Porous carbons, methods of making and using the same

Abstract

The present application relates to the technical field of lithium ion batteries, in particular to a porous carbon, a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode sheet and an electrochemical device. The porous carbon satisfies 1.5 nm <= A <= 2 nm and 2% <= B <= 16%, wherein A is the average pore diameter of the porous carbon, and B is the ratio of the pore volume with a pore diameter of 2-3 nm to the total pore volume. By controlling the values of A and B, the structural strength and stability of the porous carbon are increased, thereby significantly improving the efficiency and uniformity of silane deposition, and improving the cycle stability of the silicon-carbon negative electrode material and the electrochemical device.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to porous carbon and its preparation methods and applications, and particularly to porous carbon and its preparation methods, silicon-carbon anode materials and their preparation methods, anode sheets, and electrochemical devices. Background Technology

[0002] With the ever-increasing demand for high-energy-density batteries in fields such as electric vehicles (EVs) and energy storage systems (ESS), the theoretical specific capacity of traditional graphite anodes, at only 372 mAh / g, is gradually becoming insufficient to meet the requirements of next-generation batteries. Silicon-based materials, with a theoretical capacity as high as 4200 mAh / g, have become an ideal alternative to traditional graphite anodes. However, silicon undergoes a significant volume change after lithium intercalation, causing the original solid electrolyte interphase (SEI) film to rupture. The exposed fresh silicon surface reacts again with the electrolyte, continuously generating new and thicker SEI films, thus consuming a large amount of additional lithium and electrolyte, and leading to capacity decay and safety risks. Silicon-carbon anode materials, due to their composite design of nano-silicon and porous carbon, can effectively mitigate volume expansion while retaining high capacity, and have become a key path to overcome the capacity bottleneck.

[0003] In silicon-carbon anode materials, porous carbon possesses a high specific surface area, good conductivity, and abundant pore structure, which can buffer the volume changes of silicon during charging and discharging, thereby improving the conductivity and structural stability of the electrode. Different pore structures (such as micropores and mesopores) of porous carbon have significantly different effects on the performance of silicon-carbon anode materials. Micropores can enrich precursor molecules through physical adsorption, increasing the local precursor concentration and accelerating the deposition reaction rate; mesopores can act as "transport channels," reducing the diffusion resistance of precursors within the pores, preventing pore blockage, and ensuring a uniform and continuous deposition process.

[0004] However, the main types of porous carbon channels currently identified are micropores (<2nm), mesopores (2-50nm), and macropores (>50nm). An excessively high proportion of micropores leads to low structural strength, making channel collapse and carbon skeleton pulverization likely during deposition. Conversely, an excessively low proportion results in uneven silicon deposition and limited capacity. A high proportion of mesopores makes the porous carbon skeleton prone to deformation and collapse, and silicon easily migrates and agglomerates, compromising stability. An excessively low proportion leads to carbon skeleton pulverization during silicon expansion. Both excessively high and low micro / mesopore proportions significantly restrict the efficiency and uniformity of silane deposition and easily trigger side reactions during subsequent charge-discharge cycles, resulting in poor cycle stability. Macropores lack effective anchoring points, hindering silicon deposition; therefore, minimizing their proportion is crucial. However, an unreasonable micro / mesopore proportion leads to low porous carbon structural strength and insufficient structural stability, affecting the high capacity and long-cycle stability of silicon-carbon anodes. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides porous carbon, its preparation method, and its applications. By controlling the proportion of pores with a diameter of 2–3 nm in the porous carbon, the structural strength and stability of the porous carbon are increased, thereby significantly improving the efficiency and uniformity of silane deposition and enhancing the cycle stability of silicon-carbon anode materials and electrochemical devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a porous carbon that satisfies: 1.5nm≤A≤2nm, 2%≤B≤16%; wherein, A is the average pore size of the porous carbon, and B is the ratio of the pore volume of the porous carbon with a pore size of 2-3nm to the total pore volume.

[0008] It should be noted that in silicon-carbon anode materials, the micro-mesoporous structure inside the porous carbon plays a dual role: on the one hand, it provides sufficient buffer space for volume expansion during the silicon lithium intercalation process; on the other hand, through the interconnected pore structure, it effectively improves the wetting effect of the electrolyte and the electron transport rate, thereby endowing the silicon-carbon anode with excellent cycle stability and providing strong support for optimizing the cycle performance of electrochemical devices such as lithium batteries.

[0009] By employing the above technical solutions, micropores can provide a high specific surface area, while mesopores can alleviate the huge volume changes during silicon charging and discharging, and optimize electron and ion transport. The two work synergistically to improve electrolyte wettability and ion transport efficiency. The combination of micropore encapsulation and mesopore buffering forms a "double protection," effectively suppressing the damage to the carbon matrix caused by silicon expansion. Micropores of 1.5–2 nm can serve as "nanotemplates" for silicon deposition, spatially constraining silicon growth. The resulting nano-silicon is much smaller than traditional nano-silicon, significantly reducing the volume expansion rate and effectively preventing electrode cracking caused by particle agglomeration. Mesopores of 2–3 nm provide additional "buffer space" during silicon expansion, absorbing volume changes, preventing micropore structure collapse, maintaining electrode integrity, and reducing the diffusion resistance of silicon source precursors within the pores, thus avoiding uneven deposition.

[0010] Therefore, by controlling the average pore size of porous carbon and the proportion of pores with a diameter of 2-3 nm, it is possible to prevent excessive mesopores from causing a decrease in the proportion of micropores, without destroying the micropore-dominated structure, ensuring that porous carbon can still provide sufficient deposition sites and increase silicon loading; at the same time, it can solve the mass transfer problem of pure microporous systems, increase the structural strength and structural stability of porous carbon, significantly improve the deposition efficiency and deposition uniformity of silanes, and solve the core pain points of poor cycle stability, low first charge and discharge efficiency, and insufficient conductivity of silicon-based electrodes.

[0011] According to an embodiment of the present invention, the particle size of the porous carbon satisfies 3μm≤Dv50≤10μm.

[0012] According to an embodiment of the present invention, the specific surface area of ​​the porous carbon is 1000–3000 m². 2 / g.

[0013] According to an embodiment of the present invention, the microporosity of the porous carbon is 75% to 95%.

