Porous carbon and its preparation method and application

Abstract

The present invention discloses a porous carbon and its preparation method and application. The preparation method of porous carbon includes the following steps: S1. mixing a resin and an electrolyte in a solvent, and obtaining a porous carbon precursor by spray drying; S2. pre-carbonizing the porous carbon precursor and then activating it with water vapor to obtain porous carbon; in step S1, the mass ratio of resin to electrolyte is 100:(0.1-5); in step S2, the activation temperature is 500-1200°C. The preparation method of porous carbon of the present invention improves the interface of the nano silicon carbon negative electrode material prepared using porous carbon by controlling the mass ratio of resin to electrolyte and the activation temperature of water vapor, suppresses the generation of new SEI film, improves the capacity retention rate of the nano silicon carbon negative electrode material prepared using porous carbon, and reduces the volume expansion of the nano silicon carbon negative electrode material during charge and discharge.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery negative electrode materials, and more specifically, to porous carbon and a preparation method and application thereof. Background Art

[0002] The current actual specific capacity of graphite anode materials, 360-365 mAh / g, is close to the theoretical specific capacity of 372 mAh / g. Therefore, improving the performance of graphite anode materials has little effect on improving the performance of lithium-ion batteries. Silicon-based anode materials have the advantages of high energy density and wide distribution of raw materials, and are considered to be the most promising next-generation lithium-ion battery anode materials. Silicon-based anode materials mainly include elemental silicon anode materials, silicon monoxide anode materials, and nano-silicon-carbon anode materials. Among them, the preparation method of nano-carbon anode materials includes depositing silicon onto a porous carbon skeleton using chemical vapor deposition (CVD).

[0003] Nanocarbon negative electrode materials offer excellent performance in multiple dimensions, including gram capacity, initial efficiency, number of cycles, and rate. Furthermore, in production, nanocarbon negative electrode materials can reduce the need for pre-lithium and pre-magnesium processes, offering the potential for significant cost reductions compared to silicon dioxide negative electrode materials. However, on the one hand, nanocarbon negative electrode materials have a low capacity retention rate, resulting in a short cycle life. On the other hand, as capacity increases, nanocarbon negative electrode materials experience significant volume expansion during charge and discharge, leading to cracks and even pulverization of the material, which in turn destroys the contact between the nanocarbon negative electrode material and the current collector, adversely affecting the performance of lithium-ion batteries.

[0004] Therefore, it is of great significance to develop a new porous carbon to improve the capacity retention rate of nano-silicon-carbon negative electrode materials and reduce the volume expansion of nano-silicon-carbon negative electrode materials during charging and discharging. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of low capacity retention rate and volume expansion of nano silicon carbon negative electrode materials during charge and discharge in the prior art, and to provide a porous carbon and its preparation method and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing porous carbon, the preparation method comprising the following steps:

[0008] S1. Mixing a resin and an electrolyte in a solvent and spray drying to obtain a porous carbon precursor;

[0009] S2. Pre-carbonizing the porous carbon precursor and then activating it with water vapor to obtain porous carbon;

[0010] In step S1, the mass ratio of the resin to the electrolyte is 100:(0.1-5);

[0011] In step S2, the activation temperature is 500-1200°C.

[0012] The preparation method of porous carbon of the present invention improves the interface condition of the nano silicon carbon negative electrode material prepared using porous carbon, inhibits the generation of new SEI film, improves the capacity retention rate of the nano silicon carbon negative electrode material prepared using porous carbon, and reduces the volume expansion of the nano silicon carbon negative electrode material during charging and discharging by controlling the mass ratio of resin and electrolyte and the activation temperature of water vapor; at the same time, by controlling the activation temperature of water vapor, the brittleness and pore size of the porous carbon are also regulated, which is beneficial to improving the capacity retention rate of the nano silicon carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano silicon carbon negative electrode material during charging and discharging.

[0013] In particular, when the mass ratio of resin to electrolyte and the activation temperature of water vapor are too high or too low, it is not conducive to improving the interface conditions of nano-silicon-carbon negative electrode materials, cannot inhibit the formation of SEI film, cannot improve the capacity retention rate of nano-silicon-carbon negative electrode materials prepared using porous carbon, and cannot reduce the volume expansion of nano-silicon-carbon negative electrode materials during charging and discharging.

