Silicon-based material and preparation method thereof, composite negative material, secondary battery and electric device

Abstract

The application provides a silicon-based material, a preparation method of the silicon-based material, a composite negative electrode material, a secondary battery and an electric device. The silicon-based material comprises: a silicon nanowire, wherein an axial direction of the silicon nanowire is a <111> direction. The silicon-based material provided by the application can improve the cycle life of the secondary battery.

Description

Technical Field

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

[0002] In recent years, the application of secondary batteries, represented by lithium-ion batteries, has become increasingly widespread. Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. However, currently, secondary batteries, represented by traditional lithium-ion batteries, generally suffer from poor cycle life and rate performance, failing to meet practical application needs. Summary of the Invention

[0003] The purpose of this application is to provide a silicon-based material and its preparation method, a composite negative electrode material, a secondary battery, and an electrical device, which can improve the cycle life of the secondary battery.

[0004] To achieve the above objectives, a first aspect of this application provides a silicon-based material, comprising: silicon nanowires, wherein the axial direction of the silicon nanowires is... <111> direction.

[0005] The silicon-based material provided in this application employs a clever design to make the axial expansion of silicon nanowires relatively weak. <111> The direction, that is, the silicon nanowire has a cross-section of (111). Since the cross-section of silicon nanowire is generally composed of only a dozen atoms, even if a certain stress is generated during the expansion process, the stress can be effectively released. This can effectively reduce the volume expansion of silicon during the cycle, suppress the cracking and pulverization of silicon anode during the cycle, and improve the cycle capacity retention rate of the battery.

[0006] In some embodiments of this application, the silicon nanowires satisfy at least one of the following conditions:

[0007] (1) The average diameter of the silicon nanowires is 30 nm to 50 nm;

[0008] (2) The average length of the silicon nanowire is 1 μm to 1.5 μm.

[0009] Having an average diameter within a suitable range for silicon nanowires helps shorten the diffusion path of active ions, thus improving the rate performance of the battery. Having an average length within a suitable range for silicon nanowires helps further reduce the volume expansion of silicon during cycling, thereby improving the battery's cycle capacity retention.

[0010] In some embodiments of this application, the silicon nanowires have a carbon layer on at least a portion of their surface; optionally, the thickness of the carbon layer is 170 nm to 200 nm.

[0011] The carbon layer on the surface of silicon nanowires enhances the conductivity of the silicon anode while constraining the volume expansion of the silicon nanowires, without affecting the capacity of the silicon anode. When the thickness of the carbon layer is within a suitable range, the conductivity of the silicon anode can be further improved, while the volume expansion of the silicon nanowires can be further suppressed.

[0012] In some embodiments of this application, the mass ratio of silicon to carbon in the silicon-based material is (1-3):(2-7).

[0013] Maintaining a suitable mass ratio of silicon to carbon is beneficial for maximizing the capacity provided by silicon in silicon-based materials, while also ensuring that silicon-based materials have a high capacity for transporting electrons and active ions (such as lithium ions), thereby improving the cycle capacity retention and rate performance of batteries.

[0014] In some embodiments of this application, the volume average particle size Dv50 of the silicon-based material is 200 nm to 250 nm.

[0015] The volume average particle size Dv50 of silicon-based materials is within a suitable range, which is conducive to the close contact arrangement of silicon-based materials when forming the negative electrode film, thereby increasing the content of silicon-based materials per unit volume of the negative electrode film and thus improving the energy density of the secondary battery.

[0016] A second aspect of this application also provides a method for preparing silicon-based materials, comprising:

[0017] A silicon wafer with a (111) surface is immersed in a solution containing noble metal ions and fluorine ions to deposit noble metal nanoparticles on the surface of the silicon wafer.

[0018] The silicon wafer with noble metal nanoparticles deposited on its surface is etched in an etching solution to obtain the silicon-based material, wherein the silicon-based material includes silicon nanowires, and the axial direction of the silicon nanowires is... <111> direction.

[0019] The method provided in this application involves immersing a silicon wafer with a (111) surface in a solution containing noble metal ions and fluoride ions. Through a displacement deposition reaction between fluoride ions, noble metal ions, and silicon, noble metal nanoparticles are deposited on the surface of the silicon wafer. Then, the silicon wafer with the deposited noble metal nanoparticles is placed in an etching solution. The reaction between the etching solution and silicon etches the silicon wafer, thereby preparing a silicon wafer with an axial orientation of (111). <111> Silicon nanowires with a directional orientation (i.e., a cross-section of (111) plane).

[0020] In some embodiments of this application, the method satisfies at least one of the following conditions:

[0021] (1) The precious metals include one or more of silver, gold and platinum;

[0022] (2) In the solution containing noble metal ions and fluoride ions, the concentration of the noble metal ions is 0.2 mol / L to 0.3 mol / L, and can be selected as 0.23 mol / L to 0.25 mol / L;

[0023] (3) In the solution containing noble metal ions and fluoride ions, the concentration of fluoride ions is 25% to 35%;

[0024] (4) The silicon wafer is immersed in the solution containing noble metal ions and fluoride ions for 25s to 35s.