[0014] According to an embodiment of the present invention, the pore volume of the porous carbon is 0.6–1.2 cm³. 3 / g.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned porous carbon, comprising: The matrix carbon was subjected to a first carbonization treatment, CO2 activation, and a second carbonization treatment in sequence to obtain porous carbon; In the CO2 activation step, the CO2 introduction rate is 15–40 L / min, and the CO2 activation time is 10–20 h.

[0016] By employing the above technical solution, the average pore size and micro / mesopore ratio of porous carbon can be precisely controlled by adjusting the CO2 introduction rate and CO2 activation time, ensuring that 1.5nm ≤ A ≤ 2nm and 2% ≤ B ≤ 16%. This prevents excessive mesopores from reducing the micropore ratio, preserving the micropore-dominated structure and ensuring that porous carbon still provides sufficient deposition sites, thus increasing silicon loading. Furthermore, it solves the mass transfer problem of pure microporous systems, increases the structural strength and stability of porous carbon, significantly improves silane deposition efficiency and uniformity, and addresses the issues of poor cycle stability, low initial charge / discharge efficiency, and insufficient conductivity in silicon-based electrodes.

[0017] According to an embodiment of the present invention, the first carbonization treatment satisfies at least one of the following conditions: The heating rate of the first carbonization treatment is 5-10 °C / min; The temperature of the first carbonization treatment is 400–600°C; The heat preservation time for the first carbonization treatment is 1 to 3 hours.

[0018] According to an embodiment of the present invention, the CO2 activation temperature is 700–1000°C.

[0019] According to an embodiment of the present invention, the temperature of the second carbonization treatment is 800–1000°C.

[0020] A third aspect of the present invention provides a silicon-carbon anode material, comprising: The above-mentioned porous carbon and / or porous carbon prepared by the above-mentioned preparation method; Nano-silicon, wherein the nano-silicon is at least partially located within the pores of the porous carbon.

[0021] By adopting the above technical solution, the 2-3 nm mesopores can provide additional "buffer space" when nano-silicon expands, which can absorb volume changes, prevent the microporous structure from collapsing, maintain electrode integrity, reduce the diffusion resistance of silicon source precursor in the pores, avoid uneven deposition, increase the structural strength and structural stability of porous carbon, and improve the stability, first charge and discharge efficiency and other performance of silicon-carbon anode materials.

[0022] According to an embodiment of the present invention, the size of the nano-silicon is less than or equal to 3 nm.

[0023] According to an embodiment of the present invention, the particle size of the silicon-carbon anode material satisfies Dv99≤50μm.

[0024] According to an embodiment of the present invention, the mass percentage of nano-silicon is 30-60 wt% based on the total mass of the silicon-carbon anode material.

[0025] According to an embodiment of the present invention, the specific surface area of ​​the target silicon-carbon anode material is 1–10 m². 2 / g.

[0026] According to an embodiment of the present invention, the silicon-carbon anode material further includes a first carbon coating layer covering the surface of the nano-silicon and porous carbon, and a second carbon coating layer covering the surface of the first carbon coating layer.

[0027] According to an embodiment of the present invention, the total content of the first carbon coating layer and the second carbon coating layer in the silicon-carbon anode material is 0.7 to 3 wt%.

[0028] A fourth aspect of the present invention provides a method for preparing the above-mentioned silicon-carbon anode material, comprising: Nano-silicon is deposited in the pores of the porous carbon to obtain the silicon-carbon anode material.

[0029] According to an embodiment of the present invention, the method for preparing the silicon-carbon anode material satisfies at least one of the following conditions: The temperature for the nano-silicon deposition is 400–700°C; The deposition time for the nano-silicon is 3 to 10 hours.

[0030] According to an embodiment of the present invention, the pressure for the nano-silicon deposition is 10–30 kPa.

[0031] According to an embodiment of the present invention, the nano-silicon deposition includes: heating porous carbon, introducing a mixture of gaseous silicon source and carrier gas, and performing deposition.

[0032] According to an embodiment of the present invention, the preparation method of the silicon-carbon anode material further includes: after nano-silicon deposition, a first carbon source and a second carbon source are sequentially deposited by chemical vapor deposition to perform first carbon coating and second carbon coating.

[0033] According to an embodiment of the present invention, the method for preparing the silicon-carbon anode material satisfies at least one of the following conditions: The temperature at which the first carbon coating is applied is 500–800°C; The first carbon coating time is 2-5 hours; The temperature for the second carbon coating is 500–800°C; The second carbon coating time is 100-300 min.

[0034] A fifth aspect of the present invention provides a negative electrode sheet comprising the above-described silicon-carbon negative electrode material, and / or a silicon-carbon negative electrode material prepared by the above-described method for preparing the silicon-carbon negative electrode material.

[0035] According to an embodiment of the present invention, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer containing a negative electrode active material, the negative electrode active material including the silicon-carbon negative electrode material.

[0036] A sixth aspect of the present invention provides an electrochemical device comprising the aforementioned negative electrode plate.

[0037] According to an embodiment of the present invention, the electrochemical device includes at least one of a lithium battery or a lithium-ion battery. Therefore, the silicon-carbon anode material proposed in this application exhibits excellent volume expansion uniformity, which is beneficial for improving the stability of the electrode structure, thereby enhancing the cycle performance and other electrical properties of the electrochemical device.

[0038] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0039] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 2 of the present invention; Figure 2 This is a pore size distribution diagram of the porous carbon prepared in Example 2 of the present invention; Figure 3 A voltage-to-capacity curve of a battery containing the silicon-carbon anode material prepared in Example 2 of the present invention; Figure 4The diagram shows the first 40 charge-discharge cycles of a battery containing the silicon-carbon anode material prepared in Examples 1-2 of this invention. Detailed Implementation

[0040] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0041] It should be noted that 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 indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0044] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0045] To address the issues of low structural strength, insufficient structural stability, and poor cycle stability inherent in porous carbon, research has found that one contributing factor is the unreasonable proportion of pores with a pore size of 2–3 nm. Based on this finding, this invention proposes porous carbon with an appropriate proportion of pores with a pore size of 2–3 nm. By controlling the proportion of pores with a pore size of 2–3 nm in porous carbon, the structural strength and stability of porous carbon can be increased, thereby significantly improving the efficiency and uniformity of silane deposition and enhancing the cycle stability of silicon-carbon anode materials and electrochemical devices.

[0046] The first aspect of the present invention provides a porous carbon that satisfies: 1.5nm≤A≤2nm, 2%≤B≤16%; wherein, A is the average pore size of the porous carbon, and B is the ratio of the pore volume of the porous carbon with a pore size of 2-3nm to the total pore volume.

