CN116364937A - Nanoparticle modified ultrathin hollow sphere film and preparation method and application thereof - Google Patents

Abstract

The invention discloses a nanoparticle modified ultrathin hollow sphere film, and a preparation method and application thereof. The hollow sphere film comprises hollow spheres composed of transition metal carbon/nitride, wherein the hollow spheres are piled to form a three-dimensional porous structure; the spherical shell surface of the hollow sphere also comprises nano particles. The preparation method of the ultrathin hollow sphere film can conveniently regulate and control various parameters of the film, such as film thickness, porosity, pore volume, nanoparticle diameter and the like. Compared with the common suction filtration and drying modes, the preparation method can greatly improve the film forming rate of the ultrathin hollow sphere film preparation, and the material preparation time is shorter. The process is simple, green and environment-friendly, can be used for large-scale production, and has high practicability.

Description

Nanoparticle-modified ultra-thin hollow sphere film and its preparation method and application

technical field

The invention relates to the field of electrochemical energy storage, in particular to a nanoparticle-modified ultra-thin hollow spherical film and a preparation method and application thereof.

Background technique

In recent years, with the rapid advancement of electronic technology, more and more electronic devices are developing in the direction of thinner, lighter and higher energy density. Among the current commercial lithium-ion batteries, lithium-ion batteries assembled with graphite as the negative electrode and ternary materials as the positive electrode have an energy density of about 180Wh kg ^-1 and have been widely used in various mobile electronic devices. However, with the increasing demand for high-power energy storage devices such as electric vehicles and energy storage grids, lithium-ion batteries are no longer suitable for 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 most ideal candidates for the development of high energy density energy storage devices. Among them, metallic lithium anode has an 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 batteries. The study found that the key to the development of lithium metal secondary batteries with high energy density is to solve the safety problem of lithium negative electrodes. Lithium metal is directly used as the negative electrode, and needle-like Li dendrites will be generated during repeated electrochemical cycles due to the uneven deposition of Li. The further growth of lithium dendrites will pierce the separator and cause an internal short circuit in the battery, which will cause heating or even fire inside the battery. Therefore, the development of metal secondary batteries should solve the problem of dendrite growth.

Furthermore, the adoption of ultrathin Li metal electrodes with capacity matching that of current cathodes and improved electrochemical stripping/plating behavior plays a key role in realizing high-energy-density batteries. For example, the 300-micron-thick metal lithium strips that are commonly used in commercial use now correspond to an areal capacity density of 62mAh cm ^-2 , far exceeding the areal capacity density (3mAhg ^-1 ) of commercial embedded cathode materials. This huge difference not only causes metal The excessive waste of lithium further increases the safety hazard of the battery. Therefore, it is of great significance to develop an ultra-thin metal lithium anode with high Coulombic efficiency and high safety for the development of high energy density lithium batteries.

In order to solve the problem of dendrite growth, one of the effective solutions is to construct current collectors. Transition metal carbon/nitride (MXene) is an ideal material for constructing three-dimensional current collectors due to its light weight, high electrical conductivity, and lithium affinity. However, single-layer or few-layer MXene materials are easy to stack again, which increases the ion transport path inside the material and affects the rate performance of the battery. The introduction of hollow sphere structure into MXene by template method and the modification of MXene by inorganic nanoparticles can prevent the stacking of MXene sheets, improve the storage space of lithium, and the lithium affinity of three-dimensional current collectors. At present, many methods have been used to prepare ultra-thin porous films. Among them, the vacuum filtration method has simple equipment, controllable film thickness and porosity, and good repeatability. However, the film-forming properties of this nanoparticle-modified MXene hollow sphere film prepared by vacuum filtration are poor. During the drying process of the film, the capillary tension increases due to dehydration, which leads to the shrinkage of the capillary and the shrinkage of the material. When the film shrinks unevenly, the film is easily chapped. The stress that causes the cracking of the porous film mainly comes from the capillary force caused by the surface tension in the pores of the porous film skeleton, which rearranges the inner frame of the film and shrinks the volume. At the same time, the application of ultra-thin films in batteries usually requires that the films have certain mechanical properties and can be self-supporting to avoid the use of current collectors. However, ultra-thin films are limited by their thickness and porosity and usually have poor mechanical properties. In addition, the suction filtration of MXene materials takes a long time in an aqueous solution environment. Studying the surface, the drying rate will also affect whether the film is cracked. In order to ensure the film formation rate, the film drying rate will generally be slowed down, but it will greatly prolong the film preparation time, which is not conducive to large-scale production. The film is easy to crack, the film formation rate is low, and it takes a long time. These all limit the material preparation of ultra-thin films, making it difficult for the large-scale application of this film material in metal lithium anodes.

Contents of the invention

In order to improve the above-mentioned technical problems, the present invention provides a hollow sphere film, the hollow sphere film includes hollow spheres made of transition metal carbon/nitride, and the hollow spheres are stacked to form a three-dimensional porous structure; the spherical shell surface of the hollow spheres Nanoparticles are also dispersed.

According to an embodiment of the present invention, the transition metal carbon/nitride hollow spheres have a hollow structure.

According to an embodiment of the present invention, cavities are also formed between the transition metal carbon/nitride hollow spheres.

According to an embodiment of the present invention, the average thickness of the hollow spherical film is 10-1000 μm, preferably 10-100 μm, more preferably 10-30 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm , 9μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm.

