Silicon-oxygen-carbon composite material, preparation method thereof, negative electrode material, negative electrode sheet and lithium ion battery

Abstract

The application discloses a silicon-oxygen-carbon composite material and a preparation method thereof, a negative electrode raw material, a negative electrode sheet and a lithium ion battery, and belongs to the field of electrode materials. The silicon-oxygen-carbon composite material comprises a core and an outer layer, and the outer layer comprises a carbon coating layer and a plurality of carbon protrusions. The core is a silicon-oxygen material doped with a metal. The carbon coating layer is coated outside the core, and the plurality of carbon protrusions are formed on the outer surface of the carbon coating layer. The silicon-oxygen-carbon composite material disclosed by the application can significantly improve the reversible capacity, the initial efficiency, the rate performance and the cycle stability of the lithium ion battery based on the synergistic effect of the metalized core, the carbon coating layer with uniform thickness and the plurality of carbon protrusions distributed outside the carbon coating layer.

Description

Technical Field

[0001] This disclosure relates to the field of electrode materials, and in particular to silicon-oxygen-carbon composite materials and their preparation methods, negative electrode raw materials, negative electrode sheets, and lithium-ion batteries. Background Technology

[0002] Silicon possesses a theoretical specific capacity as high as 4200 mAh / g, making silicon-based anode materials crucial for developing high-energy-density lithium-ion batteries. However, silicon-based anode materials exhibit a large coefficient of volume expansion, with volume changes reaching up to 300% during lithiation / delithiation. This volume change leads to pulverization and fragmentation of the silicon-based anode material during charge-discharge cycles, limiting the reversible capacity, coulombic efficiency, and cycle stability of lithium-ion batteries.

[0003] Silicon-oxygen materials are a type of silicon-based anode material. Due to their high oxygen content, they exhibit significant irreversible capacity and low coulombic efficiency during the initial lithium insertion process. Related technologies utilize carbon sources to construct a carbon coating layer on the exterior of the silicon-oxygen material, forming a carbon-coated silicon-based anode material. This carbon coating layer mitigates the volume effect of silicon, reduces direct interfacial contact and side reactions between silicon and the electrolyte, and increases the surface conductivity of silicon, thereby reducing silicon volume expansion and increasing the initial efficiency and capacity of the silicon-based anode material. Methods for constructing the carbon coating layer include: solid / liquid phase hybrid carbonization (e.g., using pitch or resin as the carbon source), gas-phase pyrolysis (e.g., using acetylene or methane as the carbon source), emulsion polymerization (e.g., using polyacrylonitrile as the carbon source), and high-temperature pyrolysis (e.g., using polyvinyl alcohol or polyvinylidene fluoride as the carbon source).

[0004] However, the carbon-coated silicon-based anode materials provided by related technologies have limited effect on improving the reversible capacity, initial coulombic efficiency, rate performance, and cycle stability of silicon-based anode materials.

[0005] Public content

[0006] In view of this, this disclosure provides silicon-oxygen-carbon composite materials and their preparation methods, negative electrode raw materials, negative electrode sheets, and lithium-ion batteries, which can solve the above-mentioned technical problems.

[0007] Specifically, the following technical solutions are included:

[0008] On one hand, a silicon-oxygen-carbon composite material is provided, the silicon-oxygen-carbon composite material comprising: a core and an outer layer, the outer layer comprising: a carbon coating layer and a plurality of carbon protrusions;

[0009] The core is a silicon-oxygen material doped with metal;

[0010] The carbon coating layer covers the outside of the core, and the plurality of carbon protrusions are formed on the outer surface of the carbon coating layer.

[0011] The silicon-oxygen-carbon composite material provided in this disclosure has a core of silicon-oxygen material doped with metal. The doping of the metal into the silicon-oxygen material metallizes the silicon-oxygen material, which is beneficial to improving the conductivity and rate performance of the core. At the same time, some of the doped metal can stably combine with oxygen in the silicon-oxygen material, avoiding the irreversible loss of lithium ions by oxygen elements during the electrochemical lithium intercalation process of silicon-based anode materials, thereby improving the reversible capacity, first efficiency and cycle stability of silicon-based lithium-ion batteries.

[0012] The silicon-oxygen-carbon composite material provided in this embodiment includes an outer layer comprising a carbon coating layer and a plurality of carbon protrusions formed on the outside of the carbon coating layer. The plurality of carbon protrusions increase the specific surface area of ​​the outer layer to improve the wettability of the outer layer with the electrolyte, promote the lithium-ion diffusion and charge transfer performance on the surface of the silicon-based anode material, thereby enhancing the interfacial charge transfer capability of the silicon-oxygen-carbon composite material, which is beneficial to improving the rate performance and cycle stability of lithium-ion batteries.

[0013] The silicon-oxygen-carbon composite material provided in this disclosure includes both carbon and metal elements. Thus, during the preparation of the silicon-oxygen-carbon composite material, carbon and metal sources can be mixed with silicon-oxygen materials in the form of metal-carbon source complexes. The metal atoms in the metal source can react with the silicon-oxygen material to form a metal-doped silicon-oxygen material. The carbon source can be adsorbed and deposited on the surface of the silicon-oxygen material using metal atoms as active sites to form a carbon coating layer. This strong deposition and adsorption effect of the carbon source on the surface of the silicon-oxygen material facilitates the uniform deposition of the carbon coating layer, forming a uniform and dense carbon coating layer. The uniform coating layer avoids side reactions caused by silicon exposure in the electrolyte due to uneven coating, thus improving the cycle stability of the silicon-based anode material. When used in lithium-ion batteries, this uniformly thick carbon coating layer not only effectively prevents contact between the electrolyte and the silicon-oxygen material but also ensures uniform lithium intercalation, which also helps improve the reversible capacity, initial efficiency, rate performance, and cycle stability of the lithium-ion battery.

[0014] As can be seen, the silicon-oxygen-carbon composite material provided in this disclosure, based on the synergistic effect of the metallized core, the uniformly thick carbon coating layer, and the multiple carbon protrusions distributed on the outside of the carbon coating layer, can significantly improve the reversible capacity, first-time efficiency, rate performance, and cycle stability of lithium-ion batteries.

[0015] In some possible implementations, the size of the carbon bump is 5nm-50nm;

[0016] The size of the carbon protrusion is the size of the carbon protrusion in the direction parallel to the surface of the core.

[0017] In some possible implementations, the average distance difference MD between any two adjacent carbon protrusions is less than 20%;

[0018] in, r is the center-to-center distance between any two adjacent carbon protrusions, and n is the total number of carbon protrusions on the carbon coating layer.

[0019] In some possible implementations, the average particle size D50 of the silicon-oxygen-carbon composite material is less than or equal to 10 μm;

[0020] The thickness of the carbon coating layer is 1nm-100nm.

[0021] The aforementioned dimensional limitations of silicon-oxygen-carbon composite materials enable them to possess both excellent electrical and mechanical properties, making them suitable as negative electrode materials for the fabrication of negative electrode sheets.

[0022] In some possible implementations, the chemical formula of the silicon-oxygen material is SiO. x Where 0.5 ≤ x < 2. For example, if x is 1, then the silicon-oxygen material is silicon suboxide (SiO). Silicon-oxygen materials with this chemical formula are particularly suitable for obtaining the core of the aforementioned metallized silicon-oxygen material.

[0023] In some possible implementations, the metal includes at least one of Li, Na, K, Mg, Cu, Ag, and Al.

[0024] When metal M is selected from at least one of Li, Na, K, and Mg, this type of metal M reacts with some silicon-oxygen materials to form silicates, which makes the material of core 1 silicate / SiO2. x The combination of / Si / SiO2 (where 0.5≤x<2).

[0025] The aforementioned metal element M combines with oxygen in silicon-oxygen materials to form silicates, preemptively consuming the oxygen in the silicon-oxygen mixture and preventing irreversible lithium consumption during the electrochemical lithium intercalation process of lithium-ion batteries. This has a positive effect on improving the reversible capacity and first-time efficiency of silicon-based anode materials. Furthermore, the formed silicates possess abundant lithium-ion channels, which facilitates lithium-ion migration and diffusion, thus positively contributing to improving the rate performance of silicon-based anode materials.

[0026] When metal M is selected from at least one of Cu, Ag, and Al, this type of metal M reacts with some silicon-oxygen materials in the form of a metal complex to form a metal M-silicon alloy. This makes the material of core 1 appear as a metal M-silicon alloy / SiO. x The combination of / Si / SiO2 (where 0.5≤x<2).

[0027] The aforementioned metallic element M reacts with silicon-oxygen materials to form a metallic M-silicon alloy. This metallic M-silicon alloy has good electronic conductivity, which is of great significance for improving the electronic conductivity and rate performance of silicon-based anode materials.

