Preparation method and application of a multi-halogenated MXenes / carbon fiber lithium metal anode framework

Abstract

A preparation method and application of a multi-halogenated MXenes / carbon fiber lithium metal anode framework, which belongs to the technical field of rechargeable high specific energy secondary batteries. Method: First, prepare multi-halogenated MXene nanosheets; second, prepare an electrospinning solution precursor; third, electrospin and anneal. A multi-halogenated MXenes / carbon fiber lithium metal anode framework is used as a lithium metal anode framework to prepare a multi-halogenated MXene / carbon fiber composite lithium anode and is applied to lithium metal batteries. On the one hand, the present invention enhances the uniformity of the lithium metal deposition behavior, inhibits the formation of lithium dendrites, inhibits the consumption of the electrolyte, and prolongs the life of the lithium metal anode; on the other hand, it inhibits the volume change of the lithium metal anode during the deposition / stripping process, avoids the rupture of the SEI film, induces uniform deposition of lithium metal, and while improving the energy density of the battery, significantly improves its cycle life, stability and safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of rechargeable high specific energy secondary batteries, and particularly relates to a preparation method and application of a multi-halogenated MXenes / carbon fiber lithium metal negative electrode framework. Background Art

[0002] With the rapid development of electric vehicles, portable devices and renewable energy, the demand for high energy density energy storage secondary batteries is increasing continuously. Limited by the relatively low theoretical specific capacity of graphite negative electrodes (372 mAh / g), the energy density of commercial lithium-ion batteries has tended to reach its limit (350 Wh / kg), unable to meet the needs of people for high specific energy secondary batteries. Lithium metal has advantages such as a high theoretical specific capacity (3860 mAh / g) and a low electrode potential (-3.04 V vs. standard hydrogen electrode), and is recognized as an ideal negative electrode for realizing high energy density battery systems. Replacing the graphite negative electrode of traditional lithium-ion batteries with a lithium negative electrode will increase the energy density of the battery by ~50%. Therefore, using a lithium negative electrode is one of the important ways to improve the energy density of batteries, and a highly stable lithium negative electrode is the prerequisite and foundation for the practical application of lithium metal batteries.

[0003] Although the lithium negative electrode has great application potential, the rapid pulverization of the lithium negative electrode leads to a short lifespan of lithium metal batteries. The key reason lies in the uncontrollable growth of lithium dendrites and the huge volume change of the host-free lithium negative electrode. In recent years, researchers have proposed different strategies, such as electrolyte modification, design of artificial SEI, application of all-solid-state electrolytes, construction of framework composite lithium negative electrodes, etc. to induce uniform and dense deposition / stripping of lithium. Under mild laboratory conditions, the lifespan of the lithium negative electrode has been significantly improved. However, the currently reported solutions still cannot make the lithium negative electrode show satisfactory stability under practical conditions of low negative electrode surface capacity / positive electrode surface capacity (N / P) ratio, lean electrolyte and high rate.

[0004] To break through the bottleneck, it is extremely important to ensure uniform and dense deposition / stripping of lithium, and the key lies in regulating the mass transfer behavior of Li + The mass transfer of Li + can be divided into three steps: (i) the mass transfer process of solvated Li + from the electrolyte to the lithium negative electrode; (ii) the desolvation and migration process of solvated Li + in the SEI film; (iii) the process of Li + obtaining electrons on the electrode surface to become lithium atoms. Research shows that the deposition / stripping behavior of lithium depends on the mass transfer path, speed and uniformity of lithium ions in the lithium negative electrode interface layer and the SEI film. The uneven mass transfer flux of Li + in the lithium negative electrode interface layer and the charge transfer blockage in the SEI film (high desolvation and migration energy barriers) are the key inducements for the appearance of lithium dendrites and volume fluctuations. Therefore, understanding Li +Mass transfer law, master the regulation of Li + The means of mass transfer, and on this basis, accurately optimize the lithium deposition / stripping behavior is the key scientific issue faced by lithium anode research. Based on the above analysis, (i) use intermolecular forces such as lithium bonds to adsorb Li + , homogenize the Li + mass transfer flux near the electrode, and accelerate the replenishment of Li+ consumption, such as designing a lithiumophilic surface; (ii) construct a high-quality SEI film to reduce the desolvation energy barrier and migration energy barrier of Li + , and accelerate the mass transfer of Li + in the SEI film. For example, optimizing the electrolyte composition or constructing an artificial SEI film is a common method for regulating Li + mass transfer behavior. However, most current strategies are based on 2D planar electrodes, and the effect of alleviating the volume change of the lithium anode under practical conditions is not ideal. In contrast, a 3D skeleton with good physical confinement and mechanical properties is currently the most effective strategy to alleviate or even eliminate the volume change of the lithium anode. However, a serious problem still exists, that is, the 3D transformation of the lithium anode will be accompanied by the generation of a large amount of SEI film. The native SEI film mainly composed of organic components has a low affinity with Li + , a high desolvation energy barrier and Li + migration energy barrier, which is not conducive to the efficient desolvation and rapid migration of Li + . In view of this, the strategy of coupling the 3D skeleton with SEI film modification to regulate Li + mass transfer has been intensively studied. The magnitude of the interaction force between the electrode surface and Li + , the size, quantity and distribution of lithiumophilic sites largely determine the uniformity of Li + mass transfer flux and the mass transfer path; while the affinity between the components of the SEI film and Li + and the number of grain boundaries formed determine the desolvation energy barrier and mass transfer rate of Li + in the SEI film. Therefore, the modulation of the characteristics of the skeleton lithiumophilic sites coupled with the components of the SEI film is the main research direction for optimizing Li + mass transfer at present.