[0014] In addition, when the activation temperature of water vapor is too high, the brittleness of the porous carbon will increase, making the porous carbon prone to cracking and structural collapse, which is not conducive to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging; and when the activation temperature of water vapor is too low, the pore size of the porous carbon will be too small, that is, the activation is incomplete, affecting the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material, which is not conducive to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0015] Preferably, in step S1, the mass ratio of the resin to the electrolyte is 100:(1-5).

[0016] Preferably, in step S2, the activation temperature is 600-1100°C.

[0017] Preferably, in step S1, the resin is at least one of polyester resin, polyamide resin, phenolic resin, and polyvinyl chloride resin.

[0018] Polyester resins, polyamide resins, phenolic resins, and polyvinyl chloride resins commonly used in the art can all be used in the present invention.

[0019] Preferably, in step S1, the electrolyte is at least one of LATP (lithium aluminum titanium phosphate), LLTO (lithium lanthanum titanate), and LLZO (lithium lanthanum zirconium oxide).

[0020] Commonly used LATP (lithium aluminum titanium phosphate), LLTO (lithium lanthanum titanate), and LLZO (lithium lanthanum zirconium oxide) in the art can all be used in the present invention.

[0021] More preferably, the chemical composition general formula of the LATP (lithium aluminum titanium phosphate) is Li 1+c Al c Ti 2-c (PO4)3, 0 < c ≤ 0.5.

[0022] More preferably, the chemical composition general formula of the LLTO (lithium lanthanum titanate) is Li 3e La 2 / 3-e Ti f T 1-f O3, 0 < e < 2 / 3, 0 < f ≤ 1, where the T is independently selected from at least one of Nb, W, Hf, Ru, Mo, Nd, Ba, Ga, In, Ge, Sn, Sb, and Se.

[0023] More preferably, the chemical composition general formula of the LLZO (lithium lanthanum zirconium oxide) is Li 7-d La3Zr 2-d O 12 , 0 < d ≤ 0.7.

[0024] In the present invention, the LATP (lithium aluminum titanium phosphate), LLTO (lithium lanthanum titanate), and LLZO (lithium lanthanum zirconium oxide) can be obtained commercially or prepared by conventional preparation methods in the art. The present invention provides a preparation method for each of LATP, LAGP, and LLZO, specifically:

[0025] The preparation method of the LATP (lithium aluminum titanium phosphate) is:

[0026] Weigh the Li source, Al source, Ti source, and P source according to the molecular stoichiometric ratio, mix them, and heat-treat at 800 - 950 °C for 6 - 20 h to obtain LATP; among them, the Li source can be selected but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, etc., the Al source can be selected but not limited to alumina, aluminum nitrate, aluminum phosphate, aluminum isopropoxide, etc., the Ti source can be selected but not limited to titanium oxide, tetrabutyl titanate, titanium carbide, titanium pyrophosphate, etc., and the P source can be selected but not limited to ammonium dihydrogen phosphate, phosphorus pentoxide, titanium pyrophosphate, etc.

[0027] The preparation method of the LLTO (lithium lanthanum titanate) is:

[0028] A Li source, a La source, a Ti source, and a T source are weighed according to a molecular stoichiometric ratio, mixed, and heat-treated at 1000-1200° C. for 6-20 h to obtain LLTO; wherein the Li source may be selected from but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, etc., the La source may be selected from but not limited to lanthanum oxide, lanthanum fluoride, lanthanum acetate, etc., the Ti source may be selected from but not limited to titanium oxide, tetrabutyl titanate, titanium carbide, titanium pyrophosphate, etc., and the T source is at least one of the oxides and carbonates of Nb, W, Hf, Ru, Mo, Nd, Ba, Ga, In, Ge, Sn, Sb, and Se.

[0029] The preparation method of the LLZO (lithium lanthanum zirconium oxide) is:

[0030] Li source, La source, and Zr source are weighed according to a molecular stoichiometric ratio, mixed, and heat-treated at 900-1000° C. for 4-8 hours to obtain LLZO; wherein the Li source may be selected from but not limited to lithium carbonate, lithium hydroxide, lithium monohydrogen phosphate, lithium dihydrogen phosphate, etc., the La source may be selected from but not limited to lanthanum oxide, lanthanum carbonate, lanthanum nitrate, lanthanum hydroxide, etc., and the Zr source may be selected from but not limited to zirconium oxide, zirconium carbonate, zirconium nitrate, zirconium hydroxide, etc.

