Framework self-reinforced porous carbon, composite negative electrode active material, negative electrode material, negative electrode, preparation method and application

Abstract

The invention belongs to the field of negative electrode materials, and particularly relates to framework self-reinforced porous carbon, a composite negative electrode active material, a negative electrode material, a negative electrode, a preparation method and application. The framework self-reinforced porous carbon comprises porous carbon with a pore structure and a reinforced layer filled on the pore wall of the porous carbon; the strengthening layer comprises a ceramic layer with a nanopore structure; the material of the ceramic layer is at least one of SiC, SiOxCy, SiCN and SiBCN; wherein the value range of x in the SiOxCy is 0.5 to 1.5, and the value range of y in the SiOxCy is 0.5 to 2.5. The material provided by the invention is helpful for improving the capacity, wide temperature range and long stability of a subsequently prepared battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of battery materials, and particularly relates to the field of battery negative active materials. BACKGROUND

[0002] With the increasing demand for clean energy worldwide, applications represented by electric vehicles and large-scale energy storage systems have put unprecedented demands on the energy density of lithium-ion batteries. Silicon (Si) material is considered as a key negative material for replacing graphite and realizing the next generation of high-energy-density lithium-ion batteries due to its theoretical specific capacity of up to 4200 mAh / g (more than ten times that of commercial graphite negative electrode 372 mAh / g) and suitable lithium intercalation potential.

[0003] However, the commercial application of silicon negative electrodes faces a core obstacle: during charging and discharging (lithium intercalation / delithiation), silicon will undergo a huge volume change of more than 300%. This severe expansion and contraction leads to the pulverization of silicon particles, the loss of contact between active materials and the conductive network, and even the peeling off from the current collector, ultimately causing a sharp decline in battery capacity and a shortening of cycle life, which seriously hinders the commercialization process of silicon negative electrodes.

[0004] To address this challenge, the current mainstream technical route is to load nano-silicon in porous carbon materials to construct silicon-carbon (Si / C) composite materials. The porous carbon skeleton can provide abundant internal space to accommodate the volume expansion of silicon, and at the same time, it can maintain the conductive network of the electrode as a conductive matrix. Although this strategy has achieved certain results, new problems have also emerged: the mechanical strength and structural toughness of the porous carbon material, especially the biomass carbon, resin carbon, etc. that have undergone harsh activation treatment to obtain high porosity, are often insufficient. Under the huge stress generated by the expansion and contraction of silicon particles hundreds of times, especially in the practical high-energy-density range where the silicon loading is increased to more than 50%, the porous carbon carrier itself will experience structural fatigue, producing micro-cracks, and even breaking down, leading to irreversible collapse of the electrode structure.

[0005] The existing technology mainly focuses on post-processing of the formed silicon-carbon composite material to improve the structural stability of the silicon-carbon negative electrode. For example, the patent document with publication number CN117497764A discloses a double-layer coating technology, and the patent document with publication number CN117334855A discloses using a polymer binder to coat the surface of the composite material. The essence of these methods is to "patch" externally, restraining the overall expansion through the shell, which has certain effect, but does not solve the core problem, i.e. the insufficient mechanical properties of the porous carbon carrier itself. When the internal carbon skeleton is broken, the external coating layer also has difficulty in maintaining long-term structural integrity. At present, there are few reports on fundamentally improving the strength of the porous carbon skeleton itself to construct a high-stability silicon-carbon negative electrode.

[0006] Therefore, there is an urgent need in this field for a new technology that can strengthen the porous carbon skeleton from the inside, improve its resistance to pressure and deformation, and enable it to withstand the long-term stress impact of silicon during cycling, thereby laying the foundation for the development of long-life, high-stability, high-capacity silicon-carbon anodes. Summary of the Invention

[0007] To address the problems existing in the prior art, the primary objective of this invention is to provide a self-reinforced porous carbon with a framework, which aims to provide a porous carbon material capable of inducing silicon deposition and counteracting silicon expansion.

[0008] The second objective of this invention is to provide a method for preparing the aforementioned self-reinforced porous carbon framework.

