Porous carbon material, negative electrode material, negative electrode sheet, secondary battery, and method for manufacturing the same

Abstract

The application discloses a kind of porous carbon materials, negative electrode material, negative electrode sheet, secondary battery and its preparation method, the proportion of micropore of the porous carbon material is ≥95% in total pore volume, micropore is the pore of aperture ≤2nm;Wherein, the proportion of micropore with aperture in 0~0.44nm is recorded as X%, and 0.5≤X≤5.0;The proportion of micropore with aperture in 0.44~1.32nm is recorded as Y%, and 65≤Y≤90;The proportion of micropore with aperture in 1.32~2nm is recorded as Z%, and 5≤Z≤30;And, X+Y+Z=100.The porous carbon material disclosed in the application is mainly micropore, and the proportion of micropore is as high as 95% and above, and the electrochemical performance of the prepared negative electrode material and the secondary battery assembled therefrom is accurately controlled by accurately controlling micropore with different aperture, to prepare the negative electrode material with low expansion rate, high cycle stability, high capacity and high initial efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion batteries, specifically relating to a porous carbon material, a negative electrode material, a negative electrode sheet, a secondary battery, and a method for preparing the same. Background Technology

[0002] Silicon's ultra-high theoretical specific capacity (up to 4200 mAh / g) makes silicon-based anode materials the preferred anode materials for next-generation high-energy-density lithium-ion batteries. Currently, the anode industry is mostly focused on the strategy of preparing silicon-carbon materials on porous carbon substrates using chemical vapor deposition processes. Porous carbon can provide high conductivity and alleviate the severe volume expansion / contraction that occurs in silicon during lithium insertion / extraction.

[0003] Ideally, in chemical vapor deposition (CVD), silane molecules break down within the pores of porous carbon at high temperatures, resulting in heterogeneous nucleation and adherence growth of silicon atoms. Some pores are also reserved to mitigate silicon volume expansion. However, if the porous carbon has a small pore volume and a large pore size, silicon atoms may undergo homogeneous nucleation and growth into free silicon nanoparticles under high temperatures. This is known as silicon floating, leading to increased material expansion and severe degradation of electrochemical performance.

[0004] Therefore, the pore size distribution of porous carbon, and the adjustment of micropores, are crucial for the effective adsorption of silane molecules and for mitigating silicon volume expansion.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] To address the aforementioned problems, this invention discloses a porous carbon material, which is predominantly micropores, with a micropore content of up to 95% or more. By precisely controlling the micropores of different sizes, the electrochemical performance of the prepared anode material and the secondary battery assembled from it can be precisely controlled, so as to prepare an anode material with low expansion rate, high cycle stability, high capacity and high first-efficiency.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a porous carbon material in which micropores account for ≥95% of the total pore volume, wherein the micropores are pores with a diameter ≤2nm;

[0009] The proportion of micropores with a pore size of 0–0.44 nm is denoted as X%, where 0.5 ≤ X ≤ 5.0.

[0010] The percentage of micropores with a pore size of 0.44–1.32 nm is denoted as Y%, and 65 ≤ Y ≤ 90.

[0011] The proportion of micropores with a pore size of 1.32–2 nm is denoted as Z%, where 5 ≤ Z ≤ 30.

[0012] Furthermore, X+Y+Z=100.

[0013] In an optional embodiment, the porous carbon material has an average pore size of 1.5 ± 0.3 nm.

[0014] In an optional embodiment, the porous carbon material satisfies at least one of the following conditions:

[0015] (1) Specific surface area is 1500~2200m² 2 / g;

[0016] (2) The pore volume is 0.7–1.3 cm. 3 / g;

[0017] (3) The particle size Dv50 is 7.0±1.0μm.

[0018] In an optional embodiment, the porous carbon material satisfies at least one of the following conditions:

[0019] (1) 0.5 ≤ X ≤ 2.0; optionally, 0.5 ≤ X ≤ 1.5;

[0020] (2) 69≤Y≤90; optionally, 69≤Y≤80;

[0021] (3) 8≤Z≤30; optionally, 19≤Z≤30.