According to an embodiment of the present invention, the average inner diameter of the transition metal carbon/nitride hollow sphere is 0.05-50 μm, preferably 1-10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm , 10μm, 20μm, 30μm, 40μm, 50μm.

According to an embodiment of the present invention, the average particle diameter of the nanoparticles is 5-500nm, preferably 20-70nm, such as 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, 300nm, 400nm, 500nm.

According to an embodiment of the present invention, the transition metal carbon/nitride is selected from MXene materials commonly used in this technical field, such as at least one of the following materials: Ti ₃ C ₂ -MXenes, Ti ₂ N-MXenes, Cr ₂ C-MXenes, Ta ₄ C ₃ -MXenes, Ti ₃ CN-MXenes, Ta ₂ C-MXenes, Nb ₄ C ₃ -MXenes, Nb ₂ C-MXenes, V ₂ C-MXenes, Mo ₂ TiC ₂ -MXenes , Mo ₃ C ₂ -MXenes, V ₄ C ₃ -MXenes, etc., preferably Ti ₃ C ₂ -MXenes.

According to an embodiment of the present invention, the nanoparticles are selected from lithium-philic nanoparticles. Preferably, the nanoparticles are selected from at least one of the following materials: Au, Ag, Si, Sn, ZnO, Al ₂ O ₃ , SiO, SnO _{2 ,} etc., preferably Ag, ZnO.

According to an embodiment of the present invention, the mass ratio of the transition metal carbon/nitride to the nanoparticles is (5-100):1, for example (10-70):1.

According to an embodiment of the present invention, the loading amount of the nanoparticles on the hollow spherical film is 0.05-0.5 mg/cm ² , such as 0.1-0.3 mg/cm ² , exemplarily 0.08 mg/cm ² , 0.16 mg/cm ² , 0.2 mg/cm ² .

According to an embodiment of the present invention, the pore volume of the hollow spherical membrane is 0.1-1.5 cm ³ /g, preferably 0.3-1.0 cm ³ /g, such as 0.3 cm ³ /g, 0.42 ^{cm 3 /} g, 0.5 cm ³ /g, ^{0.6cm 3} /g, 0.66cm ³ /g, 0.84cm ³ /g.

According to an exemplary solution of the present invention, the hollow sphere film includes a honeycomb three-dimensional porous structure formed by stacking silver nanoparticles and MXene hollow spheres, and the silver nanoparticles are distributed (preferably evenly distributed) in the spheres of the MXene hollow spheres. shell surface;

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

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

The present invention also provides the preparation method of above-mentioned hollow sphere film, and described preparation method comprises the following steps:

(1) Slowly add the microsphere template dispersion liquid into the transition metal carbon/nitride dispersion liquid, and add the precursor solution of nanoparticles under stirring in an ice bath to obtain a mixed solution;

(2) The mixed solution of step (1) is vacuum filtered to obtain a film, and the film is dried after low-temperature refrigeration to obtain a dried film;

(3) Calcining the dried film in step (2) to remove the microsphere template to obtain the hollow sphere film.

According to an embodiment of the present invention, solvents in the MXene dispersion, microsphere template dispersion, and nanoparticle precursor solution can be solvents known in the art, such as ethanol, preferably absolute ethanol.

According to an embodiment of the present invention, the concentration of the transition metal carbon/nitride dispersion is not specifically limited, as long as a uniform dispersion can be obtained, such as 1-10 mg/mL, or 5-10 mg/mL .

According to the embodiment of the present invention, the concentration of the microsphere template dispersion liquid is not specifically limited, as long as a uniform dispersion liquid can be obtained, such as 1-5 mg/mL, or 1-3 mg/mL.

According to an embodiment of the present invention, the precursors of the nanoparticles are selected from substances from which the nanoparticles can be obtained, such as salts, acids and/or oxides of at least one of the following metals: Au, Ag, Si, Sn, Zn, Al, Si, Sn. Exemplarily, the precursor of the nanoparticles is selected from AgNO ₃ , HAuCl ₄ .

According to an embodiment of the present invention, the microsphere template is selected from at least one of the following microspheres: polymethyl methacrylate (PMMA), polystyrene (PS), silicon dioxide (SiO ₂ ), etc., PMMA microspheres are preferred.

According to an embodiment of the present invention, the diameter of the microsphere template is 0.05-50 μm, preferably 1-10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm , 40μm, 50μm.

According to an embodiment of the present invention, in step (1), the transition metal carbon/nitride dispersion is kept stirring. In the present invention, the stirring is not specifically limited, and stirring methods known in the art can be selected, as long as the dispersion can be kept uniform.

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

According to an embodiment of the present invention, in step (1), the precursor solution of the nanoparticles needs to be added slowly. Preferably, the adding rate of the nanoparticle precursor solution is 0.1-5 mL/min, for example 1 mL/min.

According to an embodiment of the present invention, in step (1), the temperature of the ice bath is -10-0°C. The inventors found that slowly adding the precursor solution of nanoparticles at the temperature of the ice bath is conducive to the generation of nanoparticles with the above-mentioned particle size, so that the nanoparticles can be more evenly distributed on the surface of the spherical shell of the transition metal carbon/nitride hollow spheres , to avoid nanoparticle agglomeration.

According to an embodiment of the present invention, in step (1), the concentration of the nanoparticle precursor solution is 1-10 mg/mL, for example, 5 mg/mL.

