A silicon-carbon composite material, its preparation method and application

Abstract

This invention provides a silicon-carbon composite material, its preparation method, and its application. The silicon-carbon composite material includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer; the core includes a carbon matrix and SiO₂. x The particles, wherein the carbon matrix is ​​continuously distributed and includes N channels communicating with the outside, and the SiO... x The particles fill the channels; wherein, the SiO x The particle size is 0.1-0.9 nm, 0.9 ≤ x ≤ 1.7, and N ≥ 1 and is an integer. This application's embodiments, by adjusting the structure and composition of the silicon-carbon composite material, overcome the shortcomings of silicon-based materials, such as poor stability and conductivity, thereby enabling the secondary battery to exhibit excellent energy density while also demonstrating good cycle performance, rate performance, and fast-charging performance.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, due to their high energy efficiency, environmental friendliness, and high energy density, are widely used in consumer electronics and electric vehicles, and have attracted much attention as a key technology for large-scale energy storage systems. On the one hand, with the development of 5G technology, consumer electronics will consume more power in battery antennas and radio frequencies, placing greater demands on battery capacity. On the other hand, with the popularization of pure electric vehicles and hybrid electric vehicles and the gradual phasing out of government subsidies, electric vehicles, relying on their own technological and product advantages, are particularly important for the sustainable and healthy development of the entire industry chain. This places higher demands on lithium-ion batteries, requiring them to have higher energy density and longer cycle life. The energy density of lithium-ion batteries is mainly determined by the specific capacity and potential of the positive and negative electrode materials. Graphite, as a traditional negative electrode material for lithium-ion batteries, has a relatively low theoretical specific capacity (372 mAh g / g). -1 Graphite, as a current technology, can no longer meet users' growing demand for energy density in lithium-ion batteries. Silicon, with a theoretical specific capacity of 4200 mAh / g, is the material with the highest theoretical specific capacity. Therefore, silicon-based materials are currently the most studied and considered one of the most likely alternatives to graphite as anode materials.

[0003] However, compared to traditional graphite anodes, silicon-based anodes are still in the immature stage of application in battery cells. Silicon, as a semiconductor material, has extremely low intrinsic electronic conductivity, only 2.52 × 10⁻⁶. -4 The low S / m ratio of silicon-based anode materials results in poor lithium-ion conductivity, impacting the battery's fast-charging capability. Furthermore, silicon's structural stability is questionable. During charging, as lithium ions extract from the positive electrode and embed into the silicon material, the silicon expands and pulverizes. During discharging, as lithium ions extract from the silicon, it contracts due to the formation of large voids. This expansion and contraction of the silicon-based anode during continuous charging and discharging severely affects the battery's cycle performance and rate capability. Summary of the Invention

[0004] This application provides a silicon-carbon composite material, its preparation method, and its application. By adjusting the structure and composition of the silicon-carbon composite material, the defects of poor stability and poor conductivity of silicon-based materials can be overcome, thereby enabling the secondary battery to have excellent energy density, as well as good cycle performance, rate performance, and fast charging performance.

[0005] The first aspect of this application provides a silicon-carbon composite material, which includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer;

[0006] The core comprises a carbon matrix and SiO₂. x The particles, wherein the carbon matrix is ​​continuously distributed and includes N channels communicating with the outside, and the SiO... x The particles fill the channels;

[0007] Wherein, the SiO x The particle size is 0.1-0.9 nm, 0.9 ≤ x ≤ 1.7, and N ≥ 1 and is an integer.

[0008] The silicon-carbon composite material in this embodiment has a core-shell structure, with SiO₂ in the core. x The particles are mainly used to complete the insertion and extraction of lithium ions, because SiO x The particles are extremely small, less than 1 nm in size, therefore SiO₂ is highly efficient during lithium-ion insertion / extraction. x The degree of expansion and contraction of the particles was also controlled, thus avoiding the formation of SiO₂. x The phenomenon of particle collapse and pulverization is beneficial to ensuring the structural stability of silicon-carbon composite materials; furthermore, due to SiO... x The particles fill the pores of the carbon matrix, therefore SiO x The carbon matrix surrounding the particles also affects SiO x The expansion caused by the particles acts as a buffer, thereby further improving the structural stability of the silicon-carbon composite material. Furthermore, the continuous structure of the carbon matrix and the SiO₂... x The small particle size ensures efficient transport of lithium ions and electrons, resulting in excellent conductivity of silicon-carbon composite materials.

[0009] Meanwhile, the coating structure of the silicon-carbon composite material can effectively prevent electrolyte from entering the core and causing repeated SEI film formation, effectively reducing lithium ion consumption and SiO2 content. x The reduction in effective sites for particles also allows them to act as a buffer within the core, further absorbing SiO₂. x The expansion force generated by the particles reduces the instability of the core, thereby ensuring the energy density and structural stability of the silicon-carbon composite material.

[0010] Therefore, the silicon-carbon composite material of this application embodiment, after being processed by SiO2, x While achieving high energy density, the particles also possess good structural stability and conductivity, which helps the secondary battery exhibit balanced electrical performance. It not only has high energy density, but also good cycle performance, rate performance, and fast charging performance.

[0011] In one possible implementation, the carbon matrix has a mass percentage of 10-40% based on the mass of the core. By limiting the mass content of the carbon matrix in the core, the balance of energy density, cycle performance, rate performance, and fast charging performance of the secondary battery can be greatly optimized.

[0012] In one possible implementation, the specific surface area of ​​the carbon matrix is ​​800-1400 m² / g. Since the carbon matrix has a porous structure, a larger specific surface area indicates a greater number, smaller size, and higher density of pores. Therefore, the SiO₂ filling the pores... x The more particles that are evenly and densely distributed on the surface of the carbon matrix, the more uniformly distributed SiO2 particles appear. x The particles not only improve the energy density of secondary batteries but also facilitate lithium-ion intercalation, ensuring the fast-charging capability of the batteries. Furthermore, the numerous small-sized channels help adjacent SiO₂ particles... x The particles all possess a continuous carbon matrix, which further ensures the carbon matrix's support for each SiO₂ particle. x Buffering of particle expansion force, improving SiO x The structural stability of the particles also allows for faster transport of lithium ions into the SiO2 core during charging. x Particles, during the discharge process, will transform SiO x The lithium ions that are deintercalated from the particles are conducted out of the core more quickly, thereby further improving the good rate performance and cycle performance of the secondary battery.

[0013] In one possible implementation, the specific surface area of ​​the silicon-carbon composite material is 5-20 m² / g. This specific surface area indicates that the carbon coating layer on the surface of the silicon-carbon composite material is relatively dense, thus effectively preventing the electrolyte from penetrating through the carbon coating layer and entering the core, avoiding the problem caused by SiO₂. x The potential pulverization and collapse of particles leads to the repeated formation of the SEI film, effectively suppressing lithium ion consumption and almost retaining SiO₂. x The insertion of lithium ions occurs at all effective sites in the particles, which greatly optimizes the cycle performance and rate performance of the secondary battery.

[0014] In one possible implementation, the Raman spectrum of the carbon matrix shows that 0.8 ≤ ID / IG ≤ 1.5. This ratio indicates that in the silicon-carbon composite material of this application, the carbon matrix has a high degree of graphitization, which is not only more conducive to electron conduction, but also... x During particle expansion, the highly graphitized carbon matrix also undergoes slippage, resulting in better release of SiO. x The expansion stress of particles.

[0015] In one possible implementation, the nuclear magnetic resonance spectrum of the silicon-carbon composite material includes Si-C peaks and Si-O peaks, wherein the intensity I of the Si-C peak is... Si-C The intensity of the Si-O peak I Si-O The ratio is <0.05. Unlike traditional silicon-oxygen-carbon materials, which contain a large number of Si-C bonds that affect the conductivity of the material, the silicon-carbon composite material of this application has extremely low Si-C bonds, so the carbon matrix has better conductivity and can achieve fast charging capability for secondary batteries.