[0009] The third objective of this invention is to provide a negative electrode active material (also referred to as active material or composite negative electrode active material) comprising the aforementioned self-reinforced porous carbon framework, a negative electrode material, and a negative electrode.

[0010] A third objective of this invention is to provide a method for preparing the aforementioned negative electrode active material.

[0011] A fourth objective of this invention is to provide a battery using the aforementioned negative electrode active material.

[0012] Existing technologies typically use porous carbon as a carrier for silicon or other active materials, thus utilizing the characteristics of the porous structure to buffer the expansion stress of silicon and other active materials. However, the strength of existing porous materials is not ideal, and the pore structure is prone to collapse during electrode rolling, thereby interfering with the material's performance. Furthermore, while existing porous carbon can resist the expansion of active materials to some extent, it is difficult to guide the deposition of deep pores in the active material, and it is also difficult to resist the cyclic expansion pressure caused by high loading of active materials. Moreover, materials prepared by existing methods are also difficult to withstand the high rolling pressure requirements of electrode preparation, and are prone to structural collapse during rolling. To address these problems, the present invention provides the following improvement:

[0013] A self-reinforced porous carbon framework includes porous carbon with a porous structure and a reinforcing layer filling the pore walls of the porous carbon. The reinforcing layer includes a ceramic layer with a nanoporous structure. The ceramic layer is made of at least one of SiC, SiOxCy, SiCN, and SiBCN, wherein the value of x in SiOxCy ranges from 0.5 to 1.5, and the value of y ranges from 0.5 to 2.5.

[0014] This invention innovatively forms a reinforcing layer with a porous structure within the pore walls of porous carbon. This strengthens the pore wall structure, improves its strength, and mitigates the expansion stress caused by high loading of active materials such as silicon. Furthermore, it can withstand the significant rolling pressure during anode fabrication, achieving a high degree of balance between active material loading and mechanical strength. The material described in this invention helps improve the capacity and long-term stability over a wide temperature range of the subsequently fabricated batteries.

[0015] Preferably, the porous carbon has a three-dimensional interconnected hierarchical pore structure with micron-, submicron-, and nano-sized channels. The specific surface area of ​​the porous carbon is 30–2000 m². 2 / g, pore volume 0.5~5cm 3 / g; furthermore, the specific surface area of ​​porous carbon is 100~500m². 2 / g, pore volume 1~2cm 3 / g; Furthermore, the specific surface area of ​​porous carbon is 110~200m². 2 / g, pore volume 1.5~1.8cm 3 / g.

[0016] Preferably, the porosity of the porous carbon is 60-95%; more preferably, it can be 75-85%.

[0017] Preferably, the thickness of the reinforcing layer is 5~100nm; more preferably, it can be 5~20nm.

[0018] Preferably, the pore size of the nanopores in the reinforcing layer is 5~500 nm.

[0019] The present invention also provides a method for preparing the aforementioned self-reinforced porous carbon, wherein porous carbon, organopolysilicon polymer and nanoscale polymer microspheres are dispersed in a solvent to obtain a dispersion, which is then treated under negative or positive pressure to separate and obtain the treated composite porous carbon; the solvent is a solvent that can dissolve organopolysilicon polymer but cannot dissolve nanoscale polymer microspheres; the weight ratio of porous carbon, organopolysilicon polymer and nanoscale polymer microspheres is 1:0.2~2:0.1~1;

[0020] The composite porous carbon is pre-calcined at temperature T1 for the first stage, and then calcined at temperature T2 for the second stage to obtain the self-reinforced porous carbon.

[0021] Temperature T1 is 150℃~400℃; temperature T2 is 600~1500℃.

[0022] This invention innovatively involves subjecting porous carbon, organosilicon polymers, and nanoscale polymer microspheres to negative or positive pressure assisted treatment in a dispersion system, followed by a combined two-stage calcination process. This facilitates the formation of a well-structured reinforced film on the pore walls of the porous carbon. Research in this invention demonstrates that the carbon material prepared by this method possesses excellent self-reinforcing skeletal advantages, can improve the loading of highly expandable active materials, and can resist the preparation and cyclic expansion stresses caused by high surface loading of active materials, thereby improving the stability of the material, particularly its long-term cycling stability over a wide temperature range.