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

According to an embodiment of the present invention, in step (2), the mixed solution is kept ultrasonic during the vacuum filtration process.

According to an embodiment of the present invention, in step (2), the vacuum filtration further includes rinsing with deionized water to remove the solvent. Preferably, the rinsing needs to be performed multiple times.

According to an embodiment of the present invention, in step (2), the temperature of the cryogenic refrigeration is 0-20°C, preferably 3-8°C, for example 5°C. The inventors found that drying the vacuum-filtered film after low-temperature refrigeration is beneficial to improve the film-forming rate of the film.

According to an embodiment of the present invention, in step (2), the drying is carried out under vacuum conditions. In the present invention, the drying time and temperature are not specifically limited, as long as the solvent in the film can be completely removed. Exemplarily, the drying time is 1-24 hours, such as 12 hours. Exemplarily, the drying temperature is 10-40°C, such as 20°C.

According to the embodiment of the present invention, in step (3), the conditions of the calcination are not specifically limited, as long as the microsphere template in the film can be completely removed. Exemplarily, the calcination temperature is greater than 400°C, such as 450°C. Exemplarily, the calcination time is 30-360 minutes, such as 60 minutes.

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

The present invention also provides the application of the above-mentioned hollow sphere thin film in metal secondary batteries, for example, as a current collector in metal secondary batteries; as another example, for preparing negative electrodes in metal secondary batteries.

The present invention also provides a current collector, which includes the above-mentioned hollow spherical film.

The present invention also provides a composite negative electrode, which includes the above-mentioned current collector and metal negative electrode material.

According to an embodiment of the present invention, the current collector and transition metal carbon/nitride hollow spheres have the meanings as described above.

According to an embodiment of the present invention, the metal negative electrode material is selected from at least one of metal lithium, sodium, potassium and magnesium.

According to an embodiment of the present invention, in the composite negative electrode, the areal capacity of the metal negative electrode material is 0.1-10mA hcm ^-2 , such as 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 .

Exemplarily, the metal negative electrode material is selected from lithium, and its areal capacity is 0.5-8mAh/cm ² , such as 2mA h cm ^-2 , 4mA h cm ^-2 .

According to an embodiment of the present invention, the composite negative electrode has a high energy density. Preferably, when the areal capacity of the metal negative electrode material on the composite negative electrode is 0.5-8 mA h cm ^-2 , the energy density of the negative composite electrode is 847-3170 mAh/g. Exemplarily, when the areal capacity of the metal negative electrode material on the composite negative electrode is 4 mA h cm ⁻² , the energy density of the composite negative electrode is 2691 mAh/g.

According to the embodiment of the present invention, the composite negative electrode has ultra-thin, high safety, high specific capacity, and long cycle life.

The present invention also provides a method for preparing the above-mentioned composite negative electrode. The preparation method includes: using the above-mentioned current collector as a working electrode and a metal negative electrode material as a counter electrode, and preparing the composite negative electrode by electrodeposition.

According to an embodiment of the present invention, the metal negative electrode material has the meanings described above.

According to an exemplary solution of the present invention, the composite negative electrode includes a current collector and a lithium metal negative electrode material, wherein the current collector includes Mxene and Ag nanoparticles, denoted as Ag@MXene/Li.

The present invention also provides the application of the above-mentioned current collector in a metal secondary battery, preferably in an ultra-thin energy storage device with high energy density.

The present invention also provides a metal secondary battery including the above current collector.

The metal secondary battery in the present invention refers to a secondary battery that directly uses one or more of metal lithium, sodium, potassium and magnesium as the negative electrode.

Beneficial effect:

Compared with the prior art, the preparation method of the ultra-thin hollow spherical film provided by the present invention is short in time consumption, low in cost, high in film forming rate, can be prepared in a large scale, and has high practicability.

Compared with the commonly used MXene-based membrane suction filtration method, the ultra-thin film preparation method in the present invention has higher film formation rate and faster suction filtration speed. It overcomes the technical problems such as the poor mechanical properties of the film obtained by suction filtration after the conventional MXene material is dispersed in aqueous solution or ethanol solution, and the film is chapped and pulverized due to capillary action and uneven shrinkage during the film drying process. In addition, through the preparation method of the present invention, the coating effect of the MXene material on the microsphere template can be effectively improved, and the uneven coating caused by the agglomeration between MXene sheets can be avoided. The present invention realizes the controllability of the pore volume and the interlayer spacing by reasonably controlling the thickness of the ultra-thin hollow sphere film, the inner diameter of the hollow sphere, the content of MXene, and the diameter and density of nanoparticles, and effectively improves the capacity of the current collector to accommodate the metal negative electrode material. space, and at the same time induce the uniform deposition of the metal anode material in the film, and the three-dimensional porous film material can be used as the anode current collector of the metal secondary battery.

The negative electrode prepared by using the three-dimensional current collector of the present invention is applied to metal secondary batteries, has the characteristics of flexibility and self-support, can solve the problem of dendrite growth in metal secondary batteries, and has the advantages of long life, safety and reliability.

The invention proposes an ultra-thin MXene hollow sphere film modified by nanoparticles as a three-dimensional current collector, and deposits a metal negative electrode material in the hollow sphere film by an electrodeposition method to obtain an ultra-thin metal negative electrode. The ultra-thin MXene hollow sphere thin film and lithium-philic nanoparticles of the present invention can induce the uniform deposition of metallic lithium on the surface of the spherical shell of the hollow sphere, avoiding the generation of metal dendrites (such as lithium dendrites) in the negative electrode during the charge and discharge process, stimulating The risk of short circuit of the secondary battery caused by the penetration of the separator. At the same time, the use of MXene hollow sphere thin films provides more space for metal accommodation to achieve high metal lithium loading.

