Nanoparticle-modified ultrathin hollow sphere film and preparation method and application thereof

Abstract

The application discloses a kind of nanoparticle modified ultrathin hollow sphere film and its preparation method and application.The hollow sphere film of the application includes hollow sphere of transition metal carbon / nitride, and the hollow sphere is stacked to form three-dimensional porous structure;The surface of the shell of the hollow sphere also includes nanoparticles.The preparation method of the ultrathin hollow sphere film in the application can conveniently regulate each parameter of the film, such as film thickness, porosity, pore volume, nanoparticle diameter and the like.Compared with general filtration and drying method, the preparation method can greatly improve the film formation rate of the ultrathin hollow sphere film preparation, and the material preparation time is shorter.This self-supporting ultrathin film avoids using metal current collector, reduces the cost of battery, and makes its application in ultrathin energy storage device possible.The process is simple, green and environmentally friendly, can be mass-produced, and has high practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a kind of nanoparticle modified ultrathin hollow sphere film and its preparation method and application. BACKGROUND

[0002] In recent years, with the rapid progress of electronic technology, more and more electronic devices are developing towards light and thin, high energy density. In the currently commercialized lithium ion battery, the lithium ion battery assembled with graphite as negative electrode and ternary material as positive electrode can reach an energy density of about 180Wh kg -1 It has been widely used in various mobile electronic devices. However, with the increasing demand for electric vehicles, energy storage power grid and other high-power energy storage devices, lithium ion batteries have been difficult to meet the application of high energy density energy storage devices. Metal secondary batteries have high energy density, good cycle performance and good stability, and are the best choice for developing high energy density energy storage devices. Among them, metal lithium negative electrode has ultra-high theoretical capacity (3861mAh g -1 ) and the lowest redox potential (-3.04V vs. SHE), so it is the best choice for high energy density lithium battery. Research has found that the key to developing high energy density metal lithium secondary battery lies in solving the safety problem of lithium negative electrode. Metal lithium directly as negative electrode, due to the uneven deposition of lithium, needle-shaped lithium dendrites will be produced in the repeated electrochemical cycle process. Further growth of lithium dendrites will pierce the separator, causing internal short circuit of the battery, and thus causing internal heating and even fire of the battery. Therefore, the development of metal secondary battery should also solve the problem of dendrite growth.

[0003] In addition, the use of ultrathin lithium metal electrode with capacity matching the current positive electrode and improved electrochemical stripping / plating behavior plays a key role in realizing high energy density battery. For example, the currently widely used 300 microns thick metal lithium strip corresponds to a surface capacity density of 62mAh cm -2 , far exceeding the surface capacity density (3mAh g -1 ) of the commercial embedded positive electrode material, which has a huge difference, not only causing excessive waste of metal lithium, but also further increasing the safety hazard of the battery. Therefore, it is of great significance to develop an ultrathin metal lithium negative electrode with high coulomb efficiency and high safety for the development of high energy density lithium battery.

[0004] To solve the problem of dendrite growth, one effective solution is to build a current collector. Transition metal carbide / nitride (MXene) has the advantages of light weight, high conductivity, and lithium affinity, and is an ideal material for building three-dimensional current collectors. However, single-layer or few-layer MXene materials are prone to restacking, which increases the ion transport path inside the material and affects the rate performance of the battery. By introducing hollow sphere structures into MXene through a template method, and by modifying MXene with inorganic nanoparticles, the stacking of MXene layers can be prevented, the lithium storage space can be increased, and the lithium affinity of the three-dimensional current collector can be improved. Currently, there are many methods for preparing ultra-thin porous films, among which the vacuum suction filtration method is simple in equipment, controllable in film thickness and porosity, and good in repeatability. However, the film-forming property of the nanoparticle-modified MXene hollow sphere film prepared by the vacuum suction filtration method is poor. During the drying process of the film, the capillary pore tension increases due to water loss, causing the capillary pores to shrink and the material to shrink. When the film shrinks unevenly, the film is prone to cracking. The stress that causes the porous film to crack mainly comes from the capillary force caused by the surface tension in the voids of the porous film skeleton, which causes the rearrangement of the film framework and the volume shrinkage. At the same time, ultra-thin films usually need to have certain mechanical properties when used in batteries to avoid the use of current collectors, but ultra-thin films are usually poor in mechanical properties due to their thickness and porosity. In addition, the MXene material takes a long time to filter in an aqueous solution. Research shows that the drying rate also affects whether the film cracks. In order to ensure the film-forming rate, the film drying rate is usually slowed down, but this greatly prolongs the film preparation time, which is not conducive to large-scale production. The easy cracking of the film, the low film-forming rate, and the long time-consuming all limit the material preparation of ultra-thin films, making it difficult for the film material to be widely used in metal lithium anodes. SUMMARY

[0005] To improve the above technical problems, the present application provides a hollow sphere film, which comprises hollow spheres composed of transition metal carbide / nitride, and the hollow spheres are stacked to form a three-dimensional porous structure; and the surface of the hollow sphere shell is also dispersed with nanoparticles.

[0006] According to an embodiment of the present application, the transition metal carbide / nitride hollow spheres have a hollow structure.

[0007] According to an embodiment of the present application, cavities are also formed between the transition metal carbide / nitride hollow spheres.

[0008] According to embodiments of the present application, the hollow sphere film has an average thickness of 10-1000 pm, preferably 10-100 pm, more preferably 10-30 pm, for example 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 20 pm, 30 pm, 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, 100 pm.

[0009] According to embodiments of the present application, the transition metal carbon / nitride hollow sphere has an average inner diameter of 0.05-50 pm, preferably 1-10 pm, for example 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 20 pm, 30 pm, 40 pm, 50 pm.

[0010] According to embodiments of the present application, the nanoparticle has an average particle size of 5-500 nm, preferably 20-70 nm, for example 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm.