[0047] It should be noted that in silicon-carbon anode materials, the micro-mesoporous structure inside the porous carbon plays a dual role: on the one hand, it provides sufficient buffer space for volume expansion during the silicon lithium intercalation process; on the other hand, through the interconnected pore structure, it effectively improves the wetting effect of the electrolyte and the electron transport rate, thereby endowing the silicon-carbon anode with excellent cycle stability and providing strong support for optimizing the cycle performance of electrochemical devices such as lithium batteries.

[0048] By employing the above technical solutions, micropores can provide a high specific surface area, while mesopores can alleviate the huge volume changes during silicon charging and discharging, and optimize electron and ion transport. The two work synergistically to improve electrolyte wettability and ion transport efficiency. The combination of micropore encapsulation and mesopore buffering forms a "double protection," effectively suppressing the damage to the carbon matrix caused by silicon expansion. Micropores of 1.5–2 nm can serve as "nanotemplates" for silicon deposition, spatially constraining silicon growth. The resulting nano-silicon is much smaller than traditional nano-silicon, significantly reducing the volume expansion rate and effectively preventing electrode cracking caused by particle agglomeration. Mesopores of 2–3 nm provide additional "buffer space" during silicon expansion, absorbing volume changes, preventing micropore structure collapse, maintaining electrode integrity, and reducing the diffusion resistance of silicon source precursors within the pores, thus avoiding uneven deposition.

[0049] Therefore, by controlling the average pore size of porous carbon and the proportion of pores with a diameter of 2-3 nm, it is possible to prevent excessive mesopores from causing a decrease in the proportion of micropores, without destroying the micropore-dominated structure, ensuring that porous carbon can still provide sufficient deposition sites and increase silicon loading; at the same time, it can solve the mass transfer problem of pure microporous systems, increase the structural strength and structural stability of porous carbon, significantly improve the deposition efficiency and deposition uniformity of silanes, and solve the core pain points of poor cycle stability, low first charge and discharge efficiency, and insufficient conductivity of silicon-based electrodes.

[0050] For example, the average pore size A of the porous carbon can be 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2.0 nm, etc. Micropores within these pore size ranges can serve as "nanotemplates" for silicon deposition. Their inner walls can tightly encapsulate the silicon nanoparticles, restricting their radial expansion and spatially constraining silicon growth. This prevents the silicon nanoparticles from detaching from the porous carbon, allowing the silicon source precursor to be adsorbed and decomposed within the micropores. The resulting silicon nanoparticles are much smaller than traditional silicon nanoparticles, significantly reducing volume expansion and effectively preventing electrode cracking caused by particle agglomeration. If the average pore size is too small, the nanoparticles may easily collapse; if the average pore size is too large, the framework strength may be reduced, making the particles prone to cracking and breakage, leading to rapid capacity decay.

[0051] In some embodiments, the average pore size of the porous carbon is 1.6 to 1.9 nm.

[0052] For example, the ratio B of the pore volume of 2-3 nm pores in the porous carbon to the total pore volume can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc. A mesopore ratio within this range can reduce the diffusion resistance of the silicon source precursor within the pores, avoid uneven deposition due to insufficient precursor in the deep micropores, and prevent excessive mesopores from causing a decrease in the micropore ratio. This ensures that the porous carbon can provide sufficient deposition sites and increase the silicon loading.

[0053] According to an embodiment of the present invention, the particle size of the porous carbon satisfies 3μm ≤ Dv50 ≤ 10μm, specifically such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc. This enables the porous carbon to possess high structural stability, which is beneficial for buffering volume changes during the lithium-ion insertion / extraction process on nano-silicon. Too small a particle size may cause the porous carbon to easily agglomerate, resulting in difficulties in coating and reduced initial charge / discharge efficiency.

[0054] It should be noted that the particle size distribution of the porous carbon or fumed silicon-carbon anode material is tested using a Malvern Mastersizer 2000 or Malvern Mastersizer 3000 laser particle size analyzer to obtain particle size distribution curves and key parameters.

[0055] According to an embodiment of the present invention, the specific surface area of ​​the porous carbon is 1000–3000 m². 2 / g, specifically 1000m 2 / g、1200m 2 / g, 1500m 2 / g、1800m 2 / g、2000m 2 / g、2300m 2 / g、2500m 2 / g、2800m 2 / g、3000m 2 / g etc.

[0056] It should be noted that the specific surface area mentioned in this invention is the BET specific surface area obtained by testing with a JW-BK100C specific surface area and pore size analyzer.

[0057] By employing the above technical solution, nano-silicon can achieve suitable dispersion on the aforementioned porous carbon, which helps reduce the structural damage to the silicon-carbon anode material caused by local expansion stress concentration. However, an excessively large specific surface area may increase side reactions, reduce initial charge-discharge efficiency, and increase electrolyte consumption.

[0058] According to an embodiment of the present invention, the microporosity of the porous carbon is 75% to 95%, specifically 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, 95%, etc. Within the aforementioned microporosity range, the porous carbon can accommodate a moderate amount of nano-silicon deposition, which is beneficial for achieving a high sodium ion capacity while reducing the impact of silicon volume changes on the stability of the silicon-carbon anode material. Too low a microporosity may result in insufficient nano-silicon deposition, leading to inadequate capacity; too high a microporosity may reduce the initial charge-discharge efficiency.

[0059] It should be noted that micropores are pores with a diameter of less than 2 nm, and are the smallest of the three common types of pores (micropores < 2 nm, mesopores 2 nm to 50 nm, and macropores > 50 nm). Microporosity can be calculated by utilizing the "adsorption-desorption" behavior of small molecule gases (such as N2 and CO2) within micropores at low temperatures (e.g., N2 at -196 °C). Pore parameters are calculated using adsorption isotherms. Common models include the t-plot method, the Dubinin-Radushkevich (DR) method, and the Horvath-Kawazoe (HK) method.

[0060] In some embodiments, the microporosity of the present invention is obtained by measuring the pore size distribution of porous carbon using a JW-BK100C surface area and pore size analyzer. The cumulative pore volume of the porous carbon with a pore size less than 2 nm is calculated as a using the HK method, and the total pore volume is calculated as b using the nonlocal density functional theory (NLDFT) method. The microporosity is a / b.

[0061] According to an embodiment of the present invention, the pore volume of the porous carbon is 0.6–1.2 cm³. 3 / g, specifically 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g etc. This helps to reduce the impact of volume changes in nano-silicon during lithium insertion and extraction on the structural stability of silicon-carbon anode materials.