[0022] Secondly, the present invention also provides a negative electrode material, which uses the porous carbon material as a substrate and further includes nano-silicon particles distributed in the pores of the porous carbon material, as well as an outermost carbon coating layer.

[0023] In an optional implementation, the negative electrode material satisfies at least one of the following conditions:

[0024] (a) Dv50 is 7.0±1.0μm;

[0025] (b) Specific surface area is 3±2m² 2 / g;

[0026] (c) Powder resistivity <10Ω-cm at 20MPa;

[0027] (d) Tap density is 0.9 ± 0.05 g / cm³ 3 .

[0028] Thirdly, the present invention also provides a method for preparing the above-mentioned negative electrode material, comprising the following steps:

[0029] (S1) The carbon source precursor is subjected to high-temperature carbonization treatment, and then two activation treatments are performed to obtain porous carbon material.

[0030] The two activation treatments are as follows: the first activation uses water vapor as the activating agent, and the second activation uses carbon dioxide as the activating agent.

[0031] (S2) Using the porous carbon material as a substrate, silicon deposition is performed to obtain a porous carbon substrate loaded with nano-silicon particles;

[0032] (S3) Carbon coating treatment is performed to obtain the negative electrode material.

[0033] In step (S1):

[0034] In an optional embodiment, the carbon source precursor is selected from polymeric carbon sources and / or biomass carbon sources.

[0035] Optionally, the polymeric carbon source is selected from common types such as phenolic resin and asphalt;

[0036] Optionally, the biomass carbon source is selected from common types such as coconut shells and straw.

[0037] In an optional embodiment, the high-temperature carbonization treatment is carried out at a temperature of 700–900°C;

[0038] Optionally, the high-temperature carbonization treatment time is 6 to 12 hours;

[0039] Optionally, the heating rate is selected from 10 to 20 °C / min.

[0040] In an optional embodiment, during the initial activation, the mass ratio of carbon source precursor to water vapor is (0.5-5.0):1; optionally, the mass ratio of carbon source precursor to water vapor is (0.625-5.0):1; further optionally, the mass ratio of carbon source precursor to water vapor is (1.875-5.0):1; and even more optionally, the mass ratio is 1.875:1.

[0041] In an optional embodiment, the flow rate of water vapor is 0.05 to 1 kg / h; alternatively, the flow rate of water vapor is 0.25 to 1 kg / h.

[0042] Optionally, the initial activation temperature is 700–900°C;

[0043] Optionally, the heating rate is selected from 10 to 20 °C / min;

[0044] Optionally, the initial activation time is 6 to 12 hours.

[0045] In an optional embodiment, the reactivation is performed with a carbon source precursor to carbon dioxide mass ratio of (0.3-5.0):1; optionally, the carbon source precursor to carbon dioxide mass ratio is (0.375-5.0):1; further optionally, the carbon source precursor to carbon dioxide mass ratio is (0.75-5.0):1; and even more optionally, the mass ratio is 1.875:1.

[0046] In an optional embodiment, the flow rate of carbon dioxide is 0.05 to 2 kg / h; alternatively, the flow rate of carbon dioxide is 0.25 to 2 kg / h.

[0047] Optionally, the reactivation is performed at a temperature of 900–1200°C;

[0048] Optionally, the heating rate is selected from 10 to 20 °C / min;

[0049] Optionally, the reactivation takes 6 to 12 hours.

[0050] In step (S2):

[0051] In an optional embodiment, the silicon deposition temperature is 400–600°C;

[0052] Optionally, the silicon deposition specifically involves placing a porous carbon material substrate in a raw material gas environment containing silicon source gas for vapor phase deposition.

[0053] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of silane, silane, dichlorosilane, and trichlorosilane;

[0054] Optionally, the flow rate of the feed gas containing silicon source gas is 1 to 30 L / h; more preferably, the flow rate is 10 to 30 L / h.