The present invention prepares the negative electrode by controlling parameters such as the inner diameter of the hollow sphere in the current collector, the thickness of the hollow sphere film, and the particle size of the nanoparticles, so that metal ions can quickly pass through the holes inside the hollow sphere film, and at the same time, it can better induce metal The ions are evenly deposited on the surface of the spherical shell of the hollow sphere, preventing the dendrite growth of the negative electrode from piercing the separator during the charge and discharge process.

Description of drawings

Fig. 1 is a scanning electron micrograph of the Ag@MXene ultrathin hollow sphere film in Example 1.

Fig. 2 is a high-magnification cross-sectional scanning electron micrograph of the Ag@MXene ultra-thin hollow sphere film in Example 1.

Fig. 3 is the X-ray diffraction pattern of the Ag@MXene ultrathin hollow sphere film in Example 1.

Figure 4 shows the suction filtration time (a) of the Ag@MXene ultra-thin hollow sphere membrane in Example 1 and the suction filtration time (b) of the membrane in Comparative Example 1.

Fig. 5 is an optical photo of the film formation rate of the Ag@MXene ultra-thin hollow sphere film in Example 1.

Fig. 6 is an optical photo of the large-sized Ag@MXene ultra-thin hollow spherical film in Example 1.

Figure 7 shows the Coulombic efficiency test of the Ag@MXene ultra-thin hollow sphere film and metal lithium assembled half-cell in Example 1 under the condition of current density of 0.5mA cm ^-2 and capacity of 1mA h cm ^-2 .

FIG. 8 is a scanning electron micrograph of the cross-section of the Ag@MXene ultra-thin hollow spherical film in Example 2.

Figure 9a is a high-magnification scanning electron micrograph of the Ag@MXene ultrathin hollow spherical film in Example 3.

Figure 9b is a cross-sectional scanning electron micrograph of the Ag@MXene ultra-thin hollow spherical film in Example 3.

FIG. 10 is a high-magnification scanning electron micrograph of the Ag@MXene ultra-thin hollow spherical film in Example 4.

Fig. 11 is a scanning electron micrograph of the cross-section of the Ag@MXene ultra-thin hollow spherical film in Example 5.

Fig. 12 is a high-magnification scanning electron micrograph of the Ag@MXene ultra-thin hollow spherical film in Example 6.

Figure 13 is an optical photo of the large-sized Ag@MXene ultra-thin hollow spherical film in Comparative Example 2.

Figure 14 is a scanning electron micrograph of the Ag@MXene ultrathin hollow sphere film in Comparative Example 3.

Fig. 15 is an optical photograph of the films prepared by drying in Comparative Examples 4-7 and Example 1.

Fig. 16 is an optical photograph of the film formation rate of the film prepared by the drying method in Comparative Example 7.

Detailed ways

The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following examples are only for illustrating and explaining the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies realized based on the above contents of the present invention are covered within the scope of protection intended by the present invention.

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

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

Example 1

(1) Preparation of ultrathin transition metal carbon/nitride (MXene) hollow sphere film (Ag@MXene hollow sphere film) decorated with silver nanoparticles (AgNPs)

(1) Add 600 μL of ethanol dispersion of two-dimensional Ti ₃ C ₂ -Mxenes (5 mg/mL) to 10 mL of absolute ethanol and stir, then slowly add 1.2 mL of PMMA (2 mg/mL, particle size 1.8 μm ) microsphere template dispersion, slowly add 1 mL of AgNO ₃ (5 mg/mL) solution into the above mixed solution under stirring in an ice bath (0° C.), and stir for 30 min.

(2) Keep the above mixed solution in ultrasonic, vacuum filtration; after the suction filtration is completed, add 10mL of deionized water to rinse three times to obtain a film, remove the diaphragm and filter membrane at the same time when the film is not dry, and refrigerate at 5°C 1h; the film was flattened with a glass plate and transferred to a vacuum oven, and dried in vacuum at room temperature to obtain a dried film.

(3) Remove the dried film from the filter membrane, and under the protection of argon atmosphere, calcinate it in a carbonization furnace at 450°C, the heating rate is 5°C/min, and keep it for 1h after the heating is completed, that is, silver nanoparticles modified MXene hollow sphere film with a pore volume of 0.66 cm ³ /g, which is denoted as Ag@MXene hollow sphere film, which is the porous three-dimensional current collector of this embodiment.

In Figure 1, a and b are scanning electron microscope images 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 sheets of the dried film are uniform and dense. Wrapped on PMMA microsphere template. Figure 1 c is the cross-sectional view of the dried film after calcination to remove the PMMA microsphere template. It can be seen that the thickness of the film has no obvious change after calcination, and the hollow sphere skeleton composed of Mxene is left after the PMMA microsphere template is removed. The ball skeleton is stacked into an ultra-thin porous film with a honeycomb structure. The hollow sphere film has a hollow structure, which can provide sufficient space to accommodate the deposition of metal anode materials, which is conducive to the preparation of metal lithium anodes with high areal capacity.

