A power-type silicon-carbon composite material and a method for preparing the same

Abstract

The application discloses a power type silicon-carbon composite material and a preparation method thereof, characterized in that the composite material presents a core-shell structure, the inner core is a metal and heteroatom co-doped silicon-carbon alloy material, and the outer shell is a fast ion conductor doped amorphous carbon material. The preparation process is as follows: a large-pore porous carbon is prepared, metal lithium and heteroatoms are deposited through a gasification method, then silane gas is introduced to obtain a silicon-carbon precursor material, and finally, a silicon-carbon composite material is obtained through double-target magnetron sputtering. The obtained material utilizes alloy binding to restrain the expansion of nanosilicon in the charging and discharging process and the metal heteroatoms to improve the electronic conductivity of the material. Meanwhile, the outer layer of the fast ion conductor restrains the expansion of the inner core and improves the ion conduction rate, thereby improving the initial efficiency and the rate performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion electrode material preparation, specifically a power-type silicon-carbon composite material and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, large-scale energy storage, and high-end portable electronic devices, the market has placed stringent demands on battery energy density, fast-charging performance, and cycle stability. Silicon-carbon materials are composed of porous carbon and nano-silicon deposited within the porous structure, with passivated surfaces. Due to the poor electronic conductivity of the porous carbon structure itself and the poor interface between the nano-silicon and the porous carbon, the material exhibits poor fast-charging performance and low compressive strength. Although some researchers have improved the material's fast-charging performance by doping its core with heteroatoms (e.g., nitrogen, boron) or coating its surface with materials possessing high electronic or ionic conductivity, the improvement has been limited. For example, patent application CN202310356573.7 discloses a metal-doped amorphous carbon-coated silicon-carbon composite material, its preparation method, and its application, including a core structure and an outer shell structure coated on the core structure. The core structure comprises porous carbon particles and nano-silicon grains deposited inside the porous carbon via silane pyrolysis. The outer shell structure comprises metal generated through the pyrolysis of organometallic compounds and amorphous carbon. While the power performance of the outer shell is improved, the ionic conductivity of the outer shell is not improved, limiting the improvement in power performance and failing to improve the core power. It is evident that single heteroatom doping has limited impact on ion conductivity improvement, failing to meet the ion transport requirements during high-rate charging. Traditional coating layers (such as amorphous carbon) can suppress expansion to some extent, but their low ionic conductivity increases interfacial impedance, resulting in insufficient power performance improvement. Therefore, developing a silicon-carbon composite material that simultaneously improves electronic conductivity, ion conductivity, and reduces expansion is crucial to overcoming existing technological bottlenecks and meeting the demands of high-end applications. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] To improve the power performance of silicon-carbon materials, this invention prepares a silicon-carbon composite material by fabricating large-pore porous carbon, depositing metallic lithium, heteroatoms, and nano-silicon, thereby enhancing the electronic and ionic conductivity of the material, reducing defects, and depositing fast ion conductors on its surface. Simultaneously, a method for preparing a power-type silicon-carbon composite material is provided.

[0005] The purpose of this invention is to propose a power-type silicon-carbon composite material, characterized in that: the composite material exhibits a core-shell structure, the core is a silicon-carbon alloy material co-doped with metal and heteroatoms, and the outer shell is composed of amorphous carbon material doped with fast ion conductors. Calculated based on a composite material mass ratio of 100%, the outer shell accounts for 1-10 wt% of the total mass.

[0006] Furthermore, the doping metal is one of lithium, magnesium, zinc, or nickel.

[0007] Furthermore, the doped heteroatom is one of nitrogen, sulfur, or phosphorus.

[0008] Furthermore, the outer shell is divided into a carbon-rich inner layer, a mixed transition layer, and a fast ion-rich outer layer; the thickness ratio is 15-25%: 25-35%: 45-55%;

[0009] The present invention also aims to provide a method for preparing a power-type silicon-carbon composite material, characterized by comprising the following steps:

[0010] Step S1:

[0011] The carbon source, activator, and dopant are mixed evenly according to the mass ratio of carbon source: activator: dopant = 100:10-30:1-5. First, the temperature is raised to 600-800℃ for carbonization for 0.5-2 hours, then the temperature is raised to 1000-1300℃, and water vapor is introduced at a flow rate of 100-500 SCCM for 30-300 minutes to obtain porous carbon.