[0028] All of the aforementioned metals can improve the conductivity and rate performance of the core, and can also increase the diffusion depth of active lithium inside the core, thereby improving the reversible capacity, first-time efficiency, rate performance and cycle stability of lithium-ion batteries.

[0029] On the other hand, this disclosure also provides a method for preparing a silicon-oxygen-carbon composite material, the silicon-oxygen-carbon composite material as shown above;

[0030] The preparation method of the silicon-oxygen-carbon composite material includes:

[0031] The carbon source, metal source, and silicon-oxygen material are stirred in a dispersion solvent for a first set time, and then a solid-liquid separation process is performed to obtain a precursor of silicon-oxygen-carbon composite material; wherein, the solid-liquid separation process includes: volatilization drying process or distillation process.

[0032] The precursor of the silicon-oxygen-carbon composite material is calcined under a protective atmosphere to obtain the silicon-oxygen-carbon composite material.

[0033] The method for preparing silicon-oxygen-carbon composite materials provided in this disclosure involves thoroughly mixing a carbon source, a metal source, and silicon-oxygen materials in a dispersion solvent. During this process, the carbon source and the metal source can complex with each other to form a metal-carbon source complex, which is uniformly free in the dispersion solvent.

[0034] After stirring, solid-liquid separation is achieved through evaporation drying or distillation. In this separation method, as the dispersing solvent gradually decreases, the free metal-carbon source complex in the dispersing solvent accumulates layer by layer on the surface of the silicon-oxygen material, forming crystalline clusters and ultimately forming the precursor of the silicon-oxygen-carbon composite material. In this precursor, the metal source in the metal-carbon source complex can be adsorbed onto the surface of the silicon-oxygen material, resulting in a morphology where silicon-oxygen material, metal source, and carbon source are distributed sequentially from the inside out.

[0035] By calcining the precursor of the silicon-oxygen-carbon composite material under a protective atmosphere, the metal source spontaneously enters the interior of the silicon-oxygen material and reacts with it, leaving vacancies on the surface of the silicon-oxygen material. The remaining carbon source collapses and shrinks around the silicon-oxygen material as the core and enters the aforementioned vacancies, thus forming a carbon layer structure with protruding surfaces. After calcination, the silicon-oxygen material reacts with the metal source to form a metallized core, while the carbon layer structure carbonizes to form an outer layer with a carbon coating and multiple carbon protrusions.

[0036] In some possible implementations, the solid-liquid separation process is performed under continuous stirring to prevent the precursor of the silicon-oxygen-carbon composite material from depositing in the dispersion solvent, thereby improving the dispersion of the precursor of the silicon-oxygen-carbon composite material and preventing clustering.

[0037] In some possible implementations, stirring the carbon source, metal source, and silicon oxide material in the dispersion solvent for a first predetermined time includes:

[0038] The carbon source and the metal source are subjected to a complexation reaction in the dispersion solvent to form a raw material system containing a metal source-carbon source complex;

[0039] The silicon-oxygen material is added to the raw material system and stirred for the first set time.

[0040] In some possible implementations, the metal source includes at least one of elemental Li, elemental Na, elemental K, and elemental Mg.

[0041] In some possible implementations, the metal source is a carbon-containing metal complex.

[0042] In some possible implementations, the carbon-containing metal complex includes at least one of lithium methyl, copper phthalocyanine, and aluminum acetylacetonate.

[0043] In some possible implementations, the dispersing solvent includes at least one of dimethyl carbonate, tetrahydrofuran, toluene, benzene, diethyl ether, propylene oxide, ketones, and ethylene glycol dimethyl ether.

[0044] In some possible implementations, the first set time is 3 to 24 hours.

[0045] In some possible implementations, the calcination process includes:

[0046] Under the condition that the heating rate is greater than or equal to 5°C / min, the precursor of the silicon-oxygen-carbon composite material is heated to the calcination temperature, and the silicon-oxygen-carbon composite material is calcined at the calcination temperature for a second set time.

[0047] By controlling the heating rate during calcination to ≥5℃ / min, it is possible to avoid the carbon layer structure with protrusions on the surface of the silicon-oxygen-carbon composite material precursor from randomly connecting together under the drive of thermal motion due to excessively long carbonization heating process. This avoids the formation of irregular, non-uniform, unevenly sized, and fragmented carbon layers, ensuring that the outer layer has a dense carbon coating layer and multiple uniformly distributed carbon protrusions, thus guaranteeing the excellent electrochemical performance brought by the outer layer.

[0048] In some possible implementations, the calcination temperature is 400℃ to 1200℃, and the second set time is 0.5h to 10h, to ensure that the silicon-oxygen material can be fully metallized and that the outer layer obtains the desired morphology.

[0049] On another front, a negative electrode material is also provided, which includes: silicon-based negative electrode material, conductive agent, and binder;

[0050] The silicon-based anode material is any of the silicon-oxygen-carbon composite materials shown above.

[0051] On the other hand, a negative electrode sheet is also provided, which is prepared using the aforementioned negative electrode raw materials.

[0052] For example, the preparation method of the negative electrode sheet is as follows: dissolve the binder in a polar solvent to obtain a glue solution; mix the glue solution with a silicon-based negative electrode material and a conductive agent, and stir evenly to obtain a negative electrode slurry; coat the negative electrode slurry onto two opposite surfaces of the current collector, and then dry and roll-press them in sequence to obtain the negative electrode sheet.

[0053] On the other hand, a lithium-ion battery is also provided, which includes the aforementioned negative electrode sheet.

[0054] In addition to the aforementioned negative electrode, the lithium-ion battery provided in this embodiment also includes a positive electrode, an electrolyte, a separator, and an encapsulation layer.

[0055] The electrolyte fills the space between the negative and positive electrode plates, and the separator is located in the electrolyte to isolate the negative and positive electrode plates. The encapsulation layer is used to encapsulate the negative electrode plate, positive electrode plate, electrolyte, and separator as a whole.

[0056] Lithium-ion batteries store and release energy by the insertion and extraction of lithium ions between the negative and positive electrodes. The electrolyte is the carrier for the transfer of lithium ions between the negative and positive electrodes. The separator is ion-conducting but electronically insulating. The separator is used to ensure the migration of lithium ions while separating the negative and positive electrodes to prevent short circuits. Attached Figure Description

[0057] Figure 1 A schematic diagram of an exemplary silicon-oxygen-carbon composite material provided in an embodiment of this disclosure;

[0058] Figure 2 This is a schematic diagram of the first process used to illustrate the structural synthesis mechanism of silicon-oxygen-carbon composite materials in an embodiment of this disclosure;

[0059] Figure 3 This is a schematic diagram of the second process used to illustrate the structural synthesis mechanism of silicon-oxygen-carbon composite materials in an embodiment of this disclosure;

[0060] Figure 4 A schematic diagram of the third process used to illustrate the structural synthesis mechanism of silicon-oxygen-carbon composite materials, provided in an embodiment of this disclosure;

[0061] Figure 5 A schematic diagram of the fourth process for illustrating the structural synthesis mechanism of silicon-oxygen-carbon composite materials provided in this embodiment of the disclosure;

[0062] Figure 6 A schematic diagram of the fifth process for illustrating the structural synthesis mechanism of silicon-oxygen-carbon composite materials provided in this embodiment of the disclosure;

[0063] Figure 7 This is a schematic diagram of the structure of an exemplary lithium-ion battery provided in an embodiment of the present disclosure;

[0064] Figure 8 EDS diagram of the silicon-oxygen-carbon composite material provided in Embodiment 1 of this disclosure;

[0065] Figure 9 EDS diagram of the silicon-oxygen-carbon composite material provided in Comparative Example 2 of this disclosure;

[0066] Figure 10 SEM images of silicon-oxygen-carbon composite materials obtained by conventional carbon coating provided in the embodiments of this disclosure at different magnifications;

[0067] Figure 11 SEM images of silicon-oxygen-carbon composite materials obtained by conventional carbon coating and pre-lithiation provided in the embodiments of this disclosure at different magnifications;

[0068] Figure 12 SEM images of silicon-oxygen-carbon composite materials obtained according to this disclosure at different magnifications, provided for embodiments of this disclosure.

[0069] in, Figures 10-12 In the SEM images involved, S4800 refers to the model of the scanning electron microscope, 3.0kV refers to the accelerating voltage of the scanning electron microscope, 8.1mm refers to the focal length, 10k and 50k refer to different magnifications, and 1.00μm and 5.00μm refer to different scales.