[0023] In this invention, the organopolysiloxane polymer includes at least one of polycarbosilane, polysilane, polysilazane, polycarbosilazane, and polyborosilicate.

[0024] Preferably, the D50 of the nanoscale polymer microspheres is 0.5 nm to 200 nm, and more preferably 5 to 25 nm.

[0025] Preferably, the specific surface area of ​​the porous carbon is 30~2000 m². 2 / g, pore volume 0.5~5cm 3 / g; furthermore, the specific surface area of ​​porous carbon is 100~500m². 2 / g, pore volume 1~2cm 3 / g. In this invention, the average pore size of the porous carbon is more than 1.5 times the D50 particle size of the nanoscale polymer microspheres, and can be 2 to 10 times; or even 2 to 5 times.

[0026] Preferably, the nanoscale polymer microspheres are made of at least one of polymethyl methacrylate (PMMA), polystyrene (PS), polyvinyl alcohol (PVA), and polyacrylonitrile (PAN).

[0027] The solvent is a nonpolar aliphatic hydrocarbon solvent, including at least one of pentane, n-hexane, heptane, octane, isooctane, petroleum ether, cyclopentane, cyclohexane, methylcyclohexane, and decahydronaphthalene.

[0028] In this invention, the weight ratio of porous carbon, organopolysilicon polymer and nanoscale polymer microspheres in the dispersion is 1:0.5~0.75:0.15~0.25.

[0029] In this invention, the concentration of porous carbon in the dispersion can be 1~10 mL / g, and more specifically 4~6 mL / g.

[0030] The negative pressure is -0.5 to -0.05 MPa.

[0031] The positive pressure is 0.2~2MPa.

[0032] In this invention, the temperature of the first stage of roasting can be 200~400℃.

[0033] The temperature for the second stage of roasting can be 500~600℃.

[0034] In this invention, the atmosphere for the heating and holding processes of the first stage of calcination is a protective atmosphere and / or an oxygen-containing atmosphere; preferably, an oxygen-containing atmosphere. Research in this invention shows that this preferred atmosphere helps to further improve the structure and interface stability of the active layer, and helps to further improve the wide temperature range and long-cycle stability of the prepared material.

[0035] The second stage of roasting is conducted in a protective atmosphere.

[0036] The protective atmosphere includes at least one of nitrogen and rare gases.

[0037] The oxygen-containing atmosphere is at least one of oxygen or air. A protective atmosphere used as a dilution gas to regulate the oxygen partial pressure is also permitted in the oxygen-containing atmosphere.

[0038] In this invention, the oxygen in the oxygen-containing atmosphere can be 5% or more, and considering cost, it can be further 5-45%; it can also be air.

[0039] In this invention, the roasting time for the first stage is 1-4 hours, and can be further 1-2 hours; the roasting time for the second stage is 1-5 hours, and can be further 2-3 hours.

[0040] The present invention also provides a composite negative electrode active material, comprising a framework self-reinforced porous carbon and an active material supported thereon, wherein the active material comprises at least one of silicon, tin, germanium, and antimony; and the framework self-reinforced porous carbon comprises the framework self-reinforced porous carbon of the present invention.

[0041] Preferably, the content of the active material is 50~80 wt.%. This invention can achieve high load on easily expandable materials such as silicon, and even so, it can withstand large electrode rolling pressure and expansion stress during cycling, giving it excellent strength and wide temperature range stability.

[0042] Preferably, the active material comprises silicon, wherein the silicon content is 55-70 wt.%.

[0043] The present invention also provides a method for preparing the composite negative electrode active material, wherein the self-reinforced porous carbon is obtained, and the active material is loaded on the self-reinforced porous carbon to obtain the composite negative electrode active material.

[0044] Preferably, the active material is loaded onto the self-reinforced porous carbon skeleton by at least one of vapor deposition and electroless plating.