[0062] It should be noted that the pore volume of the porous carbon described in this invention was obtained by testing with a JW-BK100C surface area and pore size analyzer.

[0063] In some embodiments, the porous carbon includes one or more of resin-based, biomass-based, and petroleum coke-based materials.

[0064] In some embodiments, the porous carbon has a morphology of at least one of spherical, near-spherical, plate-like, or irregular shapes.

[0065] A second aspect of the present invention provides a method for preparing the above-mentioned porous carbon, comprising: The matrix carbon was subjected to a first carbonization treatment, CO2 activation, and a second carbonization treatment in sequence to obtain porous carbon; In the CO2 activation step, the CO2 introduction rate is 15–40 L / min, and the CO2 activation time is 10–20 h.

[0066] By employing the above technical solution, the average pore size and micro / mesopore ratio of porous carbon can be precisely controlled by adjusting the CO2 introduction rate and CO2 activation time, ensuring that 1.5nm ≤ A ≤ 2nm and 2% ≤ B ≤ 16%. This prevents excessive mesopores from reducing the micropore ratio, preserving the micropore-dominated structure and ensuring that porous carbon still provides sufficient deposition sites, thus increasing silicon loading. Furthermore, it solves the mass transfer problem of pure microporous systems, increases the structural strength and stability of porous carbon, significantly improves silane deposition efficiency and uniformity, and addresses the issues of poor cycle stability, low initial charge / discharge efficiency, and insufficient conductivity in silicon-based electrodes.

[0067] For example, the CO2 introduction rate can be 15L / min, 18L / min, 20L / min, 22L / min, 25L / min, 28L / min, 30L / min, 32L / min, 35L / min, 38L / min, 40L / min, etc., and the CO2 activation time can be 10h, 11h, 12h, 13h, 14h, 15h, 17h, 18h, 19h, 20h, etc.

[0068] According to an embodiment of the present invention, the first carbonization treatment satisfies at least one of the following conditions: The heating rate of the first carbonization treatment is 5-10 °C / min; The temperature of the first carbonization treatment is 400–600°C; The heat preservation time for the first carbonization treatment is 1 to 3 hours.

[0069] By adopting the above technical solution, the first carbonization treatment can reduce matrix carbon impurities, improve the purity of porous carbon, and reduce side reactions generated during silicon deposition.

[0070] For example, the heating rate of the first carbonization treatment can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.; the temperature of the first carbonization treatment can be 400℃, 425℃, 450℃, 475℃, 500℃, 525℃, 550℃, 575℃, 600℃, etc.; and the holding time of the first carbonization treatment can be 1h, 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h, 3h, etc.

[0071] According to an embodiment of the present invention, the CO2 activation temperature is 700-1000℃, specifically such as 700℃, 725℃, 750℃, 775℃, 800℃, 825℃, 850℃, 875℃, 900℃, 925℃, 950℃, 975℃, 1000℃, etc.

[0072] By adopting the above technical solution, chemical etching can be performed through CO2 activation to construct micropores and mesopores on the carbon framework. At the same time, it can also significantly increase the specific surface area and pore volume, provide sufficient loading sites for silicon deposition, take into account silicon dispersion and ion transport efficiency, and alleviate volume expansion.

[0073] According to an embodiment of the present invention, the temperature of the second carbonization treatment is 800 to 1000°C, specifically 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, 975°C, 1000°C, etc.

[0074] By adopting the above technical solutions, the strength of the material can be significantly improved, the expansion of silicon during charging and discharging can be resisted, the cycle life can be extended, the conductivity can be further improved, and the occurrence of side reactions can be reduced.

[0075] A third aspect of the present invention provides a silicon-carbon anode material, comprising: The above-mentioned porous carbon and / or porous carbon prepared by the above-mentioned preparation method; Nano-silicon, wherein the nano-silicon is at least partially located within the pores of the porous carbon.

[0076] By adopting the above technical solution, the 2-3 nm mesopores can provide additional "buffer space" when nano-silicon expands, which can absorb volume changes, prevent the microporous structure from collapsing, maintain electrode integrity, reduce the diffusion resistance of silicon source precursor in the pores, avoid uneven deposition, increase the structural strength and structural stability of porous carbon, and improve the stability, first charge and discharge efficiency and other performance of silicon-carbon anode materials.

[0077] In some embodiments, the nano-silicon is uniformly distributed in the micropores and mesopores of the porous carbon.

[0078] According to an embodiment of the present invention, the size of the nano-silicon is less than or equal to 3nm, specifically such as 0.5nm, 1.0nm, 1.5nm, 2.0nm, 2.5nm, 3.0nm, etc.

[0079] It should be noted that the size of the nano-silicon described in this invention refers to the size of all nano-silicon particles involved in this invention. The size of the nano-silicon particles was determined using transmission electron microscopy (TEM). A small amount of deposited sample was taken in an inert atmosphere (Ar / N2), anhydrous ethanol was added, and the sample was ultrasonically dispersed for 10–30 min. After vacuum drying, the sample was quickly transferred to an electron microscope. TEM images of ≥50 silicon particles were randomly acquired, and the measurements were performed using software such as ImageJ and Digital Micrograph.

[0080] By adopting the above technical solution, the size of the nano-silicon is much smaller than that of traditional nano-silicon (usually >10nm). Nano-silicon of this size can reduce the volume expansion rate from 300% to below 150%, effectively avoiding electrode cracking caused by particle agglomeration.

[0081] According to an embodiment of the present invention, the particle size of the silicon-carbon anode material satisfies Dv99≤50μm, specifically such as 1μm, 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, and 50μm.

[0082] By adopting the above technical solution, it is beneficial to improve the conductivity, stability, and initial charge-discharge efficiency of silicon-carbon anode materials. However, excessively small particle size may increase the degree of electrode compaction, affecting Li... + The reduced transport path leads to greater dispersion of expansion stress; however, excessively large particle size can easily cause agglomeration, potentially resulting in difficulties in coating and reduced efficiency during the first charge and discharge cycle.

[0083] According to an embodiment of the present invention, based on the total mass of the silicon-carbon anode material, the mass percentage of nano-silicon is 30-60 wt%, specifically 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, etc. This is beneficial for increasing the reversible capacity of the battery, avoiding repeated SEI rupture, and improving the initial charge-discharge efficiency and cycle stability.