[0012] Step S2:

[0013] Porous carbon is transferred to a vacuum furnace, evacuated to 1-10 torr, and heated to 1000-1500℃. Then, it is deposited by gasification. A mixture of lithium metal and heteroatom gas is introduced at a flow rate of 100-500 ml / min for 30-300 min, with a volume ratio of lithium metal gas to heteroatom gas of 1-3:10. After that, the temperature is lowered to 400-600℃ and a mixture of silane gas is introduced at a flow rate of 100-500 ml / min for 60-600 min to obtain silicon-carbon precursor material.

[0014] Step S3:

[0015] According to the mass ratio of fast ion conductor to binder = 100: 1-5, the fast ion conductor and binder are mixed evenly, and then cold isostatically pressed at 50-100MPa. Then, the mixture is pressed in a hot press at 200-300℃ for 0.5-2h under a pressure of 5-20 tons to obtain the fast ion conductor target material.

[0016] Argon plasma etching of silicon-carbon precursors was performed at a power of 50W for 1-5 minutes to remove surface impurities and increase surface roughness. The silicon-carbon precursor material was placed in a reaction chamber, which was evacuated to 0.1 Torr and heated to 300-500℃ with an argon flow rate of 80-150 SCCM. A dual-target magnetron sputtering system was used, with fast ion conductor target and pure graphite target as the targets.

[0017] Stage 1: Graphite target power 200W, fast ion conductor target power 50W, time 5-15min, forming a carbon layer dominated by electron conduction;

[0018] In stage 2, the power of the graphite target is linearly reduced to 50W, while the power of the fast ion conductor target is linearly increased to 150W over a period of 10-30 minutes, forming a hybrid layer of electron and ion synergistic conduction.

[0019] Stage 3: The graphite target power is turned off, the fast ion conductor target power is 200W, and the time is 15-45min, forming a dense layer dominated by ion conduction.

[0020] After deposition, the carbon is annealed in argon at 500-600℃ for 1-3 hours to form amorphous carbon doped with fast ion conductors with a thickness of 50-500nm.

[0021] Further, in step S1, the carbon source is one of polyaniline, polyamide, polythiophene, polypyrrole, or melamine; the activator is one of phosphoric acid, zinc chloride, zinc bromide, or lithium carbonate; and the dopant is one of lithium metal, magnesium metal, zinc metal, or nickel metal.

[0022] Further, in step S2, the silane mixed gas is one of methane and ethyl silane mixed with nitrogen in a volume ratio of 1-5:10; the heteroatom gas is one of ammonia, hydrogen sulfide, and phosphine.

[0023] Furthermore, in step S3, the fast ion conductor is Li7La3Zr2O. 12 Li 1.4 Al 0.4 Ti 1.6 One of (PO4)3, Li2ZrP2O8 or LiAlSiO4; the binder is one of petroleum asphalt, coal tar pitch or lithium carboxymethyl cellulose.

[0024] Carbon sources (such as polyaniline and polypyrrole) themselves contain heteroatoms such as nitrogen. Combined with activators (such as phosphoric acid) and dopants (such as metallic lithium), a porous carbon framework containing heteroatoms and metals is formed during carbonization. Metals (such as Li and Mg), as electronic conductors, can reduce the electronic resistance of the material; heteroatoms (N, S, P) introduce lone pairs of electrons or defect sites, forming "channels" for lithium-ion adsorption and transport, thus increasing the ion conductivity. By depositing metallic lithium and heteroatoms (such as N provided by ammonia) through vacuum vaporization, the metal and heteroatoms are uniformly doped into the silicon-carbon alloy (a composite structure of nano-silicon and porous carbon), further strengthening the electron / ion conduction network. The combination of nano-silicon and porous carbon utilizes the conductivity of carbon to alleviate the intrinsic insulation of silicon, while heteroatoms (such as N) can modify the silicon-carbon interface, reducing the interfacial resistance.