[0025] The precious metal selected in this application, after forming precious metal nanoparticles on the surface of a silicon wafer, can protect the silicon wafer portion in contact with it during etching with an etching solution, preventing that portion from being corroded by the etching solution, thereby forming an axial shape. <111> Directional silicon nanowires.

[0026] In some embodiments of this application, the method satisfies at least one of the following conditions:

[0027] (1) The etching solution includes hydrogen peroxide solution and / or hydrofluoric acid solution;

[0028] Optionally, the mass percentage of hydrogen peroxide in the hydrogen peroxide solution is 20% to 23%;

[0029] Optionally, the hydrofluoric acid solution contains 28% to 31% hydrofluoric acid by mass.

[0030] (2) The etching time is 270s to 330s.

[0031] In the etching solution, the mass percentage of solute hydrogen peroxide or hydrofluoric acid is controlled within an appropriate range. This allows for a sufficient replacement reaction with silicon, achieving thorough etching of the silicon wafer without causing corrosion or other effects on the precious metal nanoparticles on the silicon wafer surface.

[0032] In some embodiments of this application, the method further includes:

[0033] The silicon nanowires are subjected to carbon coating treatment to form a carbon layer on at least a portion of the surface of the silicon nanowires;

[0034] Optionally include:

[0035] The silicon nanowires were placed in an atmosphere containing a carbon source.

[0036] The silicon nanowires are subjected to heat treatment.

[0037] By carbon coating silicon nanowires, a carbon layer can be formed on at least a portion of the surface of the silicon nanowires.

[0038] In some embodiments of this application, the method satisfies at least one of the following conditions:

[0039] (1) The carbon source includes one or more of methane, ethylene, acetylene, methanol, ethanol, benzene and toluene;

[0040] (2) The heat treatment includes: heating the silicon nanowire from 25°C to 900°C to 1000°C at a rate of 5°C / min to 15°C / min, and then holding it at that temperature for 30 min to 40 min.

[0041] Controlling the heat treatment conditions within a suitable range is beneficial to the decomposition of the carbon source and allows the carbon elements formed after decomposition to be dispersed and deposited on at least part of the surface of the silicon nanowires, forming a carbon layer of suitable thickness.

[0042] In some embodiments of this application, the carbon coating process further includes:

[0043] The carbon source is subjected to bubbling treatment;

[0044] Optionally, the bubbling rate of the bubbling treatment is 200 mL / min to 300 mL / min.

[0045] Bubbling treatment can generate porous carbon on the surface of silicon nanowires. The interlaced channels can provide a high-speed pathway for active ions (such as lithium ions) to diffuse to the surface of silicon nanowires. In addition, the porous structure of carbon can promote the release of stress after the silicon nanowires expand, reducing the volume expansion rate of the negative electrode.

[0046] A third aspect of this application provides a composite anode material, including the silicon-based material of the first aspect of this application or the silicon-based material prepared by the method of the second aspect of this application.

[0047] In some embodiments of this application, the composite negative electrode material further includes a carbon material; optionally, the carbon material includes at least one of graphite, soft carbon, and hard carbon.

[0048] In some embodiments of this application, the composite negative electrode material further includes a conductive agent, which optionally includes one or more of carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0049] In some embodiments of this application, the mass ratio of the silicon-based material to the conductive agent in the composite negative electrode material is (82-88):(8-2).

[0050] When the mass ratio of silicon-based materials to conductive agents is within a suitable range, the composite anode material can possess both high conductivity and good flexibility, which is beneficial for effectively buffering volume expansion during cycling and improving the cycle life of the battery.

[0051] The fourth aspect of this application provides a secondary battery including a negative electrode sheet, wherein the negative electrode sheet includes one of the silicon-based material of the first aspect of this application, a silicon-based material prepared by the method of the second aspect of this application, or a composite negative electrode material of the third aspect of this application.

[0052] The fifth aspect of this application provides an electrical device including a secondary battery as described in the fourth aspect of this application.

[0053] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0054] Figure 1 It is the time when silicon anode is lithiated <110> A schematic diagram of directional expansion.

[0055] Figure 2 This is a TEM image of a silicon-based material according to an embodiment of this application.

[0056] Figure 3 This is an XRD pattern of a silicon-based material according to an embodiment of this application.

[0057] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0058] Figure 5 yes Figure 4 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0059] Figure 6 This is a schematic diagram of a secondary battery according to another embodiment of this application.

[0060] Figure 7 This is a schematic diagram of a secondary battery according to another embodiment of this application.

[0061] Figure 8 yes Figure 7 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0062] Figure 9 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.