[0005] MXene materials have an extremely low Li + diffusion rate (10 -10 to 10 -9 cm 2 / s), Li + diffusion barrier (0.07 eV) and a relatively low density (between carbon materials and metals), and are widely used in the field of secondary batteries. Compared with other materials, MXene as a skeleton has the following unique advantages in regulating Li + mass transfer behavior: (i) Abundant and uniformly distributed atomic groups can serve as Li + anchor points to homogenize Li+ The mass transfer flux is increased and the lithium nucleation energy barrier is reduced; (ii) in-situ induced formation of a SEI film rich in lithium halide accelerates the desolvation and diffusion of Li + in the SEI film; (iii) the regulation of surface groups can conveniently control the interaction between the skeleton and the SEI film and Li + ; (iv) the moderate density does not significantly affect the energy density of the composite lithium anode. However, most current studies use MXene materials obtained by traditional acid etching methods as the main body to construct the skeleton, which has the following problems: (i) the surface groups are limited to three types: -OH, -O, and -F, and it is difficult to accurately regulate the content of the groups; (ii) the lithiophilicity of the -OH group is poor; (iii) the lithium halide component in the derived SEI film is single (LiF), and the Li + conductivity is low, which is not sufficient to ensure the rapid mass transfer of Li + in the SEI film. SUMMARY OF THE INVENTION

[0006] In order to solve the above technical problems, the present invention provides a preparation method and application of a multi-halogenated MXenes / carbon fiber metal lithium anode skeleton, which on the one hand enhances the uniformity of the deposition behavior of metallic lithium, inhibits the formation of lithium dendrites, inhibits the consumption of the electrolyte, and prolongs the life of the metallic lithium anode; on the other hand, it inhibits the volume change of the metallic lithium anode during the deposition / stripping process, avoids the rupture of the SEI film, induces uniform deposition of metallic lithium, improves the energy density of the battery, and significantly enhances its cycle life, stability and safety.

[0007] A preparation method of a multi-halogenated MXenes / carbon fiber metal lithium anode skeleton is specifically completed according to the following steps:

[0008] I. Preparation of multi-halogenated MXene nanosheets:

[0009] ①. Mix the MAX material with halogenated inorganic salts, grind for a period of time, and then transfer it to calcine for a period of time under an argon atmosphere to obtain a solid product; wash the solid product with hydrochloric acid to remove the unreacted halogenated inorganic salts to obtain multi-layer MXene;

[0010] ②. Dissolve lithium halide in dimethyl sulfoxide to obtain a lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L;

[0011] ③. Immerse the multi-layer MXene into the lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L, stir and react for a period of time, and then centrifuge to collect the supernatant to obtain a supernatant containing multi-halogenated MXene nanosheets;

[0012] II. Preparation of the electrospinning solution precursor:

[0013] ①. Concentrate the supernatant containing multi-halogenated MXene nanosheets by high-speed centrifugation to make the solution concentration reach 30 mg / mL to 40 mg / mL, obtaining a multi-halogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL;

[0014] ②. Add polyacrylonitrile to the multi-halogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL, stir and react for a period of time to obtain an electrospinning solution precursor;

[0015] III. Electrospinning and annealing:

[0016] ①. At a certain temperature and humidity, perform electrospinning on the electrospinning solution precursor to obtain a fiber membrane;

[0017] ②. Pre-oxidize the fiber membrane at 240 °C to 260 °C for a period of time, then transfer it to an argon atmosphere and heat it to 700 °C to 800 °C, and anneal it at 700 °C to 800 °C to obtain a multi-halogenated MXenes / carbon fiber lithium metal anode framework.

[0018] A multi-halogenated MXenes / carbon fiber lithium metal anode framework is used as a lithium metal anode framework for preparing a multi-halogenated MXene / carbon fiber composite lithium anode and is applied to a lithium metal battery.

[0019] Principle of the present invention:

[0020] Based on the problem of rapid pulverization of the practical lithium anode, the present invention uses the "targeted lithium-philic" effect of having atomic-level, abundant and uniform lithium-philic halogen groups to regulate the mass transfer of Li + at the electrode interface layer, and uses the "electrochemical scissors" effect of Li + to control the components of the SEI film and regulate the mass transfer of Li + in the SEI film, so as to achieve uniform and dense deposition / stripping of Li + ; The present invention proposes a novel MXene material with multi-halogen groups (–Cl, –Br, and –I) combined with carbon fiber as the lithium anode framework, and uses the "lithium bond" and "ion-dipole interaction" to anchor Li + from both sides, and homogenize the mass transfer flow of Li + ; Utilize the strong affinity between the rich lithium halide components in the endogenously derived SEI film of halogenated MXene and Li + and the formed abundant grain boundaries to induce the formation of a solvation sheath with a low solvent coordination number of Li + on the surface of the SEI film, realizing the efficient desolvation and rapid migration of Li + ; Use its 3D structure and pore physical confinement of lithium deposition to construct a highly stable lithium metal battery system.