[0016] In one possible implementation, the thickness of the carbon coating layer is 5-20 nm, and the interlayer spacing d002 of the carbon atoms in the carbon coating layer is 0.3354-0.34 nm. This coating layer has a high degree of graphitization, and even if the core deforms and causes compression of the coating layer, the coating layer can release stress through interlayer slip, reducing the probability of the coating layer cracking and strengthening the protective strength of the coating layer for the core, thereby further ensuring the cycle performance and rate performance of the secondary battery.

[0017] In one possible implementation, the silicon-carbon composite material further includes at least one of N, P, B, Cl, Br, and I elements. Doping with these heterogeneous elements can improve the electrical conductivity of the silicon-carbon composite material, thereby enhancing the rate performance of the secondary battery.

[0018] In one possible implementation, the silicon-carbon composite material has a particle size of 50 nm to 2 μm. Depending on the particle size, the silicon-carbon composite material of this application embodiment is suitable for different application scenarios. For example, small-particle-size silicon-carbon composite materials can be used as a matrix for anode active materials and further processed, while large-particle-size silicon-carbon composite materials can be directly used as anode active materials and mixed with conductive agents, binders, etc., to prepare the active functional layer of the anode electrode.

[0019] In one possible implementation, the silicon-carbon composite material is prepared by a method comprising the following process:

[0020] 1) Under alkaline conditions, stir the aqueous solution of trimethoxysilane compounds to make the system turbid, and collect the precursor particles.

[0021] 2) The precursor particles are sintered to obtain a silicon-carbon composite material; the sintering temperature is 900-1200℃ and the time is 1-10h.

[0022] The second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0023] 1) Stir the aqueous solution of trimethoxysilane compounds at 25-85℃ and under alkaline conditions to make the system turbid, and collect the precursor particles.

[0024] 2) The precursor particles are sintered to obtain a silicon-carbon composite material; the sintering temperature is 1000-1200℃ and the time is 1-10h.

[0025] The silicon-carbon composite material includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer;

[0026] The core comprises a carbon matrix and SiO₂. x The particles, the carbon matrix comprising N channels communicating with the outside, the SiO x The particles fill the channels;

[0027] Wherein, the SiO x The particle size is 0.1-0.9 nm, where 0.9 ≤ x ≤ 1.7.

[0028] This preparation method can safely and efficiently produce silicon-carbon composite materials that not only help secondary batteries to have high energy density, but also exhibit good cycle performance, rate performance, and fast charging performance.

[0029] In one possible implementation, in step 1), ammonia water with a volume concentration of 0.6-15% is added to the aqueous solution of the trimethoxysilane compound to adjust the pH of the system to 8-13.

[0030] In one possible implementation, the volume concentration of the trimethoxysilane compound in the aqueous solution is 0.4-5%.

[0031] The above process parameters are beneficial to the dissolution of raw materials and can produce spherical silsesquioxane precursor particles of suitable size.

[0032] In one possible implementation, the heating rate of the sintering process is 1-10 °C / min. By controlling the heating program, the degree of graphitization of the carbon matrix can be increased.

[0033] In one possible implementation, after step 1), a carbon source is introduced into the system for carbon coating.

[0034] In one possible implementation, the carbon coating is performed using a vapor deposition reaction at a temperature of 700-1200°C.

[0035] The aforementioned carbon coating process parameters not only facilitate the formation of the carbon coating layer in silicon-carbon composite materials, but also further ensure the integrity of the SiO2 core. x Particle size, to avoid SiO x The particle size increases.

[0036] In one possible implementation, the trimethoxysilane compound is selected from one or more of trimethoxysilane, methyltrimethoxysilane, N-propyltrimethoxysilane, N-octyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, N-dodecyltrimethoxysilane, (3-chloropropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, trimethoxyphenylsilane, vinyltrimethoxysilane, and 3-iodophenyltrimethoxysilane.

[0037] A third aspect of this application provides an electrode sheet comprising the silicon-carbon composite material described in the first aspect, or a silicon-carbon composite material obtained by the preparation method of the second aspect.

[0038] Because both the silicon-carbon composite material obtained in the first aspect and the silicon-carbon composite material obtained in the second aspect have high energy density, good structural stability, and good conductivity, the electrode sheet can exhibit excellent performance; for example, the electrode sheet can be a negative electrode sheet. Specifically, the electrode sheet has a stable structure, the active layer is not easily detached from the current collector, has good conductivity, and can also achieve high capacity in secondary batteries.

[0039] The fourth aspect of this application provides a secondary battery, which includes the electrode sheet described in the third aspect above.

[0040] Since the secondary battery in this application uses the aforementioned electrode sheet, it has good performance in terms of cycle performance, rate performance and fast charging performance while having high capacity.

[0041] The fifth aspect of this application provides an electronic device, wherein the driving source or energy storage source of the electronic device is the secondary battery described in the fourth aspect above.

[0042] Since electronic devices are powered or have their energy stored in the aforementioned secondary batteries, they have excellent battery life and lifespan, resulting in a superior user experience. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application;

[0044] Figure 2 This is a schematic diagram of the disassembled structure of an electronic device provided in an embodiment of this application;

[0045] Figure 3a These are SEM images of the overall morphology and microstructure of the silicon-carbon composite material of Example 1 of this application;

[0046] Figure 3bThis is a high-resolution fractured region cross-sectional HAADF phase diagram of the silicon-carbon composite material of Example 1 of this application;

[0047] Figure 3c This is a TEM image of the silicon-carbon composite material of Example 1 of this application;

[0048] Figure 3d yes Figure 3c Enlarged view of a portion of the middle coating layer;

[0049] Figure 3e This is a high-resolution STEM image of the silicon-carbon composite material of Example 1 of this application;

[0050] Figure 3f This is an EELS surface scan of the silicon-carbon composite material of Example 1 of this application;

[0051] Figure 3g This is an EELS surface scan of the silicon-carbon composite material of Example 1 of this application;

[0052] Figure 3h This is an EELS surface scan of the silicon-carbon composite material of Example 1 of this application;

[0053] Figure 4 This is the 29Si magic angle rotation nuclear magnetic resonance (MAS NMR) spectrum of the silicon-carbon composite material of Example 1 of this application;

[0054] Figure 5a This is a TEM image of the carbon matrix after etching of the silicon-carbon composite material in Example 1 of this application;

[0055] Figure 5b This is the Raman spectrum of the carbon matrix after etching of the silicon-carbon composite material in Example 1 of this application;

[0056] Figure 5c These are the N2 adsorption-desorption curves of the silicon-carbon composite material before and after etching in Example 1 of this application;

[0057] Figure 5d This is the pore size distribution curve of N2 adsorption and desorption of the silicon-carbon composite material before and after etching in Example 1 of this application;

[0058] Figure 5e This is the CO2 pore size distribution curve of the carbon matrix after etching of the silicon-carbon composite material in Example 1 of this application;

[0059] Figure 5f This is the XPS spectrum of the silicon-carbon composite material of Example 1 of this application;

[0060] Figure 6 This is a schematic diagram of the overall morphology and microstructure of the silicon-carbon composite material of Example 2 of this application;

[0061] Figure 7a This is an electron microscope image of the morphology of the silicon-oxygen-carbon anode material of Comparative Example 1 of this application;

[0062] Figure 7b This is an internal TEM image of the silicon-oxygen-carbon anode material of Comparative Example 1 of this application;

[0063] Figure 8a This is the high-resolution fractured region cross-section HAADF phase diagram of the silicon-carbon composite material of Comparative Example 2 of this application;

[0064] Figure 8b This is a TEM image of the carbon matrix after etching the silicon-carbon composite material in Comparative Example 2;

[0065] Figure 9 This is the 29Si magic angle rotation nuclear magnetic resonance (MAS NMR) spectrum of the silicon-carbon composite material in Comparative Example 2.

[0066] Explanation of reference numerals in the attached figures:

[0067] 1-current collector;

[0068] 2-Electrode active material;

[0069] 3-Conductive agent;

[0070] 4-Adhesive;

[0071] 10 - Display screen;

[0072] 30 - Circuit board;

[0073] 31-Heating element;

[0074] 40-Lithium-ion battery;

[0075] 50-Metal frame;

[0076] 52-Metal mid-plate;

[0077] 53 - Metal frame;

[0078] 60 - Rear shell;

[0079] 100 - Mobile Phone. Detailed Implementation

[0080] The terminology used in the implementation section of this application is only for explaining specific embodiments of this application and is not intended to limit this application. The implementation of the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0081] To overcome the poor structural stability of silicon-based materials, those skilled in the art have used various methods to improve silicon-based materials.

