Preparation method and application of a high-entropy alloy / carbon sphere composite with strong magnetism for modifying a current collector of a lithium metal anode

Abstract

Preparation method and application of a strongly magnetic high-entropy alloy / carbon sphere composite material for modifying a lithium metal negative electrode current collector, which relate to a preparation method and application of a lithium metal negative electrode current collector. Method: First, prepare hollow carbon spheres; second, prepare a highly magnetic high-entropy alloy / carbon sphere composite material; third, modify the lithium metal negative electrode current collector. Application of a strongly magnetic high-entropy alloy / carbon sphere composite material for modifying a lithium metal negative electrode current collector in a lithium metal battery. The strongly magnetic high-entropy alloy / carbon sphere composite material for modifying a lithium metal negative electrode current collector obtained by the present invention has a unique three-dimensional structure and a high electrochemically active specific surface area, which can evenly distribute an applied current on the entire porous framework, reduce the effective current density, and thus homogenize the electric field distribution around the framework, contributing to uniform lithium deposition; applying the strongly magnetic high-entropy alloy / carbon sphere composite material for modifying a lithium metal negative electrode current collector obtained by the present invention can achieve a Coulombic efficiency of 99.43% for the lithium negative electrode.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a current collector for a lithium metal negative electrode. Background Art

[0002] Judging from market feedback, the short driving range remains a pain point that electric vehicles urgently need to solve. The main reason is that the energy density of the "heart" of electric vehicles - lithium-ion batteries is relatively low (150 - 300 Wh / kg). Therefore, it is extremely urgent to develop secondary power batteries with high energy density, safety, and reliability. High-energy-density secondary battery systems require the use of positive and negative electrodes with high energy density. Lithium metal has advantages such as a high theoretical specific capacity (3860 mAhg -1 ) and a low electrode potential (-3.04 V vs. standard hydrogen electrode), and is recognized as an ideal negative electrode material for realizing high-energy-density battery systems. However, due to uncontrollable lithium dendrite growth and the huge volume change of the lithium-free host negative electrode, "dead lithium" accumulates rapidly, and finally leads to the pulverization failure of the lithium metal negative electrode. In addition, lithium dendrites will be generated during the cycling of the lithium negative electrode, penetrate the separator, cause short circuits, and increase the risk of battery thermal runaway. To address this issue, researchers have applied strategies such as lithiumophilic current collectors, artificial solid electrolyte interface (SEI) films, all-solid / quasi-solid electrolytes, modified SEI films, and conductive three-dimensional skeletons to protect the lithium metal negative electrode, significantly improving the cycling performance of lithium metal batteries. However, the currently reported solutions still cannot make the lithium negative electrode exhibit satisfactory stability under practical conditions of low negative electrode area capacity / positive electrode area capacity (N / P) ratio, lean electrolyte, and high rate.

[0003] To further improve the stability of the lithium negative electrode, it is extremely important to ensure uniform and dense deposition / stripping of lithium. The key lies in eliminating the concentration gradient of lithium ions at the electrode-electrolyte interface and avoiding the emergence of local hot spots. At the same time, ensure uniform and dense nucleation of lithium ions. In recent years, numerous research reports have shown that using a magnetic field as a non-contact energy transfer method, relying on the effects of magnetic force, magnetization intensity, magnetohydrodynamics, and spin effects, can effectively improve the electrochemical performance of lithium metal batteries. However, the construction of an external magnetic field will complicate the experimental process, greatly increase the experimental cost, and it is difficult to achieve large-scale application. Therefore, constructing a micro-magnetic field in the current collector / lithium negative electrode host material is the focus and hotspot of current research, and it is also one of the strategies with the most research value and application prospects. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a preparation method and application of a current collector for a lithium metal negative electrode modified with a ferromagnetic high-entropy alloy / carbon sphere composite material.