[0063] Explanation of reference numerals in the attached figures:

[0064] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0065] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the silicon-based materials and their preparation methods, composite negative electrode materials, secondary batteries, and power-consuming devices 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 the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0066] 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.

[0067] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0068] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0069] 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.

[0070] 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.

[0071] 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).

[0072] In recent years, industries such as energy storage and military have placed new demands on high-energy-density lithium-ion batteries, in which anode materials play a crucial role. Since the commercialization of rechargeable batteries, represented by lithium-ion batteries, carbon-based materials have maintained a core position in the anode field. However, their low energy density makes it difficult to meet the growing market demand. Silicon materials, with their high theoretical specific capacity of 4200 mAh / g and low lithium intercalation potential (~0.4V vs. Li), offer a more competitive alternative. + Silicon (Si) is a leading candidate for next-generation lithium-ion battery anode materials. However, the inventors discovered that single-component silicon materials have limitations in their widespread market application due to the following drawbacks. First, in terms of electronic transport, silicon's conductivity is only 10⁻⁶ ppm. -3The conductivity of silicon anodes is significantly lower than that of graphite, reaching approximately 20 S / cm, while commercially available graphite can achieve similar levels. This much lower conductivity makes silicon anodes prone to significant polarization during high-rate charge-discharge cycles, hindering their high-capacity performance and reducing the battery's rate capability. Secondly, silicon anodes experience dramatic volume expansion (~300%) during battery cycling. This drastic volume change causes irreversible damage, such as active particle pulverization, electrical contact failure, and detachment from the current collector, resulting in poor cycle capacity retention and ultimately battery failure. Finally, the SEI (solid electrolyte interphase) on the surface of the silicon anode is highly unstable, repeatedly cracking and even detaching during electrode volume expansion. Repeated charge-discharge cycles cause the electrode surface to continuously consume active lithium and electrolyte, generating new SEI, ultimately leading to the depletion of active lithium and electrolyte and reducing battery cycle life.

[0073] To address the aforementioned issues, this application proposes a silicon-based material that, by orienting silicon nanowires, can suppress cracking and pulverization of the silicon anode during cycling, thereby improving its capacity retention during cycling. Simultaneously, coating the surface of the silicon nanowires with a carbon layer can enhance the electron and active ion (such as lithium ion) transport performance of the silicon anode, thereby improving its rate performance.

[0074] Silicon-based materials

[0075] A first aspect of this application discloses a silicon-based material, comprising: silicon nanowires, wherein the axial direction of the silicon nanowires is... <111> direction.

[0076] Not intended to be limited to any theory, silicon follows a path during lithiation. <110> directional expansion is intense (e.g.) Figure 1 (as shown), but along <111> The axial expansion is relatively weak. Therefore, the silicon-based material provided in this application, through ingenious design, makes the axial expansion of the silicon nanowires relatively weak. <111> The direction, that is, the silicon nanowire has a cross-section of (111). Since the cross-section of silicon nanowire is generally composed of only a dozen atoms, even if a certain stress is generated during the expansion process, the stress can be effectively released. This can effectively reduce the volume expansion of silicon during the cycle, suppress the cracking and pulverization of silicon anode during the cycle, and improve the cycle capacity retention rate of the battery.

[0077] Furthermore, by suppressing the volume expansion of silicon during cycling, it is also beneficial to suppress the repeated cracking of the SEI on the surface of the silicon anode caused by volume expansion, reduce the continuous consumption of active lithium and electrolyte on the anode surface, and improve the cycle life of the battery.

[0078] Furthermore, the silicon nanowires have a carbon layer on at least a portion of their surface. When the silicon nanowires are also coated with a carbon layer, it can not only improve conductivity but also help form a more stable SEI on the negative electrode surface, providing constraint on the silicon nanowires and further suppressing their volume expansion.

[0079] In some embodiments, the average diameter of the silicon nanowires is 30 nm to 50 nm. For example, the average diameter of the silicon nanowires can be 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, or within any range of these values. Having an average diameter within a suitable range is beneficial for shortening the diffusion path of active ions and improving the rate performance of the battery.

[0080] In some embodiments, the average length of the silicon nanowires is 1 μm to 1.5 μm. For example, the average length of the silicon nanowires can be 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or within any range of these values. Having an average length within a suitable range is beneficial for further reducing the volume expansion of silicon during cycling and improving the cycle capacity retention of the battery.

[0081] The average diameter and average length of silicon nanowires have meanings known in the art and can be measured using instruments and methods known in the art. For example, they can be measured using a transmission electron microscope (TEM).

[0082] In some embodiments, the aspect ratio of the silicon nanowires is 37.5 to 40.5. For example, the aspect ratio of the silicon nanowires can be 37.5, 38, 38.5, 39, 39.5, 40, 40.5, or any range thereof. Controlling the aspect ratio of the silicon nanowires within a suitable range shortens the transport path of active ions, improves rate performance, and further reduces the volume expansion of silicon during cycling, thereby improving the cycle capacity retention and cycle life of the battery.