[0082] For example, the literature "Crystalline-amorphous core-shell silicon nanowires for high capacity and high current battery electrodes. Nano Lett., 2009, 491-495" introduces the core-shell design of silicon nanowires for high-power and long-life lithium-ion battery electrodes. "Silicon crystalline core-amorphous shell nanowires" are grown directly on stainless steel current collectors via a simple one-step synthesis. Due to the difference in their lithiation potentials, an amorphous silicon shell can be chosen instead of a crystalline silicon core to achieve electrochemical activity. Thus, the crystalline silicon core provides stable mechanical support and an efficient conductive path, while the amorphous shell stores Li+ ions. These core-shell nanowires exhibit a high charge storage capacity of approximately 1000 mAh / g and a capacity retention of approximately 90% after 100 cycles. They also demonstrate excellent electrochemical performance at high charge-discharge rates (6.8 A / g, approximately 20 times that of carbon at 1 h rate). The paper "A pomegranate-inspired nanoscale design for large-volume change lithium battery anodes, Nature Nanotech, 2014, 9, 187-192" proposes a layered silicon anode structure inspired by the structure of a pomegranate. Individual silicon nanoparticles are encapsulated in a conductive carbon layer, providing sufficient space for expansion and contraction after lithiation and delithiation. These hybrid nanoparticles are then encapsulated in micron-sized pouches, further encased in a thicker carbon layer that acts as a barrier to the electrolyte. This layered arrangement ensures the stability and spatial confinement of the solid electrolyte mesophase, resulting in excellent cyclability (97% capacity retention after 1,000 cycles). While these nanomaterials structurally mitigate silicon volume expansion and provide a good physical barrier against direct contact with the electrolyte, their complex internal structures and numerous internal spaces lead to issues such as large specific surface area and low tap density, hindering practical application. Moreover, whether it is core-shell silicon nanowires or yolk-shell structured silicon nanoparticles, their structural stability against external pressure is poor. They are prone to deformation and particle breakage during the actual rolling process of electrode processing, which leads to direct contact between the electrolyte and the internal silicon material, resulting in a large number of side reactions that affect the cell performance and make it difficult to reproduce the ultra-high performance described in the article.

[0083] CN102214823A, CN106816594A, and others disclose a silicon-silicon oxide composite structure, specifically a structure in which silicon particles with a diameter of 0.5-50 nm are dispersed in silicon oxide at the atomic level and / or in a microcrystalline state. To further improve the initial efficiency of silicon monoxide, lithium was added to the previous structure, resulting in a structure where 1-50 nm silicon particles are dispersed in silicates and silicon oxides at the atomic level and / or in a microcrystalline state. Specifically, the nano-silicon is uniformly dispersed in silicon oxide and / or silicates. After lithium intercalation, the silicon oxide forms a chemically inert lithium oxide and silicate network, which can act as a buffer layer to alleviate the stress caused by the expansion of the nano-silicon. This material structure disperses nano-silicon in SiO₂. x In the network of silicon and / or silicates, although the stress generated by the expansion after silicon lithium intercalation can be absorbed relatively well, the electronic conductivity of the network is very low, which affects the fast charging capability of the material.

[0084] CN107093711B et al. disclose a monodisperse SiO₂ x Mass production method of -C composite microspheres, and the structure and properties of the microspheres to improve monodisperse SiO2 x The structural stability of the -C composite microspheres is important. However, in addition to the organosilicon source, the synthesis process involves the use of phenol and formaldehyde polycondensation as additional carbon sources, thus introducing a large amount of carbon into the material, affecting its lithium intercalation capacity and first-pass efficiency. Furthermore, the presence of numerous Si-C bonds in the material prevents complete SiO2 intercalation. x Separation from the carbon network phase means that a large number of Si-C bonds will affect the internal conductivity of the material, and the Si bonded to C atoms has very low electrochemical activity, which will negatively affect the material's lithium intercalation capacity and fast charging capability.

[0085] To address the aforementioned deficiencies, a first aspect of this application provides a silicon-carbon composite material. This silicon-carbon composite material includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer; the core includes a carbon matrix and SiO₂. x The particles, wherein the carbon matrix is ​​continuously distributed and includes N channels communicating with the outside, and the SiO... x The particles fill the channels; wherein, the SiO x The particle size is 0.1-0.9 nm, 0.9 ≤ x ≤ 1.7, and N ≥ 1 and is an integer.

[0086] The silicon-carbon composite material in this application embodiment has a core-shell structure, wherein the core includes a carbon matrix and pores (SiO2) disposed in the surface pores of the carbon matrix. x SiO₂ particles with a maximum size of 0.1-0.9 nm x It should be noted that the SiO in the silicon-carbon composite material implemented in this application is particulate. xThe particles are all located inside the pores of the carbon matrix, and the embodiments of this application are not limited to SiO. x The filling degree of the particles in the pores can be less than or equal to 100%. In the embodiments of this application, the pores refer to accommodating spaces with a certain depth, resembling worms and connected to the outside, and the carbon matrix refers to a continuously distributed carbon structure with a certain volume.

[0087] As a silicon-based material with high specific capacity, the SiO core... x Particles can significantly improve the energy density of silicon-carbon composite materials, thereby enabling secondary batteries containing silicon-carbon composite materials to have higher energy densities. To overcome SiO... x The poor stability of the particle structure is a defect in the SiO2 implementation of this application. x The particle size is extremely small, only 0.1-0.9 nm, therefore even if lithium-ion intercalation leads to SiO2... x The particles expand in volume, but the degree of expansion is extremely low, and collapse and pulverization are virtually nonexistent; meanwhile, as a SiO2... x The carbon matrix, which provides space for SiO2 particles, can not only accommodate SiO2 x The expansion of the particles provides a buffering effect and can also effectively separate adjacent SiO₂ particles. x Particles, avoiding SiO x The excessive expansion of particles due to agglomeration further maintains the SiO₂ content. x The structural stability of the particles. Therefore, the silicon-carbon composite material of the present application can overcome the defects of poor structural stability and easy expansion of silicon-based materials.

[0088] In addition, small-sized SiO x The particles also shorten the lithium ion time in SiO2. x The internal transport path of the particles improves the diffusion rate of lithium ions, and SiO x The lithium oxide produced during the reaction between the particles and the intercalated lithium ions also contributes to improved ionic conductivity. Within the core, the continuously distributed carbon matrix effectively acts as both a continuous ion-conducting network and a conductive network, providing a platform for lithium ion intercalation into SiO₂. x The particle path also enables the generated electrons to be quickly output to the external circuit, thus the silicon-carbon composite material of this application embodiment exhibits good conductivity.

[0089] Because silicon-based materials are prone to expansion and pulverization, their specific surface area increases repeatedly with the expansion and pulverization of the silicon-based material when in contact with electrolyte. This leads to the repeated formation of an SEI film on the surface of the silicon-based material, consuming more electrolyte. This not only causes a large consumption of lithium ions but also increases gas production, creating a safety hazard. In the silicon-carbon composite material of this application embodiment, the carbon coating layer, as an outer shell structure, at least covers part of the core surface. It acts as a barrier to prevent electrolyte intrusion into the core, reducing the contact area between the electrolyte and the core, especially with SiO₂. x The contact area of ​​the particles is increased to avoid excessive lithium loss and excessive gas production.

[0090] The silicon-carbon composite material of this application embodiment includes high-specific-capacity SiO₂ in its core. x Particles, and by controlling SiO x The size and distribution of particles in SiO x The continuous carbon matrix surrounding the particles overcomes the SiO₂ x The defects of SiO2, such as easy particle expansion and poor electrical conductivity, are largely avoided. x The negative impact of particulate matter on the cycle performance, rate performance, and fast charging performance of secondary batteries is mitigated. Furthermore, the carbon coating layer covering the core surface further reduces the contact area between the silicon-carbon composite material and the electrolyte, decreasing lithium loss and gas production during long-term cycling, thus ensuring the cycle performance and safety of the secondary battery. Therefore, the silicon-carbon composite material of this application, while imparting high energy density to the secondary battery, also balances cycle performance, rate performance, and fast charging performance, resulting in a more balanced and superior electrical performance.