[0055] Optionally, the raw material gas containing silicon source gas contains an inert gas, with a volume percentage of 0-30%.

[0056] Optionally, it can be selected from inert gases such as argon and helium.

[0057] Optionally, silicon deposition is performed for 18–36 hours;

[0058] Optionally, the temperature can be raised to 400-600°C at a heating rate of 10-20°C / min and held for 0.5-2 hours before silicon deposition.

[0059] In step (S3):

[0060] In an optional embodiment, the carbon coating treatment is performed at a temperature of 500–700°C;

[0061] Optionally, the carbon coating process involves placing the silicon-deposited product in a raw material gas environment containing carbon source gas for vapor phase deposition.

[0062] Optionally, the carbon source gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butene, and 1,3-butadiene; optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0063] Optionally, the flow rate of the feed gas containing the carbon source gas is 1 to 20 L / h; more preferably, the flow rate is 5 to 15 L / h.

[0064] Optionally, the carbon coating treatment is carried out at a temperature of 500–700°C for 6–12 hours.

[0065] Optionally, the temperature can be raised to 500-700℃ at a heating rate of 10-20℃ / min and held for 0.5-2h before carbon coating treatment.

[0066] Fourthly, the present invention also provides a negative electrode sheet, comprising the aforementioned negative electrode material.

[0067] Fifthly, the present invention also provides a secondary battery, including the aforementioned negative electrode sheet.

[0068] Compared with the prior art, the present invention has the following advantages:

[0069] This invention discloses a porous carbon material and its preparation method. The porous carbon material is mainly composed of micropores, with a micropore ratio of up to 95% or more. The micropores of different pore sizes are further divided into three categories and the proportion of each category. The micropore composition in the prepared porous carbon material can be adjusted by controlling the process parameters of the two activation treatments in the preparation method.

[0070] In this invention, a negative electrode material is prepared using the above-mentioned porous carbon material as a substrate and assembled into a secondary battery. By precisely controlling the micropores of different pore sizes, the electrochemical performance of the secondary battery can be precisely controlled, so as to prepare a negative electrode material with low expansion rate, high cycle stability, high capacity and high first-time efficiency. Detailed Implementation

[0071] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] In the description of this invention, it should be noted that those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. The embodiments of this invention are described below based on its overall structure. Unless otherwise specified, the raw materials used in the embodiments of this invention were all purchased commercially.

[0073] In a first aspect, the present invention provides a porous carbon material in which micropores account for ≥95% of the total pores, wherein the micropores are pores with a diameter ≤2nm;

[0074] The proportion of micropores with a pore size of 0 to 0.44 nm is denoted as X%, and 0.5 ≤ X ≤ 5.0; specifically, it can be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 or any value within the above range;

[0075] The percentage of micropores with a pore size of 0.44 to 1.32 nm is denoted as Y%, and 65 ≤ Y ≤ 90; specifically, it can be 65, 66, 67, 68, 69, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90 or any value within the above range;

[0076] The proportion of micropores with a pore size of 1.32 to 2 nm is denoted as Z%, 5 ≤ Z ≤ 30; specifically, it can be 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30 or any value within the above range;

[0077] Furthermore, X+Y+Z=100.

[0078] In an optional embodiment, the porous carbon material has an average pore size of 1.5 ± 0.3 nm, specifically 1.2 nm, 1.25 nm, 1.3 nm, 1.35 nm, 1.4 nm, 1.45 nm, 1.5 nm, 1.55 nm, 1.6 nm, 1.65 nm, 1.7 nm, 1.75 nm, 1.8 nm or any value within the above range; optionally, the average pore size is 1.4 to 1.7 nm.