[0083] In some embodiments, the thickness of the carbon layer is 170 nm to 200 nm. For example, the thickness of the carbon layer can be 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, or within any range of these values. A suitable carbon layer thickness improves the conductivity of the silicon anode while constraining the volume expansion of the silicon nanowires, without affecting the capacity of the silicon anode.

[0084] The thickness of the carbon layer is a term known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a transmission electron microscope (TEM).

[0085] In some embodiments, the mass ratio of silicon to carbon in the silicon-based material is (1-3):(2-7). For example, the mass ratio of silicon to carbon can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 2:3, 2:5, 2:7, 3:2, 3:4, 3:5, 3:7, or any range of the above values. Maintaining a suitable mass ratio of silicon to carbon is beneficial for maximizing the capacity provided by silicon in the silicon-based material and also ensures that the silicon-based material has a high level of electron and active ion (such as lithium ion) transport capability, thereby improving the cycle capacity retention and rate performance of the battery.

[0086] The mass ratio of silicon to carbon in silicon-based materials is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, an EDS spectrometer can be used to measure this ratio, allowing for quantitative analysis of the mass ratio of silicon to carbon in silicon-based materials.

[0087] In some embodiments, the volume average particle size Dv50 of the silicon-based material is 200 nm to 250 nm. For example, the volume average particle size Dv50 of the silicon-based material can be 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, or within any range of these values. A suitable range for the volume average particle size Dv50 of the silicon-based material facilitates close contact and arrangement of the silicon-based material during the formation of the negative electrode film, thereby increasing the silicon-based material content per unit volume of the negative electrode film and thus improving the energy density of the secondary battery.

[0088] The volume average particle size Dv50 of silicon-based materials is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0089] A second aspect of this application also provides a method for preparing silicon-based materials, which may include the following steps:

[0090] S10. Immerse a silicon wafer with a (111) surface in a solution containing noble metal ions and fluorine ions to deposit noble metal nanoparticles on the surface of the silicon wafer.

[0091] S20. The silicon wafer with noble metal nanoparticles deposited on its surface is etched in an etching solution to obtain the silicon-based material, wherein the silicon-based material includes silicon nanowires, and the axial direction of the silicon nanowires is... <111> direction.

[0092] The method provided in this application involves immersing a silicon wafer with a (111) surface in a solution containing noble metal ions and fluoride ions. Through a displacement deposition reaction between fluoride ions, noble metal ions, and silicon, noble metal nanoparticles are deposited on the surface of the silicon wafer. Then, the silicon wafer with the deposited noble metal nanoparticles is placed in an etching solution. The reaction between the etching solution and silicon etches the silicon wafer, thereby preparing a silicon wafer with an axial orientation of (111). <111> Silicon nanowires with a directional orientation (i.e., a cross-section of (111) plane).

[0093] In some embodiments, the displacement reaction in step S10 above can be exemplified by the following formulas (1) and (2):

[0094] 4F - +Si+4H + →SiF4(g)↑+4H· (1)

[0095] H·+Ag + +OH - →Ag + H₂O (2)

[0096] It should be noted that H· in the above formulas (1) and (2) represents proton hydrogen. The proton hydrogen (H·) generated in reaction (1) can reduce noble metal ions in the solution to noble metals, as shown in reaction (2), thereby realizing the displacement deposition of noble metal nanoparticles on the silicon wafer surface.

[0097] In some embodiments, the precious metal includes one or more of silver, gold, and platinum. The precious metal selected in this application, after forming precious metal nanoparticles on the silicon wafer surface, can protect the silicon wafer portion in contact with it during etching with an etching solution, preventing that portion from being corroded by the etching solution, thereby forming an axial [missing information]. <111> Directional silicon nanowires.

[0098] In some embodiments, the concentration of the noble metal ions in the solution containing noble metal ions and fluoride ions is 0.2 mol / L to 0.3 mol / L. For example, the concentration of the noble metal ions can be 0.22 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L, or within any range of the above values. Optionally, the concentration of the noble metal ions is 0.23 mol / L to 0.25 mol / L. A suitable concentration of noble metal ions within this range facilitates a displacement reaction between the ions and the silicon wafer and fluoride ions, thereby forming noble metal nanoparticles on the silicon wafer surface.

[0099] In some embodiments, the reactants providing the fluoride ions may include, but are not limited to, hydrofluoric acid and fluoride salts, such as sodium fluoride, potassium fluoride, etc.