[0091] As a component of the core, the carbon matrix can comprise 10-40% by mass within the core. It is understandable that the carbon matrix and SiO₂... x As particles are the main components of the core, the mass percentages of both in the core and the core show opposite trends; that is, as the mass percentage of the carbon matrix in the core increases, SiO₂... x The mass percentage of particles in the core decreases; when the mass percentage of the carbon matrix in the core decreases, SiO... x The mass percentage of particles in the core increases. Although SiO x A higher particle mass content contributes to improving the energy density of secondary batteries, but this also leads to increased SiO₂ content. x The expansion and aggregation of particles are also quite severe. Therefore, when the mass percentage of the carbon matrix in the core is 10-40%, it is possible to effectively achieve the carbon matrix's influence on SiO while maintaining a satisfactory energy density in the secondary battery. x The buffering and separating effects of the particles balance the composition of SiO₂.x The positive and negative effects of the particles ensure the cycle performance and rate performance of the secondary battery. Simultaneously, the aforementioned carbon matrix mass percentage guarantees good conductivity in the silicon-carbon composite material, thereby improving the fast-charging capability of the secondary battery.

[0092] In one possible implementation, the specific surface area of ​​the carbon matrix is ​​800-1400 m² / g, indicating that a large number of channels are distributed on the surface of the carbon matrix. It is understandable that the larger the N value, the better the SiO₂ content. x The more particles there are, the better for SiO2. x The particles have a high distribution density on the carbon matrix surface, making it easier for lithium ions to form on SiO₂. x Intercalation occurs on the particle surface, accelerating the lithium-ion intercalation rate and facilitating fast charging of rechargeable batteries. Furthermore, the numerous porous structures indicate that a carbon matrix surrounds the SiO₂ matrix. x The surrounding area of ​​the particle ensures the SiO2 x The independence of particle distribution is achieved by reducing SiO₂. x The aggregation of particles further improves the structural stability of silicon-carbon composite materials, thereby ensuring the cycle performance and rate performance of secondary batteries.

[0093] Furthermore, the specific surface area of ​​the silicon-carbon composite material in this application embodiment is 5-20 m² / g. The relatively small specific surface area of ​​the silicon-carbon composite material indicates a dense surface structure. This not only reduces the contact area between the electrolyte and the surface of the silicon-carbon composite material, preventing the formation of a large-area SEI film and thus avoiding electrolyte loss, but also effectively prevents the electrolyte from entering the core and preventing SiO₂ from forming. x The expansion and pulverization of particles leads to excessive consumption of electrolyte. Therefore, the specific surface area of ​​this silicon-carbon composite material helps to improve the cycle performance and rate performance of the secondary battery by reducing lithium loss.

[0094] Furthermore, the dense surface of the silicon-carbon composite material reduces the contact between the core and the electrolyte, preventing other compounds in the electrolyte from preferentially reacting with SiO₂ over lithium ions. x The particles react, therefore in this embodiment, SiO x The particles have more effective sites for lithium ion intercalation, enabling the secondary battery to exhibit satisfactory cycle performance and rate performance.

[0095] To further ensure the excellent conductivity of the carbon matrix and the protection of SiO2 x The buffering effect of the particles can be achieved by selecting a carbon matrix with a high degree of graphitization. Specifically, in the Raman spectrum of the carbon matrix, 0.8 ≤ ID / IG ≤ 1.5. The inventors found that carbon matrices with ID / IG in this range are more effective when subjected to SiO₂. xThe degree of slippage between interlayers caused by the stress generated by particle expansion can effectively release stress without damaging the carbon coating.

[0096] Furthermore, the use of different positive electrode active materials, electrolytes, or separators in secondary batteries will affect their fast-charging performance. Therefore, generally speaking, for the aforementioned different positive electrode active materials, electrolytes, and separators, when the carbon matrix's conductivity is 0.8 ≤ ID / IG ≤ 1.5, the conductivity of the carbon matrix can be largely guaranteed to be outstanding, thus maximizing the optimization of the secondary battery's fast-charging performance.

[0097] Besides ensuring the graphitization degree of the carbon matrix, in one possible implementation, the silicon-carbon composite material of this application differs from traditional silicon-oxygen-carbon materials in that it has a large number of Si-C bonds that limit the material's electrical conductivity. The nuclear magnetic resonance spectrum of the silicon-carbon composite material of this application includes Si-C peaks and Si-O peaks, and the intensity of the Si-C peak is I. Si-C The intensity of the Si-O peak I Si-O The ratio is <0.05. This is understandable, as the core of silicon-carbon composites includes both silicon and carbon elements, but the Ig of silicon-carbon composites... Si-C / I Si-O The extremely low conductivity indicates that the carbon matrix in the core exists basically independently and does not form many bonds with silicon, which further ensures the excellent conductivity of carbon, thus enabling the secondary battery to exhibit more outstanding fast charging performance.

[0098] In one possible implementation, the carbon coating layer can be a structure with a thickness of 5-20 nm and a carbon atom interlayer spacing d002 of 0.3354-0.34 nm.

[0099] As mentioned above, the carbon coating layer in the silicon-carbon composite material of this application is mainly used to isolate the electrolyte from the core, thereby avoiding excessive lithium loss and affecting the cycle performance and rate performance of the secondary battery. Specifically, the carbon coating layer with the above parameters can not only effectively isolate the electrolyte from the core, but also ensure that the carbon atom interlayer spacing d002 can effectively absorb the expansion force and release the expansion force through interlayer slip when the core expands, thus avoiding the loss of SiO2 during long-term cycling. x Excessive particle expansion may lead to the rupture of the carbon coating layer, which further reduces the probability that the electrolyte may come into contact with the core, thus helping to maintain the cycle performance and rate performance of the secondary battery.

[0100] In addition to Si, O, and C, the silicon-carbon composite material of this application embodiment also includes at least one of the heterogeneous elements such as N, P, B, Cl, Br, and I. Specifically, the raw materials for preparing the silicon-carbon composite material may contain the above-mentioned heterogeneous elements, which are then doped into the silicon-carbon composite material. The specific doping sites are located in SiO. x In particles and / or a carbon matrix. Doping with heterogeneous elements is beneficial for improving the electrical conductivity of silicon-carbon composite materials, thereby enhancing the fast-charging performance and rate performance of secondary batteries.

[0101] In specific applications, the silicon-carbon composite material of this application can be used as a matrix for other processes as needed, or it can be directly mixed with conductive agents to prepare the active functional layer of the electrode sheet. The silicon-carbon composite material of this application has a particle size of 50 nm-2 μm, and the above-mentioned scenarios can be achieved by selecting silicon-carbon composite materials with different particle sizes. Taking the preparation of a negative electrode sheet as an example, specifically, silicon-carbon composite materials with smaller particle sizes are easier to use as a matrix for further processing of the negative electrode active material, while silicon-carbon composite materials with larger particle sizes can be directly used as the negative electrode active material.

[0102] In one possible implementation, the silicon-carbon composite material of this application embodiment is prepared by a method including the following process:

[0103] 1) Under alkaline conditions, stir the aqueous solution of trimethoxysilane compounds to make the system turbid, and collect the precursor particles.

[0104] 2) The precursor particles are sintered to obtain a silicon-carbon composite material; the sintering temperature is 900-1200℃ and the time is 1-10h.

[0105] In this embodiment, a silicon-carbon composite material with the above-mentioned structure is obtained by using trimethoxysilane compounds as raw materials and through processes such as dissolution and sintering.

[0106] The aqueous solution of the trimethoxysilane compound in step 1) can be prepared by adding the trimethoxysilane compound to water and stirring for 10-30 minutes. In one possible implementation, the volume concentration of the aqueous solution of the trimethoxysilane compound is 0.4-5%.