[0079] In an optional embodiment, the porous carbon material satisfies at least one of the following conditions:

[0080] (1) Specific surface area is 1500~2200m² 2 / g; specifically, it can be 1500m 2 / g, 1550m 2 / g, 1600m 2 / g、1650m 2 / g、1700m 2 / g、1750m2 / g、1800m 2 / g、1850m 2 / g、1900m 2 / g、1950m 2 / g、2000m 2 / g、2050m 2 / g、2100m 2 / g、2150m 2 / g、2200m 2 / g or any value within the above range;

[0081] (2) The pore volume is 0.7–1.3 cm. 3 / g; specifically, it can be 0.7cm 3 / g, 0.75cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g, 0.95cm 3 / g, 1.0cm 3 / g, 1.05cm 3 / g, 1.1cm 3 / g, 1.15cm 3 / g, 1.2cm 3 / g, 1.25cm 3 / g, 1.3cm 3 / g or any value within the above range;

[0082] (3) The particle size Dv50 is 7.0±1.0μm; specifically, it can be 6.0μm, 6.2μm, 6.5μm, 6.7μm, 6.9μm, 7.0μm, 7.2μm, 7.5μm, 7.7μm, 8.0μm or any value within the above range; optionally, the particle size Dv50 is 6.9~7.2μm.

[0083] In an optional embodiment, the porous carbon material satisfies at least one of the following conditions:

[0084] (1) 0.5 ≤ X ≤ 2; optionally, 0.5 ≤ X ≤ 1.5;

[0085] (2) 69≤Y≤90; optionally, 69≤Y≤80;

[0086] (3) 8≤Z≤30; optionally, 19≤Z≤30.

[0087] Secondly, the present invention also provides a negative electrode material, which uses the porous carbon material as a substrate and further includes nano-silicon particles distributed in the pores of the porous carbon material, as well as an outermost carbon coating layer.

[0088] In an optional implementation, the negative electrode material satisfies at least one of the following conditions:

[0089] (a) Dv50 is 7.0 ± 1.0 μm; specifically, it can be 6.0 μm, 6.2 μm, 6.5 μm, 6.7 μm, 6.9 μm, 7.0 μm, 7.2 μm, 7.5 μm, 7.7 μm, 8.0 μm or any value within the above range;

[0090] (b) Specific surface area is 3±2m² 2 / g; specifically, it can be 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g、2m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.8m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g or any value within the above range;

[0091] (c) Powder resistance <10Ω-cm at 20MPa; specifically, it can be 0.01Ω-cm, 0.05Ω-cm, 0.1Ω-cm, 0.5Ω-cm, 1Ω-cm, 2Ω-cm, 3Ω-cm, 4Ω-cm, 5Ω-cm, 6Ω-cm, 7Ω-cm, 8Ω-cm, 9Ω-cm, 9.5Ω-cm, 9.9Ω-cm or any value within the above range;

[0092] (d) Tap density is 0.9 ± 0.05 g / cm³ 3 Specifically, it can be 0.85 g / cm³. 3 0.86 g / cm 3 0.87g / cm 3 0.88g / cm 3 0.89g / cm 3 0.90g / cm 3 0.91g / cm 3 0.92g / cm 3 0.93g / cm 30.94g / cm 3 0.95g / cm 3 Or any value within the above range.

[0093] Thirdly, the present invention also provides a method for preparing the above-mentioned negative electrode material, comprising the following steps:

[0094] (S1) The carbon source precursor is subjected to high-temperature carbonization treatment, and then two activation treatments are performed to obtain porous carbon material.

[0095] The two activation treatments are as follows: the first activation uses water vapor as the activating agent, and the second activation uses carbon dioxide as the activating agent.

[0096] (S2) Using the porous carbon material as a substrate, silicon deposition is performed to obtain a porous carbon substrate loaded with nano-silicon particles;

[0097] (S3) Carbon coating treatment is performed to obtain the negative electrode material.

[0098] In step (S1):

[0099] In an optional embodiment, the carbon source precursor is selected from polymeric carbon sources and / or biomass carbon sources.