[0025] The outer shell is divided into a "carbon-rich inner layer - hybrid transition layer - fast ion-rich outer layer," fabricated in stages using dual-target magnetron sputtering. The carbon-rich inner layer (high-power graphite target) ensures continuous electron conduction, preventing the outer shell from becoming a bottleneck for electron transport. The hybrid transition layer (lower graphite power, higher fast ion conductor power) balances electron and ion conduction, reducing interlayer impedance. The fast ion-rich outer layer (such as LLZO or LATP) utilizes the high ionic conductivity of the fast ion conductor itself to significantly improve the lithium-ion transport rate on the material surface, solving the problem of poor ionic conductivity in traditional carbon-coated layers. The core co-doping combined with a layered outer shell design enhances both electron and ion conductivity.

[0026] After carbonization at 600-800℃, the carbon source is activated by introducing water vapor at 1000-1300℃, forming a large-pore porous structure. The large pore size provides a "buffer space" for the volume expansion of nano-silicon, reducing stress concentration caused by silicon particle expansion and preventing the porous carbon framework from breaking. The amorphous carbon deposited by magnetron sputtering has a certain degree of flexibility and can deform with the expansion and contraction of silicon; fast ion conductors (such as LLZO) form a dense layer, physically constraining the volume expansion of silicon; staged deposition and annealing (500-600℃) enhance the interfacial bonding between the outer shell and the core, preventing the outer shell from detaching during expansion and further improving structural stability. Expansion is suppressed through a dual mechanism of "porous carbon space buffering" and "flexible outer shell constraint."

[0027] The silicon-carbon precursor is etched using argon plasma (50W, 1-5 min) to remove surface impurities and increase roughness, thereby improving the bonding area and adhesion between the shell and the core, and reducing interfacial contact resistance. The "hybrid transition layer" of the shell achieves a smooth transition from "carbon-rich" to "fast-ion-rich" by linearly adjusting the sputtering power of graphite and the fast-ion conductor. This avoids interfacial barriers caused by abrupt changes in material properties (such as differences in electronic / ionic conductivity), allowing for smoother transport of lithium ions and electrons at the interface. Through plasma etching and the transition layer design, the interfacial impedance is optimized, improving fast-charging performance.

[0028] Beneficial effects:

[0029] 1. By co-doping the core metal (such as lithium and magnesium) with heteroatoms (such as nitrogen and sulfur), the metal enhances electronic conduction, and the heteroatoms construct ion transport channels; the outer shell adopts a layered design of a carbon-rich inner layer, a mixed transition layer and a fast ion-rich outer layer, which takes into account the continuity of electronic and ion conduction. The two work together to form an efficient charge transport network, breaking through the conduction bottleneck of traditional silicon-carbon materials.

[0030] 2. The large-pore porous carbon framework provides a buffer space for the volume expansion of silicon, reducing stress concentration; the outer shell forms a flexible constraint through the composite structure of dense fast ion conductor and amorphous carbon, and the dual mechanism inhibits silicon particle pulverization and ensures the structural integrity during material recycling.

[0031] 3. The silicon-carbon precursor is subjected to plasma etching to remove impurities and increase surface roughness, thereby enhancing the adhesion of the shell; the shell transition layer eliminates the interfacial barrier through composition gradient changes, reduces lithium-ion transport resistance, and significantly improves the kinetic performance during high-rate charging.

[0032] 4. Vacuum deposition allows metals, heteroatoms, and nano-silicon to permeate evenly into porous carbon, preventing component agglomeration; dual-target magnetron sputtering achieves a gradient distribution of components in each layer of the shell by precisely controlling power and time, ensuring stable and consistent overall material performance.

