Negative active material, method for preparing the same, negative electrode sheet, secondary battery, and electric device

Abstract

The application relates to a negative electrode active material and a preparation method thereof, a negative electrode sheet, a secondary battery and a power utilization device. The negative electrode active material comprises an MXene three-dimensional material with a three-dimensional network skeleton and a silicon material layer arranged on at least part of the surface of the MXene three-dimensional material, wherein the MXene three-dimensional material comprises an MXene material, and a general structure formula of the MXene material is M n+1 X n wherein M comprises at least one of Ti, Nb, V, Mo, Zr, Cr, W and Ta; X comprises at least one of C and N; and n is 1, 2 or 3. The negative electrode active material can reduce the expansion force of the battery, improve the energy density and cycle life under high rate of the lithium ion battery, and thus a lithium ion battery with relatively optimal comprehensive performance is obtained.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of lithium-ion batteries, especially with their widespread use in new energy electric vehicles, higher demands have been placed on their energy density and fast charging capabilities. However, the theoretical specific capacity of currently commercially available graphite anode materials is only 372 mAh / g, which is relatively low and cannot meet the ever-increasing demand for high capacity and high power. Therefore, finding higher-capacity electrode materials to replace commercially available graphite anodes has become an important research direction for lithium-ion battery anodes.

[0003] Silicon is currently the material with the highest known lithium intercalation specific capacity (3579-4200 mAh / g), and also possesses advantages such as low discharge potential and abundant natural reserves, making it the most promising alternative to graphite as a lithium-ion battery anode material. However, during lithium-ion intercalation and deintercalation, silicon materials undergo volume changes of up to 300%, leading to problems such as electrode structure damage, electrical connection failure, and continuous consumption of active materials, ultimately resulting in battery performance degradation, such as poor cycle performance. Nanostructuring or silicon-carbon composites are commonly used methods to mitigate the volume change of silicon during battery cycling, but the improvement effects are not ideal, especially regarding cycle stability under high-rate rapid charge-discharge conditions. Therefore, existing anode active materials still require further improvement. Summary of the Invention

[0004] Therefore, it is necessary to provide a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device to improve the cycle stability of the battery under high-rate rapid charge and discharge conditions.

[0005] To achieve the above objectives, a first aspect of this application provides a negative electrode active material, comprising: an MXene three-dimensional material having a three-dimensional network framework and a silicon material layer disposed on at least a portion of the surface of the MXene three-dimensional material, wherein the MXene three-dimensional material comprises MXene material, and the general structural formula of the MXene material is Mn+1Xn, wherein M comprises at least one of Ti, Nb, V, Mo, Zr, Cr, W and Ta; X comprises at least one of C and N; and n is 1, 2 or 3.

[0006] The aforementioned negative electrode active material includes MXene three-dimensional material and a silicon material layer disposed on the surface of MXene three-dimensional material. MXene three-dimensional material has a three-dimensional network framework, which provides buffer space for the volume change of silicon, reducing the negative electrode expansion rate. Furthermore, MXene material, the main component of MXene three-dimensional material, has the characteristics of high electronic conductivity and fast lithium-ion transport. The silicon material disposed on the surface of MXene three-dimensional material can shorten the lithium-ion transport path, promote the rapid transport of lithium ions, and thus improve the rate performance of the negative electrode. At the same time, the three-dimensional network framework of MXene three-dimensional material forms a three-dimensional conductive network, which can also solve the problem of low conductivity of silicon material itself and improve the cycle stability of the battery under high-rate fast charge and discharge conditions.

[0007] In some embodiments, the MXene includes one or more of Ti2C and Ti3C2.

[0008] In some embodiments, the MXene material satisfies at least one of the following characteristics (1) to (3):

[0009] (1) The sheet diameter of MXene is 2-10 μm;

[0010] (2) MXene has 1 to 5 layers;

[0011] (3) The thickness of MXene sheets is 1nm to 10nm.

[0012] In some embodiments, the MXene three-dimensional material satisfies at least one of the following characteristics (4) to (5):

[0013] (4) The mesoporous rate of MXene three-dimensional materials is 30% to 70%;

[0014] (5) The density of MXene three-dimensional material is 10 mg / cm³. 3 ~60mg / cm 3 .

[0015] In some embodiments, the MXene three-dimensional material is MXene aerogel;

[0016] Optionally, the MXene aerogel further includes graphene;

[0017] Optionally, based on the total mass of the MXene aerogel, the graphene content is 3% to 70%, and more preferably 20% to 60%.

[0018] In some embodiments, the thickness of the silicon material layer is 5nm to 100nm, and optionally 10nm to 80nm.

[0019] In some embodiments, the average volumetric particle size Dv50 of the silicon material in the silicon material layer is 2nm to 30nm, and can be selected as 3nm to 10nm.

[0020] In some embodiments, the silicon material layer is connected to at least a portion of the surface of the MXene three-dimensional material via chemical bonds. Optionally, the surface of the MXene three-dimensional material has active carbon sites formed thereon, and the silicon material layer is connected to at least a portion of the surface of the MXene three-dimensional material by bonding to the active carbon sites.

[0021] In some embodiments, the negative electrode active material satisfies at least one of the following characteristics (6) to (9):

[0022] (6) The average volumetric particle size Dv50 is 5μm to 20μm;

[0023] (7) Specific surface area is 1m² 2 / g~30m 2 / g;

[0024] (8) Based on the mass of the negative electrode active material, the mass content of silicon is 1% to 70%;

[0025] (9) Based on the mass of the negative electrode active material, the mass content of MXene material is 30% to 99%.