[0005] A preparation method of a current collector for a lithium metal negative electrode modified with a ferromagnetic high-entropy alloy / carbon sphere composite material is specifically completed according to the following steps:

[0006] I. Preparation of hollow carbon spheres:

[0007] ①. Mix absolute ethanol, deionized water and ammonia water, stir for a period of time at room temperature to obtain mixed solution I; add tetraethyl orthosilicate dropwise to mixed solution I, then add resorcinol solution and formaldehyde solution, and stir for a period of time at room temperature to obtain a precursor solution;

[0008] ②. Transfer the precursor solution to a reaction kettle, and carry out hydrothermal reaction for a period of time at 100°C - 200°C, and naturally cool to room temperature to obtain reaction product I; carry out centrifugal washing and drying on reaction product I to obtain SiO₂@phenolic resin microspheres;

[0009] ③. Under the protection of a nitrogen atmosphere, heat the SiO₂@phenolic resin microspheres to the carbonization temperature, and carbonize for a period of time at the carbonization temperature to obtain reaction product II; immerse reaction product II in NaOH solution for a period of time, then wash with deionized water until neutral, and dry to obtain hollow carbon spheres;

[0010] II. Preparation of high-magnetic high-entropy alloy / carbon sphere composites:

[0011] ①. Weigh 2 - 5 different metal salts according to an equimolar ratio and add them to deionized water, then successively add FeCl₂·4H₂O, CoCl₂·6H₂O and NiCl₂·6H₂O with an equimolar ratio to one of the metal salts, stir evenly, and then ultrasonically form a uniform solution to obtain mixed solution II;

[0012] ②. Immerse the hollow carbon spheres in mixed solution II, stir for a period of time, and then dry the mixture using a rotary evaporator to obtain reaction product III; anneal reaction product III for a period of time under the protection of a mixed gas atmosphere of H₂ and Ar and at a temperature of 800°C - 1000°C to obtain high-magnetic high-entropy alloy / carbon sphere composites;

[0013] III. Modifying the current collector of the lithium metal negative electrode:

[0014] ①. Add the high-magnetic high-entropy alloy / carbon sphere composites and polyvinylidene fluoride to N-methylpyrrolidone, and ultrasonically for a period of time to obtain a viscous slurry;

[0015] ②. Coat the viscous slurry on one surface of a double-sided smooth copper foil, and then dry it in vacuum to obtain a current collector of a strongly magnetic high-entropy alloy / carbon sphere composite modified lithium metal negative electrode.

[0016] Application of a current collector of a strongly magnetic high-entropy alloy / carbon sphere composite modified lithium metal negative electrode in a lithium metal battery.

[0017] Principle of the present invention:

[0018] Based on the serious problem of lithium dendrite growth in practical lithium anodes, the present invention uses a high-magnetic high-entropy alloy / carbon sphere composite material to modify the traditional lithium anode current collector. This current collector has the following effects in suppressing lithium dendrite growth: (1) The cocktail synergy effect between different constituent elements in the high-entropy alloy realizes multiple lithium ion transport paths and abundant active sites; (2) The existence of the high-entropy effect makes the high-entropy alloy have active sites with gradient absorption energy, which is conducive to selectively binding lithium ions, thus providing a low potential barrier for uniform lithium nucleation; (3) Multiple transport paths promote the diffusion behavior of lithium ions and uniform lithium deposition; (4) There are a large number of micro-magnetic fields around the nano-high-entropy alloy. The magnetic vortex effect under the action of the magnetic field helps to eliminate the concentration gradient at the electrode-electrolyte interface and induces the uniform distribution of lithium ions; (5) The special structure of the composite carbon spheres also helps to homogenize the distribution of the electric field on the surface of the current collector and avoid the occurrence of the "tip effect". Based on the above advantages, the strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector can enhance the uniformity of the lithium deposition behavior of metal lithium, inhibit the generation of lithium dendrites, inhibit the consumption of the electrolyte, extend the life of the metal lithium anode, improve the energy density of the battery, and significantly improve its cycle life, stability and safety.

[0019] The present invention includes the following beneficial effects:

[0020] 1. The strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector obtained by the present invention has a unique three-dimensional structure. The continuous conductive network of the three-dimensional porous conductive framework has a relatively high electrochemically active specific surface area, which can evenly distribute the applied current on the entire porous framework, reduce the effective current density, thereby homogenizing the distribution of the electric field around the framework. The uniform electric field can homogenize the mass transfer flux of lithium ions and contribute to uniform lithium deposition;

[0021] 2. The strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector obtained by the present invention has a gradient binding energy with lithium ions, making the strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector have excellent lithium affinity, reducing the lithium nucleation energy barrier, and ensuring uniform and dense lithium nucleation;

[0022] 3. The surface of the strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector obtained by the present invention has a large number of micro-magnetic fields. Under the action of the Lorentz force, the lithium ions exhibit a magnetic vortex effect, which helps to eliminate the concentration gradient at the electrode-electrolyte interface and induces the uniform distribution of lithium ions;

