A porous carbon material and a preparation method thereof, a silicon-carbon negative electrode material and a preparation method and use thereof

Abstract

The application provides a porous carbon material and a preparation method thereof, a silicon-carbon negative electrode material and a preparation method and application thereof. The preparation method of the porous carbon material comprises the following steps: mixing a thermosetting resin and a thermoplastic resin with a lithium carboxylate segment, heating and melting, carbonizing, and obtaining the porous carbon material. In the process of preparing the porous carbon material, the thermoplastic resin with the lithium carboxylate segment is used as a soft template, and is matched with the thermosetting resin, so that the porous carbon material with a large number of mesopores and suitable specific surface, pore volume and pore size and lithium oxide dispersed on the surface is obtained. Further, the silicon-carbon negative electrode material deposited in the pores of the porous carbon material is obtained by taking the porous carbon material as a carrier, the structure of the silicon-carbon negative electrode material is stable, and the Coulomb efficiency and cycle performance of the silicon-carbon negative electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a porous carbon material and its preparation method, a silicon-carbon anode material and its preparation method and its applications. Background Technology

[0002] Lithium-ion batteries are secondary batteries that release and store energy by moving lithium ions between the positive and negative electrodes. Due to their advantages such as high energy density, wide operating voltage range, wide operating temperature range, and no memory effect, they are widely used in electronic products, electric vehicles and other fields.

[0003] Currently, the main negative electrode material for commercially available lithium-ion batteries is graphite. Graphite has a low and wide discharge platform, high stability, and low cost. Its capacity is generally 340-365mAh / g, making it the most widely used negative electrode material in lithium-ion batteries.

[0004] However, traditional graphite materials are insufficient for applications requiring high energy density. Silicon, as an anode material, boasts a theoretical specific capacity of up to 4200 mAh / g (Li₂Si₅), more than ten times that of graphite, making it a hot research topic for numerous research institutions and companies. However, silicon anode materials experience volume changes exceeding 300% during lithium delithiation and intercalation, leading to pulverization and detachment of the anode material during battery charging and discharging, resulting in poor battery cycle performance. Furthermore, silicon, as a semiconductor, has relatively low conductivity and a slow electron transfer rate. Addressing these shortcomings of silicon anode materials, how to suppress volume expansion and contraction, increase cycle life, and improve electronic conductivity have become several crucial issues that must be resolved in the field of silicon anode materials.

[0005] Currently, to address the performance deficiencies of silicon anode materials, the commonly used modification methods in the industry mainly include (1) silicon material nano-sizing and (2) designing silicon-carbon composite materials. However, due to the limited cost of nano-silicon preparation and the impact of severe agglomeration on the nano-silicon coating process, volume expansion and pulverization problems still hinder the development of silicon-based anode materials.

[0006] CN109659551A discloses a method for preparing a low-expansion silicon anode material for lithium-ion batteries. The method involves dispersing nano-silicon powder in ultrapure water to prepare a silicon slurry; adding hydroquinone, formaldehyde, and sodium carbonate to the silicon slurry to prepare a silica sol; forming the silica sol to obtain a silica gel; aging and carbonizing the silica gel to obtain a carbonized material; pulverizing and classifying the carbonized material to obtain a silicon-carbon composite material A; impregnating and coating the silicon-carbon composite material A with mesophase pitch to obtain a coating material B; and further carbonizing and sieving the coating material B to obtain the low-expansion silicon anode material for lithium-ion batteries. This method is complex, involves multiple heat treatment steps, and has high energy consumption, making it unsuitable for industrialization.

[0007] The composite of carbon and silicon is mainly achieved through certain physical and chemical methods to form a "core-shell" or "embedded" structure of carbon and silicon, such as CN1304187A and CN1681145A. The carbon precursors used in these documents mainly include one or more of epoxy resin, phenolic resin, polyacrylonitrile, polystyrene, and pitch. Therefore, the carbon tightly coating silicon materials produced improves the cycle performance of the anode materials to a certain extent.

[0008] However, the carbon-silicon composite materials obtained by these preparation methods have a dense carbon shell structure. Although this partially alleviates the stress problem caused by silicon volume changes during charging and discharging, it also makes it difficult for the electrolyte to react completely and quickly with the silicon active material. Therefore, the maximum capacity of the silicon material is often not fully utilized, and it is difficult to charge and discharge quickly.

[0009] Although porous carbon materials are considered to help improve the capacity for active ions and exhibit high initial capacity due to their rich pore structure, existing porous carbon materials generally have the disadvantage of low initial charge-discharge efficiency. The specific reasons are still inconclusive, but it is generally believed to be related to their large surface area and many defects. Low initial charge-discharge efficiency will not only reduce the utilization rate of the negative electrode material, but also reduce the utilization rate of the positive electrode material and the electrolyte, thus hindering the improvement of energy density and the reduction of cost.

[0010] How to obtain high-performance porous carbon materials with distinct pore layers, and then use them in silicon-carbon anode materials to improve the electrochemical performance of the anode materials, especially the coulombic efficiency and cycle performance, is an urgent technical problem to be solved. Summary of the Invention

[0011] The purpose of this invention is to provide a porous carbon material and its preparation method, a silicon-carbon anode material and its preparation method, and its applications. In the preparation of the porous carbon material, this invention uses a thermoplastic resin with lithium carboxylic acid segments as a soft template, combined with a thermosetting resin, to obtain a porous carbon material with numerous mesopores, suitable specific surface area, pore volume, and pore size, and lithium oxide dispersed on its surface. Furthermore, using the porous carbon material as a carrier, a silicon-carbon anode material deposited within its pores is obtained, exhibiting structural stability and improved coulombic efficiency and cycle performance.