[0026] A second aspect of this application provides a method for preparing the aforementioned negative electrode active material, comprising:

[0027] Provide the MXene three-dimensional material;

[0028] The silicon material layer is formed on the MXene three-dimensional material.

[0029] In some embodiments, the method for preparing the MXene three-dimensional material includes the following steps:

[0030] S11. Mix the MXene material, graphene oxide, dispersant, and reducing agent to obtain a mixture;

[0031] S12. The mixture is subjected to a hydrothermal reaction to obtain MXene gel;

[0032] S13. Freeze-dry the MXene gel to obtain MXene three-dimensional material.

[0033] In some embodiments, step S11 further includes: adding a second etchant to the mixture to etch and form the active carbon sites; optionally, the etchant is Ni. 2+ Salt.

[0034] In some embodiments, the weight ratio of the second etchant to the MXene material is 0.05 to 0.3.

[0035] In some embodiments, the method for forming the silicon material layer includes at least one of chemical vapor deposition, physical vapor deposition, plasma spraying, and screen printing, with chemical vapor deposition being an option.

[0036] A third aspect of this application provides a negative electrode sheet, comprising the negative electrode active material of the first aspect of this application or the negative electrode active material prepared by the method of the second aspect of this application.

[0037] A fourth aspect of this application provides a secondary battery, including the negative electrode sheet of the third aspect of this application.

[0038] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0039] Invention Effects

[0040] The negative electrode active material provided in this application includes an MXene three-dimensional material and a silicon material layer disposed on the surface of the MXene three-dimensional material. The MXene three-dimensional material has a three-dimensional network framework, which provides a buffer space for the volume change of silicon, reducing the expansion rate of the negative electrode. Furthermore, the main component of the MXene three-dimensional material, MXene, has the characteristics of high electronic conductivity and fast lithium-ion transport. The silicon material disposed on the surface of the MXene three-dimensional material can shorten the lithium-ion transport path, promote the rapid transport of lithium-ions, and thus improve the rate performance of the negative electrode. At the same time, the three-dimensional network framework of the MXene three-dimensional material forms a three-dimensional conductive network, which can also solve the problem of low conductivity of silicon material itself and improve the cycle stability of the battery under high-rate fast charge and discharge conditions. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0042] Figure 2 for Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0043] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0044] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0045] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0046] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0047] Explanation of reference numerals in the attached figures:

[0048] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0049] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0055] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0056] The term "aerogel" refers to a lightweight solid material composed of aggregated nanoparticles forming a nanoframework and a porous three-dimensional network, with the pores filled with a gaseous dispersion medium. Aerogels typically refer to nanoscale porous solid materials formed through the sol-gel method, where gas replaces the liquid phase in the gel using a specific drying process. It's important to note that the internal structure of aerogels features relatively uniform pore sizes, ranging from 2 to 50 nm, and most pores are interconnected. The most significant characteristic of aerogels is their low density; they are even considered the least dense solid in the world.

[0057] Currently, to meet market demand, the energy density of rechargeable batteries, represented by lithium-ion batteries, is increasing. Furthermore, with the continuous development of new energy electric vehicles, problems such as range anxiety and long charging times are becoming increasingly prominent. In this context, improving the fast-charging capability of high-energy-density batteries has become a key focus of next-generation battery development. Simultaneously, to improve energy density, silicon-based materials have been introduced into the selection of active materials for rechargeable batteries. Silicon-based materials undergo volume expansion during rechargeable battery cycling. At the same time, silicon, being a semiconductor, has low conductivity and poor high-power discharge performance. During high-rate fast charging, the volume change of silicon-based materials is even greater, exceeding 300%, leading to the destruction of the negative electrode conductive network. To address the volume change problem of silicon negative electrode materials, existing technologies focus on developing suitable carriers. However, given the increasingly stringent requirements for battery fast-charging capabilities, the inventors discovered that simply using a carrier to ensure the expansion space of silicon has limited effect on improving the high-rate fast-charging capability of the negative electrode material. Shortening the lithium-ion transport path allows the anode to have the ability to rapidly transport lithium ions, thereby greatly improving its fast-charging capability. Therefore, it is necessary to construct a negative electrode active material that can provide enough space to accommodate changes in the volume of silicon material and shorten the lithium-ion transport path in order to solve the cycle stability problem of high-energy-density batteries under high-rate fast charge and discharge conditions.

[0058] Negative electrode active materials

[0059] Therefore, a first aspect of this application provides a negative electrode active material, comprising an MXene three-dimensional material having a three-dimensional network framework and a silicon material layer disposed on at least a portion of the surface of the MXene three-dimensional material, wherein the MXene three-dimensional material comprises MXene material, and the general structural formula of the MXene material is M. n+1 X n M includes at least one of Ti, Nb, V, Mo, Zr, Cr, W and Ta; X includes at least one of C and N; and n is 1, 2 or 3.

