sheet is a composite lithium metal composed of metal, polymer, or woven fabric (even including lithiophilic materials), with an array structure in at least one cross-section perpendicular to the thickness. In this case, firstly, the structure of the composite components in the lithium metal composite sheet is disordered, making it impossible to determine the presence sites of the metal and lithiophilic materials, and the deposition process cannot control the deposition behavior of lithium, which can easily cause problems such as volume expansion; secondly, the active metal is mixed with the composite components in advance, and its distribution in the array structure is also random, making it impossible to achieve quantitative and controllable preparation through simple methods.

[0030] The following, combined with Figure 1 The following is an illustrative description of the preparation method of the three-dimensional composite current collector provided by the present invention. The preparation method may include the following steps: (1) forming a three-dimensional carbide precursor doped carbon fiber precursor composite by at least one of electrospinning, hydrothermal, and solvothermal methods through a precursor solution containing carbide precursors and carbon fiber precursors; (2) performing carbonization reduction on the three-dimensional carbide precursor doped carbon fiber precursor composite to convert the carbide precursors into carbides and carbonize the carbon fiber precursors into carbon fibers, thereby obtaining a three-dimensional carbide doped carbon fiber matrix; (3) depositing a gradient metal layer on the bottom of the three-dimensional carbide doped carbon fiber matrix by magnetron sputtering, thereby obtaining the three-dimensional composite current collector.

[0031] In some embodiments, in step (1), the carbide precursor can include a transition metal organic complex or a mixture of a transition metal-containing salt and an organic component, preferably the molar ratio of the transition metal-containing salt to the organic component can be 0.1-0.5:0.1-1.5, the transition metal organic complex can include molybdenum acetylacetone, nickel acetylacetone, tungsten acetylacetone, titanium acetylacetone oxide, niobium oxalate, vanadium triisopropylacetylacetone, the transition metal-containing salt can include ammonium molybdate, ammonium tungstate, ammonium fluorotitanate, ammonium niobate, ammonium vanadate, and the organic component can include glucose, urea; the carbon fiber precursor can include at least one of an organic precursor, carbon cloth fiber, and biomass carbon material, the organic precursor is preferably polyacrylonitrile; and the solvent of the precursor solution can include N,N-dimethylformamide DMF.

[0032] In the precursor solution, the mass ratio of the carbon fiber precursor to the carbide precursor can be 1-1.5:0.2-0.8; preferably, the mass ratio of the carbon fiber precursor to the solvent can be 0.05-0.15, and the mass percentage of the carbide precursor can be 1-6%. By controlling the suitable mass ratio of each component in the precursor solution, the pore size, thickness, and uniform distribution of the carbide of the matrix can be controlled.

[0033] In the preparation process of the precursor solution, the stirring temperature can be 40-60°C, the stirring rate can be 200-500 r / min, and the stirring time can be 18-24 h.

[0034] In some embodiments, in step (1), the parameters of electrospinning can include a spinning voltage of 10-20 kV, a flow rate of 0.2-1.0 mL / h, a distance between the injector needle and the collector (spinning receiving distance) of 15-20 cm, a receiving roller speed of 400-800 rpm, and a time of 12-36 h.

[0035] In some embodiments, in step (1), the parameters of hydrothermal method can include a temperature of 150-300°C and a time of 12-24 h.

[0036] In some embodiments, in step (1), the parameters of the solvothermal process can include a temperature of 150-300°C, a time of 12-24h, and the solvent used can include ethylene glycol, N,N-dimethylformamide.

[0037] In some embodiments, in step (1), the process can further include electrospinning, hydrothermal, and vacuum drying the composite at a high temperature of 50-60°C for 12-24h after the solvothermal process.

[0038] In some embodiments, in step (2), the carbon nanofiber precursor formed by electrospinning can be pre-oxidized at a low temperature before being carbonized and reduced with the carbon fiber precursor composite, the temperature of the low-temperature pre-oxidation can be 200-250°C, the heating rate can be 1-2°C / min, and the pre-oxidation time can be 2-5h.

[0039] The pre-oxidation process converts the linear PAN molecular chain into a thermally stable ladder structure through chemical cross-linking, preventing the fiber from melting or decomposing during subsequent high-temperature carbonization. If the oxidation time is too long, the C=C bonds will break, forming low-molecular-weight fragments, which will make the resulting carbon nanofiber brittle. If the time is too short, the linear PAN molecules will remain too much, causing local rupture during carbonization, which will seriously affect the performance of the current collector.