[0033] 5. Through a synergistic strategy of “core metal-heteroatom co-doping to enhance conduction + large-pore porous carbon to buffer expansion + shell layered design to optimize interface”, the problems of poor electronic / ionic conduction, large volume expansion and high interface impedance of traditional silicon-carbon materials are specifically solved, and the power performance (fast charging) and cycle stability are significantly improved, making it suitable for high-end scenarios such as new energy vehicles and large-scale energy storage. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 The image shows a SEM image of the fast ion conductor-coated silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] With regard to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0042] Example 1

[0043] A method for preparing a power-type silicon-carbon composite material includes the following steps:

[0044] Step S1:

[0045] 100g of polyaniline, 20g of phosphoric acid and 3g of lithium metal were mixed evenly in a sealed environment. First, the temperature was raised to 700℃ for carbonization for 1 hour, then the temperature was raised to 1200℃ and water vapor was introduced at a flow rate of 300 SCCM for 120 minutes to obtain porous carbon.

[0046] Step S2:

[0047] Porous carbon was transferred to a vacuum furnace, evacuated to 5 torr, and heated to 1250℃. Then, it was deposited by vaporization. A mixture of lithium metal gas and ammonia gas (volume ratio of lithium metal gas to ammonia gas = 2:10) was introduced at a flow rate of 300 ml / min for 150 min. After that, the temperature was lowered to 500℃ and a mixture of silane gas (volume ratio of silane to nitrogen gas = 3:10) was introduced at a flow rate of 300 ml / min for 150 min to obtain silicon-carbon precursor material.

[0048] Step S3:

[0049] 100g Li7La3Zr2O 12 (LLZO) was mixed evenly with 3g of petroleum asphalt and then pressed by a hot press at 80MPa under a pressure of 10 tons and a temperature of 250℃ for 1h to obtain a fast ion conductor composite material.

[0050] 100g of silicon-carbon precursor was plasma etched for 3 minutes and then placed in the reaction chamber.

[0051] Reactor chamber vacuum 0.1 Torr, 400℃, argon gas 100 SCCM, dual-target sputtering:

[0052] Stage 1: Graphite 200W, LLZO 50W, 10min;

[0053] Phase 2: Graphite power linearly decreases to 50W, LLZO power linearly increases to 150W, 20min;

[0054] Phase 3: Graphite off, LLZO 200W, 30 min;

[0055] Annealed at 550℃ for 2 hours, the shell accounts for 5 wt% of the total mass and has a thickness of 200 nm.

[0056] Finally, a silicon-carbon composite material was obtained.

[0057] Example 2

[0058] A method for preparing a power-type silicon-carbon composite material includes the following steps:

[0059] Step S1:

[0060] 100g of polyamide, 15g of zinc chloride and 2g of magnesium metal were mixed evenly in a sealed environment. First, the temperature was raised to 700℃ for carbonization for 0.8h, then the temperature was raised to 1100℃ and water vapor was introduced at a flow rate of 100SCCM for 90min to obtain porous carbon.

[0061] Step S2:

[0062] Porous carbon was transferred to a vacuum furnace, evacuated to 1 torr, and heated to 1000℃. Then, it was deposited by gasification. A mixture of magnesium metal and hydrogen sulfide gas (volume ratio of magnesium metal gas to hydrogen sulfide gas = 1:10) was introduced at a flow rate of 100 ml / min for 300 min. After that, the temperature was lowered to 400℃ and a mixture of silane gas (volume ratio of silane gas to nitrogen gas = 2:10) was introduced at a flow rate of 100 ml / min for 600 min to obtain silicon-carbon precursor material.

[0063] Step S3:

[0064] 100gLi 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) was mixed evenly with 1g of coal tar pitch and then pressed for 2h at 100℃ under a pressure of 5 tons to obtain a fast ion conductor composite material.

[0065] 100g of silicon-carbon precursor was plasma etched for 3 minutes and then placed in the reaction chamber.

[0066] The reaction chamber was maintained at a vacuum of 0.1 Torr, 400°C, and 100 SCCM of argon gas. Dual-target sputtering was employed.

[0067] Phase 1: Graphite 200W, LATP 50W, 10min;

[0068] Phase 2: Graphite power linearly decreased to 50W, LATP linearly increased to 150W, 15min;

[0069] Phase 3: Graphite off, LATP 200W, 25 min;

[0070] Annealed at 550℃ for 2 hours, the shell accounts for 5 wt% of the total mass and has a thickness of 200 nm.

[0071] Finally, a silicon-carbon composite material was obtained.