[0070] The reference numerals in the attached figures represent:

[0071] 1-Kernel,

[0072] 2-Outer layer,

[0073] 21-Carbon coating,

[0074] 22-Carbon protrusion,

[0075] 100-Negative electrode plate,

[0076] 200-Positive electrode sheet,

[0077] 300-electrolyte,

[0078] 400-diaphragm,

[0079] 500-Encapsulation layer. Detailed Implementation

[0080] To make the technical solutions and advantages of this disclosure clearer, the embodiments of this disclosure will be described in further detail below with reference to the accompanying drawings.

[0081] Silicon possesses a theoretical specific capacity as high as 4200 mAh / g, making silicon-based anode materials crucial for developing high-energy-density lithium-ion batteries. However, silicon-based anode materials exhibit a large coefficient of volume expansion, with volume changes reaching up to 300% during lithiation / delithiation. This volume change leads to pulverization and fragmentation of the silicon-based anode material during charge-discharge cycles, limiting the reversible capacity, coulombic efficiency, and cycle stability of lithium-ion batteries.

[0082] For example, silicon suboxide is a common silicon-based anode material, which is of great significance for the development of ultra-high capacity lithium-ion batteries. However, as mentioned above, due to the large volume expansion coefficient of silicon-based anode materials, and the high oxygen content in silicon-oxygen materials, a large amount of irreversible capacity and a low coulombic efficiency are generated during the first lithium intercalation process. This inherent disadvantage has prevented silicon-based anode materials, represented by silicon suboxide, from being widely used at present.

[0083] Related technologies utilize carbon sources to construct a carbon coating layer on the exterior of silicon-oxygen materials, forming carbon-coated silicon-based anode materials. This carbon coating layer mitigates the volume effect of silicon, reduces direct interfacial contact and side reactions between silicon and the electrolyte, and increases the surface conductivity of silicon, thereby reducing silicon volume expansion and increasing the initial efficiency and capacity of the silicon-based anode material. Methods for constructing the carbon coating layer include: solid / liquid phase mixed carbonization (e.g., using pitch or resin as the carbon source), gas-phase pyrolysis (e.g., using acetylene or methane as the carbon source), emulsion polymerization (e.g., using polyacrylonitrile as the carbon source), and high-temperature pyrolysis (e.g., using polyvinyl alcohol or polyvinylidene fluoride as the carbon source), etc.

[0084] However, in constructing the carbon coating layer, the carbon source exhibits weak adsorption on the surface of the silicon-oxygen anode material, relying solely on van der Waals forces. This prevents uniform deposition on the silicon-oxygen anode material surface, resulting in either difficulty in obtaining a stably adsorbed carbon coating layer or uneven thickness, with some areas being thicker than others. Consequently, when the silicon-oxygen anode material provided by this technology is used in lithium-ion batteries, the uneven carbon coating layer easily leads to contact between the electrolyte and the silicon-based anode material, causing interfacial side reactions and continuous electrolyte consumption. This results in problems such as low initial coulombic efficiency (ICE) and rapid cycle degradation in lithium-ion batteries. Furthermore, the uneven carbon coating layer can also lead to inconsistent stress release after local lithium intercalation, resulting in internal stress imbalance and particle pulverization caused by local expansion of silicon-based anode material particles. This further contributes to problems such as low capacity, low ICE, and rapid cycle degradation in lithium-ion batteries. In addition, the carbon coating layer designed in the relevant technology has poor wetting effect with the electrolyte, resulting in reduced interfacial charge transfer capacity and poor rate performance of lithium-ion batteries.

[0085] It is evident that the carbon-coated silicon-based anode materials provided by the relevant technologies have limited effect on improving the reversible capacity, initial coulombic efficiency, and cycle stability of lithium-ion batteries.

[0086] According to one aspect of the embodiments of this disclosure, a silicon-oxygen-carbon composite material is provided, as shown in the attached figure. Figure 1 As shown, the silicon-oxygen-carbon composite material includes a core 1 and an outer layer 2. The outer layer 2 includes a carbon coating layer 21 and multiple carbon protrusions 22. The core 1 is a silicon-oxygen material doped with metal. The carbon coating layer 21 covers the outside of the core 1, and multiple carbon protrusions 22 are formed on the outer surface of the carbon coating layer 21.

[0087] The silicon-oxygen-carbon composite material provided in this embodiment has a core 1 that is a silicon-oxygen material doped with metal. The doping of the metal into the silicon-oxygen material metallizes the silicon-oxygen material, which is beneficial to improving the conductivity and rate performance of the core 1. At the same time, the partially doped metal is stably combined with the oxygen in the silicon-oxygen material, avoiding the irreversible loss of lithium ions by oxygen elements during the electrochemical lithium intercalation process of silicon-based anode materials, thereby improving the reversible capacity, first efficiency and cycle stability of silicon-based lithium-ion batteries.

[0088] The silicon-oxygen-carbon composite material provided in this embodiment includes an outer layer 2 comprising a carbon coating layer 21 and a plurality of carbon protrusions 22 formed on the outside of the carbon coating layer 21. The plurality of carbon protrusions 22 increase the specific surface area of ​​the outer layer 2 to improve the wettability of the outer layer 2 with the electrolyte, promote the lithium-ion diffusion and charge transfer performance on the surface of the silicon-based anode material, thereby enhancing the interfacial charge transfer capability of the silicon-oxygen-carbon composite material, which is beneficial to improving the rate performance and cycle stability of the lithium-ion battery.

[0089] The silicon-oxygen-carbon composite material provided in this embodiment includes both carbon and metal elements. Thus, during the preparation of the silicon-oxygen-carbon composite material, the carbon source and metal source can be mixed with the silicon-oxygen material in the form of a metal-carbon source complex. The metal atoms in the metal source can react with the silicon-oxygen material to form a metal-doped silicon-oxygen material. The carbon source can be adsorbed and deposited on the surface of the silicon-oxygen material using metal atoms as active sites to form a carbon coating layer 21. This strong deposition and adsorption effect of the carbon source on the surface of the silicon-oxygen material facilitates the uniform deposition of the carbon coating layer 21 on the surface of the silicon-oxygen material, forming a uniform and dense carbon coating layer 21. The uniform coating of the carbon coating layer 21 can avoid the side reactions caused by silicon exposure in the electrolyte due to uneven coating, thus improving the cycle stability of the silicon-based anode material. When used in lithium-ion batteries, this uniformly thick carbon coating layer 21 not only effectively prevents the electrolyte from contacting the silicon-oxygen material but also ensures uniform lithium intercalation, which also helps to improve the capacity, initial efficiency, rate performance, and cycle stability of the lithium-ion battery.

[0090] As can be seen, the silicon-oxygen-carbon composite material provided in this embodiment of the present disclosure, based on the synergistic effect of the metallized core 1, the uniformly thick carbon coating layer 21, and the multiple carbon protrusions 22 distributed on the outside of the carbon coating layer 21, can significantly improve the reversible capacity, first efficiency, rate performance and cycle stability of lithium-ion batteries.

[0091] In this embodiment of the disclosure, the average particle size D50 of the silicon-oxygen-carbon composite material is less than or equal to 10 μm. The average particle size D50 is obtained by observing the entire silicon-oxygen-carbon composite material under an electron microscope. This average particle size D50 refers to the equivalent diameter of the largest particle when the cumulative distribution in the particle size distribution curve reaches 50%. For example, the average particle size D50 of the silicon-oxygen-carbon composite material is 1 μm-10 μm. Further examples include, but are not limited to, the average particle size D50 of the silicon-oxygen-carbon composite material as follows: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0092] In some examples, the thickness of the carbon coating layer 21 is 1 nm to 100 nm, where the thickness of the carbon coating layer 21 is the dimension of the carbon coating layer 21 along the diameter direction of the core 1. For example, the thickness of the carbon coating layer 21 includes, but is not limited to: 1 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0093] Multiple carbon protrusions 22 are uniformly distributed on the exterior of the carbon coating layer 21, making the outer surface of the carbon coating layer 21 uneven. For example, the structure of the carbon protrusions 22 includes, but is not limited to, various geometric shapes such as arc-shaped protrusions, conical protrusions (such as cones or pyramids), and cylindrical protrusions (such as cylinders or prisms). The structural arrangement of the carbon protrusions 22 on the carbon coating layer 21 can improve the contact area between the silicon-oxygen-carbon composite material and the electrolyte, and facilitates deep lithium intercalation.

[0094] In some examples, the size of the carbon bump 22 is 5nm-50nm; wherein, the size of the carbon bump 22 is the size of the carbon bump 22 in the direction along the surface of the core 1.

[0095] The dimensions at various locations on the carbon bump 22 may change along the diameter direction of the core 1, but will still remain within the aforementioned 5nm-50nm range. For example, the dimensions of the carbon bump 22 may be 10nm-50nm, 20nm-50nm, 30nm-50nm, 40nm-50nm, 10nm-20nm, 10nm-30nm, 10nm-40nm, 20nm-30nm, 20nm-40nm, etc. Furthermore, the dimensions of the carbon bump 22 may include, but are not limited to, 5nm, 10nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, etc.