[0045] As an optional approach, the self-reinforced porous carbon skeleton is used as a skeleton and pre-treated with CVD silicon deposition to obtain the composite negative electrode active material.

[0046] The CVD silicon deposition process can be conventional. For example, the silicon source for CVD silicon deposition can be at least one of hydrosilane, chlorosilane, dimethylsilane, diethylsilane, methylmonochlorosilane, methyldichlorosilane, and methyltrichlorosilane.

[0047] The atmosphere for CVD silicon deposition may also include at least one diluent gas from nitrogen and rare gases, wherein the silicon source content may be 1 to 30% v%, or more specifically 5 to 20% v.

[0048] The temperature for the CVD silicon deposition process can be 400~900℃, or even 450~650℃. The time can be 1~10h, or even 3~8h.

[0049] In this invention, the active material may also contain carbon materials, which can be obtained through a conventional CVD carbon deposition process. Preferably, the CVD carbon deposition process can be performed after the CVD silicon deposition step.

[0050] The carbon source for CVD carbon deposition includes at least one of gaseous alkanes, alkenes, alkynes, benzene, alcohols, aldehydes, and phenols.

[0051] The atmosphere during the CVD carbon deposition process may also include at least one diluent gas from nitrogen and rare gases, wherein the carbon source content may be 1-30 vol%, or more specifically 5-20 vol%.

[0052] The temperature for the CVD carburization process can be 400~900℃, or more specifically 450~650℃. The time can be 0.1~2h, or more specifically 0.5~1h.

[0053] The present invention also provides a negative electrode material, comprising a negative electrode active material, a conductive agent and a binder, wherein the negative electrode active material comprises the composite negative electrode active material;

[0054] Preferably, the weight ratio of the negative electrode active material, the conductive agent, and the binder is 75~95:1~15:1~15.

[0055] The present invention also provides a negative electrode, comprising a current collector and a negative electrode material composite thereon, wherein the negative electrode material is the negative electrode material described in the present invention;

[0056] The surface loading of the active material can be 2~10 mg / cm².

[0057] The present invention also provides a method for preparing a negative electrode, wherein the negative electrode material is slurried and coated onto a current collector, and then dried and rolled to obtain the negative electrode;

[0058] Preferably, the roller pressing pressure is 10~100MPa, for example, it can be 18~25MPa.

[0059] The present invention also provides a secondary battery comprising the negative electrode described herein.

[0060] The secondary battery described in this invention can be a lithium-ion battery.

[0061] Beneficial effects

[0062] This invention fundamentally improves the mechanical properties of the carbon support through an "internal skeleton reinforcement" strategy, enabling it to withstand the extreme stress of silicon under loads of 55-65% or even higher. More importantly, by creating "conductive windows" in situ within the ceramic layer, the negative impact of the low electrical conductivity of the ceramic phase is cleverly avoided, achieving a balance between the seemingly contradictory performance indicators of "high strength" and "high conductivity."

[0063] It is generally believed in the art that it is extremely difficult to achieve a synergistic effect when introducing two components into the pore and heat treatment. This invention, through the described preparation process, unexpectedly enables "network construction" and "dual pore-forming" (i.e., recreating macropores and creating nanopores within the ceramic) to occur simultaneously, producing a synergistic effect greater than the sum of its parts (1+1>2). This design allows the prepared anode to exhibit superior overall performance even with a silicon loading as high as 65%, demonstrating significant ingenuity.

[0064] The reinforcing carrier of the present invention is not only applicable to silicon anodes, but also applicable to supporting other anode active materials that undergo huge volume changes, such as tin (Sn), germanium (Ge), antimony (Sb) and their compounds, and has a wider range of application prospects. Attached Figure Description

[0065] Figure 1 SEM image of the silicon-carbon anode material prepared in Example 1;

[0066] Figure 2 SEM image of the silicon-carbon anode material prepared for Comparative Example 2. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit the scope of protection of the invention.