Figure 2 is a scanning microscope image of MXene hollow spheres. It can be seen that AgNPs are evenly distributed on the surface of the spherical shell of MXene hollow spheres. The particle size of the nanoparticles is about 60nm, and the loading capacity is 0.16mg/cm ² . Uniformly loaded AgNPs can provide more lithiophilic active sites, induce the uniform deposition of metal lithium on the surface of MXene hollow spherical shells, and avoid the growth of lithium dendrites.

Figure 3 is the XRD pattern of the Ag@MXene hollow sphere film. It can be seen that the film includes MXene and Ag.

It can be seen from a in Figure 4 that by selecting ethanol as the dispersant, rapid suction filtration can be achieved, and the duration of suction filtration is about 3-4min. Vacuum drying the film after suction filtration after refrigeration can improve the shrinkage of the film during drying, and avoid cracking or even pulverization caused by uneven shrinkage during the drying process of the film. As shown in Figure 5, the film after drying in this embodiment The film forming rate is 100%.

In addition, Figure 6 is an optical photo of the ultra-thin Ag@MXene hollow sphere film. The diameter of the Ag@MXene hollow sphere film can reach 40 mm. It can be seen that the preparation method of the present invention can realize the preparation of large-sized hollow sphere films.

(2) Preparation of metal lithium anode using silver nanoparticles (AgNPs) modified ultrathin transition metal carbon/nitride (MXene) hollow sphere film (Ag@MXene) as current collector

The working electrode is the above-mentioned Ag@MXene hollow sphere thin film, and the counter electrode is lithium metal. The lithium metal composite negative electrode is prepared by electrodeposition, which is denoted as Ag@MXene/Li. The areal capacity of the lithium metal negative electrode material is 2mA h cm ^{- 2} .

(3) Assembling the half-cell and its performance test

The above-mentioned ultra-thin Ag@MXene hollow sphere film is used as the positive electrode, metal lithium is used as the negative electrode, and the DME/DOL (volume ratio is 1:1) LiTFSI electrolyte containing 1% lithium nitrate is assembled to obtain a metal lithium secondary battery. A charge-discharge tester was used to conduct a constant-current charge-discharge test on the above-mentioned battery. The test cut-off capacity was 1 mA h cm ^-2 , and the test temperature was 25°C. As shown in FIG. 7 , after testing, the coulombic efficiency of the hollow sphere film reaches 98% at a current density of 0.5 mA/cm ² (see b in FIG. 7 ). Moreover, it can be seen from a in Figure 7 that the voltage of the battery remains stable after 50 cycles, and the polarization voltage is relatively small, about 13mV (a in Figure 7, where 1st, 2nd, and 40th represent 1 cycle, 2nd, and 40th, respectively. 2 laps, 40 laps corresponding to the charging and discharging platform curve).

(4) Electrochemical test of metal lithium secondary battery

The above-mentioned Ag@MXene/Li is used as a metal negative electrode, lithium iron phosphate is used as a positive electrode (LFP), and the above-mentioned electrolyte is used to assemble a metal lithium secondary battery. Use a charge-discharge meter to conduct a constant-current charge-discharge test on the above-mentioned battery. The test temperature is 25°C, and the test charge-discharge range is 2–4V. The full battery assembled with Ag@MXene/Li and LFP in Example 1 has a specific capacity of about 156mA hg ^-1 and a capacity retention rate of 94.6% after 100 cycles in a long-term cycle test at a rate of 0.5C.

Example 2

(1) Preparation of Ag@MXene hollow sphere film: This example is the same as Example 1, except that the amount of MXene dispersion and PMMA microsphere template dispersion is increased to three times that of Example 1, namely 1.8mL : 3.6mL to obtain the current collector of this embodiment; the loading capacity of Ag nanoparticles on the current collector is 0.16mg/cm ² , the pore volume is 0.66cm ³ /g, and the film formation rate is 100%.

(2) Preparation of metal lithium negative electrode with ultra-thin transition metal carbon/nitride (MXene) hollow sphere film (Ag@MXene) modified by silver nanoparticles (AgNPs) as current collector: This example is the same as Example 1, but different The difference is that the current collector prepared in this embodiment is used;

(3) Assembling the half-cell and its performance test: This example is the same as Example 1, except that the metal lithium negative electrode prepared in this example is used.

Fig. 8 is a scanning micrograph of the cross-section of the dried film prepared in Example 2. The average thickness of the Ag@MXene hollow sphere film is about 75 μm, and the average particle size of the nanoparticles is 60 nm. Compared with Example 1, in Example 2, the thickness of the Ag@MXene hollow sphere film was controllably adjusted to maintain the film formation rate of the film, which proves that the preparation method in this application can realize the preparation of hollow sphere films with different thicknesses, and more Thick films can deposit metal lithium with a higher areal capacity inside the film to meet the needs of various application scenarios with different thicknesses.

According to the half-cell test, the half-cell composed of current collector and lithium sheet has a lithium deposition/stripping efficiency of 97.5% at a current density of 0.5mA/cm ² , and the voltage remains stable after 50 cycles, and the battery polarization voltage is about 15mV.

Example 3

(1) Preparation of Ag@MXene hollow sphere film: This example is the same as Example 1, except that the current collector of this example is obtained by using a PMMA microsphere template with an average particle diameter of 6 μm; The loaded amount of Ag nanoparticles is 0.16 mg/cm ² , the pore volume is 0.84 cm ³ /g, and the film formation rate is 100%.