[0012] To achieve this objective, the present invention employs the following technical solution:

[0013] In a first aspect, the present invention provides a method for preparing a porous carbon material, the method comprising the following steps:

[0014] The porous carbon material is obtained by mixing a thermosetting resin and a thermoplastic resin containing lithium carboxylic acid segments, heating and melting the mixture, and then carbonizing it.

[0015] In this invention, the thermoplastic resin containing lithium carboxylic acid segments is a copolymer.

[0016] For example, a thermoplastic resin with lithium carboxylic acid segments has the structure shown in Formula I:

[0017]

[0018] Wherein, N is selected from substituted or unsubstituted C2-C15 straight-chain hydrocarbon groups or branched hydrocarbon groups, aryl groups, and combinations thereof. In addition, the N segment may contain chemical bonds of other atoms, such as ester bonds, amide bonds, etc.; M is selected from substituted or unsubstituted C2-C15 straight-chain hydrocarbon groups or branched hydrocarbon groups, aryl groups, and combinations thereof. In addition, the M segment may contain chemical bonds of other atoms, such as ester bonds, amide bonds, urethane bonds, ether bonds, urea bonds, etc.; n and m are each independently 1 to 500. For example, n and m can each be independently 1, 50, 100, 150, 200, 250, 300, 350, 400, 450, or 500, etc.

[0019] This invention does not impose specific requirements or limitations on the preparation method of thermosetting resin, as long as the thermosetting resin required by this invention can be obtained, it can be obtained by curing a thermosetting resin precursor with a fixed combination of curing agents, or it can be obtained by directly using a thermosetting resin that does not require a curing agent.

[0020] In preparing porous carbon materials, this invention uses a thermoplastic resin with lithium carboxylic acid segments as a soft template, combined with a thermosetting resin, to obtain a porous carbon material with a large number of mesopores and suitable specific surface area, pore volume, and pore size, with lithium oxide dispersed on the surface. Furthermore, using the porous carbon material as a carrier, a silicon-carbon anode material deposited in its pores is obtained, which has a stable structure and improves its coulombic efficiency and cycle performance.

[0021] In this invention, the lithium carboxylate segments in the thermoplastic resin serve as a soft film plate, ultimately forming pores. On the other hand, during the carbonization process, due to compatibility, the lithium carboxylate groups migrate to the surface of the carbon material. After carbonization, lithium oxide is formed on the surface of the porous carbon. The lithium oxide on the surface becomes part of the battery SEI film, thereby improving the coulombic efficiency of the material and giving the negative electrode material good ion conduction performance, which in turn improves the rate performance of the material. Moreover, since it exists in the form of segments in the thermoplastic resin, it can be uniformly dispersed in the porous carbon precursor prepared by in-situ polymerization, which also improves the stability of the material.

[0022] The non-carboxylic acid lithium segment of the thermoplastic resin (such as the M segment in Formula I) can also serve as a soft template, which ultimately decomposes and vaporizes during carbonization. Depending on its dispersion in the matrix, the soft template can provide a large number of mesopores (2-50 nm) for porous carbon products. Larger mesopores are beneficial to silicon deposition kinetics and can increase the amount of silicon deposited. However, if the pore size is too large, the particle size of the deposited silicon will be large, which is easy to pulverize and break during battery cycling, which is not conducive to cycling performance. On the other hand, the M segment also serves as a bridge to connect with thermosetting resin, realizing the combination between thermosetting resin and thermoplastic resin, so as to avoid uneven porosity in porous carbon materials. Therefore, if it is simply a lithium carboxylic acid structure (or a copolymer structure of lithium carboxylic acid), it will be difficult for the silicon generated by subsequent silane cracking to be uniformly deposited in the carbon material, affecting the subsequent application of porous carbon materials.

[0023] In this invention, the thermoplastic resin and thermosetting resin in Formula I are combined. The thermosetting resin plays the role of pore formation and carbon skeleton in the system. The gas generated by the cracking of resin hard carbon can provide a small number of micropores and mesopores for porous carbon products. The combination of the two resins achieves good pore volume and pore size distribution. Both are indispensable. If the thermoplastic resin is missing, a good and uniform silane cracking deposition effect cannot be achieved. If the thermosetting resin is missing, the residual carbon value of the carbon material will be too low, and effective carbon formation will not be possible.

[0024] Preferably, the mass ratio of the thermosetting resin to the thermoplastic resin with lithium carboxylic acid segments is 100:(20-120), for example, 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, 100:100, 100:110, or 100:120.

[0025] In this invention, if the mass ratio of thermosetting resin to thermoplastic resin with lithium carboxylate segments is too high, that is, if too little thermoplastic resin with lithium carboxylate segments is added, it will be detrimental to the formation of mesopores during carbonization, ultimately resulting in poor silane pyrolysis deposition effect; on the other hand, if the mass ratio is too low, that is, if too much thermoplastic resin with lithium carboxylate segments is added, it will make the mesopore size of the carbon material too large, ultimately resulting in a large volume of deposited silicon, which is detrimental to the material's cycle performance.

[0026] Preferably, the thermosetting resin includes any one or a combination of at least two of phenolic resin, epoxy resin, unsaturated polyester, furan resin or melamine resin.

[0027] Preferably, the lithium carboxylate in the lithium carboxylate chain segment includes lithium acrylate and / or lithium ammonate.

[0028] For example, when the lithium carboxylic acid segment is a lithium acrylate segment, the thermoplastic resin may have the structural formula of Formula II:

[0029]

[0030] In Formula II, R is selected from any one or a combination of at least two of -H, C1-C5 alkyl, C1-C5 alkenyl, alkynyl, cyano, and amino groups, wherein R1, R2, and R3 are each independently selected from any one of -H, -CH3, or -OH, M1 is selected from substituted or unsubstituted C2-C10 straight-chain or branched olefinic groups, and x and y are each independently integers from 1 to 500.