[0068] In the various embodiments and comparative examples, the performance of the framework self-reinforced porous carbon was tested using the following indicators:

[0069] Single-particle strength: The indentation hardness of a single particle was tested using a nanoindenter.

[0070] The electrochemical performance of the negative electrode material was tested by assembling it into a CR2032 coin cell:

[0071] A homogeneous slurry was prepared by mixing the negative electrode active material, conductive agent (Super P), and binder (PAA) in deionized water at a weight ratio of 90:5:5. The slurry was then uniformly coated onto a copper foil current collector. The coated electrode was dried at 80°C and then thoroughly dried under vacuum at 120°C for 12 hours. The dried electrode was then rolled using a roller press at a pressure of 20 MPa to increase its compaction density.

[0072] The rolled electrode sheets were cut into 12mm diameter discs to serve as working electrodes, with lithium metal sheets as counter electrodes and Celgard 2400 as separators. They were then assembled into button cells in an argon-filled glove box.

[0073] The electrolyte was a solution of 1 M LiPF6 dissolved in EC / DEC / DMC (volume ratio 1:1:1), with 5 wt% FEC added.

[0074] Capacity: gram capacity (mAh / g) tested at a 0.1C rate.

[0075] First-time efficiency: The ratio of the initial discharge capacity to the initial charge capacity, i.e., the initial coulombic efficiency (%).

[0076] 2C rate: The ratio of discharge capacity at 2C rate to discharge capacity at 0.1C rate.

[0077] High-temperature cycling retention: The ratio (%) of capacity to initial stable capacity after 800 cycles at 60℃ and 1C rate.

[0078] Low-temperature cycling retention: The ratio (%) of capacity to initial stable capacity after 800 cycles at 0℃ and 1C rate.

[0079] Capacity retention at room temperature: the ratio (%) of capacity to initial stable capacity after 1800 cycles at 25℃ and 1C.

[0080] In the following examples, unless otherwise stated, the inert gas refers to Ar gas.

[0081] Example 1

[0082] Step 1:

[0083] 100g of polycarbosilane (as a SiC ceramic precursor) and 30g of PMMA microspheres with an average particle size of 20nm were weighed and dispersed in 1000mL of n-hexane to prepare a mixture. 200g of porous carbon (phenolic resin-based porous carbon with a specific surface area of ​​130m²) was weighed. 2 / g, total pore volume 1.60cm³ 3 Sample S1 was obtained by subjecting a sample (g, average pore size 50 nm, porosity 80%) to negative pressure treatment (-0.1 MPa, 2 h). After drying, the sample was heated to 200 °C (Temperature T1) at 5 °C / min and held for 2 h in an air atmosphere, and then heated to 1200 °C (Temperature T2) at 3 °C / min and held for 2 h in an inert atmosphere (Ar) to obtain sample S1.

[0084] Step 2:

[0085] The sample S1 (as a carrier) obtained in step 1 was placed in a fluidized bed reactor with silane (SiH4) as the silicon source gas and argon as the carrier gas (the volume ratio of silane to carrier gas was 1:10). The silicon was precipitated at 500℃ (temperature T3) for 6 hours. Subsequently, acetylene was used as the carbon source and argon as the carrier gas (the volume ratio of carbon source to carrier gas was 1:10). The carbon was precipitated at 600℃ (temperature T4) for 0.5 hours to obtain a silicon-carbon composite anode active material SiC-S1 with 60wt% silicon loading.

[0086] Example 2

[0087] Compared with Example 1, the only difference is that the porous charcoal is replaced with biomass coconut shell-based porous charcoal (specific surface area 121 m²). 2 / g, total pore volume 1.65cm³ 3 / g, average pore size 51nm, porosity 79%), and other steps were the same as in Example 1 to obtain the negative electrode active material SiC-S2.

[0088] Example 3

[0089] Compared with Example 1, the only difference is that the porous carbon is replaced with porous petroleum coke-based porous carbon (specific surface area 135m²). 2 / g, total pore volume 1.58cm³ 3 / g, average pore size 48nm, porosity 81%), and other steps were the same as in Example 1 to obtain the negative electrode active material SiC-S3.