[0031] In the present invention, “weighing by molecular stoichiometric ratio” means weighing by the ratio of the amount of substance (i.e., molar ratio) of each element in the general chemical formula. For example, the general chemical formula of LATP (lithium aluminum titanium phosphate) is Li 1+c Al c Ti 2-c (PO4)3, in the preparation method of LATP, "weighing according to the molecular stoichiometric ratio" specifically refers to weighing the Li source, Al source, Ti source, and P source respectively according to the ratio of the amount of substances of the elements Li, Al, Ti, and P (i.e., the molar ratio) (1+c):c:(2-c):3.

[0032] Preferably, in step S1, the solvent is at least one of ethanol, methanol, ethylene glycol, ethylene triol, n-butanol, propylene glycol, and butanol.

[0033] Preferably, in step S1, the solid-to-liquid ratio of the resin to the solvent is (1-30) g: (70-99) mL.

[0034] Preferably, in step S1, the spray drying temperature is 60°C-180°C, the solution feed flow rate is 3-30 L / min, and the atomization pressure is 0.01-2 MPa.

[0035] Preferably, in step S2, the pre-carbonization temperature is 400-900°C.

[0036] More preferably, in step S2, the pre-carbonization temperature is 650-800°C.

[0037] In the present invention, the size of the pre-carbonization temperature will also affect the brittleness and pore size of the porous carbon. If the pre-carbonization temperature is too high, the brittleness of the porous carbon will increase, making the porous carbon more prone to fragmentation and structural collapse, and it will not be possible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging. If the pre-carbonization temperature is too low, it will affect the carbonization degree of the porous carbon material, making the pore size of the porous carbon more likely to be smaller, and the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material will also be more easily affected, and it will not be possible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0038] Preferably, in step S2, the pre-carbonization time is 0.5-4 hours.

[0039] Preferably, in step S2, the pre-carbonization is performed under the protection of an inert gas, and the inert gas is at least one of nitrogen, helium, neon, and argon.

[0040] Preferably, in step S2, the activation time is 2-8 hours.

[0041] In a second aspect, the present invention provides a porous carbon prepared by the preparation method described in the first aspect.

[0042] Preferably, the median particle size (D50) of the porous carbon is 1.5-15 μm, and the specific surface area is 800-2000 m 2 / g, pore size is 0.5-2nm.

[0043] More preferably, the median particle size (D50) of the porous carbon is 5.0-6.5 μm, and the specific surface area is 1100-2000 m 2 / g, pore size is 1.5-2.0nm.

[0044] More preferably, the median particle size (D50) of the porous carbon is 5.21-6.01 μm, and the specific surface area is 1176-1987 m 2 / g, pore size is 1.5667-1.9244nm.

[0045] In a third aspect, the present invention provides an application of porous carbon in negative electrode materials.

[0046] In a fourth aspect, the present invention provides a method for preparing a nano-silicon-carbon negative electrode material, the preparation method comprising the following steps:

[0047] S1. Under inert gas protection, silicon is deposited on the porous carbon as described in the second aspect by chemical vapor deposition (CVD) using a silicon source gas to obtain a nano-silicon-carbon precursor;

[0048] S2. Under the protection of an inert gas, the nano-silicon-carbon precursor is carbon-coated using a carbon source gas through chemical vapor deposition (CVD) to obtain a nano-silicon-carbon negative electrode material.

[0049] Preferably, in step S1, the silicon source gas is at least one of monosilane, disilane, dichlorosilane, silicon tetrachloride, dichlorodihydrosilane, and trichlorosilane.

[0050] Preferably, in step S1 and / or step S2, the inert gas is at least one of nitrogen, helium, neon and argon.

[0051] Preferably, in step S1, the flow rate ratio of the silicon source gas to the inert gas is (0.1-0.5):1.

[0052] Preferably, in step S1, the silicon deposition temperature is 400-700° C. and the time is 1-6 hours.

[0053] Preferably, in step S2, the carbon source gas is at least one of acetylene, methane, propane, and cyclohexane.

[0054] Preferably, in step S2, the flow rate ratio of the carbon source gas to the inert gas is (0.1-0.5):1.