[0031] Preferably, the mixed raw materials also include asphalt.

[0032] Preferably, the mass ratio of the thermosetting resin, thermoplastic resin and asphalt is 100:(20-120):(0-40), for example, 100:20:5, 100:30:10, 100:40:15, 100:50:20, 100:60:25, 100:70:30, 100:80:35, 100:90:40, 100:100:5, 100:110:25 or 100:120:40, etc.

[0033] In this invention, adding too much asphalt will cause the asphalt to melt and fill the pores during carbonization. On the other hand, the carbon asphalt will gradually collapse during carbonization, resulting in a small specific surface area of ​​the carbon material, making it unsuitable for silicon deposition.

[0034] Preferably, the softening point of the asphalt is 70 to 250°C, such as 70°C, 90°C, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C.

[0035] In the process of preparing porous carbon materials, if the softening point of the asphalt is too high, it will cause the asphalt to be unable to mix effectively and fully with the polymer carbon source, resulting in uneven distribution of porous carbon pores.

[0036] Preferably, the asphalt includes coal tar pitch and / or petroleum asphalt.

[0037] Preferably, the mixing time is 10 to 40 minutes, such as 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes.

[0038] Preferably, the carbonization includes sequentially performing a first heat treatment, a second heat treatment, and a third heat treatment.

[0039] In this invention, a first heat treatment achieves complete curing of the thermosetting resin; a second heat treatment reduces the escape of volatiles, which is more conducive to the growth of the carbon layer; and a final third heat treatment avoids the carbonization temperature being too low, which would result in incomplete escape of volatiles and a small specific surface area of ​​the porous carbon material, which would be insufficient for silicon deposition. At the same time, it ensures the effective removal of heteroatoms to guarantee the coulombic efficiency of the final anode material.

[0040] Preferably, the temperature of the first heat treatment is 100 to 300°C, such as 100°C, 130°C, 150°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, or 300°C.

[0041] Preferably, the duration of the heat treatment is 1 to 4 hours, for example, 1 hour, 2 hours, 3 hours, or 4 hours.

[0042] Preferably, the temperature of the secondary heat treatment is 350 to 500°C, such as 350°C, 360°C, 380°C, 400°C, 430°C, 450°C, 480°C, or 500°C.

[0043] Preferably, the duration of the secondary heat treatment is 1 to 4 hours, such as 1 hour, 2 hours, 3 hours, or 4 hours.

[0044] Preferably, the temperature of the three heat treatments is 800 to 1500°C, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, or 1500°C.

[0045] Preferably, the duration of the three heat treatments is 1 to 4 hours, for example, 1 hour, 2 hours, 3 hours, or 4 hours.

[0046] In a second aspect, the present invention provides a porous carbon material, which is prepared by the method for preparing porous carbon materials as described in the first aspect; the surface of the porous carbon material contains lithium oxide.

[0047] The porous carbon material provided by this invention has a suitable mesoporous structure, and its specific surface area, pore volume, and pore size are conducive to the subsequent deposition of silicon materials. The uniformly dispersed lithium oxide on the inner surface of the carbon material can be used as one of the SEI film components of the anode material, realizing pre-lithiation and thus improving the coulombic efficiency, rate performance, and cycle performance of the material.

[0048] Preferably, the D50 of the porous carbon material is 5 to 8 μm, such as 5 μm, 6 μm, 7 μm or 8 μm.

[0049] Preferably, the specific surface area of ​​the porous carbon material is 100–1000 m². 2 / g, for example, 100m 2 / g、200m 2 / g、300m 2 / g、400m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g or 1000m 2 / g etc.

[0050] Preferably, the pore volume of the porous carbon material is 0.5 to 1.5 cc / g, for example, 0.5 cc / g, 0.7 cc / g, 0.8 cc / g, 0.9 cc / g, 1.0 cc / g, 1.1 cc / g, 1.2 cc / g, 1.3 cc / g, 1.4 cc / g, or 1.5 cc / g.

[0051] Preferably, the average pore size of the porous carbon material is 16-40 nm, for example, 16 nm, 17 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, or 40 nm.

[0052] Thirdly, the present invention provides a silicon-carbon anode material, wherein nano-silicon particles are deposited in the pores of the porous carbon material as described in the second aspect.

[0053] The silicon-carbon anode material provided by this invention has nano-silicon deposited in the pores of porous carbon, which is beneficial for silicon to be uniformly dispersed in the porous carbon with a nano-particle size.

[0054] Preferably, the nano-silicon is also doped with any one or a combination of at least two of nitrogen, phosphorus, or boron.

[0055] In this invention, by doping nano-silicon to produce nano-silicon with Frankel defects, the conductivity of the silicon material itself is improved.

[0056] Preferably, the silicon-carbon anode material is coated with a carbon layer.

[0057] In this invention, a lithium-doped carbon layer is further coated on the surface of the silicon-carbon anode material, achieving pre-lithiation at the material level, while reducing the specific surface area of ​​the anode material, thereby improving the coulombic efficiency.

[0058] Preferably, the carbon layer also includes lithium.

[0059] Fourthly, the present invention provides a method for preparing a silicon-carbon anode material as described in the third aspect, the method comprising the following steps:

[0060] The reactant gas and the protective gas are mixed, and nano-silicon is deposited in the pores of porous carbon by vapor phase deposition to obtain the silicon-carbon anode material. The reactant gas includes a gaseous silicon source.

[0061] In this invention, the preparation of porous carbon materials and subsequent silicon-carbon anode materials can be carried out in a continuous production process.

[0062] Preferably, with the total volume of the reactant gas and the protective gas being 100%, the volume percentage of the reactant gas is 5% to 10%, for example, 5%, 6%, 7%, 8%, 9%, or 10%.

[0063] Preferably, the gaseous silicon source includes any one or a combination of at least two of silane, ethylsilane, or methylsilane.