[0096] Furthermore, the average distance difference MD between any two adjacent carbon protrusions 22 is less than 20%, where, r is the center distance between any two adjacent carbon protrusions 22, and n is the total number of carbon protrusions 22 on the carbon coating layer 21.

[0097] The aforementioned dimensional limitations of silicon-oxygen-carbon composite materials enable them to possess both excellent electrical and mechanical properties, making them suitable as negative electrode materials for the fabrication of negative electrode sheets.

[0098] In this embodiment of the disclosure, the carbon coating layer 21 is uniformly distributed on the outer surface of the core 1, and the carbon coating layer 21 has at least the following advantages:

[0099] The carbon coating layer 21 possesses sufficient mechanical strength to ensure the integrity of silicon-oxygen particles during the lithium insertion / extraction process in active silicon, suppressing silicon-oxygen particle pulverization, improving structural stability, and thus enhancing the overall cycle performance of the lithium-ion battery. The carbon coating layer 21 is sufficiently dense, preventing the electrolyte from contacting the silicon-oxygen material through it, thereby inhibiting side reactions between the electrolyte and the silicon-oxygen material. The carbon coating layer 21 exhibits excellent conductivity, significantly improving the electron gain / loss ability of active silicon-oxygen, enhancing the lithium insertion / extraction efficiency of the silicon-oxygen material, promoting capacity utilization and deep lithium insertion, and improving the reversible capacity and first-time efficiency of the lithium-ion battery.

[0100] The outer layer 2, which includes the carbon coating layer 21 and the carbon protrusions 22, is made of carbon. That is, the raw materials for preparing the outer layer 2 include at least carbon elements. Furthermore, the raw materials for preparing the outer layer 2 may also include doping elements to further improve the conductivity and stability of the outer layer 2.

[0101] In some examples, the raw materials for preparing the outer layer 2 include carbon and doping elements, wherein the weight percentage of the doping elements is less than or equal to 5%. For example, the doping elements include, but are not limited to, N, P, and F elements. These doping elements can not only improve the conductivity of the outer layer 2, but also reduce the lithium-ion migration barrier on the surface of the core 1, thereby improving the lithium-ion migration efficiency.

[0102] For core 1, it is a silicon-oxygen material doped with metal. Depending on the specific type of metal, there can be different combinations between the metal and the silicon-oxygen material. For example, there are some metals that tend to react with silicon dioxide to form silicates; for example, there are also some metals that tend to react with elemental silicon to form alloys.

[0103] In some examples, the metal includes at least one of Li, Na, K, Mg, Cu, Ag, and Al.

[0104] When metal M is selected from at least one of Li, Na, K, Mg, and Al, this type of metal M reacts with at least a portion of the silicon-oxygen material to form silicates, which makes the material of core 1 silicate / SiO2. x The combination of / Si / SiO2 (where 0.5≤x<2).

[0105] The aforementioned metal element M combines with oxygen in silicon-oxygen materials to form silicates, preemptively consuming the oxygen in the silicon-oxygen mixture and preventing irreversible lithium consumption during the electrochemical lithium intercalation process of lithium-ion batteries. This has a positive effect on improving the reversible capacity and first-time efficiency of silicon-based anode materials. Furthermore, the formed silicates possess abundant lithium-ion channels, which facilitates lithium-ion migration and diffusion, thus positively contributing to improving the rate performance of silicon-based anode materials.

[0106] When metal M is selected from at least one of Cu and Ag, this type of metal M reacts with some silicon-oxygen materials in the form of a metal complex to form a metal M-silicon alloy. This makes the material of core 1 appear as a metal M-silicon alloy / SiO. x The combination of / Si / SiO2 (where 0.5≤x<2).

[0107] The aforementioned metallic element M reacts with silicon-oxygen materials to form a metallic M-silicon alloy. This metallic M-silicon alloy has good electronic conductivity, which is of great significance for improving the electronic conductivity and rate performance of silicon-based anode materials.

[0108] All of the aforementioned metals can improve the conductivity and rate performance of the core 1, and can also increase the diffusion depth of active lithium inside the core 1, thereby improving the reversible capacity, first efficiency, rate performance and cycle stability of the lithium-ion battery.

[0109] The reason why the aforementioned metals can increase the diffusion depth of active lithium within the core 1 is that the diffusion depth of active lithium within the core 1 is related to the lithium-ion diffusion coefficient of the core 1. The higher the lithium-ion diffusion coefficient, the greater the diffusion depth of lithium ions under the same driving force. In this disclosure, if the metal forms a silicate with the silicon-oxygen material, the silicate has multidimensional lithium-ion diffusion channels, thereby achieving the purpose of increasing the lithium-ion diffusion coefficient; if the metal forms an alloy with the silicon-oxygen material, the conductivity of the alloy increases, the charge transfer impedance decreases, and the lithium-ion diffusion resistance decreases, which can also achieve the purpose of increasing the lithium-ion diffusion coefficient.

[0110] In this embodiment, the chemical formula of the silicon-oxygen material involved is SiO₂. x Where 0.5≤x<2, for example, if x is 1, then the silicon-oxygen material is silicon suboxide SiO. Silicon-oxygen materials with this chemical formula are particularly suitable for obtaining the core 1 of the above-mentioned metallized silicon-oxygen material.

[0111] In some examples, the silicon oxide material provided in this disclosure is in powder form, and the average particle size D50 of the silicon oxide material is less than or equal to 10 μm, including but not limited to: less than or equal to 9.5 μm, less than or equal to 9 μm, less than or equal to 8 μm, less than or equal to 7 μm, less than or equal to 6 μm, less than or equal to 5 μm, etc.

[0112] According to another aspect of the present disclosure, a method for preparing a silicon-oxygen-carbon composite material is also provided, the method comprising:

[0113] Step 1: Stir the carbon source, metal source, and silicon-oxygen material in a dispersion solvent for a set time, then perform solid-liquid separation to obtain the precursor of the silicon-oxygen-carbon composite material. This solid-liquid separation includes either evaporation drying or distillation.

[0114] Step 2: Under a protective atmosphere, the precursor of the silicon-oxygen-carbon composite material is calcined to obtain the silicon-oxygen-carbon composite material.

[0115] In some examples, the molar ratio of silicon-oxygen material (e.g., silicon suboxide) to metal source is 1:0.05 to 1:1 (e.g., 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, etc.);

[0116] In some examples, the molar ratio of silicon-oxygen material (e.g., silicon suboxide) to carbon source is 1:0.05 to 1:0.5 (e.g., 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.);

[0117] In some examples, the mass ratio of the silicon-oxygen material (e.g., silicon suboxide) to the dispersion solvent is 1:0.5 to 1:1 (e.g., 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, etc.).

[0118] The proportions of the above raw materials are within the range mentioned above, which is conducive to obtaining a carbonaceous outer layer of suitable thickness.

[0119] The method for preparing silicon-oxygen-carbon composite materials provided in this disclosure involves thoroughly mixing a carbon source, a metal source, and silicon-oxygen materials in a dispersion solvent. During this process, the carbon source and the metal source can complex with each other to form a metal-carbon source complex, which is uniformly free in the dispersion solvent.

[0120] After stirring, solid-liquid separation is achieved through evaporation drying or distillation. In this separation method, as the dispersion solvent gradually decreases (i.e., the dispersion solvent decreases slowly), it promotes the layer-by-layer deposition of free metal-carbon source complexes on the surface of the silicon-oxygen material, forming crystalline clusters and ultimately forming the precursor of the silicon-oxygen-carbon composite material. In this precursor, the metal source in the metal-carbon source complex can be adsorbed onto the surface of the silicon-oxygen material, resulting in a morphology where silicon-oxygen material, metal source, and carbon source are distributed sequentially from the inside out.

[0121] By calcining the precursor of the silicon-oxygen-carbon composite material under a protective atmosphere, the metal source spontaneously enters the interior of the silicon-oxygen material and reacts with it, leaving vacancies on the surface of the silicon-oxygen material. The remaining carbon source collapses and shrinks around the silicon-oxygen material as the core and enters the aforementioned vacancies, thus forming a carbon layer structure with protruding surfaces. After calcination, the silicon-oxygen material reacts with the metal source to form a metallized core, while the carbon layer structure carbonizes to form an outer layer with a carbon coating and multiple carbon protrusions.