[0055] Preferably, in step S2, the carbon coating is carried out at a temperature of 400-800°C and for a time of 1-6 hours.

[0056] In a fifth aspect, the present invention provides a nano-silicon-carbon negative electrode material prepared by the preparation method described in the fourth aspect.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The preparation method of porous carbon of the present invention improves the interface condition of the nano silicon carbon negative electrode material prepared using porous carbon, inhibits the generation of new SEI film, improves the capacity retention rate of the nano silicon carbon negative electrode material prepared using porous carbon, and reduces the volume expansion of the nano silicon carbon negative electrode material during charging and discharging by controlling the mass ratio of resin and electrolyte and the activation temperature of water vapor; at the same time, by controlling the activation temperature of water vapor, the brittleness and pore size of the porous carbon are also regulated, which is beneficial to improving the capacity retention rate of the nano silicon carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano silicon carbon negative electrode material during charging and discharging.

[0059] In the present invention, the size of the pre-carbonization temperature will also affect the brittleness and pore size of the porous carbon. If the pre-carbonization temperature is too high, the brittleness of the porous carbon will increase, making the porous carbon more prone to fragmentation and structural collapse, and it will not be possible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging. If the pre-carbonization temperature is too low, it will affect the carbonization degree of the porous carbon material, making the pore size of the porous carbon more likely to be smaller, and the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material will also be more easily affected, and it will not be possible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging. DETAILED DESCRIPTION

[0060] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0061] The experimental methods in the following Examples, Comparative Examples, Application Examples, and Comparative Application Examples where specific conditions are not specified are generally based on conventional conditions in the art or conditions recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets.

[0062] In the various embodiments and comparative examples of the present invention, the use of reagents is as follows:

[0063] The chemical formula of LATP (lithium aluminum titanium phosphate) is Li 1.4 Al 0.4 Ti 1.6 (PO4)3, which is prepared by weighing lithium carbonate, aluminum oxide, titanium oxide, and ammonium dihydrogen phosphate according to a molecular stoichiometric ratio (i.e., the molar ratio of lithium carbonate, aluminum oxide, titanium oxide, and ammonium dihydrogen phosphate is 0.7:0.2:1.6:3), mixing, and heat treating at 800°C for 15 hours to obtain LATP;

[0064] The chemical formula of LLTO (lithium lanthanum titanate) is Li 0.3 La 0.567 TiO3, which is prepared by weighing lithium carbonate, lanthanum oxide, and titanium oxide according to a molecular stoichiometric ratio (i.e., the molar ratio of lithium carbonate, lanthanum oxide, and titanium oxide is 0.15:0.28:1), mixing, and heat treating at 1100° C. for 12 hours to obtain LLTO;

[0065] The chemical formula of LLZO (lithium lanthanum zirconium oxide) is Li 6.5 La3Zr 1.5 O 12The preparation method comprises the following steps: weighing lithium carbonate, lanthanum oxide, and zirconium oxide according to a molecular weight ratio (i.e., the molar ratio of lithium carbonate, lanthanum oxide, and zirconium oxide is 3.25:1.5:1.5), mixing, and heat treating at 900° C. for 6 h to obtain LLZO;

[0066] Phenolic resin, commercially available.

[0067] Example 1

[0068] This embodiment provides a porous carbon, the preparation method of which includes the following steps:

[0069] S1. 5 g of phenolic resin was dissolved in 95 mL of anhydrous ethanol, and then 0.15 g of LLTO (lithium lanthanum titanate) electrolyte was added and dissolved and mixed under ultrasonication for 30 min. The mixture was spray dried in a spray dryer at 110°C, a solution feed flow rate of 5 L / min, and an atomization pressure of 0.5 MPa to obtain a porous carbon precursor.

[0070] S2. The porous carbon precursor prepared in step S1 is placed in a CVD rotary furnace. Under the protection of argon, the temperature is raised to 700°C at a rate of 2°C / min and kept at 700°C for 2 hours for pre-carbonization. The temperature is then lowered to 400°C at a rate of 10°C / min, and then naturally cooled. The temperature is then raised to 900°C at a rate of 5°C / min, and water vapor is introduced at 900°C for activation for 5 hours to obtain porous carbon.

[0071] In step S1, the mass ratio of the phenolic resin to the electrolyte LLTO is 100:3.