[0064] Preferably, the temperature of the vapor deposition is 500 to 950°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or 950°C.

[0065] The temperature range for vapor deposition provided by this invention is applicable to a variety of equipment, including but not limited to fluidized beds or intermittent furnaces.

[0066] Preferably, the vapor deposition time is 50 to 720 min, for example, 50 min, 100 min, 150 min, 200 min, 250 min, 300 min, 350 min, 400 min, 450 min, 500 min, 550 min, 600 min, 650 min, 700 min, or 720 min.

[0067] Preferably, the reaction gas further includes a second reaction gas.

[0068] Preferably, the second reaction gas includes any one or a combination of at least two of the following: acetonitrile vapor, urea vapor, low molecular weight amide vapor, low molecular weight alicyclic amine vapor, low molecular weight aniline vapor, diazomethane, diazomethane vapor, borane, pyridineborane, borate ester, phenylboronic ester, red phosphorus vapor, alkyl phosphate triester, aryl phosphate triester, or aralkyl phosphate triester.

[0069] Any one or at least two combinations.

[0070] Preferably, the flow rate ratio of the gaseous silicon source to the second reactive gas is (100-70):(0-30), such as 99:1, 95:5, 90:10, 85:15, 80:20, 75:25 or 70:30, etc.

[0071] Preferably, the material after vapor deposition is mixed with asphalt for coating and then carbonized to obtain a carbon-coated silicon-carbon anode material.

[0072] Preferably, the asphalt includes modified asphalt.

[0073] Preferably, the D50 of the modified asphalt is 3 to 5 μm, for example, 3 μm, 4 μm or 5 μm.

[0074] Preferably, the modification method of the modified asphalt includes:

[0075] Modified asphalt is obtained by melt-blending asphalt with lithium-containing compounds.

[0076] In this invention, modified asphalt is used to coat silicon-carbon anode materials, which not only obtains a surface carbon layer but also improves the pre-doped lithium, thereby enhancing the coulombic efficiency of the anode materials.

[0077] Preferably, the asphalt includes petroleum asphalt and / or coal tar pitch.

[0078] Preferably, the softening point of the asphalt is >150℃, for example, 180℃, 200℃, 250℃ or 300℃.

[0079] Preferably, the lithium-containing compound includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide, lithium chloride, lithium sulfate, lithium nitrate, lithium phosphate, lithium acetate, lithium citrate, or lithium oxalate.

[0080] Preferably, the mass ratio of the asphalt to the lithium-containing compound is (100-90):(0-10), for example, 99:1, 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9 or 90:10, etc.

[0081] Preferably, the method of mixed coating includes vacuum impregnation-secondary granulation.

[0082] The vacuum impregnation-secondary granulation method provided by this invention coats modified asphalt onto silicon-carbon materials. The granulation process is carried out under negative pressure. The negative pressure environment is conducive to the asphalt penetrating into the pores of the silicon-carbon materials, thereby reducing the specific surface area of ​​the final product, improving coulombic efficiency, increasing vibration and compaction density, and improving energy density.

[0083] Fifthly, the present invention also provides a lithium-ion battery comprising the silicon-carbon anode material as described in the third aspect.

[0084] Compared with the prior art, the present invention has the following beneficial effects:

[0085] In the preparation of porous carbon materials, this invention uses a thermoplastic resin with lithium carboxylic acid segments as a soft template, combined with a thermosetting resin, to obtain a porous carbon material with numerous mesopores and suitable specific surface area, pore volume, and pore size, with lithium oxide dispersed on the surface. The lithium oxide on the surface can serve as the SEI of the anode material, improving its performance. Furthermore, using the porous carbon material as a carrier, a silicon-carbon anode material deposited within its pores is obtained. This anode material has a stable structure, avoiding the impact of nano-silicon agglomeration on the composite anode, ultimately improving its coulombic efficiency and cycle performance. The silicon-carbon anode material obtained by the preparation method provided by this invention, with the addition of asphalt during the preparation of porous carbon and the adjustment of the mass ratio of thermoplastic and thermosetting resins, when used in batteries, achieves an effective capacity of over 1911.24 mAh / g in the first cycle, a coulombic efficiency of over 89.35% in the first cycle, and a capacity retention rate of over 91.63% after 100 cycles, thus improving the overall performance of the battery. Attached Figure Description

[0086] Figure 1 The electrochemical performance graph of the battery provided in Example 1 is shown. Detailed Implementation

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0088] Example 1

[0089] (1) Thermosetting resin (obtained by mixing and curing Resol phenolic resin and hexamethylenetetramine), thermoplastic resin powder, and petroleum asphalt (softening point of 120℃) are mixed for 30 min, wherein the mass ratio of thermosetting phenolic resin, thermoplastic resin powder and petroleum asphalt is 100:100:5, to obtain a solid powder premix, wherein the structural formula of thermoplastic resin is shown in I-1 (where n is 100 and m is 110).

[0090]

[0091] (2) The solid powder premix described in step (1) is heated and melted, then subjected to a first heat treatment at 180°C for 3 hours, followed by a second heat treatment at 420°C for 3 hours, and finally a third heat treatment at 1000°C for 2.5 hours. After crushing, a D50 of 7 μm and a specific surface area of ​​450 m² are obtained. 2 / g, porous carbon material with a pore volume of 1cc / g and an average pore size of 27-28nm (lithium oxide uniformly dispersed on the surface);

[0092] Furthermore, the present invention also provides a silicon-carbon anode material, the surface of which is coated with a lithium-doped carbon layer, the coated material being a porous carbon material (nano-silicon doped with boron) prepared in Example 2 with deposited nano-silicon.