[0011] According to embodiments of the present application, the transition metal carbon / nitride is selected from MXene materials commonly used in the art, for example at least one selected from the group consisting of Ti3C2-MXenes, Ti2N-MXenes, Cr2C-MXenes, Ta4C3-MXenes, Ti3CN-MXene, Ta2C-MXenes, Nb4C3-MXenes, Nb2C-MXenes, V2C-MXenes, Mo2TiC2-MXenes, Mo3C2-MXenes, V4C3-MXenes, and the like, preferably Ti3C2-MXenes.

[0012] According to embodiments of the present application, the nanoparticle is selected from nanoparticles having a lithophilic property. Preferably, the nanoparticle is at least one selected from the group consisting of Au, Ag, Si, Sn, ZnO, Al2O3, SiO, SnO2, and the like, preferably Ag, ZnO.

[0013] According to embodiments of the present application, the mass ratio of the transition metal carbon / nitride and the nanoparticle is (5-100):1, for example (10-70):1.

[0014] According to embodiments of the present application, the loading amount of the nanoparticle on the hollow sphere film is 0.05-0.5 mg / cm2, for example 0.1-0.3 mg / cm2. 2 , for example 0.1-0.3 mg / cm2. 2, exemplary is 0.08mg / cm 2 , 0.16mg / cm 2 , 0.2mg / cm 2 .

[0015] According to an embodiment of the present application, the pore volume of the hollow sphere film is 0.1-1.5cm 3 / g, preferably 0.3-1.0cm 3 / g, for example 0.3cm 3 / g, 0.42cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.66cm 3 / g, 0.84cm 3 / g.

[0016] According to an exemplary embodiment of the present application, the hollow sphere film comprises a honeycomb-like three-dimensional porous structure formed by stacking silver nanoparticles and MXene hollow spheres, and the silver nanoparticles are distributed (preferably uniformly distributed) on the surface of the shell of the MXene hollow spheres.

[0017] Preferably, the pore volume of the hollow sphere film is 0.3-1.0cm 3 / g, the thickness is about 20-30μm, and the loading amount of silver nanoparticles on the hollow sphere film is 0.1-0.3mg / cm 2 .

[0018] Preferably, the particle size of the silver nanoparticles is 20-70nm.

[0019] The present application also provides a preparation method of the above-mentioned hollow sphere film, which comprises the following steps:

[0020] (1) slowly adding a microsphere template dispersion liquid into a transition metal carbide / nitride dispersion liquid, adding a nanoparticle precursor solution under ice bath stirring to obtain a mixed solution;

[0021] (2) vacuum filtering the mixed solution of step (1) to obtain a film, and after low-temperature refrigeration, drying the film to obtain a dried film;

[0022] (3) calcining the dried film of step (2) to remove the microsphere template to obtain the hollow sphere film.

[0023] According to an embodiment of the present application, the solvents in the MXene dispersion liquid, the microsphere template dispersion liquid, and the nanoparticle precursor solution can be selected from solvents known in the technical field, for example, all being ethanol, preferably all being anhydrous ethanol.

[0024] According to an embodiment of the present application, the concentration of the transition metal carbon / nitride dispersion liquid is not particularly limited as long as a uniform dispersion liquid can be obtained, for example, 1-10 mg / mL, for example, 5-10 mg / mL.

[0025] According to an embodiment of the present application, the concentration of the microsphere template dispersion liquid is not particularly limited as long as a uniform dispersion liquid can be obtained, for example, 1-5 mg / mL, for example, 1-3 mg / mL.

[0026] According to an embodiment of the present application, the precursor of the nanoparticle is selected from substances that can obtain the nanoparticle, for example, selected from at least one of the following metals: Au, Ag, Si, Sn, Zn, Al, Si, Sn. Illustratively, the precursor of the nanoparticle is selected from AgNO3, HAuCl4.

[0027] According to an embodiment of the present application, the microsphere template is selected from at least one of the following microspheres: polymethyl methacrylate (PMMA), polystyrene (PS), silicon dioxide (SiO2), etc., preferably PMMA microspheres.

[0028] According to an embodiment of the present application, the diameter of the microsphere template is 0.05-50 μm, preferably 1-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm.

[0029] According to an embodiment of the present application, in step (1), the transition metal carbon / nitride dispersion liquid is kept stirring. In the present application, the stirring is not particularly limited, and any stirring method known in the art can be used as long as the dispersion liquid is kept uniform.

[0030] According to an embodiment of the present application, in step (1), the mass ratio of transition metal carbon / nitride to microsphere template in the mixed solution is (1-10):(1-5), preferably (3-10):(1-3), for example, 1:1, 3:2.4, 5:2, 10:1. The inventors have found that the transition metal carbon / nitride hollow spheres prepared by using the mass ratio of transition metal carbon / nitride to microsphere template in the present application have a thinner shell, which is beneficial to provide a faster ion transmission path and avoid MXene sheet stacking.

[0031] According to an embodiment of the present application, in step (1), the precursor solution of the nanoparticle needs to be added slowly. Preferably, the addition speed of the precursor solution of the nanoparticle is 0.1-5 mL / min, for example, 1 mL / min.

[0032] According to an embodiment of the present application, in step (1), the ice-bath temperature is -10-0℃. The inventors have found that slow addition of the precursor solution of the nanoparticles at the ice-bath temperature is conducive to the formation of the nanoparticles with the above-mentioned particle size, so that the nanoparticles can be more uniformly distributed on the shell surface of the transition metal carbon / nitride hollow sphere, avoiding agglomeration of the nanoparticles.

[0033] According to an embodiment of the present application, in step (1), the concentration of the precursor solution of the nanoparticles is 1-10 mg / mL, for example, 5 mg / mL.

[0034] According to an embodiment of the present application, in step (1), the mass ratio of the precursor of the nanoparticles to the transition metal carbon / nitride in the mixed solution is (0.1-1):(0.5-5), for example, 0.6:1.

[0035] According to an embodiment of the present application, in step (2), the mixed solution is kept under ultrasonic during the vacuum filtration.