(2) Preparation of metal lithium negative electrode:

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

(3) Assembling the half-cell and its performance test:

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

Figure 9a is a scanning microscope image of the AgNPs-modified MXene hollow spheres prepared in Example 3, the Ag@MXene hollow spheres have a diameter of about 6-7 μm and the average particle size of the nanoparticles is 60 nm. Figure 9b is a cross-sectional scanning electron microscope image of the AgNPs-modified MXene hollow spheres prepared in Example 3, and the average thickness of the Ag@MXene hollow sphere film is about 30 μm. Compared with Example 1, in Example 3, the diameter of the Ag@MXene hollow spheres is controllably adjusted, the pore volume of the film is increased (0.84cm ³ /g), and the film formation rate of the film is maintained, which proves that the present application The preparation method can realize the preparation of hollow spherical membranes with different porosities and pore diameters, and the membranes with higher porosity can deposit metal lithium with higher areal capacity inside the membranes to realize lithium negative electrodes with high areal capacity. After testing, the current collector and lithium sheet form a battery, and the lithium deposition/stripping efficiency reaches 98.5% at a current density of 0.5mA/cm ² , the voltage remains stable after 50 cycles, and the battery polarization is about 13mV.

Example 4

(1) Preparation of Ag@MXene hollow sphere film: this example is the same as Example 3, the difference is that the concentration of _AgNO3 added is 0.5mg/mL; the current collector of this example is obtained; The loaded amount of Ag nanoparticles is 0.08 mg/cm ² , the pore volume is 0.66 cm ³ /g, and the film formation rate is 100%.

(2) Preparation of metal lithium negative electrode:

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

(3) Assembling the half-cell and its performance test:

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

Figure 10 is a scanning microscope image of the AgNPs-modified MXene hollow sphere prepared in Example 4. Only a small amount of silver nanoparticles were observed on the shell surface of the Ag@MXene hollow sphere, with an average particle size of 30 nm. Compared with Example 3, in Example 4, the content of Ag in the Ag@MXene hollow spheres was controllably adjusted, and a smaller amount of Ag-modified MXene hollow spheres was used to reduce the cost of film preparation and maintain the film formation rate of the film, proving that this The preparation method in the application can realize the preparation of hollow sphere films modified by metal nanoparticles with different loads.

After testing, the current collector and lithium sheet form a half-cell, and the deposition/stripping efficiency of lithium reaches 97.4% at a current density of 0.5mA/cm ² , the voltage remains stable after 50 cycles, and the polarization voltage of the half-cell is about 14mV.

Example 5

(1) Preparation of Ag@MXene hollow sphere film: This example is the same as Example 1, except that. Adjust the ratio of MXene dispersion liquid and PMMA microsphere template dispersion liquid to 1:1, that is, 0.6mL:0.6mL; obtain the current collector of this embodiment; the loading capacity of Ag nanoparticles on the current collector is 0.16mg/cm ² , the pore volume is 0.42 cm ³ /g, and the film formation rate is 100%.

(2) Preparation of metal lithium negative electrode:

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

(3) Assembling the half-cell and its performance test:

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

Figure 11 is a scanning micrograph of the cross-section of the MXene hollow sphere film modified by AgNPs prepared in Example 5. The average thickness of the film is about 20-30 μm, the average particle size of the nanoparticles is 60nm, and the porosity of the film is reduced. The film is denser. Compared with Example 1, the proportion of PMMA template microspheres was reduced in Example 4 so as to regulate the porosity of the film and maintain the film-forming rate of the film. After testing, the current collector and lithium sheet form a battery, and the lithium deposition/stripping efficiency reaches 97.8% at a current density of 0.5mA/cm ² , the voltage remains stable after 50 cycles, and the battery polarization is about 14mV.

Example 6

(1) Preparation of Ag@MXene hollow sphere thin film: This example is the same as Example 3, except that the MXene dispersion and PMMA dispersion are mixed and frozen at -10°C, and silver nitrate solution is slowly added . The current collector of this example was obtained; the Ag nanoparticle loading on the current collector was 0.16 mg/cm ² , the pore volume was 0.84 cm ³ /g, and the film formation rate was 100%.

(2) Preparation of metal lithium negative electrode:

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

(3) Assembling the half-cell and its performance test:

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

Fig. 12 is a scanning microscope image of the AgNPs-modified MXene hollow sphere prepared in Example 6, the hollow sphere is evenly decorated with AgNPs, and the average particle size of the silver nanoparticles is about 50nm. Compared with Example 3, in Example 6, the reaction rate of MXene reducing _AgNO3 was regulated by controlling the temperature to form silver nanoparticles with smaller particle size, which can improve the utilization rate of silver nanoparticles and induce the uniform deposition of metal lithium in the hollow space. on the spherical shell. After testing, the current collector and lithium sheet form a battery, and the deposition/stripping efficiency of lithium reaches 98.3% at a current density of 0.5mA/cm ² , the voltage remains stable after 50 cycles, and the battery polarization is about 13mV.

Comparative example 1

Other conditions are the same as in Example 1, except that the solvent of the MXene dispersion and the PMMA dispersion is deionized water.

b in Fig. 4 is the time spent in the suction filtration process in Comparative Example 1, which is about 10 minutes. Compared with Example 1, the use of deionized water as the dispersant in Comparative Example 1 greatly reduces the suction filtration speed, which takes about three times as long as that in Example 1, and does not have practical benefits in practical applications.