[0072] Examples 2-4 and Comparative Examples 1-2

[0073] Examples 2-4 and Comparative Examples 1-2 provide different porous carbons, which differ from Example 1 in that the mass ratios of the phenolic resin and the electrolyte LLTO (lithium lanthanum titanate) are different. The rest are consistent with Example 1, as shown in the following table:

[0074] Table 1 Mass ratio of phenolic resin and electrolyte LLTO in Examples 1-4 and Comparative Examples 1-2

[0075]

[0076] Examples 5-8 and Comparative Examples 3-4

[0077] Examples 5-8 and Comparative Examples 3-4 provide different porous carbons, which differ from Example 1 in that the activation temperature in step S2 is different, and the rest are consistent with Example 1, as shown in the following table:

[0078] Table 2 Activation temperature in step S2 of Examples 1, 5-8 and Comparative Examples 3-4

[0079]

[0080]

[0081] Examples 9-12

[0082] Examples 9-12 provide different porous carbons, which differ from Example 1 in that the pre-carbonization temperature in step S2 is different, and the rest are consistent with Example 1, as shown in the following table:

[0083] Table 3 Pre-carbonization temperature in step S2 of Examples 1, 9-12

[0084] Pre-carbonization temperature in step S2 / °C Example 1 700 Example 9 800 Example 10 650 Example 11 400 Example 12 900

[0085] Examples 13-14

[0086] Examples 13-14 provide different porous carbons. The difference between them and Example 1 is that the type of electrolyte in step S1 is different. The rest is consistent with Example 1, as shown in the following table:

[0087] Table 4 Electrolyte types in step S1 of Examples 1, 13-14

[0088] Type of electrolyte in step S1 Example 1 LLTO (Lithium Lanthanum Titanate) Example 13 LATP (lithium aluminum titanium phosphate) Example 14 LLZO (lithium lanthanum zirconium oxide)

[0089] Example 15

[0090] This embodiment provides a porous carbon, which differs from Example 13 in that 0.05 g of electrolyte LATP (lithium aluminum titanium phosphate) is used instead of 0.15 g of electrolyte LATP (lithium aluminum titanium phosphate), and the rest is consistent with Example 13.

[0091] Comparative Example 5

[0092] This comparative example provides a porous carbon, which differs from Example 1 in that spray drying is not performed in step S1, and the rest is consistent with Example 1, specifically as follows:

[0093] S1. Dissolve 5 g of phenolic resin in 95 mL of anhydrous ethanol, then add 0.15 g of LLTO (lithium lanthanum titanate) electrolyte, dissolve and mix under ultrasonication for 30 min, and then dry in a vacuum oven at 110°C to obtain a porous carbon precursor;

[0094] S2. The porous carbon precursor prepared in step S1 is placed in a CVD rotary furnace. Under the protection of argon, the temperature is raised to 700°C at a rate of 2°C / min and kept at 700°C for 2 hours for pre-carbonization. The temperature is then lowered to 400°C at a rate of 10°C / min, and then naturally cooled. The temperature is then raised to 900°C at a rate of 5°C / min, and water vapor is introduced at 900°C for activation for 5 hours to obtain porous carbon.

[0095] In step S1, the mass ratio of the phenolic resin to the electrolyte LLTO is 100:3.

[0096] Comparative Example 6

[0097] This comparative example provides a porous carbon, which differs from Example 1 in that no pre-carbonization is performed in step S2, and the rest is consistent with Example 1, as follows:

[0098] S1. 5 g of phenolic resin was dissolved in 95 mL of anhydrous ethanol, and then 0.15 g of LLTO (lithium lanthanum titanate) electrolyte was added and dissolved and mixed under ultrasonication for 30 min. The mixture was spray dried in a spray dryer at 110°C, a solution feed flow rate of 5 L / min, and an atomization pressure of 0.5 MPa to obtain a porous carbon precursor.

[0099] S2. The porous carbon precursor obtained in step S1 is placed in a CVD rotary furnace, heated to 900°C at 5°C / min, and activated by introducing water vapor at 900°C for 5h to obtain porous carbon;

[0100] In step S1, the mass ratio of the phenolic resin to the electrolyte LLTO is 100:3.