[0021] The preparation method and application of the multi-halogenated MXenes / carbon fiber lithium metal anode framework of the present invention have the following beneficial effects:

[0022] 1. The multi-halogenated MXenes / carbon fiber lithium metal anode framework obtained in the present invention has a unique three-dimensional porous structure. The continuous conductive network of the three-dimensional porous conductive framework has a high electrochemically active specific surface area, which can evenly distribute the applied current on the entire porous framework, reduce the effective current density, and thus homogenize the distribution of the electric field around the framework; the uniform electric field can homogenize the lithium ion mass transfer flux, which helps to deposit lithium evenly.

[0023] 2. There is a high binding energy between the surface of the multi-halogenated MXenes / carbon fiber lithium metal anode framework obtained in the present invention and lithium ions, which gives the MXene / carbon fiber framework excellent lithiophilicity on the surface. At the same time, the halogen groups on the surface of the multi-halogenated MXene material can serve as atomic-level nucleation sites, reducing the lithium nucleation energy barrier and ensuring uniform and dense lithium nucleation.

[0024] 3. The multi-halogenated MXenes / carbon fiber lithium metal anode framework obtained in the present invention can form a SEI film rich in lithium halide during the battery cycling process. The SEI film rich in lithium halide components can effectively accelerate the desolvation of Li + and its migration in the SEI film, thereby inhibiting the growth of lithium dendrites.

[0025] 4. Applying the multi-halogenated MXenes / carbon fiber lithium metal anode framework obtained in the present invention can make the Coulombic efficiency of the lithium anode reach 99.83%, and it can stably cycle for more than 17000 h. The soft-pack battery using the multi-halogenated MXene / carbon fiber composite lithium anode can stably cycle 300 times, which is much higher than that of the conventional lithium metal anode.

[0026] 5. The preparation method of the multi-halogenated MXenes / carbon fiber lithium metal anode framework of the present invention is simple and easy to implement, does not require complex process flows and equipment, the raw materials required for preparing the framework are low-cost, and expensive catalysts or rare metals are not required during the preparation process. Therefore, it has a low cost advantage; a large amount of toxic or environmentally polluting substances are not required during the preparation process, and at the same time, the effective utilization of resources can be realized, meeting the environmental protection requirements; the preparation method of the present invention has been verified by multiple experiments, has strong reproducibility and stability, and can ensure the consistency of product quality. Description of the Drawings

[0027] Figure 1 is the preparation flow chart of a multi-halogenated MXenes / carbon fiber lithium metal anode framework of the present invention;

[0028] Figure 2Scanning electron microscope image of the multi-halogenated MXenes / carbon fiber lithium metal anode framework prepared in Example 1;

[0029] Figure 3 X-ray photoelectron spectroscopy image of the depth etching of the solid electrolyte interface film on the surface of the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1;

[0030] Figure 4 Coulombic efficiency test chart of lithium metal deposition / stripping on the multi-halogenated MXenes / carbon fiber lithium metal anode framework prepared in Example 1;

[0031] Figure 5 Cyclic life test chart of the lithium-lithium symmetric battery assembled with the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1;

[0032] Figure 6 Cyclic performance chart of the soft-pack battery assembled with the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1 as the anode and the commercial lithium iron phosphate electrode as the cathode;

[0033] Figure 7 Cyclic performance chart of the soft-pack battery assembled with the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 2 as the anode and the commercial lithium iron phosphate electrode as the cathode;

[0034] Figure 8 Cyclic performance chart of the soft-pack battery assembled with the MXene / carbon fiber composite lithium anode prepared in Comparative Application Example 1 as the anode and the commercial lithium iron phosphate electrode as the cathode. Detailed implementation mode

[0035] Detailed implementation mode 1: A preparation method of a multi-halogenated MXenes / carbon fiber lithium metal anode framework is specifically completed according to the following steps:

[0036] 1. Preparation of multi-halogenated MXene nanosheets:

[0037] ①. Mix the MAX material with the halogenated inorganic salt, grind for a period of time, and then transfer it to calcine for a period of time under an argon atmosphere to obtain a solid product; wash the solid product with hydrochloric acid to remove the unreacted halogenated inorganic salt to obtain multi-layer MXene;

[0038] ②. Dissolve lithium halide in dimethyl sulfoxide to obtain a lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L;

[0039] ③ Immerse the multi-layer MXene into a lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L, stir and react for a period of time, then centrifuge and collect the supernatant to obtain a supernatant containing multi-halogenated MXene nanosheets;

[0040] II. Preparation of electrospinning solution precursor:

[0041] ① Use the method of high-speed centrifugation to concentrate the supernatant containing multi-halogenated MXene nanosheets to make the concentration of the solution reach 30 mg / mL to 40 mg / mL, and obtain a multi-halogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL;

[0042] ② Add polyacrylonitrile to the multi-halogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL, stir and react for a period of time to obtain an electrospinning solution precursor;

[0043] III. Electrospinning and annealing:

[0044] ① At a certain temperature and humidity, perform electrospinning on the electrospinning solution precursor to obtain a fiber membrane;

[0045] ② Pre-oxidize the fiber membrane at 240 °C to 260 °C for a period of time, then transfer it to an argon atmosphere and heat it up to 700 °C to 800 °C, and anneal it at 700 °C to 800 °C to obtain a multi-halogenated MXenes / carbon fiber lithium metal negative electrode skeleton.