[0100] In some embodiments, the concentration of fluoride ions in the solution containing noble metal ions and fluoride ions is 25% to 35%. For example, the concentration of fluoride ions can be 25%, 27%, 29%, 31%, 33%, 35%, or within any range of these values. A suitable concentration of fluoride ions in the solution allows for an effective displacement reaction with silicon; when the concentration of fluoride ions is relatively low, displacement deposition with silicon may not easily occur; when the concentration of fluoride ions is relatively high, it may cause some corrosion to the formed noble metal nanoparticles.

[0101] In some embodiments, the silicon wafer is immersed in the solution containing noble metal ions and fluoride ions for 25 to 35 seconds. For example, the immersion time can be 27, 29, 31, or 33 seconds, or any value within this range. Controlling the immersion time of the silicon wafer in the solution containing noble metal ions and fluoride ions within a suitable range ensures the sufficient conduct of the displacement deposition reaction without affecting the formed noble metal nanoparticles.

[0102] In some embodiments, the etching solution includes a hydrogen peroxide solution and / or a hydrofluoric acid solution. The etching solution described above in this application can achieve sufficient etching of the silicon wafer through a displacement reaction with silicon, thereby obtaining silicon nanowires.

[0103] In some embodiments, the mass percentage of hydrogen peroxide in the hydrogen peroxide solution is 20% to 23%. For example, the mass percentage of hydrogen peroxide in the hydrogen peroxide solution can be 20%, 21%, 22%, 23%, or within any range of the above values.

[0104] In some embodiments, the hydrofluoric acid solution contains 28% to 31% by mass. For example, the hydrofluoric acid solution may contain 29%, 29.5%, 30% by mass, or any of the above values.

[0105] In the above-mentioned etching solution, the mass percentage of the solute hydrogen peroxide or hydrofluoric acid is controlled within an appropriate range. This allows for a sufficient replacement reaction with silicon, achieving thorough etching of the silicon wafer without causing corrosion or other effects on the precious metal nanoparticles on the silicon wafer surface.

[0106] In some embodiments, the etching time is 270 s to 330 s. For example, the etching time can be 280 s, 290 s, 300 s, 310 s, 320 s, or any range of these values. An etching time within a suitable range is beneficial for fully realizing the displacement reaction between silicon and the etching solution, resulting in a sufficient number of silicon nanowires.

[0107] In some embodiments, the method may further include the following step S30:

[0108] S30. The silicon nanowires are subjected to carbon coating treatment to form a carbon layer on at least a portion of the surface of the silicon nanowires.

[0109] In some embodiments, step S30 may optionally include the following steps:

[0110] S310. Place the silicon nanowires in an atmosphere of carbon source;

[0111] S320. The silicon nanowires are subjected to heat treatment.

[0112] It is understandable that the aforementioned carbon coating process can be performed in a CVD (chemical vapor deposition) growth apparatus. When performed in a CVD growth apparatus, the carbon coating process can be controlled by adjusting the amount of carbon source introduced.

[0113] In some embodiments, the heat treatment includes heating the silicon nanowires from 25°C to 900°C to 1000°C at a rate of 5°C / min to 15°C / min, and then holding at that temperature for 30 min to 45 min. Controlling the heat treatment parameters within a suitable range is beneficial for the decomposition of the carbon source and allows the carbon elements formed after decomposition to be dispersed and deposited on at least a portion of the surface of the silicon nanowires, forming a carbon layer of suitable thickness.

[0114] In this application, the type of carbon source is not particularly limited and can be selected according to actual needs, as long as it can provide carbon elements. For example, the carbon source can be a gaseous or liquid organic compound. The gaseous organic compound can include one or more of methane, ethylene, and acetylene; the liquid organic compound can include one or more of methanol, ethanol, benzene, and toluene.

[0115] It is understood that when the carbon source is a liquid phase (e.g., methanol, ethanol, benzene, or toluene), step S30, which involves carbon coating the silicon nanowires, may further include the following steps:

[0116] S330. The carbon source is subjected to bubbling treatment.

[0117] In some embodiments, a mixture of hydrogen and an inert gas can be introduced into the carbon source to perform bubbling treatment on the carbon source, wherein the proportion of hydrogen in the mixture does not exceed 5%. Optionally, the type of inert gas is not particularly limited and can be selected according to actual needs. For example, the inert gas can be argon, helium, neon, and combinations thereof.

[0118] In this application, the bubbling process can generate porous carbon on the surface of silicon nanowires. The interlaced channels can provide a high-speed pathway for active ions (such as lithium ions) to diffuse to the surface of silicon nanowires. In addition, the porous structure of carbon can promote the release of stress after the silicon nanowires expand, thereby reducing the volume expansion rate of the negative electrode.

[0119] In some embodiments, the bubbling rate of the bubbling treatment is 200 mL / min to 300 mL / min. For example, the bubbling rate of the bubbling treatment can be 220 mL / min, 240 mL / min, 260 mL / min, 280 mL / min, or within any range of the above values.