[0122] In this embodiment of the disclosure, the carbon source, metal source, and silicon-oxygen material are stirred in a dispersion solvent for a first predetermined time. Exemplarily, this first predetermined time is 3 to 24 hours, including, but not limited to, 3 hours, 5 hours, 7 hours, 8 hours, 10 hours, 13 hours, 15 hours, 17 hours, 20 hours, 22 hours, and 24 hours. Within this time range, the carbon source and metal source fully complex, forming a desired metal-carbon source complex, and the surface of the silicon-oxygen material is fully adsorbed with the metal-carbon source complex, forming a precursor of a highly dispersed silicon-oxygen-carbon composite material.

[0123] In some examples, the carbon source, metal source, and silicon oxide material are stirred in the dispersion solvent at temperatures ranging from room temperature to 60°C, for example, room temperature of 20°C-28°C.

[0124] In this embodiment, the evaporation drying or distillation process can be carried out in various ways, as long as it is ensured that the dispersing solvent does not carry away the carbon source adsorbed on the silicon-oxygen material during the removal process. For example, natural evaporation drying at room temperature, or evaporation drying assisted by forced air at a certain temperature, or evaporation drying assisted by vacuum at a certain temperature, etc.

[0125] Furthermore, in this embodiment of the present disclosure, the solid-liquid separation further includes: a filtration process or a drying process, which is configured to improve the efficiency of solid-liquid separation without affecting the stacking adsorption of the carbon source on the surface of the silicon-oxygen material.

[0126] In some examples, a certain period of filtration or drying can be performed before evaporation drying or distillation to remove most of the excess solvent, and then evaporation drying or distillation can be used to remove the remaining dispersed solvent. For example, evaporation drying or distillation can be performed when the amount of solvent is separated into half of the remaining amount.

[0127] In other examples, after evaporation drying or distillation, once it is ensured that the carbon source has been completely stacked and adsorbed onto the surface of the silicon oxide material, the residual dispersing solvent can be removed by filtration or drying.

[0128] It is evident that the above-mentioned filtration or drying processes first ensure that the carbon source is fully stacked and adsorbed on the surface of the silicon-oxygen material, and secondly improve the efficiency of solid-liquid separation.

[0129] In this embodiment of the invention, solid-liquid separation is assisted and promoted by evaporation drying or distillation steps, rather than by conventional filtration methods (e.g., vacuum filtration, suction filtration, thermal filtration, etc.). This is because research has shown that if conventional filtration methods are used throughout the solid-liquid separation process, no protrusions (i.e., carbon protrusions) will form on the carbon coating layer. When conventional filtration methods are used, the dispersion solvent is removed from its initial sufficient state in a short time. During the rapid loss of the dispersion solvent, the carbon source, which is completely dispersed in the dispersion solvent, will flow along with the solvent. For example, carbon sources such as aromatic compounds are completely dispersed and dissolved in the dispersion solvent in the initial state. As the dispersion solvent is rapidly removed, the carbon source flows along with it and will not spontaneously form π-π conjugated crystals and precipitate from the dispersion solvent. Therefore, it is impossible to form stacked crystalline clusters on the surface of the silicon oxide material, and thus impossible to synthesize the special morphology of carbon protrusions on the carbon coating layer after calcination. The solid-liquid separation method described in the embodiments of this disclosure effectively avoids the aforementioned technical problems and effectively promotes the formation of carbon protrusions.

[0130] In some possible implementations, the above-mentioned solid-liquid separation process is performed under continuous stirring to prevent the precursor of the silicon-oxygen-carbon composite material from depositing in the dispersion solvent, thereby improving the dispersion of the precursor of the silicon-oxygen-carbon composite material and preventing clustering.

[0131] In the embodiments of this disclosure, all stirring processes are implemented in ways including but not limited to: magnetic stirring, stirring paddle, etc.

[0132] In some possible implementations, stirring the carbon source, metal source, and silicon oxide material in a dispersion solvent for a first predetermined time includes: causing the carbon source and metal source to undergo a complexation reaction in the dispersion solvent to form a raw material system containing a metal source-carbon source complex; adding the silicon oxide material to the raw material system and stirring for the first predetermined time.

[0133] The metal source and carbon source are mixed with the silicon-oxygen material in the form of a metal-carbon source complex. When they are added to the dispersion solvent and stirred for a certain period of time, the metal source in the metal-carbon source complex can be adsorbed on the surface of the silicon-oxygen material, so that the precursor of the silicon-oxygen-carbon composite material presents a form in which silicon-oxygen material-metal source-carbon source are distributed from the inside to the outside.

[0134] In this embodiment, the carbon source includes, but is not limited to, ethers, alcohols, carboxylic acids, ketones, aromatic compounds, and polymers. For example, polymers include, but are not limited to, polyethylene glycol and polyacrylic acid. Aromatic compounds include, but are not limited to, biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, pyrene, tetraphenylene oxide, and their branched derivatives. For example, these modified products are aromatic compounds modified with the following groups: alkane groups, alcohol groups, nitride groups, sulfide groups, ether groups, ketone groups, ester groups, etc.

[0135] (1) In some implementations, the metal source includes at least one of elemental Li, elemental Na, elemental K, and elemental Mg.

[0136] The aforementioned metals are metallic elements capable of "metal solvation". Both the metal source and the carbon source can be fully dissolved in the dispersion solvent. In the solvent environment provided by the dispersion solvent, the active groups in the carbon source can complex with the metal in the metal source to form a metal source-carbon source complex.

[0137] The following example, using elemental Li as the metal source, aromatic compounds as the carbon source, and silicon suboxide (SiO) as the silicon-oxygen material, illustrates the formation mechanism of the silicon-oxygen-carbon composite structure:

[0138] As attached Figure 2 As shown, in the solvent environment provided by the dispersion solvent, the aromatic compound comes into contact with lithium metal and undergoes a complexation reaction to form a metal source-carbon source complex with a lithium metal end and an aromatic carbon end, wherein the lithium metal is used as the core dopant element and the aromatic carbon end is used as the carbon source.

[0139] As attached Figure 3 As shown, after the metal-carbon source complex comes into contact with SiO material in the dispersion solvent, its lithium end adsorbs onto the surface of the SiO material, forming a precursor of the silicon-oxygen-carbon composite material. This precursor exhibits a SiO-Li-aromatic compound distribution from the inside out. In this precursor, the intermolecular interactions change depending on the molecular orientation. After the lithium end adsorbs onto the SiO material surface, the aromatic compound molecules are aligned, and different aromatic compound molecules are lateral to each other, causing mutual repulsion. This results in relatively independent adsorption structures on the SiO material surface, effectively preventing the aromatic compounds from clustering and ensuring uniform distribution. This facilitates the subsequent acquisition of a uniformly thick carbon coating layer.

[0140] As attached Figure 4As shown, metal-carbon source complexes adsorbed on the surface of SiO material serve as the base layer. Other metal-carbon source complexes are adsorbed and stacked on the surface of the base layer, and so on, with the metal-carbon source complexes stacking sequentially to form a stacked structure of "SiO-Li-aromatic-Li-aromatic-Li-aromatic…". Because aromatic compound molecules are relatively small compared to SiO material, their stacking orientation is varied and irregular, achieving random stacking growth.

[0141] As attached Figure 5 As shown, affected by the potential difference, the potential of the metal source-carbon source complex (i.e., Li-aromatic complex) is between that of lithium metal and SiO material. Therefore, lithium at the lithium end of the metal source-carbon source complex will spontaneously enter the interior of SiO material. After entering the interior of SiO material, lithium leaves vacancies on the surface of SiO material. In this way, the remaining aromatic compounds enter the vacancies as carbon sources, causing the aromatic compounds to collapse and shrink around the center of the base layer, forming a carbon layer structure with protrusions on the surface.

[0142] As attached Figure 6 As shown, during the calcination process (i.e., the high-temperature carbonization process), SiO material reacts with lithium to form lithium silicate salt, forming a core of silicon-oxygen material doped with metal (the core material is a combination of lithium silicate salt / SiO / Si / SiO2). Simultaneously, the carbon layer structure carbonizes according to its structural prototype to form a carbonaceous outer layer, resulting in a carbon coating and multiple carbon protrusions on this outer layer. Figure 6 The location of the carbon coating layer in the diagram indicates that it forms on the surface of the core, and the locations of the multiple carbon protrusions indicate that they are located on the surface of the carbon coating layer.

[0143] (2) In other implementations, the metal source is a carbon-containing metal complex, for example, the carbon-containing metal complex includes at least one of lithium methyl, copper phthalocyanine, and aluminum acetylacetonate. Taking lithium methyl as an example, it has lithium as the metal source and methyl groups as the carbon source.

[0144] In this implementation, a carbon-containing metal complex is directly selected as the metal source, providing both a metal source and a carbon source. The metal in this type of carbon-containing metal complex reacts with silicon-oxygen materials to form a metal-silicon alloy. In some examples, the carbon source used in this application is also the aforementioned carbon-containing metal complex; that is, the carbon-containing metal complex simultaneously provides both a metal source and a carbon source.