[0107] The embodiments of this application do not limit the specific types of trimethoxysilane compounds, and may be selected from at least one of trimethoxysilane, methyltrimethoxysilane, N-propyltrimethoxysilane, N-octyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, N-dodecyltrimethoxysilane, (3-chloropropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, trimethoxyphenylsilane, vinyltrimethoxysilane, 3-iodophenyltrimethoxysilane, etc. When multiple trimethoxysilane compounds are selected, the embodiments of this application do not limit the proportion between the various compounds.

[0108] It is understandable that by selecting trimethoxysilane compounds, it is possible to achieve the doping of heterogeneous elements in silicon-carbon composite materials and to control the mass content of the carbon matrix in silicon-carbon composite materials.

[0109] The temperature range for step 1) above is relatively wide, generally controlled between 0℃ and 100℃, and can be further adjusted to 25-85℃. During the preparation process, the precursor particle size can be controlled by regulating the temperature in step 1). Specifically, the choice of temperature has a significant impact on the precursor particle size, and the particle size gradually decreases as the temperature increases.

[0110] Under alkaline conditions, the trimethoxysilane aqueous solution undergoes hydrolysis to form a white emulsion. Stirring continues until the color of the white emulsion no longer changes, at which point stirring is stopped. After a period of settling and aging, the mixture is filtered to collect the precursor particles, specifically spherical silsesquioxane precursors. Generally, the duration of continuous stirring and settling is 0.5–24 hours.

[0111] In step 1), alkalinity refers to a pH range of 8-13 for the system. One possible implementation is to achieve this alkalinity by adding ammonia to an aqueous solution of trimethoxysilane. The inventors have found that the concentration of ammonia has a significant impact on the size of the precursor particles; a volume concentration of 0.6-15% ammonia helps control the precursor particle size to 400-600 nm. Within this range, as the ammonia concentration increases, the precursor particle size first decreases and then tends to stabilize.

[0112] In step 2), the aforementioned collected precursor particles are sintered at 1000-1200℃ for 1-10 hours to obtain a silicon-carbon composite material. Before sintering, the precursor particles can be washed with ethanol and dried.

[0113] During sintering at 1000-1200℃, the C=C groups in the precursor particles lose hydrogen, carbonize, and connect to form a continuous carbon matrix, thereby bonding SiO₂. x SiO2 segmented into 0.1-0.9 nm x The precursor particles fill the carbon matrix, and the breaking of Si-C bonds in the precursor particles also forms a carbon matrix. Furthermore, the high-temperature sintering and carbonization process promotes the flow of lightweight carbon from the precursor particles to the particle surface, where it carbonizes to form a carbon coating layer, thus obtaining a silicon-carbon composite material. The inventors discovered that during the sintering process of 1-10 hours, the degree of graphitization of the carbon matrix is ​​affected to varying degrees with the extension of sintering time.

[0114] The second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0115] 1) Under alkaline conditions, stir the aqueous solution of trimethoxysilane compounds to make the system turbid, and collect the precursor particles.

[0116] 2) The precursor is sintered to obtain a silicon-carbon composite material; the sintering temperature is 900-1200℃ and the time is 1-10h.

[0117] The silicon-carbon composite material includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer;

[0118] The core comprises a carbon matrix and SiOx particles. The carbon matrix includes N channels communicating with the outside, and the SiOx particles fill the channels.

[0119] The size of the SiOx particles is 0.1-0.9 nm, where 0.9 ≤ x ≤ 1.7.

[0120] This application uses trimethoxysilane compounds as raw materials and obtains a silicon-carbon composite material with the above-mentioned structure through dissolution, sintering, and other processes. This silicon-carbon composite material overcomes the defects of silicon-based materials in terms of structural stability and poor conductivity, and can improve the energy density of secondary batteries while achieving a balanced performance in cycle performance, rate performance, and fast charging performance.

[0121] The aqueous solution of the trimethoxysilane compound in step 1) can be prepared by adding the trimethoxysilane compound to water and stirring for 10-30 minutes. In one possible implementation, the volume concentration of the aqueous solution of the trimethoxysilane compound is 0.4-5%.

[0122] The embodiments of this application do not limit the specific types of trimethoxysilane compounds, and may be selected from at least one of trimethoxysilane, methyltrimethoxysilane, N-propyltrimethoxysilane, N-octyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, N-dodecyltrimethoxysilane, (3-chloropropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, trimethoxyphenylsilane, vinyltrimethoxysilane, 3-iodophenyltrimethoxysilane, etc. When multiple trimethoxysilane compounds are selected, the embodiments of this application do not limit the proportion between the various compounds.

[0123] It is understandable that by selecting trimethoxysilane compounds, it is possible to achieve the doping of heterogeneous elements in silicon-carbon composite materials and to control the mass content of the carbon matrix in silicon-carbon composite materials.

[0124] In existing technologies, alcohol-based additives are often added to the system to adjust the hydrolysis reaction of silane compounds. To control costs, simplify the process, and increase the environmental adaptability of the material synthesis, this application employs an alcohol-free hydrolysis method. By stirring the trimethoxysilane aqueous solution under alkaline conditions, not only is the dissolution of the trimethoxysilane facilitated, but the size of the precursor can also be controlled by adjusting the temperature.

[0125] In this embodiment, the temperature range for step 1) is relatively wide, generally controlled between 0°C and 100°C, and further can be 25-85°C. During the preparation process, the precursor particle size can be controlled by controlling the temperature of step 1). Specifically, the choice of temperature has a significant impact on the size of the precursor particles, and the size of the precursor particles gradually decreases as the temperature increases.

[0126] Under alkaline conditions, the trimethoxysilane aqueous solution undergoes hydrolysis to form a white emulsion. Stirring continues until the color of the white emulsion no longer changes, at which point stirring is stopped. After a period of settling and aging, the mixture is filtered to collect the precursor particles, specifically spherical silsesquioxane precursors. Generally, the duration of continuous stirring and settling is 0.5–24 hours.

[0127] In step 1), alkalinity refers to a pH range of 8-13 for the system. One possible implementation is to achieve this alkalinity by adding ammonia to an aqueous solution of trimethoxysilane. The inventors have found that the concentration of ammonia has a significant impact on the size of the precursor particles; a volume concentration of 0.6-15% ammonia helps control the precursor particle size to 400-600 nm. Within this range, as the ammonia concentration increases, the precursor particle size first decreases and then tends to stabilize.

[0128] In step 2), the aforementioned collected precursor particles are sintered at 1000-1200℃ for 1-10 hours to obtain a silicon-carbon composite material. Before sintering, the precursor particles can be washed with ethanol and dried.

[0129] During the sintering process, the C=C groups in the precursor particles lose hydrogen, carbonize, and connect to form a continuous carbon matrix, thereby bonding SiO₂. x SiO2 segmented into 0.1-0.9 nm x The precursor particles fill the carbon matrix, and the breaking of Si-C bonds in the precursor particles also forms a carbon matrix. Furthermore, the high-temperature sintering and carbonization process promotes the flow of lightweight carbon from the precursor particles to the particle surface, where it carbonizes to form a carbon coating layer, thus obtaining a silicon-carbon composite material. The inventors discovered that during the sintering process of 1-10 hours, the degree of graphitization of the carbon matrix is ​​affected to varying degrees with the extension of sintering time.

[0130] The sintering process needs to be carried out under an inert / reducing atmosphere, which includes, but is not limited to, one or more of N2, Ar, and H2. In one possible implementation, the sintering process can be carried out in a high-temperature furnace.

[0131] In the specific sintering process, the precursor particles can be placed in a high-temperature furnace, and the temperature can be gradually increased to the target temperature by setting a heating program (heating rate) before sintering for 1-10 hours. In one possible implementation, a heating rate of 1-10℃ / min during sintering is conducive to the formation of a denser and more continuous carbon matrix, thereby facilitating lithium-ion conduction.

[0132] Furthermore, after step 1), the carbon content in the carbon coating layer on the core surface can be adjusted by introducing a carbon source into the system. Specifically, the carbon source can be introduced before, during, or after step 2). The carbon source can be, for example, at least one of alkanes, alkenes, alkynes, and benzene. In one possible implementation, adjusting the carbon content of the carbon coating layer on the core surface using chemical vapor deposition (CVD) is beneficial for improving the graphitization degree of the carbon coating layer. Specifically, the CVD temperature is 700-1200°C.

