Two-dimensional material-coated silicon composite material and preparation method thereof, negative electrode, lithium-ion battery and electric vehicle

Abstract

The present invention discloses a two-dimensional material-coated silicon composite material, a preparation method thereof, a negative electrode, a lithium-ion battery, and an electric vehicle. The preparation method of the two-dimensional material-coated silicon composite material comprises the following steps: a mixing step: mixing a MXene material with silicon and / or silicon oxide to obtain a mixture or composite; a heating step: mixing a component A with the mixture and then heating it, wherein the component A is a simple substance of element A, a hydride of element A, or a compound capable of reacting to generate a simple substance of element A or a hydride of element A, so that the MXene material and the element A react to form a MAX phase structure. The two-dimensional material-coated silicon composite material obtained by the present invention has a coating structure with a dense core and a fluffy and partially blocked outer shell. This can effectively alleviate the huge volume change of silicon powder during charging and discharging, effectively prevent the aggregation of silicon powder, improve the conductivity of the entire electrode, and enhance the cycle life and rate performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials and lithium-ion batteries, and in particular relates to a two-dimensional material-coated silicon composite material and a preparation method thereof, a negative electrode, a lithium-ion battery and an electric vehicle. Background Art

[0002] With the rapid development of electric vehicles and electronic devices, people have higher and higher requirements for energy storage devices. Lithium-ion batteries, as electrochemical energy storage devices widely used in daily life, have attracted much attention. However, the traditional graphite anode materials matched with commercial lithium-ion batteries have relatively low theoretical specific capacity (372 mAh g -1 ), it is difficult to meet the market demand for high energy density energy storage devices. Silicon-based materials have extremely high theoretical specific capacity (4200 mAh g -1 Silicon anodes are widely considered to be an ideal anode material to replace graphite due to their advantages, such as a low lithium storage voltage (approximately 0.4 V), abundant reserves, and low toxicity. However, the low ionic and electronic conductivity of silicon anodes, their significant volume expansion (approximately 300%) before and after cycling, and the formation of an unstable solid electrolyte interphase (SEI) lead to low coulombic efficiency and poor cycling performance, hindering their commercial application. Summary of the Invention

[0003] The purpose of the present invention is to address the problem of large volume changes of silicon-based materials in lithium-ion battery electrodes during charging and discharging. The invention provides a method for coating silicon powder with a new two-dimensional material. Based on the excellent softness of the two-dimensional material MXene, silicon powder for lithium-ion batteries is coated and encapsulated through van der Waals forces or bonding to obtain a silicon powder material stably coated with the two-dimensional material; the coating structure has a dense core and a fluffy and partially blocked shell, which can effectively alleviate the huge volume changes of silicon powder during charging and discharging, and effectively prevent the aggregation of silicon powder, thereby improving the conductivity of the entire electrode and improving the cycle life and rate performance of the lithium-ion battery.

[0004] A first aspect of the present invention provides a method for preparing a two-dimensional material-coated silicon composite material, wherein the two-dimensional material-coated silicon composite material comprises a core and a coating layer, wherein the core comprises silicon and / or silicon oxide, and the preparation method comprises the following steps:

[0005] Mixing step: mixing the MXene material with the silicon and / or silicon oxide to obtain a mixture or composite;

[0006] Heating step: mixing component A with the mixture and then heating it, wherein component A is a simple substance of element A, a hydride of element A, or a compound that can react to generate a simple substance of element A or a hydride of element A, so that the MXene material partially reacts with the element A to form a MAX phase structure, thereby realizing the bonding and encapsulation of the MXene material to silicon and / or silicon oxide.

[0007] In some embodiments, the chemical formula of the MXene material is represented by M n+1 X n T x , wherein M is selected from one or more transition metal elements, X is selected from one or more carbon, nitrogen or boron elements, T x Represents a functional group, including one or more of -F, -Cl, -Br, -I, -O, -S, -OH, -NH4, 1≤ n ≤4; preferably, the M is selected from at least one of titanium (Ti), vanadium (V), molybdenum (Mo), niobium (Nb), tantalum (Ta), tungsten (W), and chromium (Cr).

[0008] In some embodiments, the above-mentioned element A is selected from one or more of aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), cadmium (Cd), indium (In), tin (Sn), lead (Pb), bismuth (Bi), and antimony (Sb).

[0009] In some embodiments, the mixing step more specifically includes: dispersing the MXene material with silicon and / or silicon oxide in a solvent and mixing them.