[0036] According to an embodiment of the present application, in step (2), the vacuum filtration further comprises rinsing with deionized water to remove the solvent. Preferably, the rinsing needs to be performed for multiple times.

[0037] According to an embodiment of the present application, in step (2), the low-temperature refrigeration temperature is 0-20℃, preferably 3-8℃, for example, 5℃. The inventors have found that low-temperature refrigeration of the film after vacuum filtration is conducive to improving the film forming rate of the film.

[0038] According to an embodiment of the present application, in step (2), the drying is performed under vacuum. The time and temperature of the drying are not specifically limited in the present application, as long as the solvent in the film can be completely removed. Illustratively, the drying time is 1-24 h, for example, 12 h. Illustratively, the drying temperature is 10-40℃, for example, 20℃.

[0039] According to an embodiment of the present application, in step (3), the calcination conditions are not specifically limited, as long as the microsphere template in the film can be completely removed. Illustratively, the calcination temperature is greater than 400℃, for example, 450℃. Illustratively, the calcination time is 30-360 minutes, for example, 60 minutes.

[0040] According to an embodiment of the present application, in step (3), the calcination is performed under an inert atmosphere, preferably under an argon atmosphere.

[0041] The present application also provides use of the above-mentioned hollow sphere film in a metal secondary battery, for example, as a current collector in a metal secondary battery; or for preparing a negative electrode in a metal secondary battery.

[0042] The present application also provides a current collector comprising the hollow-sphere film as described above.

[0043] The present application also provides a composite negative electrode comprising the current collector as described above and a metal negative material.

[0044] According to an embodiment of the present application, the current collector, the transition metal carbon / nitride hollow sphere has the meaning as described above.

[0045] According to an embodiment of the present application, the metal negative material is selected from at least one of lithium, sodium, potassium and magnesium.

[0046] According to an embodiment of the present application, in the composite negative electrode, the surface capacity of the metal negative material is 0.1-10mA h cm -2 , for example, 1mA h cm -2 , 2mA h cm -2 , 3mA h cm -2 , 4mA h cm -2 , 5mA h cm -2 , 6mA h cm -2 , 7mA h cm -2 , 8mA h cm -2 , 9mA h cm -2 , 10mA h cm -2 .

[0047] Illustratively, the metal negative material is selected from lithium, and the surface capacity thereof is 0.5-8mAh / cm 2 , for example, 2mA h cm -2 , 4mA h cm -2 .

[0048] According to an embodiment of the present application, the composite negative electrode has a high energy density. Preferably, when the surface capacity of the metal negative material on the composite negative electrode is 0.5-8mA h cm -2 , the energy density of the composite negative electrode is 847-3170mAh / g. Illustratively, when the surface capacity of the metal negative material on the composite negative electrode is 4mA h cm -2 , the energy density of the composite negative electrode is 2691mAh / g.

[0049] According to an embodiment of the present application, the composite negative electrode has an ultra-thin, high safety, high specific capacity and long cycle life.

[0050] The application also provides a preparation method of the composite negative electrode, comprising: taking the current collector as a working electrode and the metal negative electrode material as a counter electrode, and preparing the composite negative electrode by an electrodeposition method.

[0051] According to an embodiment of the application, the metal negative electrode material has the meaning as described above.

[0052] According to an exemplary embodiment of the application, the composite negative electrode comprises a current collector and a lithium metal negative electrode material, wherein the current collector comprises Mxene and Ag nanoparticles, denoted as Ag@MXene / Li.

[0053] The application also provides an application of the current collector in a metal secondary battery, preferably in an ultrathin high-energy-density energy storage device.

[0054] The application also provides a metal secondary battery comprising the current collector.

[0055] The metal secondary battery in the application refers to a secondary battery directly using one or more of metal lithium, sodium, potassium and magnesium as a negative electrode.

[0056] Advantages:

[0057] Compared with the prior art, the preparation method of the ultrathin hollow sphere film provided by the application has the advantages of short time consumption, low cost, high film formation rate, and high scalability, and has high practicability.

[0058] Compared with the common MXene-based film filtration method, the ultrathin film preparation method in the application has higher film formation rate and faster filtration speed. The technical problems of poor mechanical property of the film obtained by filtering the dispersed MXene material in an aqueous solution or an ethanol solution, and cracks and pulverization of the film caused by uneven shrinkage due to capillary action during film drying are overcome. In addition, the preparation method of the application can effectively improve the coating effect of the MXene material on the microsphere template and avoid uneven coating caused by aggregation between MXene layers. By reasonably controlling the thickness of the ultrathin hollow sphere film, the inner diameter of the hollow sphere, the content of MXene, and the diameter and density of the nanoparticles, the application realizes the controllability of the pore volume and the interlayer spacing, effectively increases the space for accommodating the metal negative electrode material of the current collector, and simultaneously induces the uniform deposition of the metal negative electrode material in the film. The three-dimensional porous film material can be used as a metal secondary battery negative electrode current collector.

[0059] The negative electrode prepared by using the three-dimensional current collector of the application applied to a metal secondary battery has the characteristics of flexibility and self-supporting, can solve the problem of dendrite growth in the metal secondary battery, and has the advantages of long service life and safety and reliability.

[0060] The application provides a kind of nanoparticle modified ultrathin MXene hollow sphere film as three-dimensional current collector, and the metal negative electrode material is deposited in the hollow sphere film by electrodeposition method to obtain an ultrathin metal negative electrode.The ultrathin MXene hollow sphere film and the nanoparticle with lithium affinity of the application can induce the uniform deposition of metal lithium on the surface of the hollow sphere shell, avoid the generation of metal dendrites (such as lithium dendrites) in the charging and discharging process of the negative electrode, and the risk of short circuit of the secondary battery caused by the puncture of the separator.At the same time, the MXene hollow sphere film provides more space for metal storage, realizing high metal lithium loading.