[0133] A third aspect of this application provides an electrode sheet comprising the silicon-carbon composite material of the first aspect or the silicon-carbon composite material prepared in the second aspect.

[0134] The electrode sheet in the embodiments of this application can be a positive electrode sheet or a negative electrode sheet.

[0135] Taking the negative electrode as an example, in one possible implementation, silicon-carbon composite material, conductive agent, and binder are added to a solvent and stirred to disperse them to obtain a negative electrode slurry. The negative electrode slurry is then coated onto at least one surface of a negative electrode current collector (generally copper foil), and the solvent is dried. The negative electrode slurry is transformed into a negative electrode active layer, resulting in the negative electrode of this embodiment. For example, the conductive agent can be selected from, but is not limited to, at least one of super-P, conductive carbon black, carbon nanotubes, and acetylene black; the binder can be selected from, but is not limited to, one of polyvinylidene fluoride (PVDF) or polyethylene oxide (PEO); and the solvent can be distilled water.

[0136] Since the silicon-carbon composite material of the first aspect or the silicon-carbon composite material prepared by the aforementioned second aspect has high energy density and good structural stability and conductivity, the negative electrode active layer of the electrode sheet is not easy to fall off from the current collector surface and has good conductivity. It can not only improve the energy density of the secondary battery, but also take into account the cycle performance, rate performance and fast charging performance of the secondary battery.

[0137] The fourth aspect of this application provides a secondary battery, which includes the electrode sheet described in the third aspect above.

[0138] The secondary battery of this application embodiment, due to the inclusion of the aforementioned electrode sheets, significantly improves energy density, cycle performance, rate performance, and fast charging performance. This secondary battery can be, for example, a lithium-ion battery or a sodium-ion battery.

[0139] Taking the negative electrode as an example, the secondary battery in this application embodiment includes a positive electrode, a separator, and an electrolyte, in addition to the negative electrode.

[0140] In one possible implementation, the positive electrode sheet includes a positive electrode active layer disposed on at least one surface of a positive electrode current collector (typically aluminum foil). Specifically, a positive electrode slurry is coated onto at least one surface of the positive electrode current collector, and then the solvent in the positive electrode slurry is dried to obtain the positive electrode sheet. The positive electrode slurry includes at least a positive electrode active material, a conductive agent, a binder, and a solvent. Exemplarily, the positive electrode active material may be selected from, but is not limited to, at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate; the conductive agent may be selected from, but is not limited to, at least one of super-P, conductive carbon black, carbon nanotubes, and acetylene black; the binder may be selected from, but is not limited to, polyvinylidene fluoride (PVDF) or polyethylene oxide (PEO); and the solvent may be N-methylpyrrolidone (NMP).

[0141] In one possible implementation, the diaphragm may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0142] In one possible implementation, the electrolyte includes at least an organic solvent and a lithium salt. The organic solvent may be selected from at least one of ethylene carbonate, butenyl carbonate, propylene carbonate, methyl ethyl carbonate, vinylene carbonate, vinylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, difluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and dipropyl carbonate. The lithium salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0143] The fifth aspect of this application provides an electronic device, wherein the driving source or energy storage unit of the electronic device is the secondary battery described in the fourth aspect above.

[0144] The electronic device of this application embodiment has excellent battery life and service life because it uses the aforementioned secondary battery as a driving source or energy storage unit, resulting in high user satisfaction.

[0145] Among them, electronic devices may include, but are not limited to, mobile or fixed terminals with batteries such as mobile phones, tablets, laptops, ultra-mobile personal computers (UMPCs), handheld computers, walkie-talkies, netbooks, POS machines, personal digital assistants (PDAs), wearable devices, and virtual reality devices.

[0146] In this embodiment, a mobile phone 100 is used as an example for explanation. The mobile phone 100 can be a foldable phone or a candybar phone. In this embodiment, a candybar phone 100 is used as an example. Figure 1 and Figure 2 The structure of mobile phone 100 is shown; see [link / reference]. Figure 1 and Figure 2 As shown, the mobile phone 100 may include: a display screen 10, a back cover 60, a metal frame 50, a circuit board 30, and a secondary battery 40 located between the display screen 10 and the back cover 60. The display screen 10 is disposed on one side of the metal frame 50, and the back cover 60 is disposed on the other side of the metal frame 50.

[0147] The display screen 10 can be an organic light-emitting diode (OLED) display screen or a liquid crystal display (LCD). The back cover 60 can be a metal back cover 60, a glass back cover 60, a plastic back cover 60, or a ceramic back cover 60. The metal frame 50 can be made of magnesium alloy or aluminum alloy.

[0148] It should be noted that, in this embodiment, the material of the metal frame 50 includes, but is not limited to, a frame made of metal materials such as magnesium alloy, aluminum alloy, and titanium alloy. The metal frame 50 can also be a non-metallic frame made of materials such as ceramic. The specific materials of the display screen 10, the back cover 60, and the metal frame 50 are set according to the actual application, and are not limited in this embodiment.

[0149] The metal frame 50 may include a metal plate 53 and a metal border 52 surrounding the bottom frame. The metal border 52 may include a top border and a bottom border arranged opposite each other, as well as two side borders located between the top border and the bottom border. The metal border 52 and the metal plate 53 may be connected by welding, snap-fitting, or integral molding.

[0150] The circuit board 30 and the secondary battery 40 can be disposed on the metal plate 53 of the metal frame 50. For example, the circuit board 30 and the secondary battery 40 can be disposed on the side of the metal plate 53 facing the rear shell 60, or the circuit board 30 and the secondary battery 40 can be disposed on the side of the metal plate 53 facing the display screen 10. When the circuit board 30 is disposed on the metal plate 53, an opening can be provided in the metal frame 50 to place the components on the circuit board 30 at the opening of the metal frame 50.

[0151] The circuit board 30 can be a printed circuit board (PCB), and the circuit board 30 has a heating element 31. The heating element 31 can be the main chip in the electronic device, such as a power amplifier, application processor (Central Processing Unit, CPU), power management IC (PMIC), or radio frequency chip.

[0152] The secondary battery 40 can be connected to the charging management module (not shown) and the circuit board 30 via a power management module. The power management module receives input from the secondary battery 40 and / or the charging management module, and supplies power to the processor, internal memory, external memory, display screen 10, camera, and communication module. The power management module can also monitor parameters such as the capacity, cycle count, and health status (leakage current, impedance) of the secondary battery 40. In some other embodiments, the power management module can be located within the processor of the circuit board 30. In still other embodiments, the power management module and the charging management module can be housed in the same device.

[0153] It is understood that the structures illustrated in the embodiments of this application do not constitute a specific limitation on the mobile phone 100. In other embodiments of this application, the mobile phone 100 may include more or fewer components than illustrated, or combine some components, or split some components, or have different component arrangements. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0154] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0155] The silicon-carbon composite material and the secondary battery of this application will be described in detail below through specific embodiments.

[0156] Example 1

[0157] The silicon-carbon composite material of this embodiment was prepared according to the following method:

[0158] 1) Measure 30 ml of deionized water and place it in a water bath to maintain a constant temperature of 85°C. Add 0.5 ml of trimethoxytrimethoxysilane and stir for 10 min to obtain an aqueous solution of trimethoxytrimethoxysilane.

[0159] Under stirring conditions, 0.2 ml of ammonia (25 wt.% - 28 wt.%) was added to an aqueous solution of trimethoxytrimethoxysilane to adjust the pH of the system to 8-9 to promote hydrolysis and form a white emulsion. The mixture was stirred for 3 h. After filtration, the solid product was washed with alcohol and dried to obtain a spherical trimethoxysilsesquiane precursor.

[0160] 2) Place the spherical trimethoxysilsesquiane precursor into a tube furnace, set the heating rate to 10°C / min, and hold at 1000°C for 5 hours under an argon protective atmosphere. After 4.5 hours of holding, introduce a methane / hydrogen mixture (10% vol.: 90% vol.) at a flow rate of 100 sccm, and stop the gas flow after 0.5 hours. Remove the material when the tube furnace naturally cools to below 100°C; this is the silicon-carbon composite material of this embodiment.