[0023] 4. The existence of the micro-magnetic field on the surface of the strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector obtained by the present invention can also induce the deposition of lithium ions at the bottom of lithium dendrites and avoid the occurrence of the tip effect;

[0024] 5. The current collector of the lithium metal anode modified with the ferromagnetic high-entropy alloy / carbon sphere composite material obtained by applying the present invention can achieve a Coulomb efficiency of 99.43% for the lithium anode, and can stably cycle for more than 12,000 h. The soft-pack battery using the lithium metal anode composite with the current collector modified by the ferromagnetic high-entropy alloy / carbon sphere composite material can stably cycle 500 times, which is much higher than the battery using a conventional current collector;

[0025] 6. The preparation method of the current collector of the lithium metal anode modified with the ferromagnetic high-entropy alloy / carbon sphere composite material of the present invention is simple and easy to implement, and does not require complex process flows and equipment. The preparation method of the present invention has been verified by multiple experiments, and has strong reproducibility and stability, which can ensure the consistency of product quality. Brief Description of the Drawings

[0026] Figure 1 It is the micro-morphology of the high-magnetic high-entropy alloy / carbon sphere composite material prepared in the second step of Example 1. The left figure is a scanning electron microscope image, and the right figure is a transmission electron microscope;

[0027] Figure 2 It is the distribution map of different metal elements of the high-magnetic high-entropy alloy / carbon sphere composite material prepared in the second step of Example 1;

[0028] Figure 3 It is to simulate the movement trajectory and distribution of lithium ions around lithium dendrites without a magnetic field using a multi-physics field simulation software;

[0029] Figure 4 It is to simulate the movement trajectory and distribution of lithium ions around lithium dendrites with a magnetic field using a multi-physics field simulation software;

[0030] Figure 5 It is to simulate the distribution of the surface electric field and lithium ion concentration field of the current collector of the lithium metal anode modified with the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1 using a multi-physics field simulation software;

[0031] Figure 6 It is the Coulomb efficiency test chart of lithium metal deposition / stripping on the current collector of the lithium metal anode modified with the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1;

[0032] Figure 7 It is the cycle life test chart of the lithium-lithium symmetric battery assembled with the lithium metal anode composite with the current collector modified by the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1;

[0033] Figure 8 It is the cycle life test chart of the lithium metal soft-pack battery assembled with the lithium metal anode composite with the current collector modified by the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1. Detailed Embodiments

[0034] Specific Embodiment 1: A preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector is specifically completed according to the following steps:

[0035] I. Preparation of hollow carbon spheres:

[0036] ①. Mix absolute ethanol, deionized water and ammonia water, stir for a period of time at room temperature to obtain a mixed solution I; drop tetraethyl orthosilicate into the mixed solution I, then add resorcinol solution and formaldehyde solution, and stir for a period of time at room temperature to obtain a precursor solution;

[0037] ②. Transfer the precursor solution to a reaction kettle, and carry out a hydrothermal reaction at 100°C to 200°C for a period of time, and naturally cool to room temperature to obtain a reaction product I; centrifuge and wash the reaction product I, and dry it to obtain SiO2@phenolic resin spheres;

[0038] ③. Under the protection of a nitrogen atmosphere, heat the SiO2@phenolic resin spheres to the carbonization temperature, and carbonize for a period of time at the carbonization temperature to obtain a reaction product II; immerse the reaction product II in a NaOH solution for a period of time, and then wash it with deionized water until neutral, and dry it to obtain hollow carbon spheres;

[0039] II. Preparation of a strong magnetic high-entropy alloy / carbon sphere composite material:

[0040] ①. Weigh 2 to 5 different metal salts according to an equimolar ratio and add them to deionized water, and then successively add FeCl2·4H2O, CoCl2·6H2O and NiCl2·6H2O with an equimolar ratio to one of the metal salts, stir evenly, and then ultrasonically form a uniform solution to obtain a mixed solution II;

[0041] ②. Immerse the hollow carbon spheres in the mixed solution II, stir for a period of time, and then dry the mixture using a rotary evaporator to obtain a reaction product III; anneal the reaction product III under the protection of a mixed gas atmosphere of H2 and Ar at a temperature of 800°C to 1000°C for a period of time to obtain a strong magnetic high-entropy alloy / carbon sphere composite material;

[0042] III. Modification of the metal lithium negative electrode current collector:

[0043] ①. Add the strong magnetic high-entropy alloy / carbon sphere composite material and polyvinylidene fluoride to N-methylpyrrolidone, and ultrasonically for a period of time to obtain a viscous slurry;

[0044] ②. Coat the viscous slurry on one surface of a double-sided smooth copper foil, and then dry it in vacuum to obtain a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector.