[0093] (3) The porous carbon particles obtained in step (2) are put into a gas phase high temperature reactor with nitrogen as the protective gas, silane as the reaction gas 1 and pyridine borane as the reaction gas 2 (the ratio of reaction gas to protective gas is 10:90). The flow rate ratio of reaction gas 1 to reaction gas 2 is 80:20. They must be premixed in the gas path (reaction gas) in advance. Gas phase pyrolysis (gas phase deposition) is carried out in the fluidized bed. First, nitrogen is introduced to achieve fluidization of porous carbon particles. Then, the bed temperature is raised to 650°C and the reaction gas is introduced. The temperature is maintained for 100 min to obtain uncoated nano-silicon deposited in the porous carbon pores as silicon-carbon anode material.

[0094] (4) The uncoated silicon-carbon anode material from step (3) is first melt-premixed with modified asphalt (petroleum asphalt with a softening point of 90°C and lithium carbonate in a mass ratio of 90:10) for solid-phase coating, and then subjected to vacuum impregnation-secondary granulation process, specifically including:

[0095] Vacuum impregnation should be carried out above the softening point of asphalt and below the decomposition temperature of asphalt (generally 300℃). The heating should be set in three stages: 1. The softening point is heated to 300℃ and held under negative pressure for 2 hours; 2. The temperature is increased from 300℃ to 350℃ and held under negative pressure for 1 hour; 3. The temperature is increased from 350℃ to 650℃, nitrogen gas is introduced for protection, and the temperature is held for 1.5 hours. Then, carbonization is carried out using the carbonization process in step (2) to obtain the silicon-carbon anode material.

[0096] Figure 1 The electrochemical performance graph of the battery provided in Example 1 is shown. Figure 1 As can be seen, after pre-lithiation, Example 1 exhibits high initial efficiency and good cycling performance, retaining over 95% of its capacity after 100 cycles (compared to the capacity after delithiation in the second cycle). This high initial efficiency and capacity retention can be attributed to the uniform lithium doping in the material, effectively compensating for the irreversible lithium consumption caused by SEI film formation; and the high-pore-volume porous carbon limiting the volume expansion of nano-silicon, suppressing silicon pulverization and shedding.

[0097] Example 2

[0098] (1) Thermosetting resin (obtained by mixing and curing DGEBA type epoxy resin with m-phenylenediamine), thermoplastic resin powder, and petroleum asphalt (softening point of 250℃) are mixed for 35 minutes, wherein the mass ratio of thermosetting resin, thermoplastic resin powder and petroleum asphalt is 100:120:20, to obtain a solid powder premix, wherein the structural formula of thermoplastic resin is shown in II-1 (where n is 150 and m is 200).

[0099]

[0100] (3)(2) The solid powder premix described in step (1) is heated and melted, then subjected to a first heat treatment at 200°C for 2 hours, followed by a second heat treatment at 500°C for 4 hours, and finally a third heat treatment at 800°C for 1 hour. After crushing, a D50 of 5.5 μm and a specific surface area of ​​950 m² are obtained. 2 / g, porous carbon material (lithium oxide uniformly dispersed on the surface) with a pore volume of 0.9cc / g and an average pore size of 25nm.

[0101] Furthermore, the present invention also provides a silicon-carbon anode material, the surface of which is coated with a lithium-doped carbon layer, the coated material being a porous carbon material (nano-silicon doped with phosphorus) prepared in Example 1 with deposited nano-silicon.

[0102] The preparation method of the silicon-carbon anode material is as follows:

[0103] (3) The porous carbon particles obtained in step (2) are put into a gas phase high temperature reactor with nitrogen as the protective gas, silane as the reaction gas 1 and red phosphorus vapor as the reaction gas 2 (the ratio of reaction gas to protective gas is 5:95). The flow rate ratio of reaction gas 1 to reaction gas 2 is 90:10. They must be premixed in the gas path in advance (reaction gas). Gas phase pyrolysis (gas phase deposition) is carried out in the fluidized bed. First, nitrogen is introduced to achieve fluidization of porous carbon particles. Then, the bed temperature is raised to 550°C and the reaction gas is introduced. The temperature is maintained for 150 min to obtain uncoated nano-silicon deposited in the porous carbon pores as silicon-carbon anode material.

[0104] (4) The uncoated silicon-carbon anode material from step (3) is coated with modified asphalt (petroleum asphalt with a softening point of 250℃ and lithium carbonate are pre-mixed by melting, with a mass ratio of 98:2), and then subjected to a vacuum impregnation-secondary granulation process, specifically including:

[0105] Vacuum impregnation should be carried out above the softening point of asphalt and below the decomposition temperature of asphalt (generally 300℃). The heating should be set in three stages: 1. The softening point is heated to 300℃ and held under negative pressure for 2 hours; 2. The temperature is increased from 300℃ to 450℃ and held under negative pressure for 0.5 hours; 3. The temperature is increased from 450℃ to 500℃, nitrogen gas is introduced for protection, and the temperature is held for 2 hours. Then, carbonization is carried out using the carbonization process in step (2) to obtain the silicon-carbon anode material.

[0106] Example 3

[0107] (1) Thermosetting resin (furfural-furfuryl alcohol type furan resin and maleic anhydride mixed and cured), thermoplastic resin powder and petroleum asphalt (softening point of 80℃) were mixed for 30 min, wherein the mass ratio of thermosetting furan resin, thermoplastic resin powder and petroleum asphalt was 100:120:10, to obtain a solid powder premix, wherein the structural formula of thermoplastic resin is shown in III-1 (where n is 150 and m is 150).

[0108]

[0109] (2) The solid powder premix described in step (1) is heated and melted, then subjected to a first heat treatment at 100°C for 4 hours, followed by a second heat treatment at 350°C for 4 hours, and finally a third heat treatment at 1200°C for 4 hours. After crushing, a D50 of 6 μm and a specific surface area of ​​550 m² are obtained. 2 / g, porous carbon material (lithium oxide uniformly dispersed on the surface) with a pore volume of 1.1cc / g and an average pore size of 29nm.