[0090] Example 4

[0091] Compared with Example 1, the only difference is that polycarbosilane is replaced with polysilazane (to form a SiCN ceramic phase precursor), and all other steps are the same as in Example 1, to obtain the negative electrode active material SiC-S4.

[0092] Example 5

[0093] Compared with Example 1, the only difference is that the PMMA microspheres are replaced with PS microspheres. All other steps are the same as in Example 1, and the negative electrode active material SiC-S5 is obtained.

[0094] Example 6

[0095] Compared with Example 1, the difference is that in step 1, the negative pressure treatment is replaced with positive pressure treatment, and the pressurized gas is nitrogen. The positive pressure is 1.0 MPa. Other operations and parameters are the same as in Example 1, and the negative electrode active material is SiC-S6.

[0096] Example 7

[0097] Compared with Example 1, the only difference is that the parameters are changed, and the difference in steps is as follows:

[0098] Step 1: Weigh 150g of polycarbosilane and 45g of PMMA microspheres with an average particle size of 18nm and disperse them in 1000mL of petroleum ether to prepare a mixture. Weigh 200g of phenolic resin-based porous carbon (same as in Example 1) and subject it to negative pressure treatment (-0.15MPa, 1.5h). Temperature T1 is 300℃, and the holding time at this temperature is 1.5h; temperature T2 is 1100℃, and the holding time is 3h.

[0099] In step 2, the volume ratio of silicon source gas to carrier gas in the atmosphere of the silicon deposition stage is 1:15; the temperature T3 is 550℃; and the silicon deposition time is 5h.

[0100] In the atmosphere of the carbon deposition stage, the carbon source atmosphere is methane, the volume ratio of carbon source to carrier gas is 1:15; the temperature T3 is 550℃, and the carbon deposition time is 1h.

[0101] The subsequent steps were exactly the same as in Example 1, resulting in sample S7, which was then prepared as the negative electrode active material SiC-S7.

[0102] Example 8

[0103] Compared with Example 1, the only difference is that in step 1, the temperature T1 is increased and the atmosphere during the heat preservation process is Ar; all other operations and parameters are the same as in Example 1. The negative electrode active material prepared is SiC-S8.

[0104] Comparative Example 1

[0105] Compared with Example 1, the only difference is that untreated phenolic resin porous carbon is directly used as a carrier and directly subjected to the deposition process in step 2. All other operations and parameters are the same as in Example 1, and the resulting negative electrode active material is SiC-D1.

[0106] Comparative Example 2

[0107] Compared with Example 1, the only difference is that PMMA is not added to the mixture in step 1. All other operations and parameters are the same as in Example 1, resulting in the comparative negative electrode active material SiC-D2.

[0108] Comparative Example 3

[0109] Compared to Example 1, the only difference is that the porous carbon is pretreated in step 2 before being treated in step 1. All other operations and parameters are the same as in Example 1, and the resulting comparative negative electrode active material is labeled SiC-D3.

[0110] Comparative Example 4

[0111] Compared with Example 1, the only difference is that in step 1, no polycarbosilane was added. The other operations and parameters are the same as in Example 1, and the comparative negative electrode active material SiC-D4 is obtained.

[0112] Comparative Example 5

[0113] Compared with Example 1, the only difference is that in step 1, an equal weight of tetraethoxysilane (TEOS) is used to replace polycarbosilane. Other operations and parameters are the same as in Example 1, resulting in the comparative negative electrode active material SiC-D5.

[0114] Comparative Example 6

[0115] Compared with Example 1, the only difference is that in step 1, the negative pressure process is replaced by the normal pressure process, while other operations and parameters are the same as in Example 1, resulting in the comparative negative electrode active material SiC-D6.

[0116] Comparative Example 7

[0117] Compared with Example 1, the only difference is that in step 1, the heat preservation process of step 1 is omitted, and the temperature is directly raised to temperature T2. Other operations and parameters are the same as in Example 1, and the comparative negative electrode active material SiC-D7 is obtained.