[0045] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is as follows: In the mixed solution I described in step ①, the volume ratio of absolute ethanol, deionized water, and ammonia water is (65 - 75):(5 - 15):(25 - 40); the volume ratio of tetraethyl orthosilicate to the mixed solution I in step ① is (1 - 5):(110 - 120). Other steps are the same as those in Specific Embodiment 1.

[0046] Specific Embodiment 3: The difference between this embodiment and either Specific Embodiment 1 or 2 is as follows: In step ①, the mass ratio of the resorcinol solution to the volume of the mixed solution I is (0.1 g - 0.5 g):(110 mL - 120 mL); the mass fraction of the resorcinol solution is 90% - 98%; in step ①, the volume ratio of the formaldehyde solution to the mixed solution I is (0.1 - 1):(110 - 120); the mass fraction of the formaldehyde solution is 93% - 98%. Other steps are the same as those in Specific Embodiment 1 or 2.

[0047] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is as follows: In step ①, mix absolute ethanol, deionized water, and ammonia water, and stir at room temperature for 20 min - 40 min to obtain the mixed solution I; add tetraethyl orthosilicate dropwise to the mixed solution I, then add the resorcinol solution and the formaldehyde solution, and stir at room temperature for 20 h - 26 h to obtain the precursor solution. Other steps are the same as those in Specific Embodiments 1 to 3.

[0048] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is as follows: In step ②, the hydrothermal reaction time is 2 h - 4 h; in step ②, use deionized water to centrifuge and wash the reaction product I 3 - 5 times, the centrifugation speed for washing is 5000 r / min - 8000 r / min, and the time for each centrifugation and washing is 5 min - 10 min; in step ②, place the reaction product I in a vacuum drying oven at a temperature of 60°C - 80°C and dry for 10 h - 12 h. Other steps are the same as those in Specific Embodiments 1 to 4.

[0049] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is as follows: In step ③, the carbonization temperature is 800°C - 1000°C; in step ③, the carbonization time is 1 h - 3 h; in step ③, the concentration of the NaOH solution is 2.5 mol / L - 3 mol / L; in step ③, immerse the reaction product II in the NaOH solution for 4 days - 6 days; in step ③, the drying temperature is 50°C - 80°C, and the drying time is 12 h - 16 h. Other steps are the same as those in Specific Embodiments 1 to 5.

[0050] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is as follows: The metal salts described in Step 2① are H2PtCl6·6H2O, CuCl2·2H2O, WCl4·4H2O, CrCl2·2H2O, MnCl2·3H2O, ZnCl2·6H2O or CuCl2·2H2O; the total molar amount of the metal salts in the mixed solution Ⅱ described in Step 2① is 1×10 - 4 mol. Other steps are the same as those in Embodiments 1 to 6.

[0051] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is as follows: The mass-volume ratio of the hollow carbon spheres to the mixed solution Ⅱ described in Step 2② is (0.1g - 0.3g):(1mL - 4mL); the volume ratio of H2 to Ar in the mixed gas of H2 and Ar described in Step 2② is 5:1; the annealing time described in Step 2② is 2h - 3h; in Step 2②, the hollow carbon spheres are immersed in the mixed solution Ⅱ, stirred for 8h - 12h, and then the mixture is dried using a rotary evaporator at 60℃ - 80℃ to obtain the reaction product Ⅲ. Other steps are the same as those in Embodiments 1 to 7.

[0052] Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is as follows: The mass ratio of the high-magnetic high-entropy alloy / carbon sphere composite material to polyvinylidene fluoride described in Step 3① is 90:(1 - 10); the mass-volume ratio of the high-magnetic high-entropy alloy / carbon sphere composite material to N-methylpyrrolidone described in Step 3① is 90mg:(500μL - 1000μL); the ultrasonic time described in Step 3① is 20min - 40min; the coating thickness of the viscous slurry on the copper foil described in Step 3② is 5μm - 10μm; the temperature of the vacuum drying described in Step 3② is 60℃ - 80℃, and the vacuum drying time is 10h - 12h. Other steps are the same as those in Embodiments 1 to 8.