[0161] Figure 3a This is a schematic diagram of the overall morphology and microstructure of the silicon-carbon composite material of Example 1 of this application. Figure 3a It can be seen that the silicon-carbon composite material of Example 1 consists of microspheres with a uniform size distribution and a diameter of around 300 nm.

[0162] Figure 3b This is a high-resolution HAADF phase diagram of the fractured region section of the silicon-carbon composite material of Example 1 of this application. From... Figure 3b As can be seen, the worm-like SiOx (brighter areas) formed by mutual bridging in the internal structure of the silicon-carbon composite material are distributed in the continuous carbon matrix (darker areas).

[0163] Figure 3c This is a TEM image of the silicon-carbon composite material of Example 1 of this application. Figure 3d yes Figure 3c A magnified view of a point in the middle coating layer. (See image below.) Figure 3c As shown, the surface of the silicon-carbon composite material has a carbon coating layer (the part above the dashed line), and the coating layer is composed of ordered graphitized carbon. Figure 3d The d002 is 0.336 nm and the coating thickness is 10 nm.

[0164] Figure 3e This is a STEM image of the silicon-carbon composite material of Example 1 of this application. Figure 3f-3h This is an EELS surface scan of the silicon-carbon composite material of Example 1 of this application. From... Figure 3e Obvious graphitized carbon streaks can be observed, corresponding to Figure 3f-3h EELS surface scans show that a graphitized carbon layer is formed on the material surface. Figure 3f The area below the dashed line is green, and the area above the dashed line is black, indicating that silicon is evenly distributed in the material. Figure 3g This is a carbon element test of the entire particle. The area below the dashed line is red and the area above the dashed line is black, indicating that there are two forms of carbon in the material: carbon elements that are uniformly distributed inside the particle and carbon layers that coat the surface of the particle. Figure 3h It can be understood as Figure 3f and Figure 3g The composite image shows that the particle surface does indeed have a carbon coating layer, and the particle interior has a structure in which silicon and carbon are evenly distributed.

[0165] Figure 4 This is the 29Si magic angle rotation nuclear magnetic resonance (MAS NMR) spectrum of the silicon-carbon composite material of Example 1 of this application, wherein the [missing information] is located at 78.0 cm⁻¹. -1 The chemical shift characteristic peak belongs to the Si-C peak and can be attributed to 78.0 cm⁻¹. -1 The peak intensity I(Si-C) of the chemical shift Si-C is attributable to 111.0 cm⁻¹. -1 The ratio of the peak intensity I(Si-O) of chemically shifted Si-O(3) satisfies the relationship I(Si-C) / I(Si-O)<0.05.

[0166] The silicon-carbon composite material of Example 1 was etched using hydrofluoric acid, wherein the SiO₂... x It was etched away, leaving 15 wt.% carbon matrix. Figure 5a This is a TEM image of the carbon matrix after etching of the silicon-carbon composite material in Example 1 of this application. Figure 5a As shown, the carbon matrix is ​​continuously distributed and has multiple pore structures, which is a continuously distributed carbon network structure. Figure 5b This is the Raman spectrum of the carbon matrix after etching the silicon-carbon composite material of Example 1 of this application. Figure 5b As shown, the carbon matrix has a high degree of graphitization, with ID / IG = 0.9.

[0167] Before and after etching the silicon-carbon composite material of Example 1, the specific surface area of ​​the silicon-carbon composite material before etching and the carbon matrix after etching were tested using the nitrogen adsorption-desorption method. Figure 5c These are the N2 adsorption-desorption curves of the silicon-carbon composite material before and after etching in Example 1 of this application. Figure 5d These are the N2 adsorption-desorption pore size distribution curves of the silicon-carbon composite material before and after etching in Example 1 of this application. Combined with the BET adsorption isotherm equation, the specific surface area of ​​the silicon-carbon composite material before etching is 10 m² / g. 2 / g, while the specific surface area of ​​the etched carbon matrix is ​​as high as 1200m². 2 / g.

[0168] In addition, CO2 adsorption-desorption tests were used to test the etched carbon matrix. Figure 5e This is the CO2 pore size distribution curve of the carbon matrix after etching of the silicon-carbon composite material in Example 1 of this application. It can be seen that the carbon matrix in the gray area in the upper right corner is rich in white pores of 0.3nm-0.9nm, which is similar to SiO₂. x The particle size corresponds to the size.

[0169] Figure 5f This is the XPS spectrum of the silicon-carbon composite material of Example 1 of this application. According to... Figure 5f It can be seen that the silicon oxide in the silicon-carbon composite material of this embodiment is specifically SiO2.1.48 .

[0170] Example 2

[0171] The silicon-carbon composite material of this embodiment was prepared according to the following method:

[0172] 1) Measure 50 ml of deionized water, add 1.0 ml of 3-ureapropyltrimethoxysilane to it, and stir at room temperature for 30 min to obtain an aqueous solution of 3-ureapropyltrimethoxysilane;

[0173] Under stirring conditions, 0.5 ml of ammonia (25 wt.% - 28 wt.%) was added to an aqueous solution of 3-ureapropyltrimethoxysilane to make the pH of the system about 9 to promote hydrolysis and form a white suspension. The mixture was stirred for 24 h, filtered, dried and then pellets were obtained to form the ureapropyltrimethoxysilsesquisilane precursor.

[0174] 2) Place the ureapropyltrimethoxysilsesquisilane precursor into a tube furnace, set the heating rate to 5°C / min, and hold it at 1000°C for 8 hours in an argon protective atmosphere. When the tube furnace naturally cools down to below 100°C, remove the material, which is the silicon-carbon composite material of this embodiment.

[0175] Figure 6 This is a schematic diagram of the overall morphology and microstructure of the silicon-carbon composite material of Example 2 of this application. Figure 6 It can be seen that the silicon-carbon composite material of Example 2 consists of microspheres with a uniform size distribution and a diameter of around 1 μm.

[0176] Comparative Example 1

[0177] Comparative Example 1 is a commercially available silicon-oxygen-carbon anode material. Figure 7a This is a SEM image of the morphology of the silicon-oxygen-carbon anode material of Comparative Example 1 of this application. Figure 7b This is an internal TEM image of the silicon-oxygen-carbon anode material of Comparative Example 1 of this application. Figure 7a As shown, the silicon-oxygen-carbon anode material in Comparative Example 1 is an irregular bulk material with a D50 size of 5-6 μm. From... Figure 7b As can be seen, the internal structure of the silicon-oxygen-carbon anode material in Comparative Example 1 consists of approximately 5nm silicon-oxygen nanoparticles dispersed in a carbon matrix.

[0178] Comparative Example 2

[0179] The silicon-carbon composite material of this comparative example was prepared according to the following method:

[0180] 1) Disperse 1 mL of ammonia in a mixed solution of 20 mL of water and 10 mL of ethanol, stir for 1 h, then add 1 mL of vinyltriethoxysilane, and stir at room temperature for 5 h to obtain a milky white solution.

[0181] The milky white material was transferred to a polytetrafluoroethylene liner, hydrothermally heated at 100°C for 12 hours, and then centrifuged. The solid phase system was washed three times with deionized water and ethanol, respectively, and then placed in a drying oven at 70°C for 12 hours.

[0182] 2) Take a certain amount of the above product and place it in a quartz ceramic boat. Place it in a tube furnace for calcination. Set the heating rate to 5℃ / min and keep it at 800℃ for 45min in an argon protective atmosphere to finally obtain the silicon-carbon composite material of Comparative Example 2.

[0183] Figure 8a This is a high-resolution fractured region cross-sectional HAADF phase diagram of the silicon-carbon composite material of Comparative Example 2 of this application, in which SiO... x The particle size is >5nm.

[0184] The silicon-carbon composite material of Comparative Example 2 was etched using hydrofluoric acid. Figure 8b This is a TEM image of the carbon matrix after etching the silicon-carbon composite material in Comparative Example 2. Figure 8b As shown, the etched carbon matrix is ​​divided into several parts and is not distributed continuously.

[0185] Figure 9 The image shows the 29Si magic angle rotation nuclear magnetic resonance (MAS NMR) spectrum of the silicon-carbon composite material in Comparative Example 2, where I(Si-C) / I(Si-O) is significantly higher than that in Example 1.