[0084] The specific surface area of ​​the target silicon-carbon anode material is 1–10 m². 2 / g, specifically 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m2 / g、9m 2 / g, 10m 2 / g etc. This reduces the direct contact between silicon and the electrolyte during charging and discharging, prevents side reactions, and improves initial charge / discharge efficiency and cycle stability.

[0085] According to an embodiment of the present invention, the silicon-carbon anode material further includes a first carbon coating layer covering the surface of the nano-silicon and porous carbon, and a second carbon coating layer covering the surface of the first carbon coating layer.

[0086] By adopting the above technical solutions, the specific surface area of ​​silicon-carbon anode materials can be reduced, the direct contact between silicon and electrolyte during charging and discharging can be reduced, side reactions can be prevented and volume expansion can be alleviated, which is conducive to building a highly conductive network, stabilizing the SEI film, and preventing silicon from being oxidized.

[0087] According to an embodiment of the present invention, the total content of the first carbon coating layer and the second carbon coating layer in the silicon-carbon anode material is 0.7 to 3 wt%, specifically 0.7 wt%, 1.0 wt%, 1.3 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%, 2.3 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, etc.

[0088] By adopting the above technical solution, it is beneficial to reduce the specific surface area of ​​silicon-carbon anode materials and improve the first cycle efficiency and cycle stability. However, if the total carbon coating content is too high, it may reduce the silicon volume fraction and reduce the capacitance.

[0089] According to an embodiment of the present invention, the content of the first carbon coating layer in the silicon-carbon anode material is 0.7 to 1.5 wt%, specifically such as 0.7 wt%, 0.8 wt%, 1.0 wt%, 1.3 wt%, 1.5 wt%, etc.; thereby, it is beneficial to provide an initial conductive network and buffer the volume expansion of silicon, thereby improving the battery's first efficiency and cycle stability.

[0090] According to an embodiment of the present invention, the content of the second carbon coating layer in the silicon-carbon anode material is 1.5 to 2.3 wt%, specifically 1.5 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, 2.3 wt%, etc.; thereby, it is beneficial to further improve conductivity and stabilize the SEI film. If the content of the second carbon coating layer is too high, it may dilute the silicon capacity and reduce the battery capacity.

[0091] According to an embodiment of the present invention, a primary carbon-coated silicon-carbon anode material is obtained by coating the nano-silicon and porous carbon surfaces with a first carbon coating layer, and a secondary carbon-coated silicon-carbon anode material is obtained by coating the surface of the first carbon coating layer with a second carbon coating layer.

[0092] In some embodiments, the specific surface area of ​​the primary carbon-coated silicon-carbon anode material is 30–100 m². 2 / g, specifically 30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g、60m 2 / g、65m 2 / g、70m 2 / g、75m 2 / g、80m 2 / g、85m 2 / g、90m 2 / g、95m 2 / g, 100m 2 / g etc. This ensures the number of open channels and silicon deposition sites, which is beneficial for improving battery capacity. However, an excessively large specific surface area may lead to more side reactions, thus reducing the initial efficiency.

[0093] In some embodiments, the specific surface area of ​​the secondary carbon-coated silicon-carbon anode material is 1–10 m². 2 / g, specifically 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g etc. This reduces the electrolyte consumption of the SEI, improving the battery's initial efficiency and cycle stability; however, an excessively small specific surface area may lead to pore blockage, reducing silicon loading and thus battery capacity.

[0094] A fourth aspect of the present invention provides a method for preparing the above-mentioned silicon-carbon anode material, comprising: Nano-silicon is deposited in the pores of the porous carbon to obtain the silicon-carbon anode material.

[0095] By adopting the above technical solution, nano-silicon is deposited in the pores of the porous carbon. The 2-3 nm mesopores can provide additional "buffer space" when the nano-silicon expands, which can absorb volume changes, prevent the microporous structure from collapsing, reduce the diffusion resistance of silicon source precursor in the pores, avoid uneven deposition, increase the structural strength and structural stability of porous carbon, and improve the stability, first charge and discharge efficiency and other properties of silicon-carbon anode materials.

[0096] According to an embodiment of the present invention, the method for preparing the silicon-carbon anode material satisfies at least one of the following conditions: The temperature for the nano-silicon deposition is 400–700°C; The deposition time for the nano-silicon is 3 to 10 hours.

[0097] By adopting the above technical solution, it is beneficial to control the size of nano-silicon, so that nano-silicon can be uniformly deposited in the pores of porous carbon, thereby improving conductivity, capacity and cycle stability; however, excessively high temperature or excessive time can easily cause silicon grains to grow, which may lead to expansion and pulverization, thus reducing battery capacity and cycle stability.

[0098] For example, the temperature for nano-silicon deposition can be 400℃, 425℃, 450℃, 475℃, 500℃, 525℃, 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, 700℃, etc.; and the time for nano-silicon deposition can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0099] According to an embodiment of the present invention, the pressure for nano-silicon deposition is 10–30 kPa, specifically 10 kPa, 12 kPa, 15 kPa, 18 kPa, 20 kPa, 23 kPa, 25 kPa, 28 kPa, 30 kPa, etc. This can increase the silane diffusion depth, accelerate the deposition rate, and achieve more compact pore filling, thereby improving battery capacity. However, excessive pressure can easily lead to pore blockage, outer wall crust formation, and coating layer rupture, which in turn reduces cycle stability.

[0100] According to an embodiment of the present invention, the nano-silicon deposition includes: heating porous carbon, introducing a mixture of gaseous silicon source and carrier gas, and performing deposition.

[0101] In some embodiments, the gaseous silicon source comprises silane. Further, the silane comprises one or more of silane (SiH4), silane (Si2H6), propane (Si3H8), methylsilane (CH3SiH3), and dimethylsilane.

[0102] In some embodiments, the carrier gas includes at least one of nitrogen, argon, and helium.

[0103] In some embodiments, the volume ratio of silicon source to carrier gas in the mixed gas is (0.5-2):1.

[0104] In some embodiments, the reaction equipment for the nano-silicon deposition is a fluidized bed.

[0105] In some embodiments, the heating rate for the nano-silicon deposition is 3–10 °C / min, specifically 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, etc. Heating rate (2–5 °C / min) - ¹). This is beneficial for uniform nucleation and increases silicon loading; however, excessively rapid heating may cause the pores to be blocked by deposition first, resulting in a reduction in internal silicon and a decrease in capacity.