[0053] Embodiment 10: This embodiment is an application of a strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector in a lithium metal battery.

[0054] The following examples are used to verify the beneficial effects of the present invention:

[0055] Example 1: A preparation method of a strong-magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector is specifically completed according to the following steps:

[0056] I. Preparation of hollow carbon spheres:

[0057] ①. Mix absolute ethanol, deionized water and ammonia water, and stir for 30 min at room temperature to obtain mixed solution I; add tetraethyl orthosilicate dropwise to mixed solution I, then add resorcinol solution and formaldehyde solution, and stir for 24 h at room temperature to obtain a precursor solution;

[0058] In the mixed solution I described in step ①, the volume ratio of absolute ethanol, deionized water and ammonia water is 70:10:33;

[0059] In step ①, the volume ratio of tetraethyl orthosilicate to mixed solution I is 1.5:113;

[0060] In step ①, the mass of the resorcinol solution described is 0.2 g:113 mL with respect to the volume of mixed solution I; the mass fraction of the resorcinol solution is 95%;

[0061] In step ①, the volume ratio of the formaldehyde solution to mixed solution I is 0.8:110; the mass fraction of the formaldehyde solution is 95%;

[0062] ②. Transfer the precursor solution to a reaction kettle, and carry out hydrothermal reaction at 100 °C for 2 h, and naturally cool to room temperature to obtain reaction product I; use deionized water to centrifugally wash reaction product I 3 times, and then dry at 60 °C for 12 h to obtain SiO2@phenolic resin microspheres;

[0063] In step ②, the centrifugal washing speed is 5000 r / min, and the time for each centrifugal washing is 5 min;

[0064] ③. Under the protection of a nitrogen atmosphere, heat the SiO2@phenolic resin microspheres to 1000 °C and carbonize at 1000 °C for 2 h to obtain reaction product II; immerse reaction product II in a 2.8 mol / L NaOH solution for 5 days, then wash with deionized water until neutral, and then dry at 60 °C for 16 h to obtain hollow carbon spheres;

[0065] II. Preparation of high-magnetic high-entropy alloy / carbon sphere composite materials:

[0066] ①. Weigh FeCl2·4H2O, CoCl2·6H2O, NiCl2·6H2O, H2PtCl6·6H2O and CuCl2·2H2O according to an equimolar ratio, add them to deionized water, stir evenly, and then ultrasonicate for 60 min at an ultrasonic power of 500 W to form a homogeneous solution to obtain mixed solution II;

[0067] In the mixed solution II described in step ②, the total molar amount of FeCl2·4H2O, CoCl2·6H2O, NiCl2·6H2O, H2PtCl6·6H2O and CuCl2·2H2O is 1×10 -4mol;

[0068] ②. Immerse the hollow carbon spheres into the mixed solution II, stir for 2 h, and then dry the mixture at 80 °C using a rotary evaporator for 12 h to obtain the reaction product III; place the reaction product III into a tube furnace at a temperature of 1000 °C, and anneal the reaction product III for 2 h under the protection of a mixed gas atmosphere of H2 and Ar to obtain a high-magnetic high-entropy alloy / carbon sphere composite material;

[0069] In step two ②, the mass ratio of the hollow carbon spheres to the volume of the mixed solution II is 0.1 g:4 mL;

[0070] In the mixed gas of H2 and Ar in step two ②, the volume ratio of H2 to Ar is 5:1;

[0071] In step two ②, the annealing temperature is 1000 °C;

[0072] III. Modify the metal lithium negative electrode current collector:

[0073] ①. Add 90 mg of the high-magnetic high-entropy alloy / carbon sphere composite material and 10 mg of polyvinylidene fluoride to 500 μL of N-methylpyrrolidone, and ultrasonically treat for 30 min to obtain a viscous slurry;

[0074] ②. Coat the viscous slurry on one surface of a smooth copper foil, and then vacuum dry at 60 °C for 12 h to obtain a metal lithium negative electrode current collector modified with a strong-magnetic high-entropy alloy / carbon sphere composite material;

[0075] In step three ②, the thickness of the viscous slurry coated on the copper foil surface is 50 μm.