[0046] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the MAX material described in step ① is Mo 2 TiAlC 2 TiSiC 2 Ti 3 AlC 2 or Ti 3 AlCN; the size of the MAX material described in step ① is 200 to 400 mesh. Other steps are the same as those in Specific Embodiment 1.

[0047] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that the halogenated inorganic salt described in step ① is CdCl 2 CdBr 2 CdI 2 NaCl, NaB, NaI, KCl, KBr, and KI, or a mixture of one or more of them; the molar ratio of the MAX material to the halogenated inorganic salt described in step ① is 1:(1 to 5); the calcination temperature described in step ① is 600 °C to 700 °C, and the calcination time is 10 h to 12 h. Other steps are the same as those in Specific Embodiment 1 or 2.

[0048] Embodiment 4: The differences between this embodiment and any one of Embodiments 1 to 3 are as follows: the grinding time described in Step ① of Step One is 10 min to 30 min; the mass fraction of hydrochloric acid described in Step ① of Step One is 35% to 38%; the number of times of washing the solid product with hydrochloric acid is 1 to 5 times; the lithium halide described in Step ② of Step One is LiCl, LiBr or LiI; the stirring reaction rate described in Step ③ of Step One is 100 r / min to 300 r / min, and the stirring reaction time is 2 h to 4 h; the centrifugation rate described in Step ③ of Step One is 8000 r / min, and the centrifugation time is 5 min to 10 min. Other steps are the same as those in Embodiments 1 to 3.

[0049] Embodiment 5: The differences between this embodiment and any one of Embodiments 1 to 4 are as follows: the mass ratio of the multi-layer MXene to the volume of the lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L described in Step ③ of Step One is (0.5 g to 1 g):(10 mL to 20 mL); the rotation speed of the high-speed centrifugation described in Step ① of Step Two is 10000 rpm / min, and the high-speed centrifugation time is 30 min to 60 min. Other steps are the same as those in Embodiments 1 to 4.

[0050] Embodiment 6: The differences between this embodiment and any one of Embodiments 1 to 5 are as follows: the mass ratio of polyacrylonitrile to the volume of the multi-halogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL described in Step ② of Step Two is (8 g to 10 g):10 mL; the stirring reaction temperature described in Step ② of Step Two is 25°C to 40°C, the stirring speed is 300 r / min to 500 r / min, and the stirring reaction time is 8 h to 12 h. Other steps are the same as those in Embodiments 1 to 5.

[0051] Embodiment 7: The differences between this embodiment and any one of Embodiments 1 to 6 are as follows: electrospinning the electrospinning solution precursor under the conditions of a temperature of 30°C to 40°C and a humidity of 30% to 40% in Step ① of Step Three; the electrospinning voltage described in Step ① of Step Three is 12 kV to 14 kV, the injection speed of the spinning solution is 0.003 cm / min to 0.005 cm / min, the rotation speed of the spinning solution receiver is 50 r / min to 100 r / min, the negative voltage during the electrospinning process is 0.1 kV to 0.5 kV, and the distance from the nozzle to the receiver is 10 cm to 15 cm. Other steps are the same as those in Embodiments 1 to 6.

[0052] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is as follows: In step 3②, the pre-oxidation time at 240°C to 260°C is 1h to 2h; in step 3②, the annealing time at 700°C to 800°C is 1h to 2h; in step 3②, the heating rate is 5°C / min to 10°C / min. Other steps are the same as those in Embodiments 1 to 7.

[0053] Embodiment 9: This embodiment is a multi-halogenated MXenes / carbon fiber lithium metal negative electrode framework used as a lithium metal negative electrode framework for preparing a multi-halogenated MXene / carbon fiber composite lithium negative electrode and applied to a lithium metal battery.

[0054] Embodiment 10: The difference between this embodiment and Embodiment 9 is as follows: The process of using a multi-halogenated MXenes / carbon fiber lithium metal negative electrode framework as a lithium metal negative electrode framework for preparing a multi-halogenated MXene / carbon fiber composite lithium negative electrode is specifically completed according to the following steps:

[0055] In a glove box filled with argon, lithium metal is infused into the multi-halogenated MXenes / carbon fiber lithium metal negative electrode framework by the method of molten lithium infusion, so that the areal capacity of the multi-halogenated MXenes / carbon fiber composite lithium negative electrode framework is 10 mAh / cm 2 ~20 mAh / cm 2 , and it is cooled at room temperature for 1h to obtain a multi-halogenated MXene / carbon fiber composite lithium negative electrode. Other steps are the same as those in Embodiment 9.