[0040] In some embodiments, in step (2), the carbonization and reduction can be carried out in an Ar / H2 mixed atmosphere, the temperature can be 600-850°C, the heating rate can be 2-3°C / min, and the time can be 2-3h.

[0041] If the high-temperature carbonization time is too long and the temperature is too high, the carbon nanofiber will be severely graphitized, and the carbon skeleton will shrink, reducing the porosity. If the high-temperature carbonization time is too short and the temperature is too low, the N and H atoms cannot be fully decomposed, resulting in low conductivity of the current collector, hindering electron transmission, and the structure is loose and the mechanical strength is poor. At the same time, the transition metal oxide cannot be completely reduced to carbide.

[0042] In some embodiments, in step (3), the time of the magnetron sputtering can be 60-360s, and the current intensity can be 6-8mA.

[0043] If the sputtering time is too long, the mass density of the current collector will increase, and a concentration gradient cannot be formed, affecting the deposition process of the current collector and easily causing lithium to be deposited on the top of the current collector. If the sputtering time is too short, the deposition site of lithium cannot be effectively controlled, and lithium cannot be deposited inside the current collector.

[0044] The carbide-doped carbon-based current collector with gradient lithiumophilicity provided in the present application can regulate the deposition of lithium ions from bottom to top due to the gradient of lithiumophilicity and electronic conductivity in the upper and lower layers of the current collector, fully utilizes the internal space of the current collector, and relieves the growth of lithium dendrites. Moreover, the light transition metal carbide-doped carbon nanofiber current collector obtained by electrospinning, hydrothermal method, solvothermal method and high-temperature carbonization technology has a large specific surface area and a low mass density, can provide sufficient deposition space for metal lithium, and can also improve the overall energy density of the battery.

[0045] In addition, the doped transition metal carbide can not only improve the fiber strength and increase the mechanical properties of the current collector, but also improve the lithiumophilicity of the current collector itself, and can catalyze the decomposition of lithium salt anions to generate an SEI film rich in inorganic matter, promote the rapid transmission of lithium ions in the current collector, and avoid the accumulation of lithium ions at the top to induce the growth of lithium dendrites.

[0046] The following examples are further illustrated to explain the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the present application all belong to the protection scope of the present application. The specific process parameters in the following examples are only one example in the appropriate range, i.e. those skilled in the art can select within the appropriate range according to the description herein, and are not limited to the specific values in the following examples. If not specifically indicated, the technical means used in the examples are the conventional means familiar to those skilled in the art.

[0047] Example 1

[0048] The preparation method of the three-dimensional composite current collector provided in the present embodiment comprises the following steps: (1) 0.5 g of acetone acetyl molybdenum is dissolved in 9.4 g of N,N-dimethylformamide, stirred at room temperature for 1 hour, then 1 g of polyacrylonitrile is added, and the reaction is continued at 60℃ for 24 h to obtain a precursor solution; The precursor solution is electrospun and assembled in an electrospinning machine, the spinning voltage is adjusted to 10 KV, the spinning receiving distance is 15 cm, the flow rate is adjusted to 0.5 mL / h, and after electrospinning for 20 h, a nanofiber spinning film is obtained, and then the spinning film is placed in a 60℃ vacuum oven for drying for 24 h; (2) The fiber spinning film is gradually heated to 250℃ at a heating rate of 1℃ / min in a muffle furnace under air atmosphere for low-temperature pre-oxidation for 3 h, and then gradually heated to 800℃ at a heating rate of 2℃ / min under hydrogen-argon atmosphere for high-temperature carbonization for 2 h to obtain a three-dimensional Mo2C-doped carbon fiber matrix; (3) Put the three-dimensional Mo2C-doped carbon fiber matrix into a sputtering cavity, and the sputtering target is a gold target. The sputtering time is 60 s, and the current intensity is 6-8 mA. Thus, a three-dimensional composite current collector plated with Au on one side is obtained.

[0049] Example 2

[0050] The preparation method of the three-dimensional composite current collector provided in this example refers to Example 1, and the main difference lies in that: In step (1), the acetone acetyl molybdenum is 0.6 g, and the polyacrylonitrile is 1.2 g.

[0051] Example 3

[0052] The preparation method of the three-dimensional composite current collector provided in this example refers to Example 1, and the main difference lies in that: In step (1), the N,N-dimethylformamide is 14.1 g, and the electrostatic spinning is 30 h.