[0101] Comparative Example 7

[0102] This comparative example provides a porous carbon, which differs from Example 1 in that water vapor is not introduced during activation in step S2. The rest is consistent with Example 1, as follows:

[0103] S1. 5 g of phenolic resin was dissolved in 95 mL of anhydrous ethanol, and then 0.15 g of LLTO (lithium lanthanum titanate) electrolyte was added and dissolved and mixed under ultrasonication for 30 min. The mixture was spray dried in a spray dryer at 110°C, a solution feed flow rate of 5 L / min, and an atomization pressure of 0.5 MPa to obtain a porous carbon precursor.

[0104] S2. The porous carbon precursor prepared in step S1 is placed in a CVD rotary furnace. Under the protection of argon, the temperature is raised to 700°C at a rate of 2°C / min and kept at 700°C for 2 hours for pre-carbonization. The temperature is then lowered to 400°C at a rate of 10°C / min, and then naturally cooled. The temperature is then raised to 900°C at a rate of 5°C / min and activated at 900°C for 5 hours to obtain porous carbon.

[0105] In step S1, the mass ratio of the phenolic resin to the electrolyte LLTO is 100:3.

[0106] Application Examples and Comparative Application Examples

[0107] Application Example 1

[0108] This application example provides a nano-silicon-carbon negative electrode material, the preparation method of which includes the following steps:

[0109] S1. The porous carbon of Example 1 was placed in a fluidized bed and continuously purged with nitrogen at a flow rate of 5 L / min to exhaust the air. The temperature was then raised to 550°C at a rate of 10°C / min. While nitrogen was continuously introduced at a flow rate of 5 L / min, a silicon source gas, monosilane, was introduced at a flow rate of 2 L / min. Silicon was deposited on the porous carbon of Example 1 by chemical vapor deposition (CVD) for 5 h to obtain a nano-silicon-carbon precursor.

[0110] S2. While continuously introducing nitrogen at a flow rate of 5 L / min, the temperature was raised to 680°C at a flow rate of 10°C / min, and then the carbon source gas acetylene was introduced at a flow rate of 2 L / min. The nano-silicon-carbon precursor was carbon-coated by chemical vapor deposition (CVD) for 2.5 hours, and then naturally cooled to obtain the nano-silicon-carbon negative electrode material.

[0111] Application Example 2-15

[0112] Application Example 2-15 provides different nano-silicon-carbon negative electrode materials. The difference between Application Example 2-15 and Application Example 1 is that Application Example 2-15 uses the porous carbon of Example 2-15 instead of the porous carbon of Example 1, and the rest is consistent with Application Example 1.

[0113] Comparative Application Examples 1-7

[0114] Comparative Application Examples 1-7 provide different nano-silicon carbon negative electrode materials. The difference between them and Application Example 1 is that Comparative Application Examples 1-7 use the porous carbon of Comparative Examples 1-7 to replace the porous carbon of Example 1, and the rest are consistent with Application Example 1.

[0115] Sample characterization

[0116] The porous carbon samples of Examples 1-15 and Comparative Examples 1-7 were characterized as follows:

[0117] (1) The median particle size (D50) of porous carbon was measured using a laser particle size analyzer, Mastersizer 3000, in accordance with the national standard GB / T 41949-2022.

[0118] (2) Measurement method of specific surface area and pore size of porous carbon: Using nitrogen as adsorbent, using TriStarⅡplus3030, the specific surface area of ​​porous carbon was tested according to the national standard GB / T 19587-2017, and the pore size of porous carbon was tested according to the national standard GB / T21650.2-2008;

[0119] The experimental results are shown in the following table:

[0120] Table 5 Characterization results of porous carbon samples of Examples 1-15 and Comparative Examples 1-7

[0121]

[0122] As can be seen from Table 5, by comparing Examples 1, 5-8 and Comparative Examples 3-4, when the activation temperature of water vapor is too low, the pore size of the porous carbon will be too small, that is, the activation will be incomplete, which will affect the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material, which is not conducive to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0123] By comparing Examples 1 and 9-12, when the pre-carbonization temperature is too low, it will affect the carbonization degree of the porous carbon material, making the pore size of the porous carbon more likely to be smaller, and the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material are also more easily affected, and it is impossible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared by using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0124] Performance Testing

[0125] The performance tests of the nano silicon carbon negative electrode materials of each application example and comparative application example are as follows:

[0126] (1) Preparation of button-type lithium-ion batteries

[0127] A1. Place the nano-silicon-carbon anode material and conductive agent (acetylene black) from each application example or comparative application example in an oven and bake at 120°C for 4 hours. Cool the mixture in a desiccator. Then, weigh the nano-silicon-carbon anode material and conductive agent (acetylene black) in a 50 mL beaker at a mass ratio of 80:10:10. Add the corresponding amounts of material to a 50 mL beaker. Add the binder solution (a 5% solution of polyvinylidene fluoride in N-methylpyrrolidone) and stir until a paste forms.