[0060] In this embodiment, the negative electrode active material includes an MXene three-dimensional material and a silicon material layer disposed on the surface of the MXene three-dimensional material. The MXene three-dimensional material has a three-dimensional network framework, which provides a buffer space for the volume change of silicon, reducing the expansion rate of the negative electrode. Furthermore, the main component of the MXene three-dimensional material, MXene, has the characteristics of high electronic conductivity and fast lithium-ion transport. The silicon material disposed on the surface of the MXene three-dimensional material can shorten the lithium-ion transport path, promote the rapid transport of lithium-ions, and thus improve the rate performance of the negative electrode. At the same time, the three-dimensional network framework of the MXene three-dimensional material forms a three-dimensional conductive network, which can also solve the problem of low conductivity of silicon material itself and improve the cycle stability of the battery under high-rate fast charge and discharge conditions.

[0061] It should be noted that the silicon material layer can be disposed on a portion of the surface of the MXene three-dimensional material, or on the entire surface of the MXene three-dimensional material; preferably, the silicon material layer is disposed on the entire surface of the MXene three-dimensional material, for example, the silicon material layer covers the three-dimensional network skeleton of the MXene three-dimensional material, and the entire three-dimensional network skeleton of the MXene three-dimensional material is covered by the silicon material layer. Furthermore, the surface formed by the silicon material layer can be a continuous surface or a discontinuous surface; preferably, the surface formed by the silicon material layer is a continuous surface.

[0062] In some implementations, the MXene material includes one or more of Ti2C and Ti3C2.

[0063] The aforementioned MXene materials inevitably undergo surface functionalization during preparation, thus their surfaces typically include one or more surface functional groups (also known as end-capping groups). In some embodiments, the surface functional groups of MXene materials include at least one of hydroxyl, halogen, and oxygen-containing functional groups. It should be noted that the surface functional groups of MXene materials are usually formed naturally during preparation; however, specific surface functional groups can also be generated through chemical treatment, thermal annealing, and mechanical exfoliation processes. Depending on the surface functional groups, MXene materials can include, but are not limited to, one or more of oxides, epoxides, hydroxides, alkoxides having 1 to 5 carbon atoms, fluorides, chlorides, bromides, or iodides. In some specific embodiments, the surface functional groups of MXene materials include F, O, and OH.

[0064] MXene is a two-dimensional layered structure, and a three-dimensional network skeleton is formed by stacking multiple two-dimensional layered structures.

[0065] In some embodiments, the sheet diameter of the MXene material is between 2 μm and 10 μm. A larger sheet diameter results in more active sites, which is more conducive to charge transport. Sheet diameters within this range exhibit better structural stability and charge transport capabilities. As an example, the sheet diameter of the MXene material can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and any value between them.

[0066] In some embodiments, the number of MXene material laminations ranges from 1 to 5, such as 2, 3, 4 layers, and any value between them. MXene materials with a lamination number within this range have a larger specific surface area, more active sites, and better electronic conductivity.

[0067] In some embodiments, the sheet thickness of the MXene material is 1 nm to 10 nm, for example, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, and any value between them. A sheet thickness within the above range results in better material conductivity and structural stability. Further optionally, the sheet thickness of the MXene material is 1 nm to 4.5 nm.

[0068] In some embodiments, the mesoporosity of the MXene three-dimensional material is 30% to 70%, for example, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and any value between them. Within this range, the MXene three-dimensional material has a higher specific surface area, allowing for more silicon material to be incorporated, resulting in a higher silicon content in the negative electrode active material, higher energy density, and better structural stability. Optionally, the mesoporosity of the MXene three-dimensional material is 40% to 60%. It should be noted that the mesoporosity of the MXene three-dimensional material refers to the porosity of mesopores with a pore size less than 50 nm in the MXene three-dimensional material.

[0069] In some embodiments, the density of the MXene three-dimensional material is 10 mg / cm³. 3 ~60mg / cm 3 By optimizing the density of MXene three-dimensional materials, the negative electrode active material can have a higher specific capacity, which can further improve the overall energy density of the battery.

[0070] In some embodiments, the MXene three-dimensional material is MXene aerogel. MXene aerogel has a three-dimensional network framework, a larger specific surface area, higher porosity, lower density, lighter material, and stronger compressive strength. It can greatly shorten the lithium-ion transport path, further improve rate performance, effectively reduce the negative electrode expansion rate, and because of its extremely low density, when combined with silicon materials, it can give the negative electrode active material a higher specific capacity by weight, which can further improve the overall energy density of the battery.

[0071] In addition to MXene, the aforementioned MXene aerogel may also include other two-dimensional layered materials to further improve its structural stability. These include graphene, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, platinum diselenide, molybdenum diselenide, tungsten diselenide, vanadium diselenide, chromium disulfide, transition metal dichalcogenides, black phosphorus, and combinations thereof, without specific limitations. It should be noted that the sheet diameter, number of sheets, and sheet thickness of other two-dimensional layered materials must match those of the MXene material to form a structurally stable aerogel. The specific selection can be made according to actual needs.

[0072] In some embodiments, the MXene aerogel comprises MXene material and graphene. Optionally, based on the total mass of the MXene aerogel, the graphene content is 3% to 70%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and any value between therewith. When the graphene content in the MXene aerogel is within the above range, the MXene aerogel structure is more stable, and the electronic conductivity and lithium-ion transport rate are better. Optionally, based on the total mass of the MXene aerogel, the graphene content is 20% to 60%.

[0073] In this application, the graphene and its mass content in the negative electrode active material can be tested using instruments and methods known in the art. For example, the Raman spectrum can be obtained using a Raman spectrometer to characterize the graphene and the Raman peak loudness can be obtained to calculate the graphene mass content.