[0056] The following examples are used to verify the beneficial effects of the present invention:

[0057] Example 1: A preparation method of a multi-halogenated MXenes / carbon fiber lithium metal negative electrode framework is specifically completed according to the following steps:

[0058] I. Preparation of multi-halogenated MXene nanosheets:

[0059] ①. Mix the MAX material with halogenated inorganic salts, grind for a period of time, and then transfer it to be calcined for a period of time in an argon atmosphere to obtain a solid product; wash the solid product with hydrochloric acid to remove the unreacted halogenated inorganic salts to obtain multi-layer MXene;

[0060] The MAX material described in step I① is Ti 3 AlC 2 ;

[0061] The size of the MAX material described in step I① is 300 mesh;

[0062] The halogenated inorganic salt described in step I① is CdCl 2, a mixture of NaCl and KCl, wherein CdCl 2 , the molar ratio of NaCl and KCl is 2:1:1;

[0063] The molar ratio of the MAX material to the inorganic halide salt described in Step ① is 1:3;

[0064] The grinding time described in Step ① is 15 min;

[0065] The calcination temperature described in Step ① is 700 °C, and the calcination time is 12 h;

[0066] The mass fraction of the hydrochloric acid described in Step ① is 35%; the number of times of washing the solid product with hydrochloric acid is 5 times;

[0067] ② Dissolve lithium halide in dimethyl sulfoxide to obtain a lithium halide dimethyl sulfoxide solution with a concentration of 0.8 mol / L;

[0068] The lithium halide described in Step ② is LiCl;

[0069] ③ Immerse the multilayer MXene into the lithium halide dimethyl sulfoxide solution with a concentration of 0.8 mol / L, stir and react for a period of time, then centrifuge, collect the supernatant, and obtain a supernatant containing multi-halogenated MXene nanosheets;

[0070] The stirring reaction rate described in Step ③ is 150 r / min, and the stirring reaction time is 2.5 h;

[0071] The centrifugation rate described in Step ③ is 8000 r / min, and the centrifugation time is 10 min;

[0072] The mass ratio of the multilayer MXene to the volume of the lithium halide dimethyl sulfoxide solution with a concentration of 0.8 mol / L described in Step ③ is 0.8 g:15 mL;

[0073] II. Preparation of electrospinning solution precursor:

[0074] ① Use high-speed centrifugation to concentrate the supernatant containing multi-halogenated MXene nanosheets to make the solution concentration reach 30 mg / mL, and obtain a multi-halogenated MXene solution with a concentration of 30 mg / mL;

[0075] The rotation speed of the high-speed centrifugation described in Step ② is 10000 rpm / min, and the high-speed centrifugation time is 60 min;

[0076] ② Add polyacrylonitrile to the multi-halogenated MXene solution with a concentration of 30 mg / mL, stir and react for a period of time to obtain an electrospinning solution precursor;

[0077] In Step ②, the mass ratio of polyacrylonitrile to the volume of the polyhalogenated MXene solution with a concentration of 30 mg / mL is 10 g:10 mL;

[0078] In Step ②, the temperature of the stirring reaction is 25 °C, the stirring speed is 300 r / min, and the stirring reaction time is 8 h;

[0079] III. Electrospinning and annealing:

[0080] ①. Electrospin the electrospinning solution precursor at a certain temperature and humidity to obtain a fiber membrane;

[0081] In Step ③①, electrospin the electrospinning solution precursor at a temperature of 30 °C and a humidity of 30%;

[0082] In Step ③①, the voltage of the electrospinning is 13 kV, the injection speed of the spinning solution is 0.0035 cm / min, the rotation speed of the spinning receiver is 80 r / min, the negative voltage during the electrospinning process is 0.2 kV, and the distance from the nozzle to the receiver is 14 cm;

[0083] ②. Pre-oxidize the fiber membrane at 250 °C for a certain period of time, then transfer it to an argon atmosphere and heat it up to 800 °C, and anneal it at 800 °C to obtain a polyhalogenated MXenes / carbon fiber lithium metal anode framework;

[0084] In Step ③②, the pre-oxidation time at 250 °C is 1 h;

[0085] In Step ③②, the annealing time at 800 °C is 2 h;

[0086] In Step ③②, the heating rate is 5 °C / min.

[0087] Example 2: The difference between this example and Example 1 is that the halogenated inorganic salt described in Step ①① is a mixture of CdCl 2 , NaBr, and KI, and the molar ratio of CdCl 2 , NaBr, and KI is 2:1:1. Other steps and parameters are the same as those in Example 1.

[0088] Comparative Example 1: The method for preparing MXene nanosheets using the traditional acid etching method and using the MXene nanosheets to prepare the MXenes / carbon fiber lithium metal anode framework is specifically completed according to the following steps:

[0089] I. Put 1 g of Ti 3 AlC 2The powder was slowly added to a mixed solution composed of 20 mL of HCl with a mass fraction of 35 wt% and 1.56 g of LiF, heated in a water bath at 38 °C for 48 h, then washed three times with 1 mol / L HCl and 1 mol / L LiCl solutions in sequence, and then washed with deionized water until neutral, and then centrifuged at 5000 r / min to collect the supernatant to obtain MXene nanosheets;

[0090] II. Preparation of electrospinning solution precursor:

[0091] ①. The supernatant containing MXene nanosheets was concentrated by high-speed centrifugation to make the concentration of the solution reach 30 mg / mL, obtaining an MXene nanosheet solution with a concentration of 30 mg / mL;

[0092] In step II①, the rotation speed of the high-speed centrifugation is 10000 rpm / min, and the time of the high-speed centrifugation is 60 min;

[0093] ②. Polyacrylonitrile was added to the MXene nanosheet solution with a concentration of 30 mg / mL, and stirred and reacted for a period of time to obtain an electrospinning solution precursor;