[0061] The application controls the inner diameter of the hollow sphere, the thickness of the hollow sphere film, the particle size of the nanoparticle and other parameters in the current collector to prepare the negative electrode, so that the metal ion can quickly pass through the hole in the interior of the hollow sphere film, and the metal ion can also be better induced to be uniformly deposited on the surface of the hollow sphere shell to prevent the growth of dendrites in the charging and discharging process of the negative electrode. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 It is the scanning electron microscope photo of Ag@MXene ultrathin hollow sphere film in Example 1.

[0063] Figure 2 It is the high-magnification cross-sectional electron scanning microscope photo of Ag@MXene ultrathin hollow sphere film in Example 1.

[0064] Figure 3 It is the X-ray diffraction pattern of Ag@MXene ultrathin hollow sphere film in Example 1.

[0065] Figure 4 It is the filtration time (a) of Ag@MXene ultrathin hollow sphere film in Example 1 and the filtration time (b) of the film in Comparative Example 1.

[0066] Figure 5 It is the optical photo of the film formation rate of Ag@MXene ultrathin hollow sphere film in Example 1.

[0067] Figure 6 It is the optical photo of large-size Ag@MXene ultrathin hollow sphere film in Example 1.

[0068] Figure 7 It is the half-cell assembled by Ag@MXene ultrathin hollow sphere film and metal lithium in Example 1, and the coulombic efficiency test under the condition of current density of 0.5mA cm -2 , and capacity of 1mA h cm -2 .

[0069] Figure 8 It is the cross-sectional electron scanning microscope photo of Ag@MXene ultrathin hollow sphere film in Example 2.

[0070] Figure 9a High magnification electron scanning microscope photo of the Ag@MXene ultrathin hollow sphere film in Example 3.

[0071] Figure 9b High magnification electron scanning microscope photo of the Ag@MXene ultrathin hollow sphere film in Example 3.

[0072] Figure 10 High magnification electron scanning microscope photo of the Ag@MXene ultrathin hollow sphere film in Example 4.

[0073] Figure 11 High magnification electron scanning microscope photo of the Ag@MXene ultrathin hollow sphere film in Example 5.

[0074] Figure 12 High magnification electron scanning microscope photo of the Ag@MXene ultrathin hollow sphere film in Example 6.

[0075] Figure 13 Optical photo of the large-size Ag@MXene ultrathin hollow sphere film in Comparative Example 2.

[0076] Figure 14 Scanning electron microscope photo of the Ag@MXene ultrathin hollow sphere film in Comparative Example 3.

[0077] Figure 15 Optical photo of the film prepared by the drying method in Comparative Examples 4-7 and Example 1.

[0078] Figure 16 Optical photo of the film formation rate of the film prepared by the drying method in Comparative Example 7. DETAILED DESCRIPTION

[0079] The technical solutions of the present application will be further described in detail below in combination with specific embodiments. It should be understood that the following examples are only illustratively described and explained the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of the present application.

[0080] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0081] The pore volume of the hollow sphere film in the following examples is measured by the BET test method known in the art, and the test instrument is an ASAP2460 (Micromeritics) surface area pore size analyzer, and nitrogen adsorption and desorption isotherms are obtained at 77.3 K.

[0082] Example 1

[0083] (I) Preparation of silver nanoparticle (AgNPs) modified ultrathin transition metal carbide / nitride (MXene) hollow sphere film (Ag@MXene hollow sphere film)

[0084] (1) 600 μL of Ti3C2-Mxenes (5 mg / mL) in ethanol was added to 10 mL of anhydrous ethanol and stirred, then 1.2 mL of PMMA (2 mg / mL, particle size 1.8 μm) microsphere template dispersion was slowly added, and 1 mL of AgNO3 (5 mg / mL) solution was slowly added under ice bath stirring (0°C), and stirred for 30 min.

[0085] (2) The above mixture was kept under ultrasonic, vacuum filtration; after filtration, 10 mL of deionized water was added to rinse three times to obtain a film, and the membrane and filter film were removed at the same time when the film was not dried, and stored in a 5°C environment for 1 h; the film was flattened with a glass plate and transferred to a vacuum oven for drying at room temperature, and a dried film was obtained.

[0086] (3) The dried film was removed from the filter film, calcined in a carbonization furnace at 450°C under argon atmosphere protection, the heating rate was 5°C / min, and after the temperature was kept for 1 h, a silver nanoparticle modified MXene hollow sphere film was obtained, the pore volume was 0.66 cm 3 / g, and was recorded as Ag@MXene hollow sphere film, which was the porous three-dimensional current collector of the present embodiment.

[0087] Figure 1 In FIG. 2a and FIG. 2b, b is a scanning electron microscope image of the cross section of the dried film before calcination, it can be seen that the average thickness of the dried film is about 20-30 μm, and the internal MXene layers of the dried film are uniformly and densely wrapped on the PMMA microsphere template. Figure 1 In FIG. 2c, c is a cross-sectional view of the dried film after calcination and removal of the PMMA microsphere template, it can be seen that the thickness of the film after calcination does not change significantly, and the MXene hollow sphere skeleton is left after the removal of the PMMA microsphere template, and the MXene hollow sphere skeleton is stacked into an ultrathin porous film with a honeycomb structure. The hollow sphere film has a hollow structure, which can provide sufficient space for the deposition of metal negative electrode materials, and is conducive to the preparation of high surface capacity metal lithium negative electrode.

[0088] Figure 2 FIG. 3 is a scanning electron microscope image of the MXene hollow sphere, it can be seen that the surface of the MXene hollow sphere is uniformly distributed with AgNPs, the particle size of the nanoparticles is about 60 nm, and the loading amount is 0.16 mg / cm 2Uniformly loaded AgNPs can provide more lithophile active sites, inducing uniform deposition of metallic lithium on the surface of the MXene hollow spherical shell and avoiding the growth of lithium dendrites.

[0089] Figure 3 The XRD pattern of the Ag@MXene hollow sphere film shows that the film consists of MXene and Ag.