[0074] In some embodiments, the thickness of the silicon material layer is 5 nm to 100 nm, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, and any value between them. It can be selected as 10 nm to 80 nm. Within this range of silicon material layer thickness, the negative electrode active material has a better silicon content, which can improve its specific capacity, as well as better conductivity and cycle performance. Optionally, the thickness of the silicon material layer is 10 nm to 80 nm.

[0075] In some embodiments, the volume average particle size Dv50 of the silicon material in the silicon material layer is 2nm to 30nm, for example, 3nm, 5nm, 7nm, 9nm, 11nm, 13nm, 15nm, 17nm, 19nm, 21nm, 23nm, 25nm, 27nm, 29nm, and any value between them. Optionally, the volume average particle size Dv50 of the silicon material in the silicon material layer is 3nm to 10nm.

[0076] The volume average particle size Dv50 of silicon material in the silicon material layer is a well-known concept in the art. It represents the particle size corresponding to a cumulative volume distribution percentage of 50%. It can be tested using instruments and methods known in the art. For example, it can be conveniently tested using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd. in the UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0077] In some embodiments, the silicon material layer is connected to at least a portion of the surface of the MXene three-dimensional material via chemical bonds.

[0078] In some embodiments, the surface of the silicon material layer contains a first functional group, such as a hydroxyl functional group and / or a carboxyl functional group, and the surface of the MXene three-dimensional material contains a second functional group, such as a carboxyl functional group and / or a hydroxyl functional group. It should be noted that the first and second functional groups are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0079] In some embodiments, active carbon sites are formed on the surface of the MXene three-dimensional material, and the silicon material layer is connected to at least a portion of the surface of the MXene three-dimensional material via silicon-carbon bonds. Understandably, these silicon-carbon bonds are formed by silicon bonding to the active carbon sites on the surface of the MXene three-dimensional material. The connection of the silicon material layer to at least a portion of the surface of the MXene three-dimensional material via silicon-carbon bonds makes the silicon material layer on the surface of the negative electrode active material less prone to detachment, thereby enhancing the bonding strength of the silicon material layer to the MXene three-dimensional material and thus better utilizing the MXene three-dimensional material's ability to accommodate volume changes in the silicon-based material.

[0080] In some embodiments, the volume average particle size Dv50 of the negative electrode active material is 5 μm to 20 μm, for example, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, and any value between them. Optionally, the volume average particle size Dv50 of the negative electrode active material is 8 μm to 15 μm.

[0081] The volume average particle size Dv50 of the negative electrode active material is a well-known concept in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%. It can be tested using instruments and methods known in the art. For example, it can be conveniently tested using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0082] In some embodiments, the specific surface area of ​​the negative electrode active material is 1 m². 2 / g~50m 2 / g, for example 5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g and any values ​​between them. Optionally, the specific surface area of ​​the negative electrode active material is 5m². 2 / g~30m 2 / g.

[0083] In some implementations, based on the mass of the negative electrode active material, the silicon mass content is 1% to 70%, for example 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and any value between them.

[0084] In some implementations, based on the mass of the negative electrode active material, the mass content of MXene material is 5% to 30%, for example 10%, 15%, 20%, 25% and any value between them.

[0085] In this application, a cross-section of the negative electrode active material particles can be prepared using a cross-section polishing instrument (such as the IB-09010CP argon ion cross-section polishing instrument from JEOL Corporation of Japan), which passes through the core of the negative electrode active material particles; then, the elemental distribution map in the cross-section is obtained by EDX or EDS elemental analysis combined with TEM or SEM (such as the X-Max EDS from Oxford Instruments Group in the UK combined with the Sigma-02-33 SEM from ZEISS in Germany); combined with methods known in the art, the structure, composition, and characteristics and content of each component of the negative electrode active material can be further obtained.

[0086] For example, to determine the mass content of silicon and MXene, a cross-section of the negative electrode active material particles is prepared using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL Corporation). This cross-section passes through the core of the negative electrode active material particles. Then, elemental analysis using EDX or EDS combined with TEM or SEM (such as the X-Max EDS from Oxford Instruments combined with the Sigma-02-33 SEM from ZEISS) is performed to obtain the elemental distribution map within the cross-section. Within a region of the cross-section, the Si content or the specific elemental content of the MXene material in that region can be determined by integrating the distribution of silicon or MXene. To improve the accuracy of the test, multiple regions (e.g., 10) can be analyzed, and the average value is taken as the test result.

[0087] For example, the thickness of the silicon material layer can be determined by preparing a cross-section of the negative electrode active material particles using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL Corporation). This cross-section passes through the core of the negative electrode active material particles. Then, elemental analysis using EDX or EDS combined with TEM or SEM (such as the X-Max EDS from Oxford Instruments and the Sigma-02-33 SEM from ZEISS) is performed to obtain the elemental distribution map in the cross-section. The thickness of the silicon material layer can be determined based on the elemental distribution of the cross-section. More precisely, the thickness of the silicon material layer can be measured at multiple (more than 3, such as 8, 10, 12, etc.) different locations on the cross-section, and the average value is recorded as the thickness of the silicon material layer.

[0088] Preparation method of negative electrode active material

[0089] A second aspect of the embodiments of this application provides a method for preparing a negative electrode active material, comprising:

[0090] S10, providing MXene 3D materials; and

[0091] S20, forming a silicon material layer on the MXene three-dimensional material.