[0110] Furthermore, the present invention also provides a silicon-carbon anode material, the surface of which is coated with a lithium-doped carbon layer, the coated material being a porous carbon material (nano-silicon doped with nitrogen) prepared in Example 2 with deposited nano-silicon.

[0111] The preparation method of the silicon-carbon anode material is as follows:

[0112] (3) The porous carbon particles obtained in step (2) are put into a gas phase high temperature reactor with nitrogen as the protective gas, reaction gas 1 is methylsilane, reaction gas 2 is acetonitrile vapor (the ratio of reaction gas to protective gas is 10:90), the flow ratio of reaction gas 1 to reaction gas 2 is 80:20, and they must be premixed in the gas path in advance (reaction gas). When the reaction is carried out in the intermittent furnace, nitrogen is first introduced to remove the oxygen atmosphere, and then the temperature is raised to 900°C and the reaction gas is introduced and kept at the temperature for 550 minutes. In addition, when using the intermittent furnace, a tail gas treatment device that can absorb silane is installed at the tail gas port to prevent dangerous situations.

[0113] (4) The uncoated silicon-carbon anode material from step (3) is coated with modified pitch (coal tar pitch with a softening point of 200℃ and lithium oxide are pre-mixed in a melt-premixed mass ratio of 95:5), and then subjected to a vacuum impregnation-secondary granulation process, specifically including:

[0114] Vacuum impregnation should be carried out above the softening point of asphalt and below the decomposition temperature of asphalt (generally 300℃). The heating should be set in three stages: 1. Heat from the softening point to 300℃ and keep under negative pressure for 2 hours; 2. Heat from 300℃ to 350℃ and keep under negative pressure for 1 hour; 3. Heat from 350℃ to 650℃, introduce nitrogen for protection, and keep under pressure for 1.5 hours. Then, carbonization is carried out using the carbonization process in step (2) to obtain the silicon-carbon anode material.

[0115] Example 4

[0116] The difference between this embodiment and embodiment 1 is that petroleum asphalt is not added in step (1) of this embodiment.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 5

[0119] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the mass ratio of thermosetting resin, thermoplastic resin powder and petroleum asphalt is 100:15:5.

[0120] The remaining preparation methods and parameters are consistent with those in Example 1.

[0121] Example 6

[0122] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the mass ratio of thermosetting resin, thermoplastic resin powder and petroleum asphalt is 100:130:5.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Example 7

[0125] The difference between this embodiment and embodiment 1 is that the softening point of petroleum asphalt in step (1) of this embodiment is 280℃.

[0126] The remaining preparation methods and parameters are consistent with those in Example 1.

[0127] Example 8

[0128] The difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, reaction gas 2 is not added, that is, the nano-silicon is not doped.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Example 9

[0131] The difference between this embodiment and embodiment 1 is that this embodiment does not perform step (4), but only steps (1), (2) and (3).

[0132] The remaining preparation methods and parameters are consistent with those in Example 1.

[0133] Example 10

[0134] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the mass ratio of petroleum asphalt to lithium carbonate is 60:40.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Example 11

[0137] The difference between this embodiment and Embodiment 1 is that lithium acrylate is replaced with lithium ammonium oxide in this embodiment, and the thermoplastic resin has the structure of Formula XI-1:

[0138]

[0139] The remaining preparation methods and parameters are consistent with those in Example 1.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that thermoplastic resin is not added in step (1) of this example.

[0142] The remaining preparation methods and parameters are consistent with those in Example 1.

[0143] Comparative Example 2

[0144] The difference between this comparative example and Example 1 is that no thermosetting resin is added in step (1) of this example.

[0145] The remaining preparation methods and parameters are consistent with those in Example 1.

[0146] Comparative Example 3

[0147] The difference between this comparative example and Example 1 is that the thermoplastic resin in this comparative example is replaced with lithium acrylate.

[0148] The remaining preparation methods and parameters are consistent with those in Example 1.

[0149] Comparative Example 4

[0150] The difference between this comparative example and Example 1 is that the thermoplastic resin in this comparative example is replaced with the structural formula shown in Formula IV-1 (m is 110):

[0151]

[0152] The remaining preparation methods and parameters are consistent with those in Example 1.

[0153] The silicon-carbon anode materials provided in Examples 1-11 and Comparative Examples 1-4 were used as anode active materials, homogenized and coated together with conductive agents and binders to prepare anode sheets, and coin lithium-ion batteries were prepared according to the conventional coin cell preparation process.

[0154] The batteries provided in Examples 1-11 and Comparative Examples 1-4 were subjected to electrochemical performance tests under the following conditions:

[0155] (1) Sample preparation: The positive electrode material is excess lithium sheet. The negative electrode material is the product of Examples 1-10 and Comparative Examples 1-4 described in this patent; the binder is styrene-butadiene rubber; the thickener is sodium carboxymethyl cellulose; the conductive agent is carbon black SP; the negative electrode formulation ratio is 85:3.2:1.8:10. Subsequently, after pulping, coating, electrode baking, electrode rolling, electrode punching, electrode weighing, assembly, and activation, a coin cell for testing is obtained.

[0156] (2) First charge and discharge reversible capacity test: The first charge and discharge performance of the coin cell was tested using an Arbin blue battery tester at a rate of 0.02C. The delithiation capacity is the effective capacity of the first cycle.

[0157] (3) Initial Coulomb efficiency: The ratio of the initial discharge capacity to the initial charge capacity is calculated from the test results in (2).