[0094] In step II②, the mass ratio of polyacrylonitrile to the volume of the MXene nanosheet solution with a concentration of 30 mg / mL is 10 g:10 mL;

[0095] In step II②, the temperature of the stirring reaction is 25 °C, the stirring speed is 300 r / min, and the time of the stirring reaction is 8 h;

[0096] III. Electrospinning and annealing:

[0097] ①. At a certain temperature and humidity, electrospinning was carried out on the electrospinning solution precursor to obtain a fiber membrane;

[0098] In step III①, electrospinning was carried out on the electrospinning solution precursor under the conditions of a temperature of 30 °C and a humidity of 30%;

[0099] In step III①, the voltage of the electrospinning is 13 kV, the injection speed of the spinning solution is 0.0035 cm / min, the rotation speed of the spinning receiver is 80 r / min, the negative voltage during the spinning process is 0.2 kV, and the distance from the nozzle to the receiver is 14 cm;

[0100] ②. The fiber membrane was pre-oxidized at 250 °C for a period of time, then transferred to an argon atmosphere and heated to 800 °C, and annealed at 800 °C to obtain an MXenes / carbon fiber lithium metal negative electrode framework;

[0101] In step III②, the pre-oxidation time at 250 °C is 1 h;

[0102] In Step ③②, the annealing time at 800 °C is 2 h;

[0103] The heating rate described in Step ③② is 5 °C / min.

[0104] Application Example 1: Using a multi-halogenated MXenes / carbon fiber lithium metal anode framework prepared in Example 1 as a lithium metal anode framework to prepare a multi-halogenated MXene / carbon fiber composite lithium anode is specifically completed according to the following steps:

[0105] In a glove box filled with argon, lithium metal is infused into the multi-halogenated MXenes / carbon fiber lithium metal anode framework by means of molten lithium infusion, so that the areal capacity of the multi-halogenated MXenes / carbon fiber composite lithium metal anode framework is 15 mAh / cm 2 and cooled at room temperature for 1 h to obtain a multi-halogenated MXene / carbon fiber composite lithium anode.

[0106] Application Example 2: Using a multi-halogenated MXenes / carbon fiber lithium metal anode framework prepared in Example 2 as a lithium metal anode framework to prepare a multi-halogenated MXene / carbon fiber composite lithium anode is specifically completed according to the following steps:

[0107] In a glove box filled with argon, lithium metal is infused into the multi-halogenated MXenes / carbon fiber lithium metal anode framework by means of molten lithium infusion, so that the areal capacity of the multi-halogenated MXenes / carbon fiber composite lithium metal anode framework is 15 mAh / cm 2 and cooled at room temperature for 1 h to obtain a multi-halogenated MXene / carbon fiber composite lithium anode.

[0108] Application Comparative Example 1: Using the MXenes / carbon fiber lithium metal anode framework prepared in Comparative Example 1 as a lithium metal anode framework to prepare a MXene / carbon fiber composite lithium anode is specifically completed according to the following steps:

[0109] In a glove box filled with argon, lithium metal is infused into the MXenes / carbon fiber lithium metal anode framework prepared in Comparative Example 1 by means of molten lithium infusion, so that the areal capacity of the MXenes / carbon fiber lithium metal anode framework prepared in Comparative Example 1 is 15 mAh / cm 2 and cooled at room temperature for 1 h to obtain a MXene / carbon fiber composite lithium anode.

[0110] The cyclic performance of the materials and the charge and discharge performance at different rates are both tested using the LAND CT3001A type Blue Electric battery test system produced by Wuhan Blue Electric Co., Ltd.

[0111] Assembly and testing of lithium-lithium symmetric batteries:

[0112] Two multi-halogenated MXene / carbon fiber composite lithium anodes prepared in Application Example 1 were used as the working electrode and the counter electrode respectively. An ether electrolyte for lithium-sulfur batteries was used as the electrolyte (LiTFSI and LiNO 3 dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, the concentration of LiTFSI was 1 mol / L, and LiNO 3 had a concentration of 0.1 mol / L), Celgard 2400 was used as the separator, and a CR-2032 type coin cell was assembled; at a current density of 1 mA / cm 2 and a capacity of 1 mAh / cm 2 , a constant current charge-discharge test was carried out, as shown in Figure 5 ;

[0113] Assembly and testing of lithium-skeleton batteries:

[0114] Using the multi-halogenated MXenes / carbon fiber metal lithium anode skeleton prepared in Example 1 as the working electrode, a lithium metal sheet as the counter electrode and the reference electrode, an ether electrolyte for lithium-sulfur batteries was used as the electrolyte (LiTFSI and LiNO 3 dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, the concentration of LiTFSI was 1 mol / L, and LiNO 3 had a concentration of 0.1 mol / L), Celgard 2400 was used as the separator, and a CR-2032 type coin cell was assembled. At a current density of 1 mA / cm 2 and a capacity of 1 mAh / cm 2 , a constant current charge-discharge test was carried out, as shown in Figure 4 ;

[0115] Assembly and testing of lithium iron phosphate soft-pack batteries:

[0116] Using the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1 as the negative electrode, a commercial lithium iron phosphate electrode sheet as the positive electrode, an ether electrolyte for lithium-sulfur batteries was used as the electrolyte (LiTFSI and LiNO 3 dissolved in a mixed solution of DOL and DME with a volume ratio of 1:1, the concentration of LiTFSI was 1 mol / L, and LiNO 3 had a concentration of 0.1 mol / L), Celgard 2400 was used as the separator, and a soft-pack battery was assembled. At a current density of 1C and a voltage window of 2.5 - 4.0 V, a constant current charge-discharge test was carried out on the assembled full cell, as shown in Figure 6 ;

[0117] Replace the multi-halogenated MXene / carbon fiber composite lithium anode with a conventional ultra-thin metallic lithium anode. Keep the others the same as above. Perform a constant current charge-discharge test on the assembled full cell at a current density of 1C and a voltage window of 2.5 - 4.0V, as shown in Figure 6 shown;

[0118] Figure 2 is the scanning electron microscope image of the multi-halogenated MXenes / carbon fiber metallic lithium anode framework prepared in Example 1;

[0119] From Figure 2 it can be seen that the multi-halogenated MXene nanosheets are uniformly embedded in CF and form a continuous three-dimensional network. Such a three-dimensional network can effectively and uniformly distribute the lithium ion mass transfer flux, relieve the volume change during the lithium deposition / stripping process, and ensure the integrity of the composite lithium anode structure.

[0120] Figure 3 is the X-ray photoelectron spectroscopy image of the depth etching of the solid electrolyte interface film on the surface of the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1;

[0121] From Figure 3 it can be known that the SEI film of the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1 contains rich LiCl and LiF components, which helps the uniform deposition of lithium.

[0122] Figure 4 is the Coulombic efficiency test chart of the deposition / stripping of metallic lithium on the multi-halogenated MXenes / carbon fiber metallic lithium anode framework prepared in Example 1;

[0123] From Figure 4 it can be seen that the multi-halogenated MXenes / carbon fiber metallic lithium anode framework prepared in the present invention can increase the Coulombic efficiency of lithium deposition / stripping to 99.83%.

[0124] Figure 5 is the cycle life test chart of the lithium-lithium symmetric battery assembled with the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1;

[0125] From Figure 5 it can be seen that the lithium-lithium symmetric battery assembled with the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1 can be stably cycled for more than 17000h.

[0126] Figure 6 is the cycle performance chart of the soft-pack battery assembled with the multi-halogenated MXene / carbon fiber composite lithium anode prepared in Application Example 1 as the anode and the commercial lithium iron phosphate electrode as the cathode;

[0127] From Figure 6It can be known that: using the multi-halogenated MXene / carbon fiber composite lithium negative electrode prepared in Application Example 1 as the negative electrode, and a commercial lithium iron phosphate electrode as the positive electrode to assemble a soft-pack battery, the initial capacity is 284.4 mAh / cm 2 , and the capacity after 300 cycles is 234.1 mAh / cm 2 , and the capacity retention rate is 82.3%, with an average attenuation of 0.059% per cycle.

[0128] Figure 7 Figure 4 shows the cycling performance of a soft-pack battery assembled with the multi-halogenated MXene / carbon fiber composite lithium negative electrode prepared in Application Example 2 as the negative electrode and a commercial lithium iron phosphate electrode as the positive electrode;

[0129] From Figure 7 it can be known that: using the multi-halogenated MXene / carbon fiber composite lithium negative electrode prepared in Application Example 2 as the negative electrode, and a commercial lithium iron phosphate electrode as the positive electrode to assemble a soft-pack battery, the initial capacity is 284.9 mAh / cm 2 , and the capacity after 350 cycles is 250.1 mAh / cm 2 , and the capacity retention rate is 87.8%, with an average attenuation of 0.035% per cycle.

[0130] Figure 8 Figure 5 shows the cycling performance of a soft-pack battery assembled with the MXene / carbon fiber composite lithium negative electrode prepared in Comparative Application Example 1 as the negative electrode and a commercial lithium iron phosphate electrode as the positive electrode;

[0131] From Figure 8 it can be known that: using the MXene / carbon fiber composite lithium negative electrode prepared in Comparative Application Example 1 as the negative electrode, and a commercial lithium iron phosphate electrode as the positive electrode to assemble a soft-pack battery, the initial capacity is 254.9 mAh / cm 2 , and the capacity after 250 cycles is 52 mAh / cm 2 , and the capacity retention rate is 20.4%, with an average attenuation of 0.32% per cycle.

[0132] It can be seen from this that: the multi-halogenated MXene / carbon fiber lithium metal negative electrode framework prepared by the present invention can significantly improve the cycle life and cycle stability of lithium metal batteries compared with the MXene / carbon fiber lithium metal negative electrode framework obtained by traditional etching methods, showing obvious performance improvement.

[0133] To sum up, it can be known that: compared with the prior art, the present invention has the following advantages and outstanding effects: by using the multi-halogenated MXenes / carbon fiber lithium metal negative electrode framework as the framework of the lithium metal negative electrode, the present invention regulates the nucleation and growth behavior of lithium, inhibits the growth of lithium dendrites, alleviates the volume change during the cycling of the lithium metal negative electrode, effectively avoids the rapid failure of the lithium metal negative electrode, and improves the Coulomb efficiency of the lithium metal negative electrode.