[0092] In some embodiments, the method for preparing the MXene three-dimensional material includes the following steps:

[0093] S11. Mix MXene material, graphene oxide, dispersant and reducing agent to obtain a mixture;

[0094] S12. The mixture is subjected to a hydrothermal reaction to obtain MXene gel;

[0095] S13. Freeze-dry the MXene gel to obtain the MXene three-dimensional material.

[0096] Optionally, in step S11, the preparation method of the MXene material includes: etching and stripping the MAX material using a first etchant. It should be noted that the first etchant is for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should it be construed as implicitly indicating the importance or quantity of the indicated technical features. The first etchant is not particularly limited, but specific examples include one or more of HF, LiF, NH4HF, HCl, H2SO4, NaOH, and KOH. The general structural formula of the MAX material is M... 1 m+1 AX 1 m , of which M 1 Includes at least one of Ti, Nb, V, Mo, Zr, Cr, W, or Ta, where A is a group III or IV element, and X... 1 It includes at least one of C or N, where m is 1, 2, or 3. The MAX material is not particularly limited and can be selected based on the actual MXene material required. Specific examples include: Ti2AlC, Ti3AlC2, Ta4AlC3, TiNbAlC, (V... 0.5 Cr 0.5 )3AlC2, V2AlC, Nb2AlC, Nb4AlC3, Ti3AlCN, Ti3SiC2, Ti2SiC, Ta4SiC3, TiNbSiC, (V 0.5 Cr 0.5 One or more of 3SiC2, V2SiC, Nb2SiC, Nb4SiC3 and Ti3SiCN.

[0097] Further optionally, the dispersant may be one or more of water, ethanol, methanol, acetone, and ethyl acetate.

[0098] Alternatively, the reducing agent can be HI, NaBH4, LiBH4, or hydrazine hydrate.

[0099] It should be noted that in step S11, the order in which MXene material, graphene oxide, dispersant and reducing agent are added is not particularly limited.

[0100] Optionally, the hydrothermal reaction temperature in step S12 is 50℃~120℃, and the reaction time is 2h~6h.

[0101] Optionally, the freeze-drying reaction temperature in step S13 is -100℃ to -20℃, and the reaction time is 12h to 48h.

[0102] In some embodiments, step S11 further includes: adding a second etchant to the mixture to etch and form the active carbon sites; optionally, the second etchant is Ni.2+ Salt. It should be noted that the second etchant is for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should it be interpreted as implicitly indicating the importance or quantity of the indicated technical features. The second etchant is not particularly limited; specific examples include: NiCl2, Ni(NO3)2, CoCl2, and Co(NO3)2. The purpose of adding the second etchant is to form defect carbon sites on the surface of the MXene 3D material, enabling the silicon material layer to bond with the MXene 3D material, thus making the bond stronger.

[0103] In some embodiments, the weight ratio of the second etchant to the MXene material is 0.05 to 0.3, for example, 0.1, 0.15, 0.2, 0.25, and any value between them. A weight ratio of the second etchant to the MXene material within the above range provides sufficient active defect sites for bonding the silicon material layer and the MXene three-dimensional material.

[0104] In some embodiments, the mass content of MXene material in the mixture is 30% to 97%, optionally 40% to 80%, based on the total mass of MXene material and graphene oxide. It should be noted that the MXene material undergoes self-assembly under the action of graphene oxide, and the mass content of MXene material in the final MXene gel is equivalent to the mass content of MXene material in the mixture, and the mass content of graphene in the final MXene gel is equivalent to the mass content of graphene oxide in the mixture.

[0105] In some embodiments, the method for forming the silicon material layer includes at least one of chemical vapor deposition, physical vapor deposition, plasma spraying, and screen printing, with chemical vapor deposition being an option.

[0106] Negative electrode sheet

[0107] A third aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which may include the composite negative electrode material of the first aspect of this application or a composite negative electrode material prepared by the method of the second aspect of this application. As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0108] The negative electrode sheet includes the negative electrode active material provided in this application, wherein the negative electrode active material can improve the cycle stability of the battery under high-rate fast charging and discharging conditions.

[0109] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0110] In some embodiments, the negative electrode active material does not exclude other negative electrode active materials besides those provided in this application. Other negative electrode active materials may be those known in the art for use in secondary batteries. As an example, other negative electrode active materials may include at least one of the following: artificial graphite, natural graphite, soft carbon, hard carbon, other silicon-based materials, tin-based materials, and lithium titanate, etc. The other silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight percentage of the negative electrode active material in the negative electrode active material layer is 70-100% by weight, based on the total weight of the negative electrode active material layer.

[0111] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode active material layer, based on the total weight of the negative electrode active material layer.

[0112] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the negative electrode active material layer, based on the total weight of the negative electrode active material layer.

[0113] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode active material layer, based on the total weight of the negative electrode active material layer.

[0114] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material provided in this application, optional other negative electrode active materials, optional binders, optional conductive agents, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then performing processes such as drying and cold pressing to obtain the negative electrode sheet. The solid content of the negative electrode slurry can be 30-70 wt%, the viscosity at room temperature can be adjusted to 2000-10000 mPa·s, and the compacted density of the negative electrode sheet can be 1.2-2.0 g / m³. 3 The thickness of the negative electrode active material layer can be 34μm to 143μm.