[0010] In some embodiments, a carbon material is further added in the mixing step, and the carbon material includes one or more of graphene, graphite, carbon nanotubes, porous carbon, and carbon fiber.

[0011] In some embodiments, in the mixing step, the silicon oxide is selected from silicon oxide and / or silicon monoxide.

[0012] In some embodiments, in the mixing step, the amount of the MXene material added to the mixture is in a mass percentage range of 0.01 wt.% to 90 wt.%; preferably, 0.5 wt.% to 20 wt.%; and more preferably, 2 wt.% to 5 wt.%.

[0013] In some embodiments, the silicon and / or silicon oxide is silicon powder for lithium-ion batteries.

[0014] In some embodiments, in the heating step, the heating temperature is between 200°C and 1000°C; preferably, between 600°C and 800°C.

[0015] In some embodiments, in the heating step, the heating time is between 0.1 h and 100 h; preferably, between 6 h and 20 h.

[0016] The second aspect of the present invention provides a two-dimensional material-coated silicon composite material, characterized in that the two-dimensional material-coated silicon composite material includes a coating layer and a core, the core is silicon and / or silicon oxide, the coating layer is MXene material, and the two-dimensional material-coated silicon composite material also has a MAX phase structure, which is obtained by heating the MXene material and component A, and the component A is a simple substance of element A, a hydride of element A, or a compound that can react to generate the simple substance of element A or the hydride of element A, thereby realizing the bonding and encapsulation of MXene material to silicon and / or silicon oxide.

[0017] In some embodiments, the MAX phase structure has a two-dimensional lamellar morphology.

[0018] In some embodiments, the element A is selected from one or more of aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), cadmium (Cd), indium (In), tin (Sn), lead (Pb), bismuth (Bi), and antimony (Sb).

[0019] In some embodiments, the two-dimensional material-coated silicon composite material further comprises: a carbon material, wherein the carbon material comprises: one or more of graphene, graphite, carbon nanotubes, porous carbon, and carbon fiber.

[0020] In some embodiments, the silicon oxide is selected from silicon oxide and / or silicon monoxide.

[0021] In some embodiments, the mass percentage of the MXene material in the two-dimensional material-coated silicon composite material is between 0.01 wt.% and 90 wt.%; preferably, between 0.5 wt.% and 20 wt.%; more preferably, between 2 wt.% and 5 wt.%.

[0022] In some embodiments, the thickness of the coating layer is between 0.3 nm and 20 μm; preferably, between 1 nm and 50 nm.

[0023] In some embodiments, the thickness of the MAX phase structure is between 0.3 nm and 2 μm.

[0024] A third aspect of the present invention provides a two-dimensional material-coated silicon composite material obtained by the above-mentioned preparation method; or, use of the above-mentioned two-dimensional material-coated silicon composite material as an electrode material for lithium-ion batteries.

[0025] A fourth aspect of the present invention provides a negative electrode for a lithium-ion battery, which contains the two-dimensional material-coated silicon composite material obtained by the above preparation method; or, the above-mentioned two-dimensional material-coated silicon composite material.

[0026] A fifth aspect of the present invention provides a negative electrode slurry for a lithium-ion battery, which contains a two-dimensional material-coated silicon composite material obtained by the above-mentioned preparation method; or, the above-mentioned two-dimensional material-coated silicon composite material; wherein, the mass percentage of the two-dimensional material-coated silicon composite material in the dry material in the negative electrode slurry is between 30% and 99%.

[0027] A sixth aspect of the present invention provides a lithium-ion battery comprising the aforementioned negative electrode; or a negative electrode obtained by coating the aforementioned negative electrode slurry.

[0028] A seventh aspect of the present invention provides an electric vehicle comprising the above-mentioned lithium-ion battery.

[0029] The beneficial technical effects of the present invention are:

[0030] 1. The two-dimensional material-coated silicon composite material and its preparation method provided herein utilize the excellent softness of the two-dimensional material MXene to coat silicon powder for lithium-ion batteries. The excess two-dimensional material after coating is encapsulated via van der Waals forces or bonding, resulting in a two-dimensional material-coated silicon powder material. This coating structure has a dense core and a fluffy, sealed shell. This unique structure differs from previously reported two-dimensional material coating structures, in which the excess portion of the coating is encapsulated via van der Waals forces or bonding. In particular, during bonding encapsulation, the two-dimensional MXene material is converted into a dense MAX phase structure. This MAX phase structure exhibits strong bonding, resolving the issue of the two-dimensional material being easily damaged and collapsed when the volume changes (>300%) in traditional two-dimensional material coating structures. This effectively mitigates the integrity of the core-shell structure during significant changes in the active material volume during electrode preparation and charge-discharge processes, thereby safeguarding the integrity of the lithium-ion battery electrodes.