[0106] In some embodiments, the time for nano-silicon deposition includes a holding pressure time and a deposition reaction time, wherein the holding pressure time is 10–50 min and the deposition reaction time is 4–8 h. For example, the holding pressure time can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, etc.; and the deposition reaction time can be 4 h, 5 h, 6 h, 7 h, 8 h, etc.

[0107] Therefore, it is possible to balance battery capacity and cycle stability. If the holding time is too short, the silane diffusion may be insufficient, resulting in shallow silicon deposition and reduced battery capacity. If the holding time is too long, the outer wall may form a crust, which may expand and crack during subsequent cycles, reducing cycle stability. If the deposition reaction time is too long, the silicon grains may grow and the loading may increase. If the grains are too large, they are prone to pulverization, which will reduce cycle stability.

[0108] According to an embodiment of the present invention, the preparation method of the silicon-carbon anode material further includes: after nano-silicon deposition, a first carbon source and a second carbon source are sequentially deposited by chemical vapor deposition to perform first carbon coating and second carbon coating.

[0109] In some embodiments, the first carbon source and the second carbon source each independently include at least one of methane, ethane, propane, butane, ethylene, propylene, butene, acetylene, propyne, butyne, pentane, hexane, pentene, hexene, pentyne, and propyne.

[0110] According to an embodiment of the present invention, the method for preparing the silicon-carbon anode material satisfies at least one of the following conditions: The temperature at which the first carbon coating is applied is 500–800°C; The first carbon coating time is 2-5 hours; The temperature for the second carbon coating is 500–800°C; The second carbon coating time is 100-300 min.

[0111] By adopting the above technical solution, the degree of graphitization of the carbon layer can be increased, preventing direct contact between nano-silicon and electrolyte, and improving conductivity and cycle stability.

[0112] For example, the temperature of the first carbon coating can be 500℃, 525℃, 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, 700℃, 725℃, 750℃, 775℃, 800℃, etc. The time for the first carbon coating can be 2h, 2.2h, 2.5h, 2.8h, 3h, 3.5h, 4h, 4.5h, 5h, etc. The second carbon coating temperature can be 500℃, 525℃, 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, 700℃, 725℃, 750℃, 775℃, 800℃, etc. The second carbon coating time is 100 min, 125 min, 150 min, 175 min, 200 min, 225 min, 250 min, 275 min, 300 min, etc.

[0113] In some embodiments, the time for the first carbon coating includes a holding time and a coating time, wherein the holding time is 10 min to 30 min and the coating time is 1 to 5 h. For example, the holding time can be 10 min, 15 min, 20 min, 25 min, 30 min, etc.; and the coating time can be 1 h, 2 h, 3 h, 4 h, 5 h, etc.

[0114] Therefore, both the conductive framework and porosity can be preserved. If the holding time is too short, the precursor may not have sufficient partial pressure, resulting in a thin and uneven carbon layer, which reduces the strength of the framework and the first efficiency. If the holding time is too long, the pores may close prematurely, limiting the space for subsequent silicon deposition and reducing the capacity. If the coating time is too long, the micropores may be overfilled, causing a sharp drop in specific surface area, reducing both silicon loading and lithium-ion channels, resulting in a double decrease in battery capacity and rate performance.

[0115] A fifth aspect of the present invention provides a negative electrode sheet comprising the above-described silicon-carbon negative electrode material, and / or a silicon-carbon negative electrode material prepared by the above-described method for preparing the silicon-carbon negative electrode material.

[0116] According to an embodiment of the present invention, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer containing a negative electrode active material, the negative electrode active material including the silicon-carbon negative electrode material.

[0117] In some embodiments, the negative electrode current collector includes any one of copper foil, nickel foil, copper-nickel composite foil, aluminum foil, carbon-based current collector, and foamed metal current collector.

[0118] In some embodiments, the negative electrode film layer further includes a binder and a conductive agent.

[0119] In some embodiments, the adhesive comprises one or more of sodium carboxymethyl cellulose (CMC), sodium alginate (SA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium polyacrylate (PAAS), styrene-butadiene rubber (SBR), polyimide (PI), polydopamine (PDA), and polyvinyl alcohol (PVA).

[0120] In some embodiments, the conductive agent includes one or more of graphite, carbon black, acetylene black, Ketjen black, graphene, and metal powder.

[0121] In some embodiments, the method for preparing the negative electrode sheet includes: The negative electrode active material, conductive agent and binder are uniformly stirred in a solvent to obtain a negative electrode slurry; The negative electrode slurry is coated onto the negative electrode current collector to obtain a negative electrode sheet.

[0122] Optionally, the solvent is at least one of deionized water and N-methylpyrrolidone (NMP).

[0123] A sixth aspect of the present invention provides an electrochemical device comprising the aforementioned negative electrode plate.

[0124] According to an embodiment of the present invention, the electrochemical device includes at least one of a lithium battery or a lithium-ion battery. Therefore, the silicon-carbon anode material proposed in this application exhibits excellent volume expansion uniformity, which is beneficial for improving the stability of the electrode structure, thereby enhancing the cycle performance and other electrical properties of the electrochemical device.

[0125] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0126] Example 1 Take 10 kg of resin-based matrix carbon, heat it to 500℃ at 5℃ / min and keep it at that temperature for 2 hours under an inert atmosphere to carry out the first carbonization treatment and obtain the carbon skeleton. The carbon framework was heated to 900°C and CO2 gas was introduced for 15 hours to activate it with CO2. The carbon was then etched to form microporous carbon. The CO2 introduction rate during the CO2 activation was 20 L / min. The microporous carbon was then subjected to a second carbonization treatment at 1000°C to obtain porous carbon. 1 kg of porous carbon was placed in a deposition furnace and heated to 500 °C under an inert atmosphere. A mixture of silane and nitrogen (volume ratio 1:1) was introduced into the deposition furnace to deposit nano-silicon for 6 h. Then the temperature was raised to 600 °C for the first carbon coating for 3 h. The temperature was then lowered to obtain a single carbon-coated silicon-carbon anode material. The silicon-carbon anode material with primary carbon coating is placed in a rotary furnace and heated to 600°C for secondary carbon coating. The coating time is 200 minutes. After cooling, the silicon-carbon anode material is obtained.

[0127] Example 2 This embodiment is based on Embodiment 1, with the only difference being that the CO2 introduction rate is 25 L / min.

[0128] Example 3 This embodiment is based on Embodiment 1, with the only difference being that the CO2 introduction rate is 30 L / min.