[0090] from Figure 4 As can be seen from Figure a, by selecting ethanol as the dispersant, rapid vacuum filtration can be achieved, with a filtration time of approximately 3-4 minutes. After vacuum filtration, the membrane is refrigerated before vacuum drying, which can improve the shrinkage during drying and prevent cracking or even pulverization caused by uneven shrinkage. Figure 5 As shown, the film formation rate of the dried film in this embodiment is 100%.

[0091] also, Figure 6 This is an optical photograph of an ultrathin Ag@MXene hollow spherical film. The diameter of the Ag@MXene hollow spherical film can reach 40 mm, which shows that the preparation method of the present invention can realize the preparation of large-size hollow spherical films.

[0092] (II) Preparation of a lithium metal anode using an ultrathin transition metal carbide / nitride (MXene) hollow spherical film (Ag@MXene) modified with silver nanoparticles (AgNPs) as the current collector.

[0093] The working electrode is the aforementioned Ag@MXene hollow spherical thin film, and the counter electrode is metallic lithium. A metallic lithium composite anode, denoted as Ag@MXene / Li, is prepared by electrodeposition. The areal capacity of the lithium metal anode material is 2 mA h cm⁻¹. -2 .

[0094] (III) Assembly of half-cells and performance testing

[0095] Using the aforementioned ultrathin Ag@MXene hollow spherical film as the positive electrode and lithium metal as the negative electrode, a lithium metal secondary battery was assembled with a DME / DOL (volume ratio 1:1) LiTFSI electrolyte containing 1% lithium nitrate. The battery was subjected to constant current charge-discharge testing using a charge-discharge apparatus, and the test cutoff capacity was 1 mA h cm⁻¹. -2 The test temperature was 25℃. For example... Figure 7 As shown, the hollow spherical film was tested at 0.5 mA / cm. 2 The coulombic efficiency of lithium reaches 98% at current density (see...) Figure 7 (b) Moreover, from Figure 7 As can be seen from Figure a, the battery voltage remains stable after 50 cycles, and the polarization voltage is relatively low, approximately 13mV. Figure 7Fig. 2 shows the charge-discharge curves of the metal lithium secondary battery of Example 1 (wherein 1st, 2nd, 40th represent the charge-discharge platform curves corresponding to 1 cycle, 2 cycles, 40 cycles, respectively).

[0096] (IV) Electrochemical test of metal lithium secondary battery

[0097] The metal lithium secondary battery was assembled by using the above Ag@MXene / Li as the metal negative electrode and lithium iron phosphate (LFP) as the positive electrode. The constant current charge-discharge test was performed on the above battery using a charge-discharge instrument, and the test temperature was 25°C. The charge-discharge interval was 2-4V. The full battery assembled by Ag@MXene / Li and LFP of Example 1 was tested at a rate of 0.5C, and the specific capacity was about 156mA h g -1 -1, and the capacity retention rate was 94.6% after 100 cycles.

[0098] Example 2

[0099] (I) Preparation of Ag@MXene hollow sphere film: The same as Example 1, except that the amount of MXene dispersion liquid and PMMA microsphere template dispersion liquid was increased to three times of that of Example 1, i.e. 1.8mL:3.6mL, to obtain the current collector of this example; the loading of Ag nanoparticles on the current collector was 0.16mg / cm 2 2, the pore volume was 0.66cm 3 3 / g, and the film forming rate was 100%.

[0100] (II) Preparation of metal lithium negative electrode with silver nanoparticle (AgNPs) modified ultrathin transition metal carbon / nitride (MXene) hollow sphere film (Ag@MXene) as the current collector: The same as Example 1, except that the current collector prepared in this example was used;

[0101] (III) Assembly of half battery and performance test: The same as Example 1, except that the metal lithium negative electrode prepared in this example was used.

[0102] Figure 8 Fig. 4 is a scanning electron microscope image of the cross section of the dried film obtained in Example 2, and the average thickness of the Ag@MXene hollow sphere film is about 75μm, and the average particle size of the nanoparticles is 60nm. Compared with Example 1, the thickness of the Ag@MXene hollow sphere film is adjusted controllably in Example 2, and the film forming rate of the film is maintained, which proves that the preparation method in this application can realize the preparation of hollow sphere films with different thicknesses, and the thicker film can deposit more metal lithium with high surface capacity in the film, meeting the needs of various application scenarios with different thicknesses.

[0103] According to the half battery test, the half battery composed of the current collector and lithium sheet had a capacity of 0.5mA / cm2 The lithium deposition / stripping efficiency reaches 97.5% at current density, and the voltage remains stable after 50 cycles, with a battery polarization voltage of approximately 15mV.

[0104] Example 3

[0105] (I) Preparation of Ag@MXene hollow sphere thin film: This embodiment is the same as Example 1, except that a PMMA microsphere template with an average particle size of 6 μm is used to obtain the current collector of this embodiment; the loading of Ag nanoparticles on the current collector is 0.16 mg / cm³. 2 The pore volume is 0.84 cm. 3 / g, film formation rate 100%.

[0106] (II) Preparation of lithium metal anode:

[0107] This embodiment is the same as Embodiment 1, except that the current collector prepared in this embodiment is used.

[0108] (III) Assembly of half-cells and performance testing:

[0109] This embodiment is the same as Embodiment 1, except that the lithium metal anode prepared in this embodiment is used.

[0110] Figure 9a The image shows a scanning microscope image of the AgNPs-modified MXene hollow spheres prepared in Example 3. The diameter of the Ag@MXene hollow spheres is approximately 6-7 μm and the average particle size of the nanoparticles is 60 nm. Figure 9b This is a cross-sectional scanning electron microscope image of the Ag@MXene hollow spheres prepared in Example 3. The average thickness of this Ag@MXene hollow sphere film is approximately 30 μm. Compared to Example 1, the diameter of the Ag@MXene hollow spheres was controllably adjusted in Example 3, increasing the pore volume of the film (0.84 cm³). 3 / g), maintaining the film formation rate, proving that the preparation method in this application can achieve the preparation of hollow spherical films with different porosities and pore sizes. Films with higher porosity can deposit metallic lithium with higher areal capacity inside the film, realizing a high areal capacity lithium anode. Testing showed that this current collector, when combined with a lithium sheet, forms a battery with a capacity of 0.5 mA / cm². 2 The lithium deposition / stripping efficiency reaches 98.5% at current density, the voltage remains stable after 50 cycles, and the battery polarization is about 13mV.