[0118] Comparative Example 8

[0119] Compared with Example 1, the only difference is that in step 1, the solvent is replaced with an equal volume of toluene, which can dissolve polycarbosilane and PMMA. Other operations and parameters are the same as in Example 1, resulting in the comparative negative electrode active material SiC-D8.

[0120] The results and data for each case are shown in Table 1:

[0121]

[0122] analyze:

[0123] Table 1 shows that all the tests of the embodiments (Examples 1 to 8) demonstrated excellent overall performance. Taking Example 1 as an example, its single-particle indentation hardness reached 2.2 GPa, which is more than 5 times that of the original carbon matrix, proving the success of the "skeletonical self-reinforcement" strategy. In addition, the embodiments of the present invention not only achieved an ultra-long cycle life at room temperature (retention rate >89% after 1800 cycles), but also maintained nearly 90% of the capacity after 800 cycles under harsh conditions of 0°C and 60°C. This demonstrates excellent wide-temperature range operation capability, solves the pain point of accelerated performance degradation of conventional silicon anodes at extreme temperatures, and has extremely high practical application value.

[0124] Comparative Examples 1 and 4 exhibited extremely poor cycling performance at all temperatures, with capacity rapidly collapsing within a short period. While Comparative Example 3 showed improved performance, its cycle retention rate at all temperatures was significantly lower than that of the embodiments of the present invention, further demonstrating the superiority of the internally integrated enhancement.

[0125] Although Comparative Examples 2 and 8 exhibit high hardness, their capacity and cycling stability are extremely poor at all temperatures. This contrasts sharply with the excellent performance of Example 1, strongly demonstrating that creating nanopores in the reinforcing layer is crucial for ensuring electrochemical activity.

[0126] The performance of Comparative Examples 5, 6, and 7 is significantly inferior to that of the embodiments of the present invention. Their performance is already poor at room temperature, and the performance degradation becomes even more pronounced under harsh high and low temperature conditions. This clearly demonstrates that employing specific organopolysilicon polymers, pressure-assisted impregnation, and a two-stage calcination process are three indispensable key steps for successfully preparing high-performance, wide-temperature-range, self-reinforced porous carbon.

[0127] In summary, this invention successfully prepared a self-reinforced porous carbon composite material through an innovative strategy of "synergistic internal reinforcement and conductive window construction." When used as a silicon anode support, it fundamentally solves the industry-wide challenge of simultaneously achieving the balance between strength, conductivity, and pore space in carbon supports. This successfully increases the silicon loading of high-performance silicon-carbon anodes to a practical range of 55-65%, while simultaneously achieving ultra-high specific capacity, initial efficiency, and unprecedented cycle stability. This invention addresses the core structural stability issue in the commercial application of high-energy-density silicon anodes, possessing significant practical application value and broad market prospects.

[0128] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent changes or modifications made by those skilled in the art without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-reinforced porous carbon framework, characterized in that, The invention includes porous carbon with a porous structure and a reinforcing layer filling the pore walls of the porous carbon. The reinforcing layer includes a ceramic layer with a nanoporous structure. The ceramic layer is made of at least one of SiC, SiOxCy, SiCN, and SiBCN. In the SiOxCy, the value of x ranges from 0.5 to 1.5, and the value of y ranges from 0.5 to 2.

5. Preferably, the porous carbon has a three-dimensional interconnected hierarchical pore structure with micron-scale, submicron-scale, and nano-scale channels. Preferably, the specific surface area of ​​the porous carbon is 30~2000 m². 2 / g, pore volume 0.5~5cm 3 / g; Preferably, the porosity of the porous carbon is 60-95%; Preferably, the thickness of the reinforcement layer is 5~100nm; Preferably, the pore size of the nanopores in the reinforcing layer is 5~500 nm.