Claims

1. A method for preparing a multi-element halogenated MXenes / carbon fiber metal lithium negative electrode skeleton, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of multi-halogenated MXene nanosheets: ①. Mix the MAX material with the halogenated inorganic salt, grind for a period of time, and then calcine for a period of time under an argon atmosphere to obtain a solid product; wash the solid product with hydrochloric acid to remove the unreacted halogenated inorganic salt to obtain a multilayer MXene; ②, dissolving lithium halide in dimethyl sulfoxide to obtain a lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L; ③. Immerse the multilayer MXene in a lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L, stir and react for a period of time, then centrifuge and collect the supernatant to obtain a supernatant containing multi-halogenated MXene nanosheets; 2. Preparation of electrospinning liquid precursor: ①, using a high-speed centrifugation method to concentrate the supernatant containing multi-halogenated MXene nanosheets to make the concentration of the solution reach 30 mg / mL to 40 mg / mL, thereby obtaining a multi-halogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL; ②, add polyacrylonitrile to a polyhalogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL, stir and react for a period of time to obtain an electrospinning liquid precursor; 3. Electrospinning and annealing: ①, electrospinning the electrospinning liquid precursor at a certain temperature and humidity to obtain a fiber membrane; ②. Pre-oxidize the fiber membrane at 240℃~260℃ for a period of time, then transfer it to an argon atmosphere and heat it to 700℃~800℃, and anneal it at 700℃~800℃ to obtain a multi-halogenated MXenes / carbon fiber lithium metal negative electrode skeleton.

2. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that The MAX material described in step 1① is Mo2TiAlC2, TiSiC2, Ti3AlC2 or Ti3AlCN; the size of the MAX material described in step 1① is 200-400 mesh.

3. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that The halogenated inorganic salt described in step 1① is one or a mixture of CdCl2, CdBr2, CdI2, NaCl, NaB, NaI, KCl, KBr and KI; the molar ratio of the MAX material described in step 1① to the halogenated inorganic salt is 1:(1-5); the calcination temperature described in step 1① is 600°C-700°C, and the calcination time is 10h-12h.

4. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that The grinding time described in step 1① is 10min to 30min; the mass fraction of the hydrochloric acid described in step 1① is 35% to 38%; the number of times the solid product is washed with hydrochloric acid is 1 time to 5 times; the lithium halide described in step 1② is LiCl, LiBr or LiI; the stirring reaction rate described in step 1③ is 100r / min to 300r / min, and the stirring reaction time is 2h to 4h; the centrifugal rate described in step 1③ is 8000r / min, and the centrifugal time is 5min to 10min.

5. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that The mass ratio of the multilayer MXene described in step 1③ to the volume ratio of the lithium halide dimethyl sulfoxide solution with a concentration of 0.5 mol / L to 1 mol / L is (0.5 g to 1 g): (10 mL to 20 mL); the speed of the high-speed centrifugation described in step 2① is 10000 rpm / min, and the time of the high-speed centrifugation is 30 min to 60 min.

6. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that The volume ratio of the mass of polyacrylonitrile described in step 2② to the polyhalogenated MXene solution with a concentration of 30 mg / mL to 40 mg / mL is (8 g to 10 g): 10 mL; the temperature of the stirring reaction described in step 2② is 25°C to 40°C, the stirring speed is 300 r / min to 500 r / min, and the stirring reaction time is 8h to 12h.

7. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that In step 3①, the electrospinning liquid precursor is electrospun at a temperature of 30℃~40℃ and a humidity of 30%~40%; the voltage of the electrospinning described in step 3① is 12kV~14kV, the injection speed of the spinning liquid is 0.003cm / min~0.005cm / min, the rotation speed of the spinning receiver is 50r / min~100r / min, the negative voltage during the spinning process is 0.1kV~0.5kV, and the distance from the nozzle to the receiver is 10cm~15cm.

8. The method for preparing a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 1, characterized in that The pre-oxidation time at 240°C to 260°C in step 3② is 1h to 2h; the annealing time at 700°C to 800°C in step 3② is 1h to 2h; the heating rate in step 3② is 5°C / min to 10°C / min.

9. Application of a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton prepared by the preparation method according to claim 1, characterized in that A multi-component halogenated MXenes / carbon fiber lithium metal negative electrode skeleton is used as a lithium metal negative electrode skeleton to prepare a multi-component halogenated MXene / carbon fiber composite lithium negative electrode and is applied to lithium metal batteries.

10. The use of a multi-element halogenated MXenes / carbon fiber lithium metal negative electrode skeleton according to claim 9, characterized in that A multi-component halogenated MXenes / carbon fiber metal lithium negative electrode skeleton is used as a metal lithium negative electrode skeleton to prepare a multi-component halogenated MXene / carbon fiber composite lithium negative electrode, which is specifically completed in the following steps: In a glove box filled with argon, metallic lithium was infused into the multi-element halogenated MXenes / carbon fiber composite metallic lithium anode skeleton by melt infusion, making the surface capacity of the multi-element halogenated MXenes / carbon fiber composite metallic lithium anode skeleton 10 mAh / cm 2 ~20mAh / cm 2 , and cooled at room temperature for 1h to obtain a multi-halogenated MXene / carbon fiber composite lithium negative electrode.

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