[0120] As a non-limiting example of step S30, silicon nanowires can be placed in a CVD growth apparatus and decomposed using ethanol as a carbon source to achieve carbon coating on the surface of the silicon nanowires. Specifically, silicon nanowires can be placed in a tube furnace of a CVD growth apparatus, and a mixture of hydrogen and argon gas can be bubbled into ethanol with a hydrogen content of 5% and a bubbling rate of 200 ml / min to 300 ml / min. Heating can be started from room temperature of 25°C at a heating rate of 5°C / min, and the temperature can be raised to 900°C and held for 30 min. After natural cooling to room temperature, the gas flow can be stopped, and the reaction product can be removed. The final material can be washed three times with deionized water and ethanol, filtered, and dried at 80°C for 12 h to obtain silicon-based material.

[0121] Composite anode materials

[0122] A third aspect of this application provides a composite anode material, including the silicon-based material of the first aspect of this application or the silicon-based material prepared by the method of the second aspect of this application.

[0123] In some embodiments, the composite negative electrode material further includes a carbon material. Optionally, the carbon material includes at least one of graphite, soft carbon, and hard carbon.

[0124] In some embodiments, the composite negative electrode material further includes a conductive agent. Optionally, the conductive agent includes one or more of carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0125] The composite anode material provided in this application, by mixing silicon-based materials with a conductive agent, can form a stable cross-linked structure, giving the composite anode material a certain degree of flexibility. This provides a buffer for drastic changes in anode volume during subsequent cycling, enhancing the mechanical stability of the anode. Simultaneously, selecting the aforementioned conductive agent to composite with the silicon-based anode material can also improve the conductivity of the silicon-based material, enabling the composite anode material to possess both high conductivity and good mechanical stability.

[0126] In some embodiments, the mass ratio of the silicon-based material to the conductive agent in the composite negative electrode material is (82-88):(8-2). For example, the mass ratio of the silicon-based material to the conductive agent can be 82:8, 82:7, 82:6, 82:5, 82:4, 82:3, 82:2, 84:8, 84:7, 84:6, 84:5, 84:4, 84:3, 84:2, 86:8, 86:7, 86:6, 86:5, 86:4, 86:3, 86:2, 88:8, 88:7, 88:6, 88:5, 88:4, 88:3, 88:2, or within any range of the above values.

[0127] When the mass ratio of silicon-based materials to conductive agents is within a suitable range, the composite anode material can possess both high conductivity and good flexibility, which is beneficial for effectively buffering volume expansion during cycling and improving the cycle life of the battery.

[0128] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0129] In one embodiment of this application, a secondary battery is provided.

[0130] 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.

[0131] [Positive electrode plate]

[0132] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0133] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0134] 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.).

[0135] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. 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 battery positive electrode active materials 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 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At 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.

[0136] In some embodiments, the positive electrode active material may also include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue 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.

[0137] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0138] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0139] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0140] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n-The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0141] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0142] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0143] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0144] In some embodiments, the positive electrode film 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.

[0145] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as 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 the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0146] The positive electrode sheet of this application does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0147] [Negative electrode plate]

[0148] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which may include the silicon-based material of the first aspect of this application and / or the composite negative electrode material of the third aspect of this application.

[0149] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0150] 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 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 (copper, copper 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.).

[0151] In some embodiments, the negative electrode active material does not exclude other negative electrode active materials besides the silicon-based materials and composite negative electrode materials provided in this application. For example, in some embodiments, the negative electrode active material may also be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material 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 material 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.

[0152] In some embodiments, the negative electrode film 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).

[0153] In some embodiments, the negative electrode film 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.

[0154] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0155] 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, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0156] The negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film 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 film layer.

[0157] [Electrolytes]

[0158] 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.

[0159] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] [Isolation membrane]

[0164] 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.

[0165] 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.

[0166] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0167] 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.

[0168] 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 material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0169] 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 4 This is an example of a square-structured secondary battery 5.

[0170] In some implementations, refer to Figure 5The 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. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or 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.

[0171] In some embodiments, the secondary battery may also be a battery module assembled from multiple battery cells. The number of battery cells in the battery module may be multiple, and the specific number may be adjusted by those skilled in the art according to the application and capacity of the battery module.

[0172] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the average 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.

[0173] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0174] 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.

[0175] In some implementations, the aforementioned battery cells can also be directly assembled into a battery pack, and the number of battery cells contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0176] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 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.

[0177] 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 a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0178] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0179] Figure 9 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0180] 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.

[0181] Example

[0182] 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.

[0183] Example 1

[0184] Preparation of silicon-based materials

[0185] The silicon wafer with the (111) surface was washed with deionized water and then dried in a drying oven at 80°C for 3 hours for later use. Solution 1 was prepared for later use, which contained 500 ml of AgNO3 solution with a concentration of 0.24 mol / L and 50 g of HF solution with a concentration of 30%. Solution 2 was prepared for later use, which contained 10 ml of H2O2 solution with a concentration of 20%, 50 g of HF solution with a concentration of 30% and 400 ml of deionized water.