[0053] Example 4

[0054] The preparation method of the three-dimensional composite current collector provided in this example refers to Example 1, and the main difference lies in that: In step (1), the acetone acetyl molybdenum is replaced by acetylacetone nickel.

[0055] Example 5

[0056] The preparation method of the three-dimensional composite current collector provided in this example refers to Example 1, and the main difference lies in that: In step (3), the sputtering target is a silver target.

[0057] Example 6

[0058] The preparation method of the three-dimensional composite current collector provided in this example refers to Example 1, and the main difference lies in that: In step (2), the high-temperature carbonization temperature is 600°C.

[0059] Example 7

[0060] The preparation method of the three-dimensional composite current collector provided in this example includes the following steps: (1) Commercial carbon cloth is ultrasonically treated with acetone, ethanol, and deionized water for 30 minutes each, and then dried in a 60°C vacuum oven for 24 h to obtain pretreated carbon cloth. A 20 ml 0.1M ammonium molybdate and 0.3M glucose aqueous solution is prepared to obtain a reaction solution. The reaction solution and the treated carbon cloth are placed in a 50 mL polytetrafluoroethylene autoclave and reacted at 180°C for 12 h. After natural cooling, the carbon cloth is taken out and washed with deionized water three times, and then dried in a 60°C vacuum oven for 12 h. (2) The carbon cloth was gradually heated to 800℃ at a heating rate of 2℃ / min under hydrogen-argon atmosphere, and high-temperature reduction was carried out for 2h to obtain a Mo2C-doped carbon cloth; (3) The Mo2C-doped carbon cloth was placed in a sputtering cavity, a gold target was used as the sputtering target, the sputtering time was 60s, and the current intensity was 6-8mA to obtain a three-dimensional composite current collector plated with Au on one side.

[0061] Comparative Example 1

[0062] The preparation method of the current collector provided in the present comparative example refers to Example 1, and the main difference is that: In step (1), no transition metal compound was added, and only 1g of polyacrylonitrile was added.

[0063] Comparative Example 2

[0064] The preparation method of the current collector provided in the present comparative example refers to Example 1, and the main difference is that: In step (1), 0.1g of molybdenum acetylacetonate and 1.2g of polyacrylonitrile were added.

[0065] Comparative Example 3

[0066] The preparation method of the current collector provided in the present comparative example refers to Example 1, and the main difference is that: In step (2), no pre-oxidation was carried out, and the carbonization was directly carried out under hydrogen-argon atmosphere at a heating rate of 2℃ / min to 800℃ for 2h.

[0067] Comparative Example 4

[0068] The preparation method of the current collector provided in the present comparative example refers to Example 1, and the main difference is that: In step (1), the temperature was gradually increased to 500℃ at a heating rate of 5℃ / min under hydrogen-argon atmosphere, and high-temperature carbonization was carried out for 0.5h.

[0069] Figure 2 It is a scanning electron microscope image of the three-dimensional composite current collector prepared in Example 1 of the present application. As can be seen from the figure, the three-dimensional composite current collector presents a loose and porous crosslinked morphology.

[0070] Figure 3 It is a scanning electron microscope image of the upper / lower layer of the three-dimensional composite current collector prepared in Example 1 of the present application after being plated with lithium (the sputtered metal side is the lower layer of the current collector, and the non-sputtered side is the upper layer of the current collector, and the deposition of 3mAh indicates the deposition of a lithium layer of 3mAh cm -2 As can be seen from the figure, lithium is deposited in the lower layer of the current collector, and only a small amount of lithium is deposited in the upper layer of the current collector, so that the lithium deposition process occurs inside the current collector.

[0071] Figure 4 This is a cycle performance diagram of a symmetrical battery prepared using the three-dimensional composite current collector prepared in Example 1 of this invention. The battery preparation process is as follows: First, a Li / three-dimensional composite current collector half-cell is assembled. Then, a 3mAh cm⁻¹ is electrochemically deposited on the three-dimensional composite current collector during the discharge process. -2 Lithium-ion batteries were assembled using electrodeposited current collectors to form symmetrical cells; electrode material: a three-dimensional composite current collector plated with lithium by electrochemical deposition; test conditions: 1 mA cm⁻¹ -2 Current density, 1 mAh cm -2 Charge / discharge capacity; Blank sample: The blank sample consists of pure carbon nanofibers without transition metal carbides or sputtered metal deposits, which were also deposited using an electrochemical deposition method with a capacity of 3 mAh / cm³. -2 Lithium was deposited to assemble a symmetrical cell. As shown in the figure, the symmetrical cell assembled with the three-dimensional composite current collector after lithium deposition achieves a performance of 1 mA / cm². -2 Stable cycling for 2000 hours at current density.