[0100] Optionally, the polymeric carbon source is selected from common types such as phenolic resin and asphalt;

[0101] Optionally, the biomass carbon source is selected from common types such as coconut shells and straw.

[0102] In an optional embodiment, the high-temperature carbonization treatment is carried out at a temperature of 700 to 900°C; specifically, it can be 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, 880°C, 900°C or any value within the above range.

[0103] Optionally, the high-temperature carbonization treatment time is 6 to 12 hours; specifically, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value within the above range.

[0104] Optionally, the heating rate is selected from 10 to 20 °C / min; specifically, it can be 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min or any value within the above range.

[0105] In an optional embodiment, during the initial activation, the mass ratio of the carbon source precursor to water vapor is (0.5–5.0):1; specifically, it can be 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, or any ratio within the above range; optionally, the mass ratio of the carbon source precursor to water vapor is (0.625–5.0):1; further optionally, the mass ratio of the carbon source precursor to water vapor is (1.875–5.0):1; more preferably, the mass ratio is 1.875:1.

[0106] In an optional embodiment, the flow rate of water vapor is 0.05 to 1 kg / h; specifically, it can be 0.05 kg / h, 0.10 kg / h, 0.15 kg / h, 0.20 kg / h, 0.25 kg / h, 0.30 kg / h, 0.35 kg / h, 0.40 kg / h, 0.45 kg / h, 0.50 kg / h, 0.60 kg / h, 0.70 kg / h, 0.80 kg / h, 0.90 kg / h, 1.00 kg / h, or any value within the above range; optionally, the flow rate of water vapor is 0.25 to 1 kg / h.

[0107] Optionally, the initial activation temperature is 700–900°C; specifically, it can be 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, 880°C, 900°C, or any value within the above range.

[0108] Optionally, the heating rate is selected from 10 to 20 °C / min; specifically, it can be 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min or any value within the above range.

[0109] Optionally, the initial activation time is 6 to 12 hours; specifically, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value within the above range.

[0110] In an optional embodiment, the reactivation involves a carbon source precursor to carbon dioxide mass ratio of (0.3–5.0):1; specifically, it can be 0.3:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, or any ratio within the above range; optionally, the carbon source precursor to carbon dioxide mass ratio is (0.375–5.0):1; further optionally, the carbon source precursor to carbon dioxide mass ratio is (0.75–5.0):1; and even more optionally, the mass ratio is 1.875:1.

[0111] In an optional embodiment, the flow rate of carbon dioxide is 0.05–2 kg / h; specifically, it can be 0.05 kg / h, 0.10 kg / h, 0.15 kg / h, 0.20 kg / h, 0.25 kg / h, 0.30 kg / h, 0.35 kg / h, 0.40 kg / h, 0.4+, and the temperature is 900–1200°C; specifically, it can be 900°C, 920°C, 950°C, 980°C, 1000°C, 1020°C, 1050°C, 1080°C, 1100°C, 1120°C, 1150°C, 1180°C, 1200°C, or any value within the above range.

[0112] Optionally, the heating rate is selected from 10 to 20 °C / min; specifically, it can be 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min or any value within the above range.

[0113] Optionally, the reactivation time is 6 to 12 hours; specifically, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value within the above range.

[0114] In step (S2):

[0115] In an optional embodiment, the silicon deposition temperature is 400–600°C; specifically, it can be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, or any value within the above range.

[0116] Optionally, the silicon deposition specifically involves placing a porous carbon material substrate in a raw material gas environment containing silicon source gas for vapor phase deposition.

[0117] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of silane, silane, dichlorosilane, and trichlorosilane;

[0118] Optionally, the feed gas containing silicon source gas has a flow rate of 1 to 30 L / h; specifically, it can be 1 L / h, 3 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 15 L / h, 18 L / h, 20 L / h, 22 L / h, 25 L / h, 28 L / h, 30 L / h, or any value within the above range; further optionally, the flow rate is 10 to 30 L / h.