[0072] Example 3

[0073] A method for preparing a power-type silicon-carbon composite material includes the following steps:

[0074] Step S1:

[0075] 100g of melamine, 25g of zinc chloride and 4g of metallic zinc were mixed evenly in a sealed environment. First, the temperature was raised to 650℃ for carbonization for 0.8h, then the temperature was raised to 1100℃ and water vapor was introduced at a flow rate of 100SCCM for 180min to obtain porous carbon.

[0076] Step S2:

[0077] Porous carbon was transferred to a vacuum furnace, evacuated to 1 torr, and heated to 1000℃. Then, it was deposited by gasification. A mixture of zinc and phosphine gas (volume ratio of zinc gas to phosphine gas = 3:10) was introduced at a flow rate of 100 ml / min for 300 min. After that, the temperature was lowered to 400℃ and a mixture of silane gas (volume ratio of silane gas to nitrogen gas = 5:10) was introduced at a flow rate of 100 ml / min for 600 min to obtain silicon-carbon precursor material.

[0078] Step S3:

[0079] 100gLi 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) was mixed evenly with 1g of coal tar pitch and then pressed for 2h at 100℃ under a pressure of 5 tons to obtain a fast ion conductor composite material.

[0080] 100g of silicon-carbon precursor was plasma etched for 3 minutes and then placed in the reaction chamber.

[0081] The reaction chamber was maintained at a vacuum of 0.1 Torr, 400°C, and 100 SCCM of argon gas. Dual-target sputtering was employed.

[0082] Phase 1: Graphite 200W, LATP 50W, 10min;

[0083] Phase 2: Graphite power linearly decreased to 50W, LATP linearly increased to 150W, 15min;

[0084] Phase 3: Graphite off, LATP 200W, 25 min;

[0085] Annealed at 550℃ for 2 hours, the shell accounts for 5 wt% of the total mass and has a thickness of 200 nm.

[0086] Finally, a silicon-carbon composite material was obtained.

[0087] Comparative Example 1:

[0088] Unlike Example 1, no lithium metal dopant is added in step S1; only the carbon source (polyaniline) and activator (phosphoric acid) are used, while everything else is the same as in Example 1.

[0089] Comparative Example 2:

[0090] Unlike Example 1, in step S1 the carbon source is graphite powder without heteroatoms (replacing polyaniline), the dopant is lithium metal, the activator is phosphoric acid, and the rest is the same as in Example 1.

[0091] Comparative Example 3:

[0092] Unlike Example 1, the three-stage sputtering was cancelled, and only a single stage (graphite 125W + LLZO 100W, total time 60min) was used, with no gradient change; otherwise, it was the same as Example 1.

[0093] (1) SEM testing

[0094] Figure 1 The silicon-carbon composite material in Example 1 has a granular structure with a porous surface, exhibiting a near-spherical structure with a reasonable size distribution and a particle size between 5μm and 10μm.

[0095] (2) Physicochemical performance testing:

[0096] The specific surface area and tap density of the silicon-carbon composite materials in Examples 1-3 and Comparative Examples 1-2 were tested according to the methods in the national standard GB / T38823-2020 "Silicon-Carbon". The powder resistivity and the compaction density of the powder material at 2T were tested using a four-probe tester. At the same time, the gas production (45℃, 48h) of the silicon-carbon composite material was tested. The test results are shown in Table 1 below.

[0097] Table 1

[0098]

[0099]

[0100] (3) Button cell battery test:

[0101] The silicon-carbon composite materials of Examples 1-3 and the silicon-based composite materials of Comparative Examples 1-3 were used as active materials to prepare electrode sheets. The specific preparation method was as follows: 9g of active material, 0.5g of conductive agent SP and 0.5g of binder LA133 were added to 220mL of deionized water and stirred evenly to obtain a slurry; the slurry was coated on a copper foil current collector to obtain the electrode sheet.

[0102] The electrode with silicon-carbon composite material of Example 1 as active material is labeled A, the electrode with silicon-carbon composite material of Example 2 as active material is labeled B, the electrode with silicon-carbon composite material of Example 3 as active material is labeled C, the electrode with silicon-based composite material of Comparative Example 1 as active material is labeled D, the electrode with silicon-based composite material of Comparative Example 2 as active material is labeled E, and the electrode with silicon-based composite material of Comparative Example 3 as active material is labeled F.