[0076] Figure 1 is the microscopic morphology of the high-magnetic high-entropy alloy / carbon sphere composite material prepared in step two of Example 1. The left figure is a scanning electron microscope image, and the right figure is a transmission electron microscope;

[0077] Figure 1 It is proved that the material is a hollow sphere with a diameter of about 400 nm, and the high-entropy alloy is evenly distributed on the surface of the carbon sphere.

[0078] Figure 2 is the distribution diagram of different metal elements of the high-magnetic high-entropy alloy / carbon sphere composite material prepared in step two of Example 1;

[0079] Figure 2 The distribution of elements such as Pt, Cu, Fe, Co, and Ni on the surface of the carbon sphere further proves that the high-entropy alloy is evenly distributed on the surface of the carbon sphere.

[0080] Comparison Figure 3 With Figure 4, it can be proved that in the presence of a magnetic field, moving lithium ions will generate a secondary vortex effect, avoiding the tip effect and ensuring uniform deposition of lithium ions.

[0081] As Figure 5 shown: The microstructure of the strong magnetic high-entropy alloy / carbon sphere composite prepared in Example 1 modified on the surface of the metal lithium negative electrode current collector can effectively homogenize the electric field and lithium ion concentration field around the current collector.

[0082] Application Example: In this example, the strong magnetic high-entropy alloy / carbon sphere composite prepared in Example 1 modified on the metal lithium negative electrode current collector was used as the current collector of the lithium metal electrode, and its performance was tested as follows:

[0083] All electrochemical tests were carried out using the LAND CT3001A type Blue Electric battery test system produced by Wuhan Blue Electric Co., Ltd.

[0084] I. Assembly and testing of lithium-lithium symmetric battery:

[0085] The composite lithium negative electrode was prepared by electrochemically depositing the strong magnetic high-entropy alloy / carbon sphere composite prepared in Example 1 on the metal lithium negative electrode current collector. The strong magnetic high-entropy alloy / carbon sphere composite prepared in Example 1 modified on the metal lithium negative electrode current collector was used as the working electrode, the commercial metal lithium sheet was used as the counter electrode, and the ether-based electrolyte (LiTFSI was dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, and then LiNO3 was added to obtain the electrolyte; the concentration of LiTFSI in the electrolyte was 1 mol / L, and the mass fraction of LiNO3 was 2 wt%) was used as the electrolyte, and Celgard 2400 was used as the separator to assemble a CR-2032 type button cell. At a current density of 1 mA cm -2 , it was deposited for 10 h.

[0086] The battery was disassembled, and the composite lithium negative electrode was taken out. The same three-dimensional composite lithium negative electrode was used as both the working electrode and the counter electrode at the same time, the ether-based electrolyte (LiTFSI was dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, and then LiNO3 was added to obtain the electrolyte; the concentration of LiTFSI in the electrolyte was 1 mol / L, and the mass fraction of LiNO3 was 2 wt%) was used as the electrolyte, and Celgard 2400 was used as the separator to assemble a CR-2032 type button cell. Under the conditions of a current density of 1 mA cm -2 , a capacity of 1 mAh cm -2 , a constant current charge-discharge test was carried out.

[0087] II. Assembly and testing of lithium-current collector battery:

[0088] To test the Coulombic efficiency of lithium metal deposition / stripping on different current collectors, a lithium metal negative electrode current collector modified with a ferromagnetic high-entropy alloy / carbon sphere composite material was used as the working electrode, a lithium metal sheet was used as the counter electrode and reference electrode, and an ether-based electrolyte was used as the electrolyte (LiTFSI was dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, and LiNO3 was added to obtain the electrolyte; the concentration of LiTFSI in the electrolyte was 1 mol / L, and the mass fraction of LiNO3 was 2 wt%), and Celgard 2400 was used as the separator to assemble a CR-2032 type button cell. Under the conditions of a current density of 1 mA cm -2 , a capacity of 1 mAh cm -2 , a constant current charge-discharge test was carried out.