[0158] (4) Capacity and retention rate after 100 cycles: After the test in step (2) is completed, the battery is charged and discharged 99 times with the same instrument parameters to obtain the delithiation capacity after 100 cycles; the delithiation capacity of the 100th cycle is divided by the delithiation capacity of the second cycle to obtain the capacity retention rate after 100 cycles.

[0159] The results are shown in Table 1.

[0160] Table 1

[0161]

[0162] The data from Examples 1 and 4 show that, in the process of preparing porous carbon, the absence of asphalt will result in an excessively large specific surface area of ​​the porous carbon, a reduced average adsorption pore size, excessive silicon deposition on the material surface, and a low initial efficiency, which is not conducive to cycling.

[0163] The data from Examples 1, 5, and 6 show that adding too little thermoplastic resin with lithium carboxylic acid segments is not conducive to silicon deposition, resulting in low material capacity. The numerous micropores inside the carbon material also lead to increased lithium ion consumption, reducing the material's initial coulombic efficiency. On the other hand, adding too much will result in the deposited silicon being too large, which is not conducive to the material's initial efficiency and cycle performance.

[0164] The data from Examples 1 and 7 show that if the softening point of the pitch is too high during the preparation of porous carbon, it will affect the amount of silicon deposited, which is detrimental to the capacity performance of the material.

[0165] The data from Examples 1 and 8 show that when preparing silicon-carbon anode materials, failure to dope nano-silicon will result in a weakening of the ability to suppress expansion during electrochemical behavior of deposited silicon, thus deteriorating cycle performance.

[0166] The data results from Examples 1 and 9 show that without subsequent carbon coating of the silicon-carbon anode material, the nano-silicon material has high activity, is easily oxidized in air and homogenization processes, reacts with water to generate hydrogen, and may even spontaneously combust, resulting in a low coulombic efficiency of the final material.

[0167] The data from Examples 1 and 10 show that adding too much lithium compound during the carbon coating process leads to excessive alkalinity of the slurry, resulting in gas generation during homogenization, side reactions, and reduced material capacity and initial efficiency.

[0168] The data from Example 1 and Comparative Examples 1 and 2 show that both thermoplastic and thermosetting resins are indispensable in the preparation of porous carbon, and they work synergistically. Without the addition of a thermoplastic resin containing lithium carboxylic acid segments, effective silane deposition cannot be achieved, resulting in extremely low material capacity. Conversely, without the addition of a thermosetting resin, the material lacks a carbon-forming framework, making it impossible to prepare porous carbon materials.

[0169] As can be seen from the data results of Example 1 and Comparative Examples 3 and 4, in the structural formula of the thermoplastic resin provided by the present invention, both the lithium carboxylate chain segment (group) and the non-carboxylate lithium chain segment (group) in the thermoplastic resin are indispensable. If the thermoplastic resin does not contain lithium carboxylate, it is impossible to achieve a high first-efficiency performance of the negative electrode material. If it is a simple lithium carboxylate structure, it is impossible to achieve a uniform porosity distribution of porous carbon material, thereby leading to a deterioration in the silane deposition effect.

[0170] In summary, this invention, in the process of preparing porous carbon materials, uses a thermoplastic resin with lithium carboxylic acid segments as a soft template, combined with a thermosetting resin, to obtain a porous carbon material with a large number of mesopores and suitable specific surface area, pore volume, and pore size, with lithium oxide dispersed on the surface. The lithium oxide on the surface can serve as the SEI of the anode material, improving its performance. Furthermore, using the porous carbon material as a carrier, a silicon-carbon anode material deposited in its pores is obtained. This anode material has a stable structure, avoiding the influence of nano-silicon agglomeration on the composite anode, ultimately improving its coulombic efficiency and cycle performance. Then, lithium-doped carbon coating is applied to the anode material to achieve pre-lithiation at the material level, while also reducing the specific surface area of ​​the anode material, thereby further improving the coulombic efficiency. The silicon-carbon anode material prepared by the method provided by this invention, by adding asphalt during the preparation of porous carbon and adjusting the mass ratio of thermoplastic resin and thermosetting resin, when the anode is used in a battery, the effective capacity of the battery in the first cycle can reach more than 1911.24 mAh / g, the coulombic efficiency in the first cycle can reach more than 89.35%, and the capacity retention rate after 100 cycles can reach more than 91.63%, thus improving the overall performance of the battery.

[0171] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing a porous carbon material, characterized by, The preparation method of the porous carbon material comprises the following steps: mixing a thermosetting resin and a thermoplastic resin with lithium carboxylate segments, heating and melting, carbonizing to obtain the porous carbon material; The thermoplastic resin with lithium carboxylate segments has the structure shown in Formula I: Formula I; N is selected from substituted or unsubstituted C2-C15 straight chain or branched alkyl, aryl and a combination thereof, M is selected from substituted or unsubstituted C2-C15 straight chain or branched alkyl, aryl and a combination thereof, n and m are each independently 1-500.

2. The method for producing a porous carbon material according to claim 1, wherein The mass ratio of the thermosetting resin and the thermoplastic resin with lithium carboxylate segments is 100: (20-120).

3. The method for producing a porous carbon material according to claim 1, wherein The thermosetting resin comprises any one or a combination of at least two of phenolic resin, epoxy resin, unsaturated polyester, furan resin or melamine resin.

4. The method for producing the porous carbon material according to claim 1, wherein The lithium carboxylate in the lithium carboxylate segment comprises lithium acrylate and / or lithium amide acid.

5. The method of claim 1, wherein the porous carbon material is prepared by a process comprising: The mixed raw materials further comprise asphalt.

6. The method for producing a porous carbon material according to claim 5, wherein The mass ratio of the thermosetting resin, the thermoplastic resin and the asphalt is 100: (20-120): (0-40).

7. The method of claim 5, wherein the porous carbon material is prepared by a process comprising: The softening point of the asphalt is 70-250℃.