Comparative example 2

This comparative example is the same as that of Example 1, except that the dispersion of MXene, PMMA and AgNPs was formed into a membrane by suction filtration, without rinsing with deionized water.

Since there is still a small amount of ethanol liquid in the film after suction filtration, during the drying process, due to the high saturated vapor pressure of ethanol, the surface liquid evaporates quickly, which is more likely to cause uneven shrinkage of the film during drying. As shown in the optical photographs in Figure 13, the film without rinsing with deionized water dried and the film was chapped due to uneven shrinkage, and the mechanical properties of the film were poor. Although the average thickness of the film is consistent with that in Example 1, which is about 20 μm, the film has poor mechanical strength due to chapping and cannot be self-supporting. Therefore, it cannot be applied in ultra-thin high energy density energy storage devices.

Comparative example 3

This comparative example is the same as Example 1, except that the ultrasonic treatment of the solution is not maintained during the membrane suction filtration process.

A and b in Figure 14 are scanning microscope images of MXene and PMMA microspheres composited in Comparative Example 3. Compared with Example 1, the MXene sheets in Comparative Example 3 are stacked and cannot be evenly wrapped on the PMMA microsphere template. This results in the agglomeration of a large number of PMMA microsphere templates and the stacking of MXene sheets. c in Figure 14 is the Ag@MXene hollow sphere film in Comparative Example 3. Compared with Example 1, a large number of cavities are generated in the hollow sphere film in Comparative Example 3, which is caused by PMMA agglomeration. In addition, it can be seen from c in Figure 14 that the MXene sheets generate dense stacking locally, which hinders the ion diffusion path and affects the rate performance of the battery, thus easily causing the generation of lithium dendrites in the negative electrode, so it cannot be applied to ultra-thin and high-energy batteries. density energy storage devices. After testing, the current collector and the lithium sheet form a half-cell, and the deposition/stripping efficiency of lithium is only 94.8% (lower than the 98% deposition/stripping efficiency of the material in Example 1) at a current density of 0.5mA/cm ² . Polarization voltage is about 15mV.

Comparative example 4

This comparative example is the same as Example 1, except that after the membrane suction filtration is completed, the drying method adopted is blast drying at 50°C.

After suction filtration, a small amount of liquid still remains in the film. During the drying process, the rapid volatilization of the surface liquid is accelerated due to the blast drying at 50°C, which is more likely to cause uneven shrinkage of the film during drying. The optical photo in Figure 15a shows that the Ag@MXene hollow sphere thin film prepared under blast drying conditions at 50 °C has severe cracks, making it difficult to form a self-supporting film. Therefore, it cannot be applied in ultra-thin high energy density energy storage devices.

Comparative example 5

This comparative example is the same as Example 1, except that after the membrane suction filtration is completed, the drying method adopted is drying at room temperature.

After suction filtration, there is still a small amount of liquid remaining in the film. During the drying process, the film shrinks due to capillary action, and in addition, the uneven shrinkage causes cracking in the film part. As shown in the optical photo in Figure 15b, the drying method of natural drying at room temperature takes longer, the shrinkage rate of the film is large, and local cracking makes it difficult to form a self-supporting film. Compared with the thin film obtained by the drying method in Example 1 in Figure 15e, the drying method of Comparative Example 5 cannot meet the material preparation requirements, so it cannot be applied to ultra-thin high energy density energy storage devices.

Comparative example 6

This comparative example is the same as Example 1, except that after the membrane suction filtration is completed, the drying method adopted is vacuum drying at 50°C.

After suction filtration, a small amount of liquid still remains in the film. During the drying process, the film shrinks due to capillary action. In addition, the uneven shrinkage causes cracking in the film part. As shown in the optical photo in c of Figure 15, the ultra-thin Ag@MXene hollow sphere film prepared by vacuum drying at 50 °C was partially cracked and difficult to form a self-supporting film. Compared with the thin film obtained by the drying method in Example 1 in Figure 15e, the drying method of Comparative Example 6 cannot meet the material preparation requirements, so it cannot be applied to ultra-thin high energy density energy storage devices.

Comparative example 7

This comparative example is the same as Example 1, except that after the membrane suction filtration is completed, the drying method adopted is vacuum drying at room temperature.

After suction filtration, there is still a small amount of liquid remaining in the film. During the drying process, the film shrinks due to capillary action, and in addition, the uneven shrinkage causes cracking in the film part. As shown in the optical photo in d of Figure 15, the ultra-thin Ag@MXene hollow sphere film prepared by vacuum drying at room temperature is partially cracked and difficult to form a self-supporting film. Compared with the film obtained by the drying method in Example 1 in Figure 15e, the drying method of Comparative Example 7 cannot meet the material preparation requirements. In addition, the film formation rate of the drying method in Comparative Example 7 is shown in Figure 16. In Figure 16, a and b are the optical photos of the film before and after drying the film, respectively. It can be seen that the film formation rate of the drying method in Comparative Example 7 Only about 36%, so it cannot be applied in ultra-thin high energy density energy storage devices.