[0129] Example 4 This embodiment is based on Embodiment 1, with the only difference being that the CO2 introduction time is 10 hours.

[0130] Example 5 This embodiment is based on embodiment 1, with the only difference being that the CO2 is introduced over a period of 13 hours.

[0131] Example 6 This embodiment is based on embodiment 2, with the only difference being that the CO2 introduction time is 10 hours.

[0132] Example 7 This embodiment is based on embodiment 2, with the only difference being that the CO2 introduction time is 13 hours.

[0133] Example 8 This embodiment is based on embodiment 3, with the only difference being that the CO2 introduction time is 10 hours.

[0134] Example 9 This embodiment is based on embodiment 3, with the only difference being that the CO2 introduction time is 13 hours.

[0135] Comparative Example 1 This comparative example is based on Example 1, except that the CO2 introduction time is 22 hours.

[0136] Comparative Example 2 This comparative example is based on Example 1, except that the CO2 introduction time is 25 hours.

[0137] Comparative Example 3 This comparative example is based on Example 1, except that the CO2 injection rate is 10 L / min.

[0138] Comparative Example 4 This comparative example is based on Example 1, except that the CO2 injection rate is 45 L / min.

[0139] Effect test 1. Scanning electron microscopy (SEM) test: The silicon-carbon anode material prepared in Example 2 was subjected to SEM testing using a Philips XL-30 field emission scanning electron microscope at 10 kV and 10 mA. The results are as follows: Figure 1 As shown.

[0140] 2. Specific surface area, pore size, and pore volume testing: The average pore size (A), the ratio of pore volume of 2-3 nm pores to total pore volume, and the specific surface area of ​​the porous carbons prepared in Examples 1-9 and Comparative Examples 1-4 were measured using a JW-BK100C surface area and pore size analyzer, as well as the specific surface area of ​​the silicon-carbon anode material. The cumulative pore volume of the porous carbon was calculated using nonlocal density functional theory (NLDFT), and the ratio of 2-3 nm pore volume to total pore volume (B) was calculated according to the following formula. The specific surface area of ​​the samples was calculated using the BET method, and the results are recorded in Table 1 and... Figure 2 .

[0141] The formula for calculating the ratio B of the 2-3 nm pore volume to the total pore volume is: B = (YX) / Z, Where X is the cumulative pore volume (cm³) of pores with a diameter less than 2 nm. 3 / g); Y represents the cumulative pore volume (cm³) of pores with a diameter less than 3 nm. 3 / g); Z represents the total pore volume (cm³). 3 / g).

[0142] The formula for calculating the specific surface area is: Specific surface area S BET =(V m ·N·σ) / (M v ) Where Vm is the monolayer saturated adsorption capacity (STP, cm³ / g). N is Avogadro's constant, with a value of 6.022 × 10⁻⁶. 23 (mol) 1 ); σ represents the cross-sectional area of ​​the adsorbate molecule; the standard value for nitrogen physisorption at 77 K is σ = 0.162 nm. 2 ; M v This is the volume of 1 mol of an ideal gas under standard conditions (cm³ / mol), approximately 22414 cm³ / mol.

[0143] Table 1. Specific surface area, pore size, and pore volume test results of silicon-carbon anode materials prepared in Examples 1-9 and Comparative Examples 1-4.

[0144] As shown in Table 1, Examples 1-9 of the present invention successfully prepared particles with an average pore size A satisfying 1.5 nm ≤ A ≤ 2 nm, a pore volume ratio B of 2-3 nm pore size satisfying 2% ≤ B ≤ 16%, a particle size satisfying 3 μm ≤ Dv50 ≤ 10 μm, and a specific surface area of ​​1000 m². 2 / g~3000m 2 / g of porous carbon was used to prepare silicon-carbon anode materials.

[0145] Comparative Examples 1 and 2 varied the CO2 introduction time, and the average pore size A, the ratio B of pore volume with a diameter of 2-3 nm to the total pore volume, the specific surface area, and the specific surface area of ​​the secondary carbon coating of the prepared porous carbon all increased. Among them, the average pore size A of Comparative Example 2 exceeded the range defined by this invention, and the B values ​​of Comparative Examples 1 and 2 all exceeded the range defined by this invention, indicating that an excessively long CO2 introduction time would result in an excessively large proportion of mesopores in the porous carbon.

[0146] Comparative Examples 3 and 4 varied the CO2 introduction rate, and the average pore size (A), the ratio of pore volume of 2-3 nm pore size to total pore volume (B), specific surface area, and secondary carbon coating specific surface area of ​​the prepared porous carbon all showed significant changes, and Dv50 increased. This indicates that both excessively fast and slow CO2 introduction rates significantly affect the pore size, micro-mesopore ratio, specific surface area, Dv50, and secondary carbon coating specific surface area of ​​porous carbon.

[0147] 3. Electrochemical performance testing: (1) Preparation of button lithium batteries Preparation of negative electrode sheet: The silicon-carbon negative electrode material prepared in Examples 1-9 or Comparative Examples 1-2, the conductive agent carbon black and the binder lithium polyacrylate (PAALi) were mixed in a mass ratio of 8:1:1. Deionized water was added and the mixture was homogenized in a ball mill for 3 hours to obtain a slurry. Copper foil with a width of 10 cm and a length of 20 cm was cut with a utility knife and coated with slurry on a heated flat plate coating machine. Then, the copper foil loaded with slurry was placed in a vacuum drying oven and dried at 60°C for 24 hours. The dried electrode sheet was taken out and punched out as a 12 mm negative electrode sheet.

[0148] Preparation of electrolyte: First, the sealed ethylene carbonate (EC) solvent was heated to liquid state in a constant temperature drying oven at 50°C. EC and propylene carbonate (PC) were measured and mixed at a molar ratio of 1:1. 5% of the total amount of EC and PC was added to fluoroethylene carbonate (FEC). The mixture was stirred on a magnetic stirrer for 4 hours to obtain a mixed solvent. LiPF6 salt was added to the mixed solvent to prepare a 1M LiPF6 electrolyte.

[0149] Separator: The lithium battery separator is made of polypropylene (PP).

[0150] Battery assembly: Place the center of the spring sheet and the washer into the negative electrode shell in sequence; Add a drop of electrolyte to the center of the pad, and place the lithium metal sheet on the pad; Add 40 μL of electrolyte to the lithium metal sheet, place a PP diaphragm, and then add another 40 μL of electrolyte. Place the negative electrode sheet with the active material coated on it facing the separator, and then put on the positive electrode shell; The assembled button cells are then packaged and left to stand at room temperature for 10 hours. Once the electrolyte, active material, and separator have been fully immersed, electrochemical testing can be carried out.