[0031] 2. The two-dimensional MXene and MAX phase materials in the two-dimensional material-coated silicon composite material have excellent electrical conductivity and a two-dimensional layered structure. When added to the negative electrode of a lithium-ion battery, they can effectively change the point-point contact mode of traditional granular conductive agents. The conductive mode between active materials such as two-dimensional material-coated silicon powder is a surface-to-surface contact mode, which greatly improves the conductivity of the electrode and enhances the rate performance and cycle stability of the lithium-ion battery.

[0032] 3. The two-dimensional material-coated silicon composite material of the present invention also has a high specific surface area and high strength. While increasing its contact area with the current collector and the electrode porosity, it also enhances the electrode strength, solves the problem of easy detachment of silicon-based electrodes in lithium-ion batteries, and improves the life and rate performance of lithium-ion batteries.

[0033] 4. The two-dimensional material-coated silicon powder material of the present invention has adjustable shell thickness, simple preparation process, mild reaction conditions, high purity of synthetic samples, high yield, good repeatability, suitable for large-scale production, and is expected to be widely used in lithium-ion battery negative electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The MXene material Ti3C2T prepared in Example 1 of the present invention x XRD spectrum of

[0035] Figure 2 The spherical aberration electron micrograph (a) and the corresponding structural schematic (b) of the MAX phase Ti3SnC2 end-capping portion generated by the bonding reaction of the two-dimensional material MXene in the two-dimensional material MXene-coated silicon composite material in Example 1 of the present invention are shown;

[0036] Figure 3 This is a schematic diagram of the structure of the two-dimensional material MXene coated silicon or silicon oxide particles of the present invention;

[0037] Figure 4 The MXene material Ti3C2Cl prepared in Example 2 of the present invention x XRD spectrum of

[0038] Figure 5 : This is a spherical aberration electron microscopy photograph of the MAX phase structure obtained by reacting Al and MXene in Example 2 of the present invention and a schematic diagram of the corresponding atomic structure;

[0039] Figure 6 XRD spectra of the MAX phase structure obtained by the synthesis reaction of different MXene materials and element A in Example 5 of the present invention;

[0040] Figure 7 These are the electrochemical performance test results of different MXene materials composited with silicon powder in Example 7 of the present invention. DETAILED DESCRIPTION

[0041] The technical solutions of the present invention are described below by means of specific embodiments. It should be understood that one or more steps mentioned in the present invention do not exclude the presence of other methods and steps before and after the combination step, or other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and does not limit the order of arrangement of each method or the scope of implementation of the present invention. Changes or adjustments in their relative relationships can also be regarded as the scope of implementation of the present invention without substantial changes in the technical content.

[0042] The sources of the raw materials and instruments used in the examples are not particularly limited and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0043] The silicon powder commonly used in lithium-ion batteries in this field is composed of elemental silicon, or a mixture of elemental silicon and silicon oxide (silicon oxide or silicon monoxide), or a partially oxidized product of elemental silicon. Its macroscopic appearance is powder, and its microscopic appearance is granular, fibrous, or irregular.

[0044] The technical concept of the present invention is based on the applicant's previous discovery that MXene materials and elemental A or compounds containing A can undergo a reverse synthesis reaction to form a MAX phase structure (recorded in patent application number 202110557381.3). The applicant uses this synthesis reaction from MXene materials to form a MAX phase structure for bonding and encapsulating the negative electrode material (silicon powder) in lithium-ion batteries, resulting in a two-dimensional silicon composite material with a unique MXene material coating and an encapsulation with a MAX phase structure, and uses this composite material as the negative electrode material of lithium-ion batteries. The following specific examples illustrate the technical features of the present invention:

[0045] Example 1

[0046] This embodiment provides a two-dimensional material-coated silicon composite material and a preparation method thereof, specifically a two-dimensional material-coated silicon powder, wherein the MXene material is Ti3C2T x The preparation comprises the steps of:

[0047] (1) Weigh 200 mL of concentrated hydrochloric acid and place it in a plastic beaker. Weigh 10 g of LiF and slowly add it to the concentrated hydrochloric acid while stirring the solution with a magnet. Weigh 10 g of the raw material MAX phase - Ti3AlC2 and slowly add it to the hydrochloric acid-LiF solution. Maintain the reaction temperature at 30°C and the stirring speed at 500 rpm. The reaction is carried out for 24 hours.

[0048] (2) The reactant obtained in step 1 was washed with deionized water until the pH reached 6, and the obtained product was ultrasonically peeled off and centrifuged at 3000 rpm to obtain the upper liquid to obtain a MXene dispersion.

[0049] The steps of preparing the two-dimensional material-coated silicon powder of the present invention include:

[0050] (3) 100 g of silicon powder for lithium-ion batteries is measured and uniformly dispersed in the MXene dispersion obtained in step 2. The mixture is stirred mechanically or ultrasonically, and then filtered and dried to obtain a mixture of MXene-coated silicon powder. The coating thickness can be adjusted by adding different mass ratios of silicon powder and MXene. In some embodiments, the preparation ratio of MXene in the mixture can be adjusted in the range of 0.01 wt.% to 90 wt.%. When the two-dimensional material of the present invention is coated with the silicon composite material as the negative electrode material of a lithium-ion battery, the mass ratio of the MXene material is preferably between 0.1 wt.% and 20 wt.%, more preferably, between 3 wt.% and 10 wt.%, and even more preferably, between 2 wt.% and 5 wt.%, that is, the mass ratio of the active material is increased as much as possible. In this embodiment, the mass ratio of MXene is about 2 wt.%.

[0051] (4) A mixture of Sn element (tin powder) and MXene-coated silicon powder obtained in step 3 was placed in a tube furnace at a molar ratio of 1:10 for reaction. The mixture was heated to 700 °C under the protection of argon and kept warm for 10 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a MAX phase Ti3SnC2 bonded and blocked MXene-coated silicon composite material.

[0052] Figure 1 This is the XRD test result of MXene material obtained by etching with hydrochloric acid-fluoride salt method. Figure 1 It can be seen that the MXene material presents a diffuse characteristic peak, which is related to the etching of Al element in Ti3AlC2 to generate a lamellar structure of Ti3C2T x , which leads to the expansion of the interlayer spacing; Figure 2 The spherical aberration electron microscope photo (a) and the corresponding atomic structure diagram (b) of the MAX phase Ti3SnC2 end-capping part generated by the bonding reaction of the two-dimensional material MXene are further given, which clearly shows the MAX phase material structure of the bonded end-capping after the reaction of part of the MXene material with element A. Since the MAX phase structure is synthesized from MXene materials with at least two layers of two-dimensional sheets, the MAX phase structure can also maintain a two-dimensional sheet morphology, that is, the end-capping of a two-dimensional MAX phase structure is obtained. The thickness of the MAX phase structure is related to the number of layers of MXene materials involved in the synthesis reaction. Figure 2The photo shows two layers of MXene material (Ti3C2T x ) and element A atoms, the thickness of the MAX phase structure obtained by the reaction of multi-layer MXene materials and element A atoms is about 2-3 nm; in other embodiments, the thickness of the MAX phase structure obtained by the reaction of multi-layer MXene materials and element A atoms can be between 0.3 nm and 20 μm, preferably, the thickness is between 1 nm and 50 nm. Figure 3 A schematic diagram of the structure of a two-dimensional material-coated silicon composite material is provided, which shows a core-shell structure model. The silicon particles are coated with a MXene material having soft properties. At the same time, the edges of the MXene material overlap and also have a MAX phase structure. This MAX phase structure realizes the bonding and encapsulation of the MXene material-coated silicon powder particles, which can improve the stability of the coating structure. It should be noted that the schematic diagram shows that the core is spherical. In the specific embodiment, the focus of the present invention is the coating structure, and the shape of the core is not limited. Other silicon or silicon oxide morphologies, such as linear and irregular shapes, are all within the concept of the present invention as long as there is a MXene-coated structure in the composite material.

[0053] The preferred method for mixing MXene material and silicon powder is to mix them in a solution because the two-dimensional material MXene material has the characteristics of softness, high specific surface area, and a negative charge on the surface. It will self-assemble on the surface of the positively charged silicon powder in the solution to form a complex with a coating structure.

[0054] Example 2

[0055] This embodiment provides another two-dimensional material-coated silicon composite material and its preparation method, wherein the MXene material is Ti3C2Cl x The preparation comprises the steps of:

[0056] (1) Ti3SiC2, CuCl2, NaCl, and KCl were weighed in a molar ratio of 1:3:2:2, and the above substances were placed in an agate mortar and ground uniformly to obtain a mixture;

[0057] (2) The mixture obtained in step 1 was placed in a tube furnace and heated, and argon was introduced as a protective gas. The reaction temperature was maintained at 750 ° C and the reaction time was 24 hours. After the reaction was completed and the temperature was naturally cooled, the product was taken out and washed clean, and dispersed in N-methylpyrrolidone (NMP) solvent to obtain MXene-Ti3C2Cl x Organic dispersion.

[0058] The steps of preparing the two-dimensional material-coated silicon composite material of the present invention include:

[0059] (3) 100 g of silicon powder for lithium-ion batteries was measured and uniformly dispersed in the MXene organic dispersion obtained in step 2. The mixture was stirred mechanically or ultrasonically, and then filtered and dried to obtain a mixture of MXene-coated silicon powder. The coating thickness can be adjusted according to the different mass ratios of silicon powder and MXene. In this embodiment, the mass proportion of MXene is 5 wt.%.

[0060] (4) A mixture of Al element (aluminum powder) and MXene-coated silicon powder obtained in step 3 was placed in a tube furnace at a molar ratio of 1:10 for reaction. The mixture was heated to 700 °C under the protection of argon and kept warm for 10 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain MAX phase Ti3AlC2 bonded and terminated MXene-coated silicon powder material.

[0061] Figure 4 The MXene material Ti3C2Cl obtained by molten salt etching in this example is given. x From the XRD spectrum, it can be seen that the MXene material presents diffuse characteristic peaks, which is related to the etching of the Al element in Ti3AlC2 to generate a lamellar structure of Ti3C2Cl2, resulting in an increase in the interlayer spacing. Figure 5 Shown is a spherical aberration electron microscope photograph of the MAX phase structure obtained after the reaction of Al element and MXene and the corresponding atomic structure schematic diagram. It can be seen that the MAX phase material structure was successfully synthesized by multi-layer MXene material and Al element atoms.

[0062] Example 3

[0063] This embodiment provides another two-dimensional material-coated silicon composite material and its preparation method, wherein the MXene material Ti3C2T x The preparation was the same as in Example 1.

[0064] The steps of preparing the two-dimensional material-coated silicon powder of the present invention include:

[0065] (1) 5 g of carbon nanotubes were measured and evenly dispersed in 200 mL of MXene dispersion to obtain a MXene mixed dispersion.

[0066] (2) 100 g of silicon powder for lithium-ion battery acid is measured and evenly dispersed in the MXene mixed dispersion obtained in step 1. The MXene-coated silicon powder is obtained by mechanical stirring or ultrasonic stirring, and then filtered and dried. The coating thickness can be adjusted according to the different mass ratios of silicon powder and MXene.

[0067] (4) The Sn element and the MXene-coated silicon powder obtained in step 2 were placed in a tube furnace at a molar ratio of 1:10 for reaction. The mixture was heated to 700 °C under the protection of argon and kept warm for 10 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a MXene-coated silicon powder material with MAX phase Ti3SnC2 bonded and blocked.

[0068] In another preferred embodiment, the heating temperature is 800 degrees and the holding time is 12 hours.

[0069] This embodiment obtains a modified two-dimensional material-coated silicon composite material containing carbon material. In another embodiment, the carbon material carbon nanotubes added in step 1 can also be replaced by one or more of graphene, graphite, porous carbon, and carbon fiber; by adding carbon materials with one-dimensional or two-dimensional morphology, the electrochemical properties or mechanical properties of the two-dimensional material-coated silicon composite material of the present invention are further improved.

[0070] Example 4

[0071] This embodiment provides another two-dimensional material-coated silicon composite material. The preparation method is similar to that of the embodiment, except that the silicon powder in Example 1 is replaced with silicon monoxide (SiO) powder to obtain a two-dimensional material-coated silicon monoxide composite material.

[0072] In other embodiments, the silicon powder in Example 1 can also be replaced by other types of silicon compounds, such as silicon dioxide; or, powder of partially oxidized elemental silicon, to obtain a two-dimensional material-coated silicon composite material.

[0073] Example 5

[0074] This embodiment provides two-dimensional material-coated silicon composite materials synthesized from several different MXene materials and element A.

[0075] In one embodiment, the preparation method is similar to that of Example 1, except that in step 4 of Example 1, the Sn element (tin powder) is replaced with the Ga element (gallium powder), and the resulting bonded-terminated MAX phase structure is Ti3GaC2.

[0076] In one embodiment, the preparation method is similar to that of Example 1, except that in step 4 of Example 1, the Sn element (tin powder) is replaced with the Ge element (germanium powder), and the resulting bonded-terminated MAX phase structure is Ti3GeC2.

[0077] In one embodiment, the preparation method is similar to that of Example 1, except that the raw material MAX phase material in step 1 is Ti2AlC, and the MXene material obtained after etching is Ti2CT x The bonded and terminated MAX phase structure obtained is Ti2SnC.

[0078] In one embodiment, the preparation method is similar to that of Example 1, except that the raw material MAX phase material in step 1 is Ti2AlC, and the MXene material obtained after etching is Ti2CT x ; In step 4, the Sn element (tin powder) is replaced with the Ge element (germanium powder), and the resulting bonded and terminated MAX phase structure is Ti2GeC.

[0079] Figure 6 The XRD spectra of Ti3GaC2, Ti3GeC2, Ti2SnC and Ti2GeC with the two-dimensional MAX phase structures prepared above are given respectively. The characteristic peaks of the MAX phase structure can be seen in their XRD spectra. At the same time, compared with traditional MAX phase materials, these characteristic peaks are relatively diffuse, which is related to the fact that the obtained MAX phase structure maintains the ultra-thin two-dimensional morphology.

[0080] In this embodiment, element A is Sn, Ga, and Ge as an example. In other embodiments, element A can also be replaced by an element. For example, element A is selected from one or more of aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), cadmium (Cd), indium (In), tin (Sn), lead (Pb), bismuth (Bi), and antimony (Sb). These elements are all A component elements in the MAX phase material. Under certain reaction conditions, they can also undergo a synthetic reaction with the MXene material to achieve bonding and packaging of the coating structure.

[0081] It should be noted that in this embodiment, the MXene material undergoes a synthesis reaction with a simple substance (powder) of element A, but the synthesis reaction is not limited to the simple substance of element A. The MXene material can also react with the hydride of A, as well as other compounds that can react to generate a simple substance of element A or a hydride of element A.

[0082] In a specific embodiment, in one implementation, the preparation method is similar to that of Example 1, except that in step 4 of Example 1, the Sn element (tin powder) is replaced with aluminum hydride (AlH3), and the resulting bonded and terminated MAX phase structure is Ti3AlC2.

[0083] Example 6

[0084] This embodiment provides a negative electrode slurry and a negative electrode for a lithium-ion battery and aspects of their preparation, wherein the negative electrode slurry comprises, in parts by weight: 50 to 90 parts of the two-dimensional material-coated silicon powder of the present invention, 0.1 to 20 parts of graphene, 3 to 15 parts of PVDF, and 5 to 20 parts of NMP.

[0085] In a preferred embodiment, the negative electrode slurry comprises, in parts by weight: 70-90 parts of two-dimensional material-coated silicon powder, 0.1-20 parts of graphene, 3-15 parts of PVDF, and 5-20 parts of NMP.

[0086] In another preferred embodiment, the negative electrode slurry comprises, in parts by weight: 70-90 parts of two-dimensional material-coated silicon powder, 0.1-10 parts of graphene, 3-10 parts of PVDF, and 5-20 parts of NMP.

[0087] The preparation method comprises the following steps: mixing two-dimensional material-coated silicon powder, graphene, and PVDF to obtain a dry material mixture; adding NMP to the dry material mixture and stirring to obtain a negative electrode slurry; coating the negative electrode slurry on a current collector copper foil and drying it to obtain a negative electrode of a lithium-ion battery.

[0088] In a specific embodiment, the two-dimensional material-coated silicon composite material obtained in Example 1 is selected in the negative electrode slurry, and includes, by weight: 85 parts of two-dimensional material-coated silicon composite material, 5 parts of graphene, 10 parts of PVDF, and 10 parts of fiber material NMP.

[0089] Example 7

[0090] In order to illustrate the use effect of the two-dimensional material-coated silicon composite material of the present invention as a negative electrode material in a lithium-ion battery, in this embodiment, the negative electrode slurry is composed of the following raw materials by weight: 8 parts of two-dimensional material-coated silicon composite material, 1 part of PVDF, 1 part of conductive carbon black and a certain proportion of NMP. After being prepared into a slurry, it is coated on a copper foil and assembled with metallic lithium into a button battery to test the electrochemical properties of the two-dimensional material-coated silicon composite material. In this embodiment, the two-dimensional material-coated silicon composite material is selected from the MXene-coated silicon powder (marked as MXene@Si) bonded and capped with the MAX phase material Ti3AlC2 prepared in Example 2.

[0091] The mixture of MXene-coated silicon powder obtained in step 3 of Example 2 (without heat treatment to form MAX phase capping) was used as control sample 1; a mixture of silicon powder and MXene material powder was simply mixed as control sample 2. The negative electrode slurry was prepared using the same method as above, and then the electrodes were coated and assembled to obtain a control sample battery. Figure 7 Figures a to c show the charge-discharge curves of batteries with MXene@Si, silicon powder coated with MAX phase structure, comparative sample 1, and comparative sample 2 as negative electrode materials at different cycle times. It can be seen that MXene@Si exhibits the highest first charge capacity (about 3500 mAhg -1 ), which is significantly higher than that of the comparative sample 1 (about 3000 mAh g -1) and comparative sample 2 (approximately 2500 mAh g -1 It can also be seen that MXene@Si also exhibits the best cycle stability. After 20 cycles, the capacity remains at about 2500 mAh g -1 , while the comparative sample 1 without bonding end-capping only retained 1250 mAh g after 20 cycles. -1 The comparison sample 2, which is a simple mixture of MXene and silicon powder, shows the worst cycling performance, with a capacity of less than 500 mAh g after 20 cycles. -1 . It can be seen that compared with the simple mixed comparative sample 2, the comparative sample 1 with MXene-coated silicon powder also has a good electrochemical performance improvement effect. However, the MXene material-coated silicon powder MXene@Si with MAX phase structure encapsulation shows the best capacity retention rate. This is due to the MXene material-coated silicon powder and the specific MAX phase bonding encapsulation. The two-dimensional material MXene is converted into a dense structure of MAX phase. The MAX phase structure has a strong bonding effect, which solves the problem that the two-dimensional material in the traditional two-dimensional material coating structure is easily destroyed and collapsed when the volume changes (>300%). This can effectively alleviate the integrity of the core-shell structure during the electrode preparation process and the huge volume change of the active material during the charge and discharge process, thereby ensuring the integrity of the lithium-ion battery electrode.

[0092] Example 8

[0093] This embodiment provides an implementation method of two-dimensional MXene-coated silicon powder, and the specific steps include:

[0094] (1) Mechanically stirring and mixing the MXene material powder and silicon powder to obtain a mixture powder;

[0095] (2) Add component A to the powder of the mixture in step 1 above, stir and mix mechanically, and then heat treat to allow element A to react with the MXene material to form a MAX phase structure for bonding and end-capping.

[0096] In this embodiment, the powder is directly mixed to avoid the dispersion and drying steps in the solvent, simplifying the process flow and being suitable for large-scale industrial production. x Mix with silicon powder in a mass ratio of 1: (1~10), and then add Ti3C2T x The molar ratio of Sn powder to Sn powder is 1: (0.1-0.5), Sn powder is added to the mixture powder, and after stirring and mixing, the mixture is placed in a high-temperature reactor under Ar atmosphere and kept at 800° C. for 12 hours. The mixture is taken out after natural cooling to obtain the MXene-coated silicon powder composite material of the present invention.

[0097] In a preferred embodiment, Ti3C2T x Mixed with silicon powder in a mass ratio of 1:9, Ti3C2T x : Sn powder molar ratio is 1: 0.2.

[0098] The two-dimensional material-coated silicon composite material of the present invention can be used as the negative electrode material for a lithium-ion battery, resulting in a lithium-ion battery with excellent performance. The present invention also encompasses electric vehicles, including electric bicycles, electric motorcycles, and electric cars, that use this lithium-ion battery as an energy storage unit. The lithium-ion battery of the present invention may also be used in other modes of transportation, such as start-stop power supplies for automobiles and ships.

[0099] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a two-dimensional material-coated silicon composite material, characterized in that: The preparation method comprises the following steps: Mixing step: mixing the MXene material with the silicon and / or silicon oxide to obtain a mixture or composite; Heating step: mixing component A with the mixture or composite and then heating it, wherein component A is a simple substance of element A, a hydride of element A, or a compound that can react to generate a simple substance of element A or a hydride of element A, so that the MXene material reacts with the element A to form a MAX phase structure; obtaining a MXene material as a coating layer, and also containing a two-dimensional material-coated silicon composite material with a MAX phase structure.

2. The preparation method according to claim 1, wherein The chemical formula of the MXene material is represented by M n+1 X n T x , wherein M is selected from one or more transition metal elements, X is selected from one or more carbon, nitrogen or boron elements, T x Represents a functional group, including one or more of -F, -Cl, -Br, -I, -O, -S, -OH, -NH4, 1≤ n ≤4; And / or, the element A is selected from one or more of aluminum, silicon, phosphorus, sulfur, iron, copper, zinc, gallium, germanium, cadmium, indium, tin, lead, bismuth, and antimony.

3. The preparation method according to claim 2, wherein The M is selected from at least one of titanium, vanadium, molybdenum, niobium, tantalum, tungsten and chromium.

4. The preparation method according to claim 1, wherein The mixing step more specifically includes: dispersing the MXene material and the silicon and / or silicon oxide in a solvent and mixing; And / or, in the mixing step, a carbon material is further added, wherein the carbon material includes one or more of graphene, graphite, carbon nanotubes, porous carbon, and carbon fiber; and / or, in the mixing step, the silicon oxide is selected from silicon oxide and / or silicon monoxide; And / or, the material morphology of the silicon and / or silicon oxide is granular, spherical or linear; And / or, in the mixing step, the amount of the MXene material added to the mixture is in a range of 0.01 wt.% to 90 wt.% by mass; And / or, the silicon and / or silicon oxide is silicon powder for lithium-ion batteries.

5. The preparation method according to claim 4, wherein The addition amount of the MXene material is between 0.5 wt.% and 20 wt.% by mass.

6. The preparation method according to claim 4, wherein The amount of the MXene material added is between 2 wt.% and 5 wt.% by mass.

7. The preparation method according to any one of claims 1 to 6, characterized in that In the heating step, the heating temperature is between 200°C and 1000°C; And / or, in the heating step, the heating time is between 0.1h and 100h.

8. The preparation method according to claim 7, wherein The heating temperature is between 600° C. and 800° C.; And / or, the heating time is between 6h and 20h.

9. A two-dimensional material-coated silicon composite material, characterized in that: The two-dimensional material-coated silicon composite material includes a coating layer and a core, the core is silicon and / or silicon oxide, the coating layer is MXene material, and the two-dimensional material-coated silicon composite material also has a MAX phase structure, which is obtained by heating the MXene material and component A. The component A is a simple substance of element A, a hydride of element A, or a compound that can generate the simple substance of element A or the hydride of element A through reaction.

10. The two-dimensional material-coated silicon composite material according to claim 9, characterized in that: The MAX phase structure has a two-dimensional lamellar morphology; And / or, the element A is selected from one or more of aluminum, silicon, phosphorus, sulfur, iron, copper, zinc, gallium, germanium, cadmium, indium, tin, lead, bismuth, and antimony.

11. The two-dimensional material-coated silicon composite material according to claim 9 or 10, characterized in that: The two-dimensional material-coated silicon composite material further comprises: Carbon materials, including one or more of graphene, graphite, carbon nanotubes, porous carbon, and carbon fibers; and / or, the silicon oxide is selected from silicon oxide and / or silicon monoxide; And / or, the material morphology of the silicon and / or silicon oxide is granular, spherical or linear; and / or, the mass percentage of the MXene material in the two-dimensional material-coated silicon composite material is between 0.01 wt.% and 90 wt.%; and / or, the coating layer has a thickness ranging from 0.3 nm to 20 μm; And / or, the thickness of the MAX phase structure is between 0.3 nm and 2 μm.

12. The two-dimensional material-coated silicon composite material according to claim 11, characterized in that: The mass percentage of the MXene material in the two-dimensional material-coated silicon composite material is between 0.5 wt.% and 20 wt.%; And / or, the coating layer has a thickness ranging from 1 nm to 50 nm.

13. The two-dimensional material-coated silicon composite material according to claim 11, characterized in that: The mass percentage of the MXene material in the two-dimensional material-coated silicon composite material is between 2 wt.% and 5 wt.%.

14. A two-dimensional material-coated silicon composite material prepared by the preparation method according to any one of claims 1 to 7; or use of the two-dimensional material-coated silicon composite material according to any one of claims 8 to 13 as an electrode material for a lithium-ion battery.

15. A negative electrode of a lithium ion battery, characterized in that: The negative electrode contains a two-dimensional material-coated silicon composite material prepared by the preparation method according to any one of claims 1 to 7; or a two-dimensional material-coated silicon composite material according to any one of claims 8 to 13.

16. A negative electrode slurry for a lithium ion battery, characterized in that: The negative electrode slurry contains a two-dimensional material-coated silicon composite material prepared by the preparation method according to any one of claims 1 to 7; Or, the two-dimensional material-coated silicon composite material according to any one of claims 8 to 13; wherein the mass percentage of the two-dimensional material-coated silicon composite material in the dry material in the negative electrode slurry is between 30% and 99%.

17. A lithium ion battery, characterized in that: Containing the negative electrode according to claim 15; or, a negative electrode obtained by coating the negative electrode slurry according to claim 16.

18. An electric vehicle, characterized in that: Contains the lithium ion battery according to claim 17.

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