[0103] The prepared electrode was then used as the positive electrode and assembled into a coin cell with lithium foil, electrolyte, and separator in a glove box where the oxygen and water content were both below 0.1 ppm. The separator was Celegard 2400; the electrolyte was a LiPF6 solution with a concentration of 1.1 mol / L, and the solvent was a mixture of ethylene carbonate (EC) and diethyl carbonate (DMC) (weight ratio 1:1). The coin cells were labeled A-1, B-1, C-1 and D-1, E-1, F-1, respectively. The performance of the coin cells was then tested using a blue electrode tester under the following conditions: 0.1C charge / discharge rate, voltage range of 0.05–2V, cycled for 3 weeks, followed by testing of the full-charge expansion of the negative electrode and its charge deceleration rate (DCR) at 50% SOC.

[0104] Table 2

[0105]

[0106] As can be seen from Table 2, the material prepared in the examples is superior to the comparative example in terms of first-time efficiency, full-charge expansion and DCR. This is because doping the material with dopants increases the pore volume, reduces silicon expansion, and reduces material defects by stepwise deposition of amorphous carbon and fast ion conductors, thereby improving first-time efficiency and reducing interface impedance and DCR.

[0107] (4) Soft package performance test:

[0108] Anode sheets were prepared by mixing 90% artificial graphite with the silicon-carbon composite materials of Examples 1-3 and Comparative Examples 1-3 as the anode material, and ternary materials (LiNi) were used to prepare the anode sheets. 1 / 3 Co 1 / 3 Mn 1 / 3 O2) was used as the positive electrode; lithium hexafluorophosphate (LiPF6) was used as the electrolyte, and a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (DEC) in a 1:1 volume ratio was used as the solvent, with an electrolyte concentration of 1.3 mol / L; a Celgard 2400 membrane was used as the separator to prepare a 5 Ah pouch cell. The prepared pouch cells were labeled A-2, B-2, C-2, D-2, E-2, and F-2, respectively. The following performance tests were performed on each pouch cell:

[0109] Full-charge expansion rate test: First, the thickness of the rolled electrode sheet is measured as D1. Then, at 100% SOC (State of Charge) of the pouch battery, the thickness of the negative electrode sheet is measured as D2. The full-charge expansion rate of the electrode sheet is calculated as: (D2 - D1) / D1 × 100%

[0110] Table 3

[0111] Serial Number Full charge expansion rate (%) A-2 33.8 B-2 35.7 C-2 32.1 D-2 38.8 E-2 41.8 F-2 43.5

[0112] As can be seen from Table 3, the full-charge expansion of the battery prepared by the material in the example is less than that in the comparison. The reason is that the surface of the material in the example is bound by the expansion of the core nano-silicon through gradient deposition of amorphous carbon and fast ion conductor, which reduces the full-charge expansion rate of the electrode.

[0113] Electrode surface resistance test:

[0114] Using a diaphragm resistance tester, the negative electrode (size 100cm) was tested. 2 The resistance was tested using a pressure of 50 kN, and the surface resistance of the electrode was calculated. The test results are shown in Table 2.

[0115] Ratio performance test:

[0116] The battery was charged at 1.0C, 3.0C, and 5.0C, and discharged at 1.0C, with the charge / discharge voltage range of 2.5-4.2V and the test temperature of 25±3.0℃. The constant current ratio of the battery was tested under different charging modes. The test results are shown in Table 4.

[0117] Table 4

[0118]

[0119] As can be seen from Table 4, based on Examples 1-3 and Comparative Examples 1-3, the porous carbon of the present invention, doped with metal gas and heteroatom gas, can reduce irreversible capacity, improve the ionic conductivity of the material, improve the first-pass efficiency, improve the ion diffusion coefficient and rate performance of the material, and coat its surface with fast ion conductors to improve the ionic conductivity of the material. Furthermore, the material of the present invention has a high specific surface area, which can shorten the liquid absorption time and improve the constant current ratio under different rate conditions.