[0145] This disclosure utilizes a dispersing solvent to provide a solvent environment. In some possible implementations, the dispersing solvent includes at least one selected from dimethyl carbonate, tetrahydrofuran, toluene, benzene, diethyl ether, propylene oxide, ketones, and ethylene glycol dimethyl ether. For example, ketones include, but are not limited to, acetone.

[0146] In this embodiment of the disclosure, the radial thickness of the carbon coating layer can be controlled by at least one of the following reaction conditions: the concentration of the metal source and the carbon source, the ratio of the carbon source to the silicon-oxygen material, the reaction time, etc.

[0147] The radial dimension of carbon protrusions can be controlled by at least one of the following reaction conditions: the type of metal source and carbon source (because different metal sources and carbon sources affect their molecular charge and interaction forces, which in turn affect the deposition morphology of carbon sources on the surface of silicon-oxygen materials), reaction time, reaction temperature, etc.

[0148] For step 2, the precursor of the silicon-oxygen-carbon composite material is calcined under a protective atmosphere to obtain the silicon-oxygen-carbon composite material. In some examples, the calcination process includes: heating the precursor of the silicon-oxygen-carbon composite material to the calcination temperature at a heating rate greater than or equal to 5°C / min, and calcining the silicon-oxygen-carbon composite material at the calcination temperature for a second predetermined time.

[0149] For example, the heating rate is 5℃ / min-10℃ / min. Further examples include, but are not limited to: 5.2℃ / min, 5.5℃ / min, 5.8℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.

[0150] By controlling the heating rate during calcination to ≥5℃ / min, it is possible to avoid the surface protrusions of the carbon layer structure in the precursor of the silicon-oxygen-carbon composite material from randomly coalescing under thermal motion due to excessively long carbonization heating processes. This prevents the formation of irregular, non-uniform, unevenly sized, and fragmented carbon layers, ensuring that the resulting outer layer has a dense carbon coating and multiple uniformly distributed carbon protrusions, thus guaranteeing the excellent electrochemical performance of the outer layer. Furthermore, to improve the safety of the calcination process, measures can be implemented to prevent temperature runaway during the heating process.

[0151] To ensure that the silicon-oxygen material can be fully metallized and that the outer layer obtains the desired morphology, the embodiments of this disclosure use a calcination temperature of 400°C to 1200°C and a second set time, that is, a calcination time of 0.5h to 10h.

[0152] For example, calcination temperatures include, but are not limited to: 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc., and calcination times include, but are not limited to: 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0153] The above calcination process is carried out under a protective atmosphere. The inert gas used in this protective atmosphere only needs to not react with the metal source and carbon source. For example, the inert gas includes, but is not limited to, argon and nitrogen. The protective atmosphere must contain less than 0.1 ppm of O2 and less than 0.01 ppm of H2O. Furthermore, before calcination, the precursor of the silicon-oxygen-carbon composite material is placed in a reaction environment with a dew point < -40°C.

[0154] In some examples, the calcination process is carried out in a firing furnace that provides the aforementioned protective atmosphere.

[0155] According to another aspect of the present disclosure, the present disclosure also provides a negative electrode material, which includes a silicon-based negative electrode material, a conductive agent, and a binder; wherein the silicon-based negative electrode material is any of the silicon-oxygen-carbon composite materials shown in the embodiments of the present disclosure.

[0156] In some examples, the conductive agent constitutes 0.02%-2% by weight in the negative electrode material, such as including but not limited to: 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, etc. Suitable conductive agents are those that do not provide additional reversible capacity, do not cause additional chemical reactions, and have electronic conductivity. In some examples, conductive agents include, but are not limited to, at least one of: conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene. Using the above-mentioned conductive agents can achieve the purpose of reducing the impedance of the negative electrode and improving rate performance.

[0157] The binder ensures adhesion and inhibits the expansion of the silicon active material, while reducing the internal resistance of the negative electrode. In some examples, the binder includes, but is not limited to, polyimide-based, polyetherimide-based, polyacrylic acid-based, polyvinyl alcohol-based, and polyacrylonitrile-based materials. In some examples, the binder has a weight percentage of 0.05%-5% in the negative electrode raw material, such as, but not limited to, 0.05%, 0.1%, 0.5%, 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc.

[0158] The silicon-based anode material is the balance, meaning that the amount of silicon-based anode material makes the total weight percentage of binder, silicon-based anode material, and conductive agent 100%.

[0159] According to another aspect of the present disclosure, the present disclosure also provides a negative electrode sheet, which is prepared using the above-mentioned negative electrode raw materials.

[0160] For example, the preparation method of the negative electrode sheet is as follows: dissolve the binder in a polar solvent to obtain a glue solution; mix the glue solution with a silicon-based negative electrode material and a conductive agent, and stir evenly to obtain a negative electrode slurry; coat the negative electrode slurry onto two opposite surfaces of the current collector, and then dry and roll-press them in sequence to obtain the negative electrode sheet.

[0161] To improve the quality of the negative electrode sheet, the negative electrode slurry can be degassed and sieved before being coated onto the two opposite surfaces of the current collector.

[0162] For example, the current collector includes, but is not limited to, at least one of: copper foil, copper mesh, carbon-coated copper foil, stainless steel foil, stainless steel mesh, carbon-coated stainless steel foil, and nickel foil.

[0163] For example, polar solvents include, but are not limited to, at least one of: N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and cyclohexanone.

[0164] According to another aspect of the present disclosure, the present disclosure also provides a lithium-ion battery including the negative electrode sheet described above.

[0165] Based on the use of the negative electrode sheet provided in the embodiments of this disclosure, the lithium-ion battery has high reversible capacity, high initial efficiency, high rate performance and strong cycle stability.

[0166] The lithium-ion battery provided in this disclosure embodiment is shown in the attached figure. Figure 7 As shown, the lithium-ion battery includes not only the negative electrode 100, but also the positive electrode 200, electrolyte 300, separator 400, and encapsulation layer 500.

[0167] The electrolyte 300 fills the space between the negative electrode 100 and the positive electrode 200, and the separator 400 is located in the electrolyte 300 to isolate the negative electrode 100 and the positive electrode 200. The encapsulation layer 500 is used to encapsulate the negative electrode 100, the positive electrode 200, the electrolyte 300, and the separator 400 as a whole.

[0168] Lithium-ion batteries store and release energy by intercalating and deintercalating lithium ions between the negative electrode 100 and the positive electrode 200. The electrolyte 300 is the carrier for the transport of lithium ions between the negative electrode 100 and the positive electrode 200. The separator 400 is ion-conducting but electronically insulating. The separator 400 is used to ensure the migration of lithium ions while separating the negative electrode 100 and the positive electrode 200 to prevent short circuits.

[0169] The positive electrode sheet includes a positive electrode active material, a conductive agent, a current collector, and a positive electrode binder. The positive electrode active material can be selected from at least one of lithium-containing layered metal oxides, lithium-containing spinel structured metal oxides, lithium metal phosphates, lithium metal fluoride sulfates, and lithium metal vanadates.

[0170] For example, lithium-containing layered metal oxides include, but are not limited to, at least one of lithium cobalt oxide (LiCoO2), nickel-cobalt-manganese ternary materials (NCM), and nickel-cobalt-aluminum ternary materials (NCA); lithium-containing spinel structure metal oxides include, but are not limited to, lithium manganese oxide (LiMn2O4); lithium metal phosphates include, but are not limited to, lithium iron phosphate (LiFePO4); lithium metal fluorinated sulfates include, but are not limited to, lithium cobalt sulfate fluoride (LiCoFSO4); and lithium metal vanadates include, but are not limited to, lithium nickel vanadate (LiNiVO4).

[0171] The conductive agents used in the positive electrode sheet include, but are not limited to, at least one of the following: conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene.

[0172] The present disclosure will be further described below through more specific embodiments. Although some specific implementations are described below, it should be understood that the present disclosure can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Where the manufacturers of reagents or instruments are not specified, they may be conventional products that can be obtained commercially. The silicon-oxygen materials involved in the following embodiments are all SiO raw materials.

[0173] Example 1

[0174] This embodiment 1 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0175] 1g of lithium metal and 5g of biphenyl were uniformly dispersed in 10g of ethylene glycol dimethyl ether. After magnetic stirring, a lithium-biphenyl complex was formed in the ethylene glycol dimethyl ether. 10g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 12 hours. The ethylene glycol dimethyl ether was then removed by evaporation drying at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0176] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 1. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 900°C at a heating rate of 5°C / min, and calcining the silicon-oxygen-carbon composite material at 900°C for 2 hours.