2. A method for preparing the framework self-reinforced porous carbon according to claim 1, characterized in that, Porous carbon, organopolysilicon polymer, and nanoscale polymer microspheres are dispersed in a solvent to obtain a dispersion, which is then treated under negative or positive pressure to separate the treated composite porous carbon. The solvent is one that can dissolve organopolysilicon polymer but cannot dissolve nanoscale polymer microspheres. The weight ratio of porous carbon, organopolysilicon polymer, and nanoscale polymer microspheres is 1:0.2~2:0.1~1. The composite porous carbon is pre-calcined at temperature T1 for the first stage, and then calcined at temperature T2 for the second stage to obtain the self-reinforced porous carbon. Temperature T1 is 150℃~400℃; temperature T2 is 600~1500℃.

3. The method for preparing self-reinforced porous carbon as described in claim 1, characterized in that, Organopolysiloxane polymers include at least one of polycarbosilane, polysilane, polysilazane, polycarbosilazane, and polyborosilazane; Preferably, the D50 of the nanoscale polymer microspheres is 0.5 nm to 200 nm, and more preferably 5 to 25 nm; Preferably, the nanoscale polymer microspheres are made of at least one material selected from polymethyl methacrylate, polystyrene, polyvinyl alcohol, and polyacrylonitrile. Preferably, the average pore size of the porous carbon is more than 1.5 times the D50 particle size of the nanoscale polymer microspheres, and more preferably 2 to 10 times. The solvent is a nonpolar aliphatic hydrocarbon solvent, preferably including at least one of pentane, n-hexane, heptane, octane, isooctane, petroleum ether, cyclopentane, cyclohexane, methylcyclohexane, and decahydronaphthalene. The negative pressure is -0.5 to -0.05 MPa; The positive pressure is 0.2~2MPa.

4. The method for preparing self-reinforced porous carbon as described in claim 1, characterized in that, The atmosphere during the heating and holding processes of the first stage of roasting is a protective atmosphere and / or an oxygen-containing atmosphere; preferably an oxygen-containing atmosphere. The atmosphere for the second stage of roasting is a protective atmosphere; The first roasting time is 1-4 hours; the second roasting time is 1-5 hours.

5. A composite negative electrode active material, characterized in that, The invention includes a framework-reinforced porous carbon and the active material supported thereon, wherein the active material includes at least one of silicon, tin, germanium, and antimony; the framework-reinforced porous carbon includes the framework-reinforced porous carbon according to claim 1, and / or the framework-reinforced porous carbon prepared by the preparation method according to any one of claims 2 to 4. Preferably, the content of the active material is 50~80 wt.%.

6. A method for preparing the composite negative electrode active material according to claim 5, characterized in that, The self-reinforced porous carbon framework is obtained, and the active material is loaded onto the self-reinforced porous carbon framework to prepare the composite negative electrode active material. Preferably, the active material is loaded onto the self-reinforced porous carbon skeleton by at least one of vapor deposition and electroless plating. The active material contains silicon, which is obtained through a CVD silicon deposition process; The silicon source for CVD silicon deposition is at least one of hydrosilane, chlorosilane, dimethylsilane, diethylsilane, methylmonochlorosilane, methyldichlorosilane, and methyltrichlorosilane. The temperature for CVD silicon deposition can be 400~900℃; The active material also includes carbon material, which can be obtained through conventional CVD carbon deposition process; The carbon source for CVD carbon deposition includes at least one of gaseous alkanes, alkenes, alkynes, benzene, alcohols, aldehydes, and phenols; The temperature for CVD carburization can be 400~900℃.

7. A negative electrode material, comprising a negative electrode active material, a conductive agent, and a binder, characterized in that, The negative electrode active material includes the composite negative electrode active material as described in claim 5; Preferably, the weight ratio of the negative electrode active material, the conductive agent, and the binder is 75~95:1~15:1~15.

8. A negative electrode, comprising a current collector and a negative electrode material composited thereon, characterized in that, The negative electrode material is the negative electrode material according to claim 7; The surface loading of the active material is 2~10 mg / cm².

9. A method for preparing a negative electrode, characterized in that, The negative electrode material is slurried and coated onto the current collector, then dried and rolled to obtain the negative electrode. Preferably, the roller pressing pressure is 10~100MPa.

10. A secondary battery, characterized in that, It includes the negative electrode as described in claim 9.

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