[0128] A2. Apply the paste evenly on the aluminum foil to obtain a single-sided surface density of 60g / m 2 The negative electrode sheet was then placed in a blast drying oven and dried at 120°C for 2 hours and pressed (the pressing density of the negative electrode sheet was 2.0 g / cm 3 ), cut into a circular negative electrode sheet with a diameter of 12 mm;

[0129] A3. In an argon atmosphere glove box, a circular negative electrode sheet was used as the negative electrode, a lithium sheet was used as the positive electrode, and a 1 mol / L LiPF6 ethylene carbonate solution and ethyl methyl carbonate (EMC) were used as the electrolyte in a volume ratio of 3:7 to form a button-type lithium-ion battery.

[0130] (2) Measurement of first charge capacity, first cycle coulombic efficiency, and capacity retention rate after 10 cycles

[0131] At 25°C and 25% humidity, button-type lithium-ion batteries were charged and discharged using a Blue Electric battery test system to measure the first charge capacity (first charge capacity) and first cycle coulombic efficiency of the button-type lithium-ion batteries prepared using the nano-silicon-carbon negative electrode materials of each application example or comparative application example;

[0132] One cycle of charge and discharge is considered one week. The initial charge capacity is M1. After 10 cycles, the charge capacity is M2. The capacity retention rate after 10 cycles is calculated by the formula [Capacity retention rate after 10 cycles (%) = (M2 / M1) × 100%];

[0133] The present invention uses the capacity retention rate after 10 cycles to characterize the capacity retention rate of the nano-silicon-carbon negative electrode material. The greater the capacity retention rate after 10 cycles, the greater the capacity retention rate of the nano-silicon-carbon negative electrode material.

[0134] (3) Measurement method of the first cycle zero-full charge expansion rate

[0135] At 25°C, before assembling into a button-type lithium-ion battery, the thickness H1 of the negative electrode (the nano-silicon-carbon negative electrode material of each application example or comparative application example) was measured. Then, the button-type lithium-ion battery was assembled and the button-type lithium-ion battery was charged and discharged using a blue battery testing system. After discharging and charging once, the battery was fully discharged again. The button-type lithium-ion battery was then disassembled in a glove box and the thickness H2 of the negative electrode (the nano-silicon-carbon negative electrode material of each application example or comparative application example) was measured. The first cycle zero-full charge expansion rate (%) = (H2-H1) / H1×100%;

[0136] The present invention uses the first cycle zero-full charge expansion rate to characterize the volume expansion of the nano silicon carbon negative electrode material during charge and discharge; the larger the first cycle zero-full charge expansion rate, the larger or more serious the volume expansion of the nano silicon carbon negative electrode material during charge and discharge;

[0137] The experimental results are shown in the following table:

[0138] Table 6 Performance test results of nano silicon carbon negative electrode materials in various application examples and comparative application examples

[0139]

[0140]

[0141] As can be seen from Table 6, the preparation method of porous carbon of the present invention improves the interface condition of the nano-silicon-carbon negative electrode material prepared using porous carbon by controlling the mass ratio of resin and electrolyte and the activation temperature of water vapor, inhibits the generation of new SEI film, improves the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon, and reduces the volume expansion of the nano-silicon-carbon negative electrode material during charge and discharge; at the same time, by controlling the activation temperature of water vapor, the brittleness and pore size of the porous carbon are also regulated, which is beneficial to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charge and discharge.