[0119] Optionally, the raw material gas containing silicon source gas contains an inert gas, with a volume percentage of 0-30%; specifically, it can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, or any value within the above range.

[0120] Optionally, it can be selected from inert gases such as argon and helium.

[0121] Optionally, silicon deposition is performed for 18 to 36 hours; specifically, it can be 18 hours, 20 hours, 24 hours, 28 hours, 32 hours, 36 hours, or any value within the above range.

[0122] Optionally, the temperature can be raised to 400-600°C at a heating rate of 10-20°C / min and held for 0.5-2 hours before silicon deposition.

[0123] In step (S3):

[0124] In an optional embodiment, the carbon coating treatment is performed at a temperature of 500–700°C; specifically, it can be 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, or any value within the above range.

[0125] Optionally, the carbon coating process involves placing the silicon-deposited product in a raw material gas environment containing carbon source gas for vapor phase deposition.

[0126] Optionally, the carbon source gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butene, and 1,3-butadiene; optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0127] Optionally, the feed gas containing carbon source gas has a flow rate of 1 to 20 L / h; specifically, it can be 1 L / h, 2 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 15 L / h, 18 L / h, 20 L / h or any value within the above range; further optionally, the flow rate is 5 to 15 L / h.

[0128] Optionally, the carbon coating treatment is carried out at a temperature of 500 to 700°C, specifically 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C or any value within the above range.

[0129] Optionally, the carbon coating treatment time is 6 to 12 hours; specifically, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value within the above range.

[0130] Optionally, the temperature can be raised to 500-700℃ at a heating rate of 10-20℃ / min and held for 0.5-2h before carbon coating treatment.

[0131] Fourthly, the present invention also provides a negative electrode sheet, comprising the aforementioned negative electrode material.

[0132] Fifthly, the present invention also provides a secondary battery, including the aforementioned negative electrode sheet.

[0133] Example 1

[0134] (S1) Place 7.5 kg of phenolic resin in a carbonization furnace. Under a nitrogen atmosphere, control the oxygen content in the carbonization furnace to be below 20 ppm. Then, heat the resin to 800°C at a heating rate of 15°C / min and hold it at that temperature for 7 hours. After holding, introduce steam at a flow rate of 0.5 kg / h for initial activation for 8 hours. Then, introduce nitrogen and heat the resin to 1100°C at a heating rate of 15°C / min. Then, introduce carbon dioxide at a flow rate of 0.5 kg / h for reactivation for 8 hours. After the material cools down, remove it, and then perform acid washing, pressure filtration, and drying to obtain porous carbon.

[0135] (S2) The porous carbon obtained in step (S1) is placed in a rotary kiln, and the oxygen content in the rotary kiln is controlled to be less than 20 ppm under a nitrogen atmosphere. Then, the temperature is increased to 500℃ at a heating rate of 15℃ / min and held for 1.5h. After that, the temperature is held for 24h under a silane gas atmosphere at a silane gas flow rate of 20L / h.

[0136] (S3) Nitrogen gas is introduced into the rotary kiln again, and the temperature is raised to 600°C at a heating rate of 15°C / min and held for 1.5h. Finally, acetylene gas is introduced at a flow rate of 10L / h and held for 8h. After the material cools down, it is taken out to obtain the silicon-carbon anode material.

[0137] Example 2

[0138] The preparation process is basically the same as in Example 1, except that the flow rate of carbon dioxide in step (S1) is replaced with 0.25 kg / h and the reactivation time is replaced with 6 h.

[0139] Example 3

[0140] The preparation process is basically the same as in Example 1, except that the flow rate of carbon dioxide in step (S1) is replaced with 2 kg / h and the reactivation time is replaced with 10 h.

[0141] Example 4

[0142] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 0.25 kg / h, the initial activation time is replaced with 6 h, the flow rate of carbon dioxide is replaced with 1 kg / h, and the reactivation time is replaced with 10 h.

[0143] Example 