[0151] (2) Test method The battery was charged and discharged using a LAND battery testing system. After charging, it was allowed to rest for 10 hours, then discharged at 0.05C to 0.005V, allowed to rest for 5 minutes, and then discharged at 50μA to 0.005V. After resting for 5 minutes, it was discharged again at 10μA to 0.005V, and finally charged at a constant current of 0.05C to 2V. This process was repeated 39 times. The initial charge-discharge efficiency, the initial charge-discharge efficiency at 0.8V, the lithium intercalation capacity, and the capacity retention rate after 40 cycles were calculated using the following formulas. The results are recorded in Table 2 and... Figures 3-4 .

[0152] The formula for calculating the initial charge-discharge efficiency is as follows: First charge / discharge efficiency = Capacity at lithium insertion cutoff voltage of 2V ÷ Capacity at lithium extraction cutoff voltage of 0.005V × 100%.

[0153] The formula for calculating the initial charge / discharge efficiency at 0.8V is as follows:

[0154] Among them, ICE 0.8V The initial coulomb efficiency (%) with a cutoff of 0.8 V; C d,1stThe first discharge specific capacity (mAh / g) is the specific capacity at which the silicon-carbon anode discharges to a cutoff of 0.8 V during the lithium removal process. C c,1st The specific capacity during the first charge (mAh / g) is the specific capacity at which the lithium intercalation process of the silicon-carbon anode is cut off at 0.005V. The formula for calculating the lithium intercalation capacity is as follows: Q c,1st =I×t c Among them, Q c,1st This is the first absolute lithium intercalation capacity (mAh); I represents the charging constant current (mA). t c The initial charging time (h) is the time taken from the start of charging until the cutoff voltage (0.005 V) is reached.

[0155] The formula for calculating the 40-cycle capacity retention rate is as follows: 40-cycle capacity retention rate = C d,40th / C d,1st ×100% Here, the 40-cycle capacity retention rate represents the capacity retention rate (%) after 40 cycles. C d,40th The discharge specific capacity (mAh / g) at the 40th cycle. C d,1st The first discharge specific capacity is expressed in mAh / g.

[0156] Table 2. Electrochemical performance test results of silicon-carbon anode materials prepared in Examples 1-9 and Comparative Examples 1-2

[0157] As shown in Table 2, the initial charge-discharge efficiency of Examples 1-9 is above 90%, and the initial charge-discharge efficiency at 0.8V is above 80%. In contrast, the initial charge-discharge efficiency of Comparative Examples 1-2 drops below 90%, and the initial charge-discharge efficiency at 0.8V of Comparative Examples 3-4 drops below 80%. Furthermore, the capacity retention rate after 40 cycles of Comparative Examples 1-2 is significantly lower than that of Example 1, and the capacity retention rate after 40 cycles of Comparative Examples 3-4 is significantly lower than that of Example 1. This indicates that the average pore size A of the porous carbon and the ratio B of the pore volume with a pore size of 2-3 nm to the total pore volume are within the limits defined in this invention, which is beneficial for improving the initial charge-discharge efficiency and cycle stability of the battery.

[0158] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are 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.

[0159] 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 porous carbon, characterized in that, It satisfies: 1.5nm≤A≤2nm, 2%≤B≤16%; where A is the average pore size of the porous carbon, and B is the ratio of the pore volume of the porous carbon with a pore size of 2-3nm to the total pore volume.

2. The porous carbon according to claim 1, characterized in that, At least one of the following conditions must be met: The particle size of the porous carbon satisfies 3μm≤Dv50≤10μm; The specific surface area of ​​the porous carbon is 1000–3000 m². 2 / g; The microporosity of the porous carbon is 75%–95%; The porous carbon has a pore volume of 0.6–1.2 cm³. 3 / g.

3. A method for preparing porous carbon as described in claim 1 or 2, characterized in that, include: The matrix carbon was subjected to a first carbonization treatment, CO2 activation, and a second carbonization treatment in sequence to obtain porous carbon; In the CO2 activation step, the CO2 introduction rate is 15–40 L / min, and the CO2 activation time is 10–20 h.

4. The method for preparing porous carbon according to claim 3, characterized in that, At least one of the following conditions must be met: The heating rate of the first carbonization treatment is 5-10 °C / min; The temperature of the first carbonization treatment is 400–600°C; The heat preservation time for the first carbonization treatment is 1 to 3 hours; The activation temperature of the CO2 is 700–1000℃; The temperature of the second carbonization treatment is 800–1000°C.

5. A silicon-carbon anode material, characterized in that, include: The porous carbon as described in claim 1 or 2 and / or the porous carbon prepared by the preparation method described in claim 3 or 4; Nano-silicon, wherein the nano-silicon is at least partially located within the pores of the porous carbon.

6. The silicon-carbon anode material according to claim 5, characterized in that, At least one of the following conditions must be met: The size of the nano-silicon is less than or equal to 3 nm; The particle size of the silicon-carbon anode material satisfies Dv99≤50μm; Based on the total mass of the silicon-carbon anode material, the mass percentage of nano-silicon is 30–60 wt%. The silicon-carbon anode material further includes a first carbon coating layer covering the surface of the nano-silicon and porous carbon, and a second carbon coating layer covering the surface of the first carbon coating layer. The total content of the first carbon coating layer and the second carbon coating layer in the silicon-carbon anode material is 0.7 to 3 wt%.

7. A method for preparing the silicon-carbon anode material as described in any one of claims 5 to 6, characterized in that, include: Nano-silicon is deposited in the pores of the porous carbon to obtain the silicon-carbon anode material.

8. The method for preparing the silicon-carbon anode material according to claim 7, characterized in that, At least one of the following conditions must be met: The temperature for the nano-silicon deposition is 400–700°C; The deposition time for the nano-silicon is 3–10 hours; The preparation method of the silicon-carbon anode material further includes: after nano-silicon deposition, a first carbon source and a second carbon source are sequentially deposited by chemical vapor deposition to perform first carbon coating and second carbon coating.

9. A negative electrode sheet, characterized in that, Includes the silicon-carbon anode material as described in claim 5 or 6, and / or the silicon-carbon anode material prepared by the method described in any one of claims 7 to 8.

10. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in claim 9.

Images