[0111] Example 4

[0112] (Ag@MXene hollow sphere film preparation: the same as example 3, except that the concentration of AgNO3 added is 0.5 mg / mL; the current collector of the present example is obtained; the loading of Ag nanoparticles on the current collector is 0.08 mg / cm 2 , the pore volume is 0.66 cm 3 / g, and the film formation rate is 100%.

[0113] (B) Preparation of metal lithium negative electrode:

[0114] The present example is the same as example 1, except that the current collector prepared in the present example is used.

[0115] (C) Assembly of half-cell and performance test:

[0116] The present example is the same as example 1, except that the metal lithium negative electrode prepared in the present example is used.

[0117] Figure 10 The scanning electron microscope image of the AgNPs modified MXene hollow sphere obtained in example 4 is shown, and only a small amount of silver nanoparticles is observed on the surface of the shell of the Ag@MXene hollow sphere, with an average particle size of 30 nm. Compared with example 3, the content of Ag in the Ag@MXene hollow sphere is controlled in example 4, and a smaller amount of Ag is used to modify the MXene hollow sphere to reduce the preparation cost of the film, and the film formation rate of the film is maintained, proving that the preparation method in the present application can realize the preparation of hollow sphere film modified by metal nanoparticles with different loadings.

[0118] The current collector was tested to form a half-cell with lithium sheet, and the lithium deposition / stripping efficiency reached 97.4% at a current density of 0.5 mA / cm 2 , and the voltage remained stable after 50 cycles, and the half-cell polarization voltage was about 14 mV.

[0119] Example 5

[0120] (A) Ag@MXene hollow sphere film preparation: the same as example 1, except that the ratio of MXene dispersion liquid and PMMA microsphere template dispersion liquid is adjusted to 1:1, i.e. 0.6 mL:0.6 mL; the current collector of the present example is obtained; the loading of Ag nanoparticles on the current collector is 0.16 mg / cm 2 , the pore volume is 0.42 cm 3 / g, and the film formation rate is 100%.

[0121] (B) Preparation of metal lithium negative electrode:

[0122] This example is the same as example 1, except that the current collector prepared in this example is used.

[0123] (III) Assembly of half-cell and performance test:

[0124] This example is the same as example 1, except that the metal lithium negative electrode prepared in this example is used.

[0125] Figure 11 The scanning microscope image of the cross section of the AgNPs modified MXene hollow sphere film prepared in example 5, the average thickness of the film is about 20-30 μm, the average particle size of the nanoparticles is 60 nm, the porosity of the film is reduced, and the film is more dense. Compared with example 1, the proportion of PMMA template microspheres is reduced in example 4 to regulate the porosity of the film, and the film forming rate of the film is maintained. Tests show that the current collector and lithium sheet form a battery, and the deposition / stripping efficiency of lithium is 97.8% at a current density of 0.5 mA / cm 2 , the voltage remains stable after 50 cycles, and the battery polarization is about 14 mV.

[0126] Example 6

[0127] (I) Preparation of Ag@MXene hollow sphere film: this example is the same as example 3, except that the MXene dispersion liquid and PMMA dispersion liquid are mixed and frozen at-10°C environment, and silver nitrate solution is slowly added. The current collector of this example is obtained; the loading amount of Ag nanoparticles on the current collector is 0.16 mg / cm 2 , the pore volume is 0.84 cm 3 / g, and the film forming rate is 100%.

[0128] (II) Preparation of metal lithium negative electrode:

[0129] This example is the same as example 1, except that the current collector prepared in this example is used.

[0130] (III) Assembly of half-cell and performance test:

[0131] This example is the same as example 1, except that the metal lithium negative electrode prepared in this example is used.

[0132] Figure 12A scanning microscope image of the obtained AgNPs modified MXene hollow spheres prepared in Example 6, the hollow spheres are uniformly modified with AgNPs, the average particle size of the silver nanoparticles is about 50 nm. Compared with Example 3, the reaction rate of MXene reducing AgN03 is controlled by controlling the temperature in Example 6, smaller silver nanoparticles are formed, which can improve the utilization rate of silver nanoparticles and induce the uniform deposition of metal lithium on the hollow sphere shell. The test shows that the current collector and lithium sheet form a battery, the lithium deposition / stripping efficiency reaches 98.3% at a current density of 0.5 mA / cm2, and the battery polarization is about 13 mV, which remains stable after 50 cycles. 2

[0133] Comparative Example 1

[0134] The other conditions are the same as those in Example 1, except that the solvent of the MXene dispersion liquid and the PMMA dispersion liquid is deionized water.

[0135] Figure 4 b is the time consumed in the filtration process in Comparative Example 1, about 10 min. Compared with Example 1, the use of deionized water as a dispersant in Comparative Example 1 greatly reduces the filtration speed, and the time consumption is about 3 times that in Example 1, which does not have practical benefits in actual application.

[0136] Comparative Example 2

[0137] This comparative example is the same as Example 1, except that after the MXene and PMMA and AgNPs dispersion liquid are filtered into a film, they are not rinsed with deionized water.

[0138] Because there is still a small amount of ethanol liquid remaining in the film after filtration, during the drying process, due to the large saturated vapor pressure of ethanol, the surface liquid quickly evaporates, which is more likely to cause uneven shrinkage of the film during drying. As shown in the optical photograph in Figure 13 , the film obtained without rinsing with deionized water shrinks unevenly after drying, causing the film to crack, and the film has poor mechanical properties. Although the average thickness of the film is consistent with that in Example 1, both are about 20 μm, but the film has poor mechanical strength due to cracking and cannot be self-supported. Therefore, it cannot be applied in ultra-thin high-energy density energy storage devices.