[0186] A silicon wafer was immersed in solution 1 to deposit silver nanoparticles onto its surface for 30 seconds. Then, the silicon wafer with deposited silver nanoparticles was transferred to solution 2 for etching for 300 seconds to prepare silicon nanowires. Finally, the nanowires were cleaned with deionized water and ethanol and then placed in a vacuum drying oven at 80°C for 8 hours to dry.

[0187] The dried silicon nanowires were placed in a CVD growth apparatus, and ethanol was used as the carbon source for decomposition to achieve carbon coating on the surface of the silicon nanowires. The CVD growth apparatus was a tube furnace reactor, into which a hydrogen-argon mixture was bubbled into ethanol. The hydrogen content was 5%, and the bubbling rate was 200 ml / min–300 ml / min. Heating began at room temperature (25°C) at a rate of 5°C / min, reaching 900°C and holding for 30 min. After natural cooling to room temperature, the gas flow was stopped, and the reaction product was removed. The final material was washed three times with deionized water and ethanol, filtered, and dried at 80°C for 12 h to obtain the silicon-based material.

[0188] Preparation of button cells

[0189] (1) Negative electrode sheet: The silicon-based material, carbon nanotubes, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) prepared above are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 85:5:5:5 to form a negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained.

[0190] (2) Counter electrode: lithium metal sheet.

[0191] (3) Separation film: polyethylene (PE) film.

[0192] (4) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1. Then, LiPF6 is uniformly dissolved in the above solution to obtain the electrolyte. Fluoroethylene carbonate (FEC) is added, wherein the concentration of LiPF6 is 1 mol / L and the mass percentage of FEC in the electrolyte is 6%.

[0193] (5) Preparation of button cell: The negative electrode, separator and lithium metal counter electrode are stacked in sequence, and the electrolyte is added to obtain a button cell.

[0194] Examples 2-18

[0195] The preparation methods of Examples 2-18 are similar to those of Example 1, except that the silicon-based materials and related parameters in their preparation process were adjusted. Specific parameters are detailed in Table 1 below. " / " indicates that the corresponding parameter does not exist.

[0196] Comparative Example 1

[0197] The preparation of the button cell is similar to that in Example 1, except that when preparing the negative electrode sheet, conventional elemental silicon of equal mass is used instead of silicon-based material.

[0198] Comparative Example 2

[0199] The fabrication of the coin cell is similar to that in Example 1, except that silicon nanowires 1 of equal mass are used instead of silicon-based material when fabricating the negative electrode. The silicon nanowires 1 have a similar structure to the silicon-based material in Example 1, the only difference being that the axial direction of the silicon nanowires 1 is... <110> direction.

[0200] Table 1

[0201]

[0202]

[0203] In addition, the silicon-based materials and coin cells obtained in Examples 1 to 18 and Comparative Examples 1 to 2 were subjected to relevant performance tests, and the test results are shown in Table 2 below.

[0204] Test section

[0205] (1) XRD testing of silicon-based materials

[0206] X-ray diffractometer model X'Pert MAD XL was used to perform crystal phase analysis on silicon-based materials.

[0207] (2) TEM testing of silicon-based materials

[0208] The morphology and composition distribution of silicon nanowires, as well as the axial distribution of silicon nanowires, were observed and tested using a Talos F200X S transmission electron microscope.

[0209] (3) Cyclic capacity retention test

[0210] The battery capacity retention test process is as follows: At 25℃, the voltage window for charging and discharging is maintained at 0.01V~3V. The lithium-ion battery is discharged at a constant current of 0.2C to 0.01V, and then charged at a constant current to 3V. This is one charge-discharge cycle, and the discharge capacity at this time is recorded as D01. After repeating the above charge-discharge process for 50 cycles, the capacity of the 50th cycle is recorded as D1.

[0211] The capacity retention rate of a lithium-ion battery after 50 cycles = D1 / D01 × 100%.

[0212] (4) Cyclic life test

[0213] The cycle test temperature is 25℃. The lithium-ion battery is charged at a constant current of 0.33C to the upper limit voltage, then charged at a constant voltage to 0.05C. After standing for 5 minutes, it is discharged at 0.33C to the lower limit voltage. The 0.33C 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 cycle life data.

[0214] Table 2

[0215]

[0216] Table 2 above shows that, compared with Comparative Example 1, the silicon-based material provided in this application can significantly improve the capacity retention and cycle performance of the battery compared with elemental silicon. Comparing the examples with Comparative Example 2 shows that when the axial direction of the silicon nanowires in Comparative Example 2 is non-axial... <111> direction( <110> When the axial direction is (not specified), its capacity retention and cycle count are significantly lower than in the example, indicating that the axial direction is (not specified). <111> Direction can improve battery cycle performance.