[0115] The thickness T of the negative electrode active material layer can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the negative electrode active material layer mentioned in this application refers to the thickness of the negative electrode active material layer in the negative electrode sheet used for battery assembly after cold pressing and compaction.

[0116] The negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode active material layer.

[0117] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0118] In one embodiment of this application, a secondary battery is provided.

[0119] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0120] Positive electrode sheet

[0121] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including the positive active material of the first aspect of this application.

[0122] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0123] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode active material accounts for 80-100% by weight of the positive electrode active material layer, based on the total weight of the positive electrode active material layer.

[0125] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20 wt% of the positive electrode active material layer based on the total weight of the positive electrode active material layer.

[0126] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent has a weight ratio of 0-20 wt% in the positive electrode active material layer, based on the total weight of the positive electrode active material layer.

[0127] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and then subjecting it to drying, cold pressing, and other processes to obtain the positive electrode sheet. The positive electrode slurry has a solid content of 40-80 wt%, a viscosity at room temperature adjusted to 5000-25000 mPa·s, and a compacted density of 3.0-3.6 g / cm³. 3 The concentration can be selected as 3.3-3.5 g / cm³. 3 The thickness of the positive electrode active material layer is 51-152 μm.

[0128] The thickness T of the positive electrode active material layer can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode active material layer mentioned in this application refers to the thickness of the positive electrode active material layer in the positive electrode sheet used for battery assembly after cold pressing and compaction.

[0129] electrolytes

[0130] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0131] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0132] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0133] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0134] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0135] Separating membrane

[0136] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0137] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0138] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0139] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0140] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0141] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0142] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0143] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0144] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0145] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0146] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0147] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0148] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0149] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0150] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0151] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0152] Example

[0153] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0154] I. Preparation Examples

[0155] Preparation Example 1

[0156] 1. Mix 50 mL of 12 mol / L concentrated hydrochloric acid and 20 g of LiF in a polytetrafluoroethylene liner (hereinafter referred to as a hydrothermal reactor) and stir at a rate of 50 rad / min to obtain a mixed solution of HCl and LiF. Place the hydrothermal reactor in an ice-water bath. Weigh 10 g of Ti3AlC2 raw material and add it to the mixed solution of HCl and LiF in 5 portions, with an interval of 20 min between each addition. The temperature of the hydrothermal reactor should not exceed 20℃. After the TiAlC raw material is added, place it in a water bath at 35℃ and stir for 24 h for etching. Centrifuge the etched solution at 5000 r / min and retain the upper black solution. Sonicate the solution for 2 h to obtain the exfoliated MXnen material, which is characterized as having the structural formula Ti3C2 and surface functional groups including F, O, and OH.

[0157] 2. MXene material and graphene oxide were dispersed in water at a weight ratio of 7:3 and mixed evenly. Then, excess HI reducing agent was added, followed by NiCl2 etchant, the amount of which was 10% of the weight of MXene material. The mixture was placed in a hydrothermal reactor, sealed, and then transferred to an 80°C oven for low-temperature hydrothermal treatment for 24 hours to obtain MXene hydrogel. The prepared MXene hydrogel was immersed in an ethanol solution for 72 hours to remove the iodine adhering to the surface, and then rinsed with water until the pH of the cleaning solution was 7. The cleaned MXene hydrogel was dried in an 80°C oven for 2 hours and then transferred to a freeze dryer. After freeze-drying at -30°C for 48 hours, MXene aerogel was obtained.

[0158] 3. Place MXene aerogel in a tube furnace to deposit a layer of nano-silicon material. Use Ar inert gas and deposit at 900℃ for 2 hours. The reaction gas source is SiH4 and C2H2 with a volume ratio of 2:1. The flow rate is 50 mL / min. The deposition temperature is 900℃ and the deposition time is 30 min. This yields MXene material with amorphous silicon deposition, which is the negative electrode active material.

[0159] SEM (Scanning Electron Microscopy) analysis revealed that the negative electrode active material exhibits a three-dimensional network structure with a three-dimensional network framework.

[0160] Preparation Examples 2-26

[0161] The preparation methods for Preparation Examples 2-26 are similar to those for Preparation Example 1. The difference lies in the adjustment of the negative electrode active material and related parameters in its preparation process, as detailed in Table 1 below. "-" indicates that the corresponding parameter does not exist.

[0162] Preparation of Comparative Example 1

[0163] The preparation method of Comparative Example 1 is similar to that of Preparation Example 1. The difference is that the deposition of the nano-silicon material layer in step 3 is replaced by mechanical mixing of the MXene aerogel and nano-silicon particles obtained in step 2. The mass of the nano-silicon particles is the same as the mass of the silicon material layer in Preparation Example 1. That is, the silicon content and MXene content in the final negative electrode active material are the same as those in Preparation Example 1.

[0164] II. Application Examples

[0165] Example 1

[0166] 1) Preparation of positive electrode sheet

[0167] The ternary material nickel-cobalt-manganese (NCM811), conductive carbon black SP, and binder PVDF were dispersed in a solvent NMP at a weight ratio of 97:2:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a positive electrode current collector aluminum foil, and then dried, cold-pressed, die-cut, and slit to obtain a positive electrode sheet with a coating weight of 0.27 g / 1540.25 mm². 2 .