[0139] Comparative Example 3

[0140] This comparative example is the same as Example 1, except that the solution is not ultrasonically treated during the film filtration process.

[0141] Figure 14 ​Figure 3a and 3b are scanning electron microscope images of MXene and PMMA microspheres composite in Comparative Example 3. Figure 3a is a scanning electron microscope image of MXene and PMMA microspheres composite in Comparative Example 3. Figure 3b is a scanning electron microscope image of MXene and PMMA microspheres composite in Comparative Example 3. Figure 3a and 3b show that the MXene layers in Comparative Example 3 are stacked and cannot uniformly wrap the PMMA microsphere template, resulting in a large number of PMMA microsphere template agglomerations and MXene layer stacking. Figure 14 Figure 3c is an optical photograph of the Ag@MXene hollow sphere film in Comparative Example 3. Figure 3c shows that a large number of cavities are generated in the hollow sphere film in Comparative Example 3 due to PMMA agglomeration. In addition, Figure 14 Figure 3d is an optical photograph of the Ag@MXene hollow sphere film in Comparative Example 3. Figure 3d shows that the MXene layers in Comparative Example 3 are locally stacked in density, hindering the ion diffusion path and affecting the rate performance of the battery, thus easily causing the generation of negative lithium dendrites, and thus cannot be applied in ultra-thin high-energy density energy storage devices. The current collector was tested with lithium sheets to form a half-cell, and the lithium deposition / detachment efficiency was only 94.8% (lower than the deposition / detachment efficiency of 98% of the material in Example 1) at a current density of 0.5 mA / cm 2 and the battery polarization voltage was about 15 mV.

[0142] Comparative Example 4

[0143] This comparative example is the same as Example 1, except that after the film is filtered, the drying method used is air drying at 50°C.

[0144] After the film is filtered, a small amount of liquid remains in the film, and during the drying process, the air drying at 50°C accelerates the rapid evaporation of the surface liquid, which more easily causes uneven shrinkage of the film during drying. For example, Figure 15 Figure 3d is an optical photograph of the Ag@MXene hollow sphere film in Comparative Example 3. Figure 3d shows that the MXene layers in Comparative Example 3 are locally stacked in density, hindering the ion diffusion path and affecting the rate performance of the battery, thus easily causing the generation of negative lithium dendrites, and thus cannot be applied in ultra-thin high-energy density energy storage devices. The current collector was tested with lithium sheets to form a half-cell, and the lithium deposition / detachment efficiency was only 94.8% (lower than the deposition / detachment efficiency of 98% of the material in Example 1) at a current density of 0.5 mA / cm

[0145] Comparative Example 5

[0146] This comparative example is the same as Example 1, except that after the film is filtered, the drying method used is air drying at 50°C.

[0147] After the film is filtered, a small amount of liquid remains in the film, and during the drying process, the air drying at 50°C accelerates the rapid evaporation of the surface liquid, which more easily causes uneven shrinkage of the film during drying. For example, Figure 15 Figure 3d is an optical photograph of the Ag@MXene hollow sphere film in Comparative Example 3. Figure 3d shows that the MXene layers in Comparative Example 3 are locally stacked in density, hindering the ion diffusion path and affecting the rate performance of the battery, thus easily causing the generation of negative lithium dendrites, and thus cannot be applied in ultra-thin high-energy density energy storage devices. The current collector was tested with lithium sheets to form a half-cell, and the lithium deposition / detachment efficiency was only 94.8% (lower than the deposition / detachment efficiency of 98% of the material in Example 1) at a current density of 0.5 mA / cm Figure 15 Figure 3d is an optical photograph of the Ag@MXene hollow sphere film in Comparative Example 3. Figure 3d shows that the MXene layers in Comparative Example 3 are locally stacked in density, hindering the ion diffusion path and affecting the rate performance of the battery, thus easily causing the generation of negative lithium dendrites, and thus cannot be applied in ultra-thin high-energy density energy storage devices. The current collector was tested with lithium sheets to form a half-cell, and the lithium deposition / detachment efficiency was only 94.8% (lower than the deposition / detachment efficiency of 98% of the material in Example 1) at a current density of 0.5 mA / cm

[0148] Comparative Example 6

[0149] The comparative example is the same as example 1, except that after the membrane is filtered, the drying method is vacuum drying at 50°C.

[0150] After the membrane is filtered, a small amount of liquid remains in the membrane. During the drying process, the membrane shrinks due to capillary action, and in addition, uneven shrinkage causes the membrane to crack in some areas. As shown in Figure 15 The optical photograph in FIG. 6c shows that the ultra-thin Ag@MXene hollow sphere membrane prepared by the drying method of vacuum drying at 50°C is partially cracked and cannot be self-supported into a film. Compared with the membrane obtained by the drying method in example 1, Figure 15 The drying method of comparative example 6 cannot meet the requirements of material preparation, and therefore cannot be applied in ultra-thin high-energy density energy storage devices, compared with the membrane obtained by the drying method in example 1.

[0151] Comparative example 7

[0152] The comparative example is the same as example 1, except that after the membrane is filtered, the drying method is vacuum drying at room temperature.

[0153] After the membrane is filtered, a small amount of liquid remains in the membrane. During the drying process, the membrane shrinks due to capillary action, and in addition, uneven shrinkage causes the membrane to crack in some areas. As shown in Figure 15 The optical photograph in FIG. 6c shows that the ultra-thin Ag@MXene hollow sphere membrane prepared by the drying method of vacuum drying at 50°C is partially cracked and cannot be self-supported into a film. Compared with the membrane obtained by the drying method in example 1, Figure 15 The drying method of comparative example 7 cannot meet the requirements of material preparation, compared with the membrane obtained by the drying method in example 1. In addition, the film formation rate of the drying method in comparative example 7 is only about 36%, as shown in Figure 16 Figure 16 The optical photographs in FIGS. 6a and 6b before and after the membrane is dried, respectively, show that the film formation rate of the drying method in comparative example 7 is only about 36%, and therefore cannot be applied in ultra-thin high-energy density energy storage devices.