[0177] Example 2

[0178] This embodiment 2 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0179] 1 g of lithium metal and 5 g of 4,4'-dimethylbiphenyl were uniformly dispersed in 10 g of ethylene glycol dimethyl ether. After magnetic stirring, a lithium-dimethylbiphenyl complex was formed in the ethylene glycol dimethyl ether. 10 g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 15 hours. The ethylene glycol dimethyl ether was then removed by evaporation drying at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0180] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 2. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 900°C at a heating rate of 5.5°C / min, and calcining the silicon-oxygen-carbon composite material at 900°C for 2 hours.

[0181] Example 3

[0182] Example 3 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0183] 1g of metallic lithium and 3g of biphenyl were uniformly dispersed in 10g of tetrahydrofuran and magnetically stirred until homogeneous, forming a lithium-biphenyl complex in ethylene glycol dimethyl ether. 10g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 12 hours. The ethylene glycol dimethyl ether was then removed by distillation at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0184] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 3. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 950°C at a heating rate of 6°C / min, and calcining the silicon-oxygen-carbon composite material at 950°C for 2 hours.

[0185] Example 4

[0186] Example 4 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0187] 1g of lithium metal and 5g of biphenyl were uniformly dispersed in 10g of ethylene glycol dimethyl ether. After magnetic stirring, a lithium-biphenyl complex was formed in the ethylene glycol dimethyl ether. 10g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 13 hours. The ethylene glycol dimethyl ether was then removed by evaporation drying at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0188] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 4. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 500°C at a heating rate of 5.8°C / min, and calcining the silicon-oxygen-carbon composite material at 500°C for 6 hours.

[0189] Example 5

[0190] Example 5 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0191] 1g of metallic sodium and 5g of biphenyl were uniformly dispersed in 10g of ethylene glycol dimethyl ether. After magnetic stirring, a sodium-biphenyl complex was formed in the ethylene glycol dimethyl ether. 10g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 13 hours. The ethylene glycol dimethyl ether was then removed by evaporation drying at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0192] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 5. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 900°C at a heating rate of 5.5°C / min, and calcining the silicon-oxygen-carbon composite material at 900°C for 3 hours.

[0193] Example 6

[0194] Example 6 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0195] 1g of copper phthalocyanine and 5g of biphenyl were uniformly dispersed in 10g of ethylene glycol dimethyl ether. After magnetic stirring, a copper phthalocyanine-biphenyl complex was formed in the ethylene glycol dimethyl ether. 10g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 12 hours. The ethylene glycol dimethyl ether was then removed by distillation at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0196] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 6. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 1000°C at a heating rate of 7°C / min, and calcining the silicon-oxygen-carbon composite material at 1000°C for 2 hours.

[0197] Example 7

[0198] Example 7 provides a silicon-oxygen-carbon composite material, which is prepared by the following method:

[0199] 1g of aluminum acetylacetonate and 5g of biphenyl were uniformly dispersed in 10g of ethylene glycol dimethyl ether. After magnetic stirring until homogeneous, an aluminum acetylacetonate-biphenyl complex was formed in the ethylene glycol dimethyl ether. 10g of SiO2 was then added to the raw material system, and the mixture was magnetically stirred for 12 hours. The ethylene glycol dimethyl ether was then removed by evaporation drying at room temperature to obtain the precursor of the silicon-oxygen-carbon composite material.

[0200] The precursor of the silicon-oxygen-carbon composite material was calcined under an argon atmosphere to obtain the desired silicon-oxygen-carbon composite material in Example 7. The calcination process included heating the precursor of the silicon-oxygen-carbon composite material to 1100°C at a heating rate of 8°C / min, and calcining the silicon-oxygen-carbon composite material at 1100°C for 1 hour.

[0201] Comparative Example 1

[0202] Comparative Example 1 provides SiO raw material, which has not undergone any treatment.

[0203] Comparative Example 2

[0204] Comparative Example 2 provides a silicon-oxygen-carbon composite material without any metal doping, which is prepared by the following method:

[0205] 5g of biphenyl was dissolved in 10g of ethylene glycol dimethyl ether. After the biphenyl was completely dissolved, 10g of SiO raw material was added to the raw material system. After magnetic stirring for 12h, the mixture was dried at room temperature and then calcined at 900℃ for 2h under Ar atmosphere to obtain silicon-oxygen-carbon composite material.

[0206] Comparative Example 3

[0207] Comparative Example 3 provides a silicon-oxygen-carbon composite material with a carbon coating obtained by chemical vapor deposition, which is prepared by the following method:

[0208] The SiO raw material was placed in a tube furnace, and the air inside the tube was evacuated and replaced with inert gas N2. After repeating this process three times, the power was turned on and the temperature was raised to 800°C at a rate of 3°C / min. The temperature was held at this temperature for 20 minutes. Then, a mixture of ethylene and nitrogen gas was introduced into the tube furnace and continued for 30 minutes to obtain a silicon-oxygen-carbon composite material.

[0209] Test case

[0210] This test example utilizes coin cell testing to evaluate the performance of the aforementioned silicon-oxygen-carbon composite material and SiO raw material in improving the initial efficiency and reversible capacity of coin cells. The carbon layer coating and uniformity of each silicon-oxygen-carbon composite material were obtained using trace carbon analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The charge-discharge regime involved in the coin cell test is as follows: constant current discharge at 0.05C to 10mV, followed by constant current discharge at 0.02C to 5mV; constant current charging at 0.05C to 1.5V; where 1C is defined as 1500mAh / g.

[0211] The test results are shown in Table 1:

[0212] Table 1

[0213]

[0214] In Table 1, Rate@0.1C, Rate@0.2C, and Rate@0.5C refer to the corresponding rates under different constant current discharge tests. The reversible capacity of the corresponding 0.1C, 0.2C, and 0.5C constant current discharge segments is compared with the reversible capacity of the first 0.05C constant current discharge segment, and the percentage value obtained is the above rate data.

[0215] As shown in Table 1, the carbon content of the materials provided in Comparative Example 1 and Comparative Example 2 is approximately 0.45%, which is relatively low. Furthermore, no carbon layer was observed in the SEM images and EDS elemental distribution. This is because in Comparative Example 2, the organic carbon source could not be effectively deposited on the surface of SiO, thus failing to form a stable carbon coating layer.

[0216] The silicon-oxygen-carbon composite materials provided in Examples 1-7 were prepared by the method provided in this disclosure, which effectively increased the carbon content of the silicon-oxygen-carbon composite materials. Combined with the EDS elemental distribution structure, it was confirmed that the silicon-oxygen material surface of the silicon-oxygen-carbon composite materials provided in Examples 1-7 was covered with a carbonaceous outer layer.

[0217] Appendix Figure 8 An EDS diagram of the silicon-oxygen-carbon composite material provided in Example 1 is shown, which characterizes the distribution of carbon, oxygen, and silicon elements in the silicon-oxygen-carbon composite material. Figure 8 As can be seen from the C kαl-2 image, the carbon elements are represented by the uniformly distributed white bright spots. It can be seen that, under the same carbon source content, the deposition amount and carbonization rate of the silicon-oxygen material surface are higher after the metal source and carbon source are complexed. Furthermore, the carbon coating layer formed by the metal carbon source is more uniform.

[0218] Appendix Figure 9An EDS diagram of the silicon-oxygen-carbon composite material provided in Comparative Example 2 is shown, which characterizes the distribution of carbon, oxygen, and silicon elements in the silicon-oxygen-carbon composite material. Figure 9 As can be seen from the C kαl-2 image, the carbon element signal is not obvious, which indicates that the carbon source in Comparative Example 2 has a low deposition amount in the silicon-oxygen material and cannot form a uniform carbon coating layer.

[0219] Appendix Figure 10 SEM images of silicon-oxygen-carbon composite materials obtained based on conventional carbon coating at different magnifications are shown, wherein the silicon-oxygen-carbon composite material is the same as the silicon-oxygen-carbon composite material provided in Comparative Example 3.

[0220] Appendix Figure 11 Examples of SEM images of silicon-oxygen-carbon composite materials obtained by conventional carbon coating and pre-lithiation at different magnifications are provided, wherein the silicon-oxygen-carbon composite material is a commercially available silicon-oxygen-carbon composite material.

[0221] Appendix Figure 12 SEM images of silicon-oxygen-carbon composite materials obtained based on embodiments of the present disclosure at different magnifications are illustrated, wherein the silicon-oxygen-carbon composite material is the silicon-oxygen-carbon composite material provided in Example 1.