[0217] 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 silicon-based material, characterized in that, include: Silicon nanowires, wherein the axial direction of the silicon nanowires is... <111> The silicon nanowires are oriented with a (111) plane as the cross-section, and the average length of the silicon nanowires is 1μm~1.5μm, and the average diameter of the silicon nanowires is 30nm~50nm.

2. The silicon-based material according to claim 1, characterized in that, The silicon nanowires have a carbon layer on at least a portion of their surface.

3. The silicon-based material according to claim 2, characterized in that, The thickness of the carbon layer is 170nm~200nm.

4. The silicon-based material according to any one of claims 1 to 3, characterized in that, In the silicon-based material, the mass ratio of silicon to carbon is (1~3):(2~7).

5. The silicon-based material according to any one of claims 1 to 3, characterized in that, The volume average particle size Dv50 of the silicon-based material is 200nm~250nm.

6. A method for preparing silicon-based materials, characterized in that, include: A silicon wafer with a (111) surface is immersed in a solution containing noble metal ions and fluorine ions to deposit noble metal nanoparticles on the surface of the silicon wafer. The silicon wafer with noble metal nanoparticles deposited on its surface is etched in an etching solution to obtain the silicon-based material, wherein the silicon-based material includes silicon nanowires, and the axial direction of the silicon nanowires is... <111> The silicon nanowires are oriented with a (111) plane as the cross-section, and the average length of the silicon nanowires is 1μm~1.5μm, and the average diameter of the silicon nanowires is 30nm~50nm.

7. The method according to claim 6, characterized in that, The method satisfies at least one of the following conditions: (1) The precious metals include one or more of silver, gold and platinum; (2) In the solution containing noble metal ions and fluoride ions, the concentration of the noble metal ions is 0.2 mol / L to 0.3 mol / L; (3) In the solution containing noble metal ions and fluoride ions, the concentration of fluoride ions is 25%~35%; (4) The silicon wafer is immersed in the solution containing noble metal ions and fluoride ions for 25s to 35s.

8. The method according to claim 7, characterized in that, In the solution containing noble metal ions and fluoride ions, the concentration of the noble metal ions is 0.23 mol / L to 0.25 mol / L.

9. The method according to any one of claims 6 to 8, characterized in that, The method satisfies at least one of the following conditions: (1) The etching solution includes hydrogen peroxide solution and / or hydrofluoric acid solution; (2) The etching time is 270s~330s.

10. The method according to claim 9, characterized in that, One or more of the following conditions must be met: (1) The mass percentage of hydrogen peroxide in the hydrogen peroxide solution is 20%~23%; (2) The hydrofluoric acid in the hydrofluoric acid solution is 28%~31% by mass.

11. The method according to any one of claims 6 to 8, characterized in that, Also includes: The silicon nanowires are carbon-coated to form a carbon layer on at least a portion of the surface of the silicon nanowires.

12. The method according to claim 11, characterized in that, The silicon nanowires are subjected to carbon coating treatment to form a carbon layer on at least a portion of the surface of the silicon nanowires, comprising: The silicon nanowires were placed in an atmosphere containing a carbon source. The silicon nanowires are subjected to heat treatment.

13. The method according to claim 12, characterized in that, The method satisfies at least one of the following conditions: (1) The carbon source includes one or more of methane, ethylene, acetylene, methanol, ethanol, benzene, and toluene; (2) The heat treatment conditions include: heating the silicon nanowires from 25°C to 900°C to 1000°C at a rate of 5°C / min to 15°C / min, and then holding the temperature for 30 min to 45 min.

14. The method according to claim 12, characterized in that, The carbon coating process further includes bubbling the carbon source.

15. The method according to claim 14, characterized in that, The bubbling rate of the bubbling treatment is 200 mL / min to 300 mL / min.

16. A composite negative electrode material, characterized in that, Includes the silicon-based material as described in any one of claims 1-5 or the silicon-based material prepared by the method described in any one of claims 6-15.

17. The composite negative electrode material according to claim 16, characterized in that, The composite anode material also includes carbon materials.

18. The composite negative electrode material according to claim 17, characterized in that, The carbon material includes at least one of graphite, soft carbon, and hard carbon.

19. The composite negative electrode material according to claim 16 or 17, characterized in that, The composite negative electrode material also includes a conductive agent.

20. The composite negative electrode material according to claim 19, characterized in that, The conductive agent includes one or more of carbon nanotubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

21. The composite negative electrode material according to claim 19, characterized in that, In the composite negative electrode material, the mass ratio of the silicon-based material to the conductive agent is (82~88):(8~2).

22. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes at least one of the silicon-based material according to any one of claims 1-5, the silicon-based material prepared by the method according to any one of claims 6-15, or the composite negative electrode material according to any one of claims 16-21.

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

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