[0186] Test case

[0187] 1. The silicon-carbon materials of Examples 1-2 and Comparative Examples 1-2 were pressed into sheets using a mercury intrusion porosimetry device, with a compaction density of 1.7 g / cm³. 3 The conductivity of the powder tablets was tested using a four-probe conductivity test, and the results are shown in Table 1.

[0188] 2. The silicon-carbon materials of Examples 1-2 and Comparative Examples 1-2 were mixed with graphite in a certain proportion to make the specific capacity uniformly 500mAh / g, and then assembled with lithium metal into coin cells.

[0189] In this process, active materials (silicon-carbon materials and graphite), acetylene black, and sodium alginate were dispersed in deionized water at a mass ratio of 70:20:10, stirred evenly, and sonicated for 4 hours to obtain an electrode slurry. The electrode slurry was then coated onto a copper foil surface and dried at 85°C to obtain a positive electrode sheet. A coin-type lithium-ion battery was assembled using 1M LiPF6 dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) as the electrolyte, a lithium foil as the negative electrode, Celgard 2400 as the separator, and CR 2025 stainless steel as the battery casing.

[0190] The cycle life and rate performance of the battery were tested using the following methods, and the results are shown in Table 1.

[0191] a. Cycle life

[0192] Using a battery charge / discharge tester, the battery was subjected to charge / discharge cycle tests at 25°C, with constant current charge / discharge performed within the voltage range of 0.01V-0.3V. As the battery cycles, its capacity continuously decreases. The number of cycles required for the capacity to decrease to 80% of its initial discharge capacity is recorded as the battery's cycle life.

[0193] b. Ratio performance

[0194] Using a battery charge-discharge tester, the battery was subjected to charge-discharge cycle tests at 25°C. Constant current charge-discharge was performed within the voltage range of 0.01V-0.3V. After each certain number of cycles, the current density was changed and the cycle was continued to test the battery's capacity release under different current densities.

[0195] Table 1

[0196]

[0197] According to Table 1:

[0198] 1. The conductivity of Examples 1-2 is significantly better than that of Comparative Examples 1-2. Therefore, the silicon-carbon composite materials of Examples 1-2 can effectively improve the fast-charging performance of secondary batteries. The reason is that: the carbon layer of Comparative Example 1 is mainly coated on the outer surface of the material and does not form an effective path for transporting lithium ions to silicon-oxygen particles. In addition, the particle size of silicon-oxygen particles is relatively large, so the lithium ion transport efficiency is not high, resulting in poor conductivity. There are a large number of Si-C bonds in Comparative Example 2, which affects the conductivity of the carbon matrix, resulting in poor conductivity.

[0199] The conductivity of Example 2 is better than that of Example 1, possibly because the silicon-carbon composite material in Example 2 has heterogeneous element doping, which greatly improves the conductivity.

[0200] 2. The cycle performance of the secondary batteries obtained by the materials in Examples 1-2 is significantly better than that of the secondary batteries obtained by the materials in Comparative Examples 1-2. The reason is that the size of the silicon-oxygen particles in the material in Comparative Example 1 is 5-6 μm, while the size of the silicon-oxygen particles in the material in Comparative Example 2 is greater than 5 nm. Therefore, the larger volume expansion during cycling can easily cause the silicon-oxygen particles to pulverize, thus affecting the cycle performance of the battery.

[0201] 3. The rate performance of the secondary battery obtained by the materials in Examples 1-2 is significantly better than that of the secondary battery obtained by the materials in Comparative Examples 1-2. The reason is that the materials in Comparative Examples 1-2 have poor conductivity, so they cannot effectively release the capacity in the battery, resulting in poor rate performance of the secondary battery obtained by the materials in Comparative Examples 1-2. This is especially true when the current density is high, which is not conducive to the release of the capacity in the battery.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer; The core comprises a carbon matrix and SiO₂. x The particles, wherein the carbon matrix is ​​continuously distributed and includes N channels communicating with the outside, and the SiO... x The particles fill the channels; Wherein, the SiO x The particle size is 0.1-0.9 nm, 0.9 ≤ x ≤ 1.7, and N ≥ 1 and is an integer; The nuclear magnetic resonance spectrum of the silicon-carbon composite material includes Si-C peaks and Si-O peaks, and the intensity I of the Si-C peak is... Si-C The intensity of the Si-O peak I Si-O The ratio is <0.

05.

2. The silicon-carbon composite material according to claim 1, characterized in that, Based on the mass of the core, the carbon matrix has a mass percentage of 10-40%.

3. The silicon-carbon composite material according to claim 1 or 2, characterized in that, The specific surface area of ​​the carbon matrix is ​​800-1400 m² / g.

4. The silicon-carbon composite material according to claim 3, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 5-20 m² / g.

5. The silicon-carbon composite material according to claim 3, characterized in that, In the Raman spectrum of the carbon matrix, 1.5 ≤ ID / IG ≤ 0.

8.

6. The silicon-carbon composite material according to claim 1, characterized in that, The thickness of the carbon coating layer is 5-20 nm, and the carbon atom spacing d002 of the carbon coating layer is 0.3354-0.34 nm.

7. The silicon-carbon composite material according to any one of claims 1-6, characterized in that, The silicon-carbon composite material also includes at least one of the elements N, P, B, Cl, Br, and I.

8. The silicon-carbon composite material according to claim 1, characterized in that, The particle size of the silicon-carbon composite material is 50 nm-2 μm.

9. The silicon-carbon composite material according to any one of claims 1-8, characterized in that, The silicon-carbon composite material is prepared by a method including the following process: 1) Under alkaline conditions, stir the aqueous solution of trimethoxysilane compounds to make the system turbid, and collect the precursor particles; 2) The precursor particles are sintered to obtain a silicon-carbon composite material; the sintering temperature is 900-1200℃ and the time is 1-10h.

10. A method for preparing a silicon-carbon composite material according to any one of claims 1-9, characterized in that, Includes the following steps: 1) Under alkaline conditions, stir the aqueous solution of trimethoxysilane compounds to make the system turbid, and collect the precursor particles; 2) The precursor particles are sintered to obtain a silicon-carbon composite material; the sintering temperature is 900-1200℃ and the time is 1-10h. The silicon-carbon composite material includes a core and a carbon coating layer, wherein at least a portion of the surface of the core is covered by the carbon coating layer; The core comprises a carbon matrix and SiO₂. x The particles, wherein the carbon matrix includes N channels communicating with the outside, and the SiOx particles fill the channels; Wherein, the SiO x The particle size is 0.1-0.9 nm, where 0.9 ≤ x ≤ 1.

7.

11. The preparation method according to claim 10, characterized in that, In step 1), ammonia water with a volume concentration of 0.6-15% is added to the aqueous solution of the trimethoxysilane compound to adjust the pH of the system to 8-13.

12. The preparation method according to claim 10, characterized in that, The aqueous solution of the trimethoxysilane compound has a volume concentration of 0.4-5%.

13. The preparation method according to claim 10, characterized in that, The heating rate of the sintering process is 1-10℃ / min.

14. The preparation method according to any one of claims 10-13, characterized in that, Following step 1), the process also includes introducing a carbon source into the system for carbon coating.

15. The preparation method according to claim 14, characterized in that, The carbon coating is performed by a vapor phase deposition reaction at a temperature of 700-1200℃.

16. The preparation method according to claim 10, characterized in that, The trimethoxysilane compounds are selected from one or more of the following: trimethoxysilane, methyltrimethoxysilane, N-propyltrimethoxysilane, N-octyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, N-dodecyltrimethoxysilane, (3-chloropropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, trimethoxyphenylsilane, vinyltrimethoxysilane, and 3-iodophenyltrimethoxysilane.

17. An electrode sheet, characterized in that, The electrode sheet comprises the silicon-carbon composite material according to any one of claims 1-9, or comprises a silicon-carbon composite material obtained by the preparation method according to any one of claims 10-16.

18. A secondary battery, characterized in that, The secondary battery includes the electrode sheet as described in claim 17.

19. An electronic device, characterized in that, The driving source or energy storage source of the electronic device includes the secondary battery as described in claim 18.

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