[0089] III. Assembly and testing of lithium iron phosphate soft-pack batteries:

[0090] The composite lithium negative electrode was prepared by electro-depositing lithium metal in the lithium metal negative electrode current collector modified with the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1, and the deposition capacity was 10 mAh cm -2 . Using a commercial lithium iron phosphate electrode sheet as the positive electrode, the loading amount of the active material was 26 mg cm -2 . An ether-based electrolyte was used as the electrolyte (LiTFSI was dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, and LiNO3 was added to obtain the electrolyte; the concentration of LiTFSI in the electrolyte was 1 mol / L, and the mass fraction of LiNO3 was 2 wt%), Celgard 2400 was used as the separator to assemble a soft-pack battery, and the electrolyte dosage was 2 g / Ah. The assembled full battery was subjected to a constant current charge-discharge test at a current density of 1C and a voltage window of 2.6 - 3.8V.

[0091] Comparative example: Using a traditional commercial double-sided smooth copper foil as the current collector and performing the same performance tests on it.

[0092] Electrochemical performance:

[0093] As Figure 6 shown, applying the lithium metal negative electrode current collector modified with the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1 can increase the Coulombic efficiency of lithium deposition / stripping to 99.83%. As Figure 7 shown, the lithium-lithium symmetric battery with the composite lithium negative electrode using the lithium metal negative electrode current collector modified with the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1 can stably cycle for more than 17000 h; as Figure 8 shown, the cycle life of the soft-pack battery (the positive active material is lithium iron phosphate) with the composite lithium negative electrode using the lithium metal negative electrode current collector modified with the ferromagnetic high-entropy alloy / carbon sphere composite material prepared in Example 1 is significantly improved compared with that using a conventional lithium metal negative electrode.

[0094] In summary, compared with the prior art, the present invention has the following advantages and prominent effects: By using the strong magnetic high-entropy alloy / carbon sphere composite material to modify the metal lithium negative electrode current collector, the present invention regulates the mass transfer behavior of lithium ions at the current collector - electrolyte interface, eliminates the lithium ion concentration gradient on the surface of the current collector, equalizes the electric field and lithium ion concentration field around the current collector, and avoids the occurrence of the tip effect. In addition, the "cocktail effect" of the high-entropy alloy enables the current collector to have a continuous lithium affinity intensity, which can reduce the lithium nucleation energy barrier, the nucleation and growth behavior of lithium, inhibit the growth of lithium dendrites, alleviate the volume change during the cycling of the metal lithium negative electrode, improve the stability of the metal lithium negative electrode, and significantly extend the cycle life and cycle capacity retention rate of the metal lithium battery.

Claims

1. A preparation method for modifying a current collector of a metallic lithium negative electrode with a strong magnetic high-entropy alloy / carbon sphere composite material, characterized in that The preparation method is specifically completed according to the following steps: I. Preparation of hollow carbon spheres: ①. Mix absolute ethanol, deionized water and ammonia water, stir for a period of time at room temperature to obtain mixed solution I; add tetraethyl orthosilicate dropwise to mixed solution I, then add resorcinol solution and formaldehyde solution, and stir for a period of time at room temperature to obtain a precursor solution; ②. Transfer the precursor solution to a reaction kettle, and carry out hydrothermal reaction at 100°C - 200°C for a period of time, and naturally cool to room temperature to obtain reaction product I; Centrifuge and wash reaction product I, and dry it to obtain SiO2@phenolic resin microspheres; ③. Under the protection of nitrogen atmosphere, heat the SiO2@phenolic resin microspheres to the carbonization temperature, and carbonize for a period of time at the carbonization temperature to obtain reaction product II; Immerse reaction product II in NaOH solution for a period of time, then wash it with deionized water until neutral, and dry it to obtain hollow carbon spheres; II. Preparation of high-magnetic high-entropy alloy / carbon sphere composite materials: ①. Weigh 2 - 5 different metal salts according to an equimolar ratio and add them to deionized water, then successively add FeCl2·4H2O, CoCl2·6H2O and NiCl2·6H2O with an equimolar ratio to one of the metal salts, stir evenly, and then ultrasonically form a uniform solution to obtain mixed solution II; ②. Immerse the hollow carbon spheres in mixed solution II, stir for a period of time, and then dry the mixture using a rotary evaporator to obtain reaction product III; anneal reaction product III under the protection of a mixed gas atmosphere of H2 and Ar at a temperature of 800°C - 1000°C for a period of time to obtain high-magnetic high-entropy alloy / carbon sphere composite materials; III. Modifying the metal lithium negative electrode current collector: ①. Add the high-magnetic high-entropy alloy / carbon sphere composite materials and polyvinylidene fluoride to N-methylpyrrolidone, and ultrasonically for a period of time to obtain a viscous slurry; ②. Coat the viscous slurry on one surface of a double-sided smooth copper foil, and then dry it in vacuum to obtain a strong-magnetic high-entropy alloy / carbon sphere composite material-modified metal lithium negative electrode current collector.