8. The method for producing a porous carbon material according to claim 5, wherein The asphalt comprises coal tar pitch and / or petroleum pitch.

9. The method of claim 1, wherein the porous carbon material is prepared by a process comprising: The mixing time is 10-40 min.

10. The method of claim 1, wherein the porous carbon material is prepared by a process comprising: The carbonization comprises sequentially performing a first heat treatment, a second heat treatment and a third heat treatment.

11. The method for producing a porous carbon material according to claim 10, wherein The temperature of the first heat treatment is 100-300℃.

12. The method of claim 10, wherein the porous carbon material is prepared by a process comprising: The time of the first heat treatment is 1-4 h.

13. The method of claim 10, wherein the porous carbon material is prepared by a process comprising: The temperature of the second heat treatment is 350-500℃.

14. The method of claim 10, wherein the porous carbon material is prepared by a process comprising: The time of the second heat treatment is 1-4 h.

15. The method for preparing porous carbon materials according to claim 10, characterized in that, The temperature of the third heat treatment is 800-1500℃.

16. The method of claim 10, wherein the porous carbon material is prepared by a method comprising: The time of the third heat treatment is 1-4 h.

17. A porous carbon material, characterized by, The porous carbon material is prepared by the preparation method of the porous carbon material according to any one of claims 1-16; and the surface of the porous carbon material contains lithium oxide.

18. The porous carbon material of claim 17, wherein, The D50 of the porous carbon material is 5-8 μm.

19. The porous carbon material of claim 17, wherein, The specific surface area of the porous carbon material is 100-1000 m 2 / g.

20. The porous carbon material of claim 17, wherein, The pore volume of the porous carbon material is 0.5-1.5 cc / g.

21. The porous carbon material of claim 17, wherein, The pore size of the porous carbon material is 16-40 nm.

22. A silicon-carbon negative electrode material, characterized in that, In the silicon-carbon negative electrode material, the nano-silicon particles are deposited in the pores of the porous carbon material according to any one of claims 17-21.

23. The silicon-carbon negative electrode material of claim 22, wherein, The nano-silicon is further doped with any one or a combination of at least two of nitrogen, phosphorus or boron elements.

24. The silicon-carbon negative electrode material of claim 22, wherein, The silicon-carbon negative electrode material is coated with a carbon layer.

25. The silicon-carbon negative electrode material of claim 24, wherein, The carbon layer further comprises lithium.

26. A method of preparing a silicon-carbon anode material as claimed in any one of claims 22-25, characterized in that, The preparation method comprises the following steps: mixing a reaction gas and a protective gas to deposit the nano-silicon in the pores of the porous carbon by a gas phase deposition method to obtain the silicon-carbon negative electrode material, and the reaction gas comprises a gas phase silicon source.

27. The method of producing a silicon-carbon negative electrode material according to claim 26, wherein The volume ratio of the reaction gas to the total volume of the reaction gas and the protective gas is 5-10%.

28. The method of producing a silicon-carbon negative electrode material according to claim 26, wherein The gas phase silicon source comprises any one or a combination of at least two of silane, ethylsilane or methylsilane.

29. The method of producing a silicon-carbon negative electrode material according to claim 26, wherein The temperature of the gas phase deposition is 500-950℃.

30. The method of producing a silicon-carbon negative electrode material according to claim 26, wherein The time of the gas phase deposition is 50-720 min.

31. The method of producing a silicon-carbon negative electrode material according to claim 26, wherein The reaction gas further comprises a second reaction gas.

32. The method of producing a silicon-carbon negative electrode material according to claim 31, wherein The second reaction gas comprises any one of acetonitrile vapor, urea vapor, low-molecular amide vapor, low-molecular alicyclic amine vapor, low-molecular aniline vapor, diazomethane, diazobenzene vapor, borane, pyridine borane, borate ester, phenyl borate ester, red phosphorus vapor, alkyl phosphoric acid triester, aryl phosphoric acid triester or aralkyl phosphoric acid triester or a combination of at least two thereof.

33. The method of producing a silicon-carbon negative electrode material according to claim 31, wherein The flow ratio of the gas-phase silicon source to the second reaction gas is (100-70):(0-30).

34. The method of producing a silicon-carbon negative electrode material according to claim 26, wherein The material after gas-phase deposition is mixed and coated with pitch, carbonized to obtain a carbon-coated silicon-carbon negative electrode material.

35. The method of producing a silicon-carbon negative electrode material according to claim 34, wherein The pitch comprises modified pitch.

36. The method of producing a silicon-carbon negative electrode material according to claim 35, wherein The D50 of the modified pitch is 3-5 μm.

37. The method of producing a silicon-carbon negative electrode material according to claim 35, wherein The modification method of the modified pitch comprises: The pitch is melt-blended with a lithium-containing compound to obtain modified pitch.

38. The method of producing a silicon-carbon negative electrode material according to claim 37, wherein The pitch comprises petroleum pitch and / or coal pitch.

39. The method of producing a silicon-carbon negative electrode material according to claim 37, wherein The softening point of the pitch is >150℃.

40. The method of producing a silicon-carbon negative electrode material according to claim 37, wherein The lithium-containing compound comprises any one of lithium carbonate, lithium hydroxide, lithium oxide, lithium chloride, lithium sulfate, lithium nitrate, lithium phosphate, lithium acetate, lithium citrate or lithium oxalate or a combination of at least two thereof.

41. The method of producing a silicon-carbon negative electrode material according to claim 37, wherein The mass ratio of the pitch to the lithium-containing compound is (100-90):(0-10).

42. The method of producing a silicon-carbon negative electrode material according to claim 37, wherein The method of mixing and coating comprises a vacuum impregnation-secondary granulation method.

43. A lithium-ion battery, characterized by, The lithium ion battery comprises the silicon-carbon negative electrode material according to any one of claims 22-25.

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