[0142] Specifically, by comparing Application Examples 1-4 and Comparative Application Examples 1-2, it can be seen that when the mass ratio of resin to electrolyte is too high or too low, it is not conducive to improving the interface conditions of the nano-silicon-carbon negative electrode material, cannot inhibit the formation of SEI film, cannot improve the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon, and cannot reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0143] By comparing application examples 1, 5-8 and comparative application examples 3-4, it can be seen that when the activation temperature of water vapor is too high or too low, it is not conducive to improving the interface conditions of the nano-silicon-carbon negative electrode material, cannot inhibit the formation of the SEI film, cannot improve the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon, and cannot reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging; in addition, when the activation temperature of water vapor is too high, it will also increase the brittleness of the porous carbon, making the porous carbon prone to fragmentation and structural collapse, which is not conducive to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging; and when the activation temperature of water vapor is too low, it will also make the pore size of the porous carbon smaller, that is, the activation is incomplete, affecting the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material, which is not conducive to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0144] By comparing application examples 1, 9-12, it can be seen that if the pre-carbonization temperature is too high, the brittleness of the porous carbon will increase, making the porous carbon more prone to fragmentation and structural collapse, and it is impossible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging to a greater extent; if the pre-carbonization temperature is too low, it will affect the carbonization degree of the porous carbon material, making the pore size of the porous carbon more likely to be smaller, and the silicon deposition and carbon coating of the porous carbon in the process of preparing the nano-silicon-carbon negative electrode material are also more easily affected, and it is impossible to increase the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using the porous carbon and reduce the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging to a greater extent.

[0145] By comparing Application Example 1 and Comparative Application Examples 5-7, it can be seen that when preparing porous carbon in the present invention, if spray drying or pre-carbonization or water vapor is not introduced during activation, it will be detrimental to improving the capacity retention rate of the nano-silicon-carbon negative electrode material prepared using porous carbon and reducing the volume expansion of the nano-silicon-carbon negative electrode material during charging and discharging.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing porous carbon, characterized in that: The preparation method comprises the following steps: S1. Mixing a resin and an electrolyte in a solvent and spray drying to obtain a porous carbon precursor; S2. Pre-carbonizing the porous carbon precursor and then activating it with water vapor to obtain porous carbon; In step S1, the mass ratio of the resin to the electrolyte is 100:(0.1-5); In step S2, the activation temperature is 500-1200°C; The electrolyte is at least one of LATP, LLTO and LLZO, and the resin is at least one of polyester resin, polyamide resin, phenolic resin and polyvinyl chloride resin.

2. The method for preparing porous carbon according to claim 1, wherein: Include at least one of the following (1)-(2): (1) In step S1, the mass ratio of the resin to the electrolyte is 100:(1-5); (2) In step S2, the activation temperature is 600-1100°C.

3. The method for preparing porous carbon according to claim 1, wherein: In step S2, the pre-carbonization temperature is 400-900°C.

4. A porous carbon, characterized in that The product is prepared by the preparation method according to any one of claims 1 to 3.

5. The porous carbon according to claim 4, wherein: The median particle size (D50) of the porous carbon is 1.5-15 μm, and the specific surface area is 800-2000 m 2 / g, pore size is 0.5-2nm.

6. Use of the porous carbon according to any one of claims 4 to 5 in negative electrode materials.

7. A method for preparing a nano-silicon-carbon negative electrode material, characterized in that: The preparation method comprises the following steps: S1. Under inert gas protection, silicon is deposited on the porous carbon according to any one of claims 4-5 by chemical vapor deposition using a silicon source gas to obtain a nano-silicon-carbon precursor; S2. Under the protection of an inert gas, the nano-silicon-carbon precursor is carbon-coated by using a carbon source gas through chemical vapor deposition to obtain a nano-silicon-carbon negative electrode material.

8. The method for preparing the nano-silicon-carbon negative electrode material according to claim 7, wherein: Include at least one of the following (1)-(2): (1) In step S1, the silicon source gas is at least one of monosilane, disilane, dichlorosilane, silicon tetrachloride, dichlorodihydrosilane, and trichlorosilane; (2) In step S2, the carbon source gas is at least one of acetylene, methane, propane, and cyclohexane.

9. The method for preparing the nano-silicon-carbon negative electrode material according to claim 7, wherein: Include at least one of the following (1)-(2): (1) In step S1, the silicon deposition temperature is 400-700°C and the time is 1-6 hours; (2) In step S2, the carbon coating temperature is 400-800°C and the time is 1-6 hours.

10. A nano silicon carbon negative electrode material, characterized in that: The product is prepared by the preparation method according to any one of claims 7 to 9.

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