2. The preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector according to claim 1, characterized in that In the mixed solution I in step I①, the volume ratio of absolute ethanol, deionized water and ammonia water is (65 - 75):(5 - 15):(25 - 40); in step I①, the volume ratio of tetraethyl orthosilicate to mixed solution I is (1 - 5):(110 - 120).

3. The preparation method of a metal lithium negative electrode current collector modified by a ferromagnetic high-entropy alloy / carbon sphere composite material according to claim 1, characterized in that In step I①, the mass ratio of the resorcinol solution to the volume of mixed solution I is (0.1g - 0.5g):(110mL - 120mL); the mass fraction of the resorcinol solution is 90% - 98%; in step I①, the volume ratio of the formaldehyde solution to mixed solution I is (0.1 - 1):(110 - 120); the mass fraction of the formaldehyde solution is 93% - 98%.

4. The preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium anode current collector according to claim 1, characterized in that In step I①, mix absolute ethanol, deionized water and ammonia water, stir at room temperature for 20min - 40min to obtain mixed solution I; add tetraethyl orthosilicate dropwise to mixed solution I, then add resorcinol solution and formaldehyde solution, and stir at room temperature for 20h - 26h to obtain a precursor solution.

5. The preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector according to claim 1, characterized in that The hydrothermal reaction time described in Step 1② is 2 h to 4 h; in Step 1②, deionized water is used to centrifugally wash the reaction product I 3 to 5 times, the centrifugal washing speed is 5000 r / min to 8000 r / min, and the time for each centrifugal washing is 5 min to 10 min; in Step 1②, the reaction product I is placed in a vacuum drying oven at a temperature of 60°C to 80°C and dried for 10 h to 12 h.

6. The preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector according to claim 1, characterized in that The carbonization temperature described in Step 1③ is 800°C to 1000°C; the carbonization time described in Step 1③ is 1 h to 3 h; the concentration of the NaOH solution described in Step 1③ is 2.5 mol / L to 3 mol / L; the time for immersing the reaction product II in the NaOH solution in Step 1③ is 4 days to 6 days; the drying temperature described in Step 1③ is 50°C to 80°C, and the drying time is 12 h to 16 h.

7. The preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector according to claim 1, characterized in that The metal salts described in Step 2① are H2PtCl6·6H2O, CuCl2·2H2O, WCl4·4H2O, CrCl2·2H2O, MnCl2·3H2O, ZnCl2·6H2O or CuCl2·2H2O; The total molar amount of metal salts in the mixed solution II described in Step 2① is 1×10 -4 mol.

8. The preparation method of a strong magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector according to claim 1, characterized in that The mass ratio of the hollow carbon spheres to the volume of the mixed solution II described in Step 2② is (0.1 g to 0.3 g):(1 mL to 4 mL); the volume ratio of H2 to Ar in the mixed gas of H2 and Ar described in Step 2② is 5:1; the annealing time described in Step 2② is 2 h to 3 h; in Step 2②, the hollow carbon spheres are immersed in the mixed solution II, stirred for 8 h to 12 h, and then the mixture is dried using a rotary evaporator at 60°C to 80°C to obtain the reaction product III.

9. The preparation method of a strongly magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector according to claim 1, characterized in that The mass ratio of the high magnetic high-entropy alloy / carbon sphere composite material to polyvinylidene fluoride described in Step 3① is 90:(1 to 10); the mass ratio of the high magnetic high-entropy alloy / carbon sphere composite material to the volume of N-methylpyrrolidone described in Step 3① is 90 mg:(500 μL to 1000 μL); the ultrasonic time described in Step 3① is 20 min to 40 min; the thickness of the viscous slurry coated on the copper foil described in Step 3② is 5 μm to 10 μm; the vacuum drying temperature described in Step 3② is 60°C to 80°C, and the vacuum drying time is 10 h to 12 h.

10. Application of a strongly magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector prepared by the preparation method according to claim 1, characterized in that Application of a strongly magnetic high-entropy alloy / carbon sphere composite material modified metal lithium negative electrode current collector in a lithium metal battery.

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