[0168] 2) Preparation of negative electrode sheet

[0169] The negative electrode active material prepared in Example 1, conductive carbon as a conductive agent, sodium carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene rubber (SBR) as a binder were mixed in a weight ratio of 96:2:1:1. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto copper foil. After the copper foil was dried at room temperature, it was transferred to an 85°C oven for drying. Then, it was cold-pressed and slit to obtain a negative electrode sheet with a coating weight of 0.17 g / 1540.25 mm². 2 .

[0170] 3) Separating membrane

[0171] A porous membrane with a thickness of 12μm was selected.

[0172] The preparation of the porous separator membrane includes: using a polyethylene microporous film as the porous separator membrane substrate, mixing inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent in a weight ratio of 3:1.5:5.5 to form a slurry, coating it onto one side of the substrate, and drying it to obtain the porous separator membrane.

[0173] 4) Preparation of electrolyte

[0174] The organic solvent is a mixture containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, wherein the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:2:1. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried lithium salt LiPF6 is dissolved in the organic solvent and mixed thoroughly to obtain the electrolyte. The concentration of the lithium salt is 1 mol / L.

[0175] 5) Battery manufacturing

[0176] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 100℃ to remove moisture, and then 320g of the appropriate electrolyte is injected. The cell is then sealed, and after processes including settling, hot and cold pressing, formation, clamping, and capacity testing, a finished battery with a capacity of 180Ah is obtained. The initial charge N / P ratio is 1.05. N / P = Negative electrode specific capacity * Negative electrode active material mass / Positive electrode specific capacity * Positive electrode active material mass

[0177] The secondary batteries of Examples 2-26 and Comparative Example 1 are prepared in a similar manner to the secondary battery of Example 1, but the corresponding negative electrode active materials of the preparation examples are used.

[0178] III. Testing Methods

[0179] 1. Specific surface area and mesoporous content test

[0180] The specific surface area and pore size distribution of the negative electrode active materials and MXene aerogels in the examples and comparative examples were measured using a specific surface area analyzer (TristarII 3020M) via nitrogen adsorption / desorption method. Specific testing was conducted according to the national standard GB / T 19587-2017.

[0181] 2. Particle size distribution test

[0182] The particle size distribution of the anode active material and silicon material in the silicon material layer of the examples and comparative examples was tested using a Malvern particle size analyzer to obtain the average volume particle size Dv50 of the silicon material in the anode active material and silicon material layer. The specific tests were conducted in accordance with the national standard GB / T19077-2016.

[0183] 3. Number of MXene layers, layer diameter, layer thickness, and interlayer spacing:

[0184] The number of MXene lamellar layers was observed using the tapping mode of an atomic force microscope (AFM), and the lamellar diameter, thickness, and spacing were measured using the microscope's built-in scale. Since MXene shapes are typically irregular, the average length of the MXene lamellar layer in both directions (connecting the two points furthest apart on the MXene surface and drawing the perpendicular bisector of that line) was taken as the MXene lamellar diameter. A sample of MXene should contain at least 100 lamellar layers. The MXene lamellar diameter is the average diameter of the MXene samples described above.

[0185] 4. MXene aerogel density test

[0186] A fixed amount of MXene aerogel is placed in a compaction mold, and the mold is placed on a compaction (mass) density meter. Different pressures are set, and the thickness of the carbon aerogel material powder under different pressures can be read on the device. The density is calculated using the formula density = mass / volume.

[0187] 5. Thickness of silicon material layer

[0188] A cross-section of the negative electrode active material particles was prepared using a cross-section polisher (such as the JEOL IB-09010CP argon ion cross-section polisher). This cross-section passed through the core of the negative electrode active material particles. Then, the elemental distribution map of the cross-section was obtained by surface scanning testing using an X-Max EDS (Oxford Instruments, UK) combined with a Sigma-02-33 SEM (ZEISS, Germany). The thickness of the silicon material layer was determined based on the elemental distribution of the cross-section. The thickness values ​​of the silicon material layer at three different locations on the cross-section were taken, and the average value was recorded as the thickness of the silicon material layer.

[0189] 6. Testing of the mass content of silicon in the negative electrode active material and the mass content of MXene material.

[0190] A cross-section of the negative electrode active material particles was prepared using a cross-section polisher (such as the JEOL IB-09010CP argon-ion cross-section polisher). This cross-section passed through the core of the negative electrode active material particles. Then, elemental distribution maps of the cross-section were obtained using surface scanning analysis (SEM) combining an X-Max EDS (Oxford Instruments) and a Sigma-02-33 SEM (ZEISS). Within a region of the cross-section, the Si content or the content of a specific element (e.g., Ti) in the silicon or MXene material was determined by integrating the distribution of silicon or a specific element in the MXene material. A total of 10 regions were analyzed, and the average value was taken as the test result.

[0191] 7. Lithium-ion battery energy density and cycle life testing

[0192] The cycle test temperature is 25℃. The battery is charged at 3C constant current to the upper limit voltage, then charged at constant voltage to 0.05C, and after resting for 5 minutes, discharged at 0.33C to the lower limit voltage. The capacity obtained in this step is the initial capacity. The capacity is multiplied by the average discharge voltage and then divided by the cell volume to obtain the energy density. The 3C charge / 0.33C discharge cycle test is performed until the capacity decays to 80% SOH. The corresponding number of cycles is recorded to obtain the corresponding lifespan data.

[0193] 8. Battery expansion force test

[0194] Before test 7, after fixing the battery in the clamp of the pressure sensor, clamp it with a fixed pressure, and perform capacity calibration and cyclic testing according to the procedure in test 7. During the cycle, monitor the change of expansion force. The ratio of the increase in expansion force when the capacity decays to 80% to the initial expansion force is the change of expansion force.