Exemplary embodiments of the present invention have been described above. However, the protection scope of the present application is not limited to the above-mentioned embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a kind of hollow sphere film, it is characterized in that, described hollow sphere film comprises the hollow sphere that transition metal carbon/nitride forms, and described hollow sphere piles up and forms three-dimensional porous structure; The spherical shell surface of described hollow sphere is also dispersed with Nanoparticles. 2. The hollow sphere thin film according to claim 1, characterized in that, the transition metal carbon/nitride hollow sphere has a hollow structure. Preferably, cavities are formed between the transition metal carbon/nitride hollow spheres. Preferably, the average thickness of the hollow sphere film is 10-1000 μm, preferably 10-100 μm, more preferably 10-30 μm. Preferably, the average inner diameter of the transition metal carbon/nitride hollow spheres is 0.05-50 μm, preferably 1-10 μm. Preferably, the average particle diameter of the nanoparticles is 5-500 nm, preferably 20-70 nm. 3. The hollow sphere thin film according to claim 1 or 2, characterized in that the transition metal carbon/nitride is selected from at least one of the following materials: Ti ₃ C ₂ -MXenes, Ti ₂ N-MXenes , Cr ₂ C-MXenes, Ta ₄ C ₃ -MXenes, Ti ₃ CN-MXene, Ta ₂ C-MXenes, Nb ₄ C ₃ -MXenes, Nb ₂ C-MXenes, V ₂ C-MXenes, Mo ₂ TiC ₂ - MXenes, Mo ₃ C ₂ -MXenes, V ₄ C ₃ -MXenes, etc., preferably Ti ₃ C ₂ -MXenes. Preferably, the nanoparticles are selected from lithium-philic nanoparticles. Preferably, the nanoparticles are selected from at least one of the following materials: Au, Ag, Si, Sn, ZnO, Al ₂ O ₃ , SiO, SnO ₂ and the like. Preferably, the mass ratio of the transition metal carbon/nitride to the nanoparticles is (5-100):1. Preferably, the loading amount of the nanoparticles on the hollow sphere film is 0.05-0.5 mg/cm ² . Preferably, the pore volume of the hollow spherical membrane is 0.1-1.5 cm ³ /g, preferably 0.3-1.0 cm ³ /g. Preferably, the hollow sphere film includes a honeycomb three-dimensional porous structure formed by stacking silver nanoparticles and MXene hollow spheres, and the silver nanoparticles are distributed (preferably evenly distributed) on the surface of the spherical shell of the MXene hollow spheres. Further preferably, the pore volume of the hollow sphere film is 0.3-1.0 cm ³ /g, the thickness is 20-30 μm, and the loading amount of silver nanoparticles on the hollow sphere film is 0.1-0.3 mg/cm ² . Further preferably, the particle size of the silver nanoparticles is 20-70nm. 4. the preparation method of the hollow sphere film described in any one of claim 1-3 is characterized in that, described preparation method comprises the following steps: (1) Slowly add the microsphere template dispersion liquid into the transition metal carbon/nitride dispersion liquid, and slowly add the precursor solution of the nanoparticles under stirring in an ice bath to obtain a mixed solution; (2) The mixed solution of step (1) is vacuum filtered to obtain a film, and the film is dried after low-temperature refrigeration to obtain a dried film; (3) Calcining the dried film in step (2) to remove the microsphere template to obtain the hollow sphere film. 5. The preparation method according to claim 4, characterized in that the concentration of the transition metal carbon/nitride dispersion is 1-10 mg/mL. Preferably, the concentration of the microsphere template dispersion is 1-5 mg/mL. Preferably, the precursors of the nanoparticles are selected from substances from which the nanoparticles can be obtained, such as salts, acids and/or oxides of at least one of the following metals: Au, Ag, Si, Sn, Zn, Al, Si, Sn. Preferably, the material of the microsphere template is selected from at least one of the following materials: polymethyl methacrylate (PMMA), polystyrene (PS), silicon dioxide (SiO ₂ ), etc., preferably PMMA Microspheres. Preferably, the microsphere template has a diameter of 0.05-50 μm, preferably 1-10 μm. 6. The preparation method according to claim 4 or 5, characterized in that, in step (1), the transition metal carbon/nitride dispersion is kept stirring. Preferably, in step (1), in the mixed solution, the mass ratio of the transition metal carbon/nitride to the microsphere template is (1-10):(1-5), preferably (3-10):( 1-3). Preferably, in step (1), the precursor solution of the nanoparticles needs to be added slowly. Preferably, in step (1), the temperature of the ice bath is -10-0°C. Preferably, in step (1), the concentration of the precursor solution of the nanoparticles is 1-10 mg/mL. Preferably, in step (1), in the mixed solution, the mass ratio of the precursor of the nanoparticles to the transition metal carbon/nitride is (0.1-1):(0.5-5). Preferably, in step (2), the mixed solution is kept ultrasonic during the vacuum filtration process. Preferably, in step (2), the vacuum filtration also includes rinsing with deionized water to remove the solvent. Preferably, the rinsing needs to be performed multiple times. Preferably, in step (2), the temperature of the cold storage is 0-20°C, preferably 3-8°C. Preferably, in step (2), the drying is carried out under vacuum conditions. Exemplarily, in step (3), the calcination temperature is greater than 400°C. Exemplarily, it is 450°C. Exemplarily, in step (3), the calcination time is 30-360 minutes. Preferably, in step (3), the calcination is performed under an inert atmosphere. 7. A current collector, the current collector comprising the hollow spherical film according to any one of claims 1-3. 8. A composite electrode comprising the current collector and metal negative electrode material according to claim 8. 9. Application of the current collector according to claim 7 or the composite electrode according to claim 8 in metal secondary batteries. 10 . A metal secondary battery comprising the current collector according to claim 7 or the composite electrode according to claim 8 .

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