[0072] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A three-dimensional composite current collector, characterized in that, The three-dimensional composite current collector includes: a three-dimensional carbide-doped carbon fiber matrix, and a gradient metal layer deposited on one side of the bottom of the three-dimensional carbide-doped carbon fiber matrix, with the concentration of metal particles gradually varying from the bottom layer to the interior of the matrix.

2. The three-dimensional composite current collector according to claim 1, characterized in that, In the three-dimensional carbide-doped carbon fiber matrix, the diameter of the carbon fiber is 200-500 nm, and the carbide includes transition metal carbides, preferably at least one of Mo2C, WC, NiC, TiC, NbC, and VC.

3. The three-dimensional composite current collector according to claim 1 or 2, characterized in that, The carbide doping ratio in the carbon fiber matrix is ​​0.1-10 wt%, the thickness of the three-dimensional carbide-doped carbon fiber matrix is ​​100-300 μm, and the specific surface area is 10-30 m². 2 / g, with a mass density of 0.1-1g cm³. -3 The pore size ranges from 5 to 50 nm, and the porosity is 70% to 90%.

4. The three-dimensional composite current collector according to any one of claims 1-3, characterized in that, The metal in the gradient metal layer includes at least one of Au, Ag, Sn, and Pt, and the particle size of the metal particles is 5-100 nm; preferably, the thickness of the gradient metal layer is 1-20 μm, and the total mass of the metal in the gradient metal layer is 5-10% of the mass of the three-dimensional composite current collector.

5. A method for preparing a three-dimensional composite current collector according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) A three-dimensional carbide precursor-doped carbon fiber precursor composite is formed by electrospinning, hydrothermal or solvothermal methods using a precursor liquid containing carbide precursor and carbon fiber precursor. (2) The three-dimensional carbide precursor doped with carbon fiber precursor composite is carbonized and reduced so that the carbide precursor is converted into carbide and the carbon fiber precursor is carbonized into carbon fiber, thereby obtaining a three-dimensional carbide doped carbon fiber matrix. (3) A gradient metal layer is deposited at the bottom of the three-dimensional carbide-doped carbon fiber matrix by magnetron sputtering to obtain the three-dimensional composite current collector.

6. The preparation method according to claim 5, characterized in that, In step (1), the carbide precursor comprises a transition metal organometallic complex or a mixture of a transition metal salt and an organic component. The transition metal organometallic complex comprises acetocetylmolybdenum, nickel acetocetylene, tungsten acetocetylene, titanium dioxide acetocetylene, niobium oxalate, and vanadium triisoacetate. The transition metal salt may comprise ammonium molybdate, ammonium tungstate, ammonium fluorotitanate, ammonium niobate, and ammonium vanadate. The organic component may comprise glucose and urea. The carbon fiber precursor comprises at least one of an organic precursor, carbon fiber, and biomass carbon material. The organic precursor is preferably polyacrylonitrile. The solvent of the precursor solution comprises N,N-dimethylformamide (DMF). In the precursor liquid, the mass ratio of carbon fiber precursor to carbide precursor is 1-1.5:0.2-0.

8.

7. The preparation method according to claim 5 or 6, characterized in that, In step (1), the parameters of electrospinning include: spinning voltage of 10-20kV, flow rate of 0.2-1.0mL / h, distance between syringe needle and collector of 15-20cm, receiver roller speed of 400-800rpm, and time of 12-36h.

8. The preparation method according to any one of claims 5-7, characterized in that, Step (2) also includes performing low-temperature pre-oxidation on the three-dimensional carbide precursor doped with carbon fiber precursor composite formed by electrospinning before carbonization and reduction. The low-temperature pre-oxidation temperature is 200-250℃, the heating rate is 1-2℃ / min, and the pre-oxidation time is 2-5h.

9. The preparation method according to any one of claims 5-8, characterized in that, In step (2), the carbonization reduction is carried out in an Ar / H2 mixed atmosphere at a temperature of 600-850℃, a heating rate of 2-3℃ / min, and a time of 2-3h.

10. The preparation method according to any one of claims 5-9, characterized in that, In step (3), the magnetron sputtering time is 60-360s and the current intensity is 6-8mA.

Images