[0120] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0121] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0122] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A power-type silicon-carbon composite material, characterized in that: The composite material exhibits a core-shell structure, with the core being a silicon-carbon alloy material co-doped with metals and heteroatoms, and the outer shell composed of amorphous carbon material doped with fast ion conductors, accounting for 5 wt% of the mass. The outer shell is divided into a carbon-rich inner layer, a mixed transition layer, and a fast ion conductor-rich outer layer; the thickness is 200 nm, and the thickness ratio is 15-25%:25-35%:45-55%. The doped metal is one of lithium, magnesium, zinc or nickel, and the doped heteroatom is one of nitrogen, sulfur or phosphorus. A method for preparing a power-type silicon-carbon composite material includes the following steps: Step S1: The carbon source, activator, and dopant are mixed evenly according to the mass ratio of carbon source: activator: dopant = 100:10-30:1-5. First, the temperature is raised to 600-800℃ for carbonization for 0.5-2 hours, then the temperature is raised to 1000-1300℃, and water vapor is introduced at a flow rate of 100-500 SCCM for 30-300 minutes to obtain large-pore porous carbon. Step S2: Porous carbon is transferred to a vacuum furnace and evacuated to 1-10 torr. It is then deposited by vaporization and heated to 1000-1500℃. A mixture of doped metal and heteroatom gas is introduced at a flow rate of 100-500 ml / min for 30-300 min. The volume ratio of doped metal gas to heteroatom gas is 1-3:

10. After cooling to 400-600℃, a silane mixture gas is introduced at a flow rate of 100-500 ml / min for 60-600 min to obtain silicon-carbon precursor material. Step S3: According to the mass ratio of fast ion conductor to binder = 100: 1-5, the fast ion conductor and binder are mixed evenly, and then cold isostatically pressed at 50-100MPa. Then, the mixture is pressed in a hot press at 200-300℃ for 0.5-2h under a pressure of 5-20 tons to obtain the fast ion conductor target material. Argon plasma etching of silicon-carbon precursors at a power of 50 W for 1-5 min is used to remove surface impurities and increase surface roughness. The silicon-carbon precursor material is placed in the reaction chamber, the chamber is evacuated to 0.1 Torr, and heated to 300-500℃ with an argon flow rate of 80-150 SCCM; a dual-target magnetron sputtering system is used, with fast ion conductor target and pure graphite target as the targets. Stage 1: Graphite target power 200 W, fast ion conductor target power 50 W, time 5-15 min, forming a carbon layer dominated by electron conduction; In stage 2, the power of the graphite target is linearly reduced to 50 W, while the power of the fast ion conductor target is linearly increased to 150 W over a period of 10-30 minutes, forming a hybrid layer of electron and ion synergistic conduction. Stage 3: The graphite target power is turned off, the fast ion conductor target power is 200 W, and the time is 15-45 min, forming a dense layer dominated by ion conduction. After deposition, the carbon is annealed in argon at 500-600℃ for 1-3 hours to form amorphous carbon doped with fast ion conductors with a thickness of 50-500 nm.

2. The power-type silicon-carbon composite material according to claim 1, characterized in that: In step S1, the carbon source is one of polyaniline, polyamide, polythiophene, polypyrrole, or melamine; the activator is one of phosphoric acid, zinc chloride, zinc bromide, or lithium carbonate; and the dopant is one of lithium metal, magnesium metal, zinc metal, or nickel metal.

3. The power-type silicon-carbon composite material according to claim 1, characterized in that: In step S2, the silane mixed gas is one of methylsilane and disilane mixed with nitrogen in a volume ratio of 1-5:10; the heteroatom gas is one of ammonia, hydrogen sulfide, and phosphine.

4. The power-type silicon-carbon composite material according to claim 1, characterized in that: The fast ion conductor in step S3 is Li7La3Zr2O 12 Li 1.4 Al 0.4 Ti 1.6 One of (PO4)3, Li2ZrP2O8 or LiAlSiO4; the binder is one of petroleum asphalt, coal tar pitch or lithium carboxymethyl cellulose.

Images