[0222] Depend on Figures 10-12 As shown, in conventional carbon coating and conventional carbon coating + pre-lithiation corresponding silicon-oxygen-carbon composite materials, the surface of some silicon-oxygen materials does not have a complete carbon coating layer, resulting in the surface of some silicon-oxygen materials being exposed (which is easily exposed to the electrolyte and thus causes more side reactions). However, the silicon-oxygen-carbon composite material provided in this embodiment has a complete and dense carbon coating layer. In addition, obvious synaptic carbon protrusions can be observed in the silicon-oxygen-carbon composite material provided in this embodiment.

[0223] As shown in Table 1, the first-efficiency of the silicon-oxygen-carbon composite materials provided in Examples 1-7 is also effectively improved compared with Comparative Examples 1-3. This indicates that the silicon-oxygen-carbon composite materials prepared based on the method provided in the embodiments of this disclosure enable both the metal source and the carbon source to play a positive role.

[0224] Compared with Example 1, Example 2 changed the type of organic carbon source. It can be seen that changing the type of carbon source can also help increase the carbon content of silicon-oxygen-carbon composite material. This also suggests that there is an optimization possibility between organic carbon source and organic solvent. By selecting and matching similar organic substances, it is beneficial to obtain silicon-oxygen-carbon composite material with better comprehensive performance.

[0225] Compared with Example 1, Example 3 reduces the amount of organic carbon source used. However, the carbon content of the silicon-oxygen-carbon composite material provided in Example 3 does not decrease significantly. This indicates that the deposition amount of the same organic carbon source has a limit. The excess carbon source is still dispersed in the dispersion solvent. The residual carbon source can be collected and recycled by means such as filtration to reduce material consumption costs.

[0226] Compared with Example 1, Example 4 has a lower calcination temperature. Although this will have a certain impact on the overall performance of the silicon-oxygen-carbon composite material, this is due to the different degrees of disproportionation caused by different temperatures. However, the carbon content of the silicon-oxygen-carbon composite material is not significantly different, which confirms that calcination at relatively low temperatures is also feasible.

[0227] Example 5 demonstrates that using sodium, a similar alkali metal, as a metal source can achieve essentially the same effect. Due to the difference in atomic weight between sodium and lithium, sodium metal is slightly less effective than lithium metal in improving the reversible capacity and first-efficiency of silicon-oxygen-carbon composites. However, the carbon content of the silicon-oxygen-carbon composites is still significantly improved.

[0228] Both Examples 6 and 7 use carbon-containing metal complexes to synthesize silicon-oxygen-carbon composite materials. The carbon-containing metal complexes also play a positive role in increasing the carbon content, which shows that the direct use of carbon-containing metal complexes is feasible and can also solve the problem of some metals being difficult to disperse. For example, metals such as Cu and Al cannot be synthesized into metal-carbon source complexes by dissolving bulk metals.

[0229] The lithium intercalation performance tests conducted on Comparative Example 3 and Example 1 at different rate ranges showed that, even under similar carbon coating conditions, the rate performance of the silicon-oxygen-carbon composite material provided in Example 1 was significantly improved compared to that of the silicon-oxygen-carbon composite material provided in Comparative Example 3. This is because the silicon-oxygen-carbon composite material provided in Example 1 not only includes a carbon coating layer in its outer layer, but also has carbon protrusions formed on the surface of the carbon coating layer. This increases the wettability of the carbonaceous outer layer of the silicon-oxygen-carbon composite material to the electrolyte, promoting interfacial transport of lithium ions.

[0230] For the terms "each", "multiple" and "any" used in the embodiments of this disclosure, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the corresponding multiples.

[0231] The above description is only for the purpose of enabling those skilled in the art to understand the technical solutions disclosed herein, and is not intended to limit the scope of this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A silicon-oxygen-carbon composite material, characterized in that, The silicon-oxygen-carbon composite material includes: a core (1) and an outer layer (2), wherein the outer layer (2) includes: a carbon coating layer (21) and a plurality of carbon protrusions (22). The core (1) is a silicon-oxygen material doped with a metal, wherein the metal is selected from at least one of Li, Na, K, Mg, and Al, and the metal forms a silicate with a portion of the silicon-oxygen material; or, the metal is selected from at least one of Cu and Ag, and the metal forms a metal with a portion of the silicon-oxygen material. Silicon alloy; The carbon coating layer (21) covers the outside of the core (1), and the plurality of carbon protrusions (22) are formed on the outer surface of the carbon coating layer (21), making the outer surface of the carbon coating layer (21) uneven. The carbon coating layer (21) and the plurality of carbon protrusions (22) are carbonized using the same carbon source. The metal-doped silicon-oxygen material is provided by a metal source and a silicon-oxygen material, and the molar ratio of the silicon-oxygen material to the metal source is 1:0.05 to 1; The molar ratio of the silicon-oxygen material to the carbon source is 1:0.05 to 0.

5.

2. The silicon-oxygen-carbon composite material according to claim 1, characterized in that, The carbon protrusion (22) has a size of 5nm-50nm; The size of the carbon protrusion (22) is the size of the carbon protrusion (22) in the direction parallel to the surface of the core (1).

3. The silicon-oxygen-carbon composite material according to claim 1, characterized in that, The average difference in distance between any two adjacent carbon protrusions (22) is MD < 20%; in, r is the center distance between any two adjacent carbon protrusions (22), and n is the total number of carbon protrusions (22) on the carbon coating layer (21).

4. The silicon-oxygen-carbon composite material according to claim 1, characterized in that, The average particle size D50 of the silicon-oxygen-carbon composite material is less than or equal to 10 μm; The thickness of the carbon coating layer (21) is 1nm-100nm.

5. The silicon-oxygen-carbon composite material according to any one of claims 1-4, characterized in that, The chemical formula of the silicon-oxygen material is SiO₂. x Where 0.5 ≤ x < 2.

6. A method for preparing a silicon-oxygen-carbon composite material, characterized in that, The silicon-oxygen-carbon composite material is as described in any one of claims 1-5; The preparation method of the silicon-oxygen-carbon composite material includes: The carbon source, metal source, and silicon oxide material are stirred in a dispersion solvent for a first predetermined time, wherein the carbon source and the metal source form a metal source. A carbon source complex is formed, and then a solid-liquid separation process is performed to obtain a precursor of a silicon-oxygen-carbon composite material; wherein, the solid-liquid separation process includes: evaporation drying or distillation to remove the solvent without carrying away the carbon source adsorbed on the silicon-oxygen material. The precursor of the silicon-oxygen-carbon composite material is calcined under a protective atmosphere to obtain the silicon-oxygen-carbon composite material.

7. The method for preparing the silicon-oxygen-carbon composite material according to claim 6, characterized in that, The solid-liquid separation process is carried out under continuous stirring.

8. The method for preparing the silicon-oxygen-carbon composite material according to claim 6, characterized in that, The step of stirring the carbon source, metal source, and silicon oxide material in a dispersion solvent for a first set time includes: The carbon source and the metal source are subjected to a complexation reaction in the dispersion solvent to form a raw material system containing a metal source-carbon source complex; The silicon-oxygen material is added to the raw material system and stirred for the first set time.

9. The method for preparing the silicon-oxygen-carbon composite material according to claim 8, characterized in that, The metal source includes at least one of elemental Li, elemental Na, elemental K, and elemental Mg.

10. The method for preparing the silicon-oxygen-carbon composite material according to claim 8, characterized in that, The metal source is a carbon-containing metal complex.

11. The method for preparing the silicon-oxygen-carbon composite material according to claim 10, characterized in that, The carbon-containing metal complex includes at least one of lithium methyl, copper phthalocyanine, and aluminum acetylacetonate.

12. The method for preparing the silicon-oxygen-carbon composite material according to claim 6, characterized in that, The dispersing solvent includes at least one of dimethyl carbonate, tetrahydrofuran, toluene, benzene, diethyl ether, propylene oxide, ketones, and ethylene glycol dimethyl ether.

13. The method for preparing the silicon-oxygen-carbon composite material according to claim 6, characterized in that, The first set time is 3 hours to 24 hours.

14. The method for preparing the silicon-oxygen-carbon composite material according to any one of claims 6-13, characterized in that, The calcination process includes: Under the condition that the heating rate is greater than or equal to 5°C / min, the precursor of the silicon-oxygen-carbon composite material is heated to the calcination temperature, and the silicon-oxygen-carbon composite material is calcined at the calcination temperature for a second set time.

15. The method for preparing the silicon-oxygen-carbon composite material according to claim 14, characterized in that, The calcination temperature is 400℃~1200℃, and the second set time is 0.5h~10h.

16. A negative electrode material, characterized in that, The negative electrode raw materials include: silicon-based negative electrode materials, conductive agents, and binders; The silicon-based anode material is the silicon-oxygen-carbon composite material according to any one of claims 1-5.

17. A negative electrode sheet, characterized in that, The negative electrode sheet is prepared using the negative electrode raw material described in claim 16.

18. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 17.

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