[0154] The above describes exemplary embodiments of the present application. However, the scope of protection of the present application is not limited to the above-described embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the present application shall be included in the scope of protection of the present application.​

Claims

1. A composite negative electrode, characterized by, The composite negative electrode comprises a current collector and a metal negative electrode material; the metal negative electrode material is selected from at least one of metal lithium, sodium, potassium and magnesium; The preparation method of the composite negative electrode comprises: taking the current collector as a working electrode and the metal negative electrode material as a counter electrode, and preparing the composite negative electrode by an electrodeposition method; The current collector comprises a hollow sphere film; the hollow sphere film comprises hollow spheres composed of transition metal carbon and / or nitride, and the hollow spheres are stacked to form a three-dimensional porous structure; the surface of the hollow sphere shell is also dispersed with nanoparticles; the nanoparticles are selected from nanoparticles with lithium affinity; the mass ratio of the transition metal carbon and / or nitride and the nanoparticles is 5-100:1; The hollow spheres of the transition metal carbon and / or nitride have a hollow structure; cavities are also formed between the hollow spheres of the transition metal carbon and / or nitride; The preparation method of the hollow sphere film comprises the following steps: (1) slowly add a microsphere template dispersion liquid to a transition metal carbon and / or nitride dispersion liquid, slowly add a precursor solution of nanoparticles under ice-bath stirring to obtain a mixed solution; the solvents in the transition metal carbon and / or nitride dispersion liquid, the microsphere template dispersion liquid and the precursor solution of nanoparticles are ethanol; the precursor of the nanoparticles is selected from at least one of the following: a salt, an acid and / or an oxide of Au, Ag, Si, Sn, Zn, Al; (2) vacuum suction filter the mixed solution of step (1) to obtain a film, and after low-temperature refrigeration, dry the film to obtain a dried film; the mixed solution is kept under ultrasonic during the vacuum suction filtering; the vacuum suction filtering also comprises rinsing with deionized water to remove the solvent; the temperature of the low-temperature refrigeration is 0-20 ℃; the drying is carried out under vacuum; (3) calcine the dried film of step (2) to remove the microsphere template to obtain the hollow sphere film.

2. The composite negative electrode according to claim 1, characterized by The average thickness of the hollow sphere film is 10-1000 μm; The average inner diameter of the hollow spheres of the transition metal carbon and / or nitride is 0.05-50 μm; The average particle size of the nanoparticles is 5-500 nm; The transition metal carbon and / or nitride is selected from at least one of the following materials: Ti3C2-MXenes, Ti2N-MXenes, Cr2C-MXenes, Ta4C3-MXenes, Ti3CN-MXene, Ta2C-MXenes, Nb4C3-MXenes, Nb2C-MXenes, V2C-MXenes, Mo2TiC2-MXenes, Mo3C2-MXenes, V4C3-MXenes; The nanoparticles dispersed on the surface of the hollow sphere shell are selected from at least one of the following materials: Au, Ag, ZnO, Al2O3, SnO2.

3. The composite negative electrode according to claim 1, characterized by The nanoparticles are loaded on the hollow sphere film in an amount of 0.05-0.5 mg / cm 2 ; The hollow sphere film has a pore volume of 0.1 to 1.5 cm 3 / g.

4. The composite negative electrode according to claim 1, characterized by The hollow sphere film has a pore volume of 0.3-1.0 cm 3 20-30 μm in thickness.

5. The composite anode according to claim 1, wherein The hollow sphere film comprises a honeycomb-shaped three-dimensional porous structure formed by stacking silver nanoparticles and MXene hollow spheres, and the silver nanoparticles are distributed on the surface of the MXene hollow sphere shell; The silver nanoparticles are loaded on the thin film of the hollow sphere in an amount of 0.1-0.3 mg / cm 2 ; the silver nanoparticles have a particle size of 20-70 nm.

6. The composite anode according to claim 1, characterized by The concentration of the transition metal carbon and / or nitride dispersion solution is 1-10 mg / mL; The concentration of the microsphere template dispersion solution is 1-5 mg / mL; The material of the microsphere template is selected from at least one of the following materials: polymethyl methacrylate, polystyrene; The diameter of the microsphere template is 0.05-50 μm.

7. The composite anode according to claim 1, wherein In step (1), the transition metal carbon and / or nitride dispersion solution is kept stirring; In step (1), the mass ratio of the transition metal carbon and / or nitride to the microsphere template in the mixed solution is 1-10:1-5; In step (1), the precursor solution of the nanoparticles needs to be added slowly; In step (1), the ice bath temperature is -10 ~ 0 ℃; In step (1), the concentration of the precursor solution of the nanoparticles is 1-10 mg / mL; In step (1), the mass ratio of the precursor of the nanoparticles to the transition metal carbon and / or nitride in the mixed solution is 0.1-1:0.5-5.

8. The composite anode according to claim 1, wherein In step (3), the temperature of the calcination is greater than 400 ℃, and the time of the calcination is 30-360 minutes; In step (3), the calcination is carried out in an inert atmosphere.

9. The composite anode according to claim 1, characterized by The surface capacity of the metal negative electrode material in the composite negative electrode is 0.1-10 mA h cm -2 .

10. The composite anode according to claim 1, characterized by when the surface capacity of the metal negative material on the composite negative electrode is 0.5-8 mA h cm -2 , the energy density of the composite negative electrode is 847-3170 mAh / g.

11. Use of the composite negative electrode according to any one of claims 1-10 in a metal secondary battery.

12. A metal secondary battery comprising the composite negative electrode according to any one of claims 1-10.

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