[0195] Table 2 presents the test results of the negative electrode active materials and battery performance of Examples 1 to 26 and Comparative Example 1.

[0196] Table 1

[0197]

[0198]

[0199] Table 2

[0200]

[0201]

[0202] Through comparison of examples and comparative examples, it can be seen that the negative electrode active material obtained by depositing a silicon material layer on the surface of MXene three-dimensional material with a three-dimensional network framework can reduce the expansion force of the battery and improve the energy density and cycle life of lithium-ion batteries at high rates. By controlling the relevant condition parameters in the preparation process of the negative electrode active material, the performance of the negative electrode sheet and the lithium-ion battery can be adjusted, thereby obtaining a lithium-ion battery with better overall performance according to actual application requirements.

[0203] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode active material, characterized in that, include: The MXene three-dimensional material having a three-dimensional network skeleton and a silicon material layer disposed on at least a portion of the surface of the MXene three-dimensional material, wherein the MXene three-dimensional material comprises MXene material, and the general structural formula of the MXene material is M. n+1 X n Wherein, M includes at least one of Ti, Nb, V, Mo, Zr, Cr, W, and Ta; X includes at least one of C and N; n is 1, 2, or 3. The MXene three-dimensional material is MXene aerogel; the MXene aerogel also includes graphene; based on the total mass of the MXene aerogel, the mass content of graphene is 3% to 70%.

2. The negative electrode active material according to claim 1, characterized in that, The MXene material includes one or more of Ti2C and Ti3C2.

3. The negative electrode active material according to claim 1, characterized in that, The MXene material satisfies at least one of the following characteristics (1) to (3): (1) The sheet diameter of MXene is 2~10μm; (2) MXene has 1 to 5 layers; (3) The thickness of MXene sheets is 1nm~10nm.

4. The negative electrode active material according to claim 1, characterized in that, The MXene three-dimensional material satisfies at least one of the following characteristics (4) to (5): (4) The mesoporous rate of MXene three-dimensional materials is 30%~70%; (5) The density of MXene three-dimensional material is 10 mg / cm³. 3 ~60mg / cm 3 .

5. The negative electrode active material according to claim 4, characterized in that, Based on the total mass of the MXene aerogel, the mass content of the graphene is 20% to 60%.

6. The negative electrode active material according to claim 1, characterized in that, The thickness of the silicon material layer is 5nm to 100nm.

7. The negative electrode active material according to claim 6, characterized in that, The thickness of the silicon material layer is 10nm~80nm.

8. The negative electrode active material according to claim 1, characterized in that, The average volumetric particle size Dv50 of the silicon material in the silicon material layer is 2nm~30nm.

9. The negative electrode active material according to claim 8, characterized in that, The average volumetric particle size Dv50 of the silicon material in the silicon material layer is 3nm~10nm.

10. The negative electrode active material according to claim 1, characterized in that, The silicon material layer is connected to at least a portion of the surface of the MXene three-dimensional material via chemical bonds.

11. The negative electrode active material according to claim 10, characterized in that, The surface of the MXene three-dimensional material has active carbon sites formed thereon, and the silicon material layer is connected to at least a portion of the surface of the MXene three-dimensional material by bonding with the active carbon sites.

12. The negative electrode active material according to any one of claims 1 to 11, characterized in that, The negative electrode active material satisfies at least one of the following characteristics (6) to (9): (6) The average volumetric particle size Dv50 is 5μm~20μm; (7) Specific surface area is 1m² 2 / g~30m 2 / g; (8) Based on the mass of the negative electrode active material, the mass content of silicon is 1%~70%; (9) Based on the mass of the negative electrode active material, the mass content of MXene material is 30%~99%.

13. A method for preparing a negative electrode active material according to any one of claims 1 to 12, characterized in that, include: Provide the MXene three-dimensional material; The silicon material layer is formed on the MXene three-dimensional material.

14. The method for preparing the negative electrode active material according to claim 13, characterized in that, The preparation method of the MXene three-dimensional material includes the following steps: S11. Mix the MXene material, graphene oxide, dispersant, and reducing agent to obtain a mixture; S12. The mixture is subjected to a hydrothermal reaction to obtain MXene gel; S13. Freeze-dry the MXene gel to obtain MXene three-dimensional material.

15. The method for preparing the negative electrode active material according to claim 14, characterized in that, Step S11 further includes: adding a second etchant to the mixture to etch and form the active carbon sites.

16. The method for preparing the negative electrode active material according to claim 15, characterized in that, The second etchant is Ni 2+ Salt.

17. The method for preparing the negative electrode active material according to claim 15, characterized in that, The weight ratio of the second etchant to the MXene material is 0.05 to 0.

3.

18. The method for preparing the negative electrode active material according to any one of claims 13 to 17, characterized in that, The method for forming the silicon material layer includes at least one of chemical vapor deposition, physical vapor deposition, plasma spraying, and screen printing.

19. The method for preparing the negative electrode active material according to claim 18, characterized in that, The silicon material layer is formed by chemical vapor deposition.

20. A negative electrode sheet, characterized in that, Includes the negative electrode active material according to any one of claims 1-12 or the negative electrode active material prepared by the method according to any one of claims 13-19.

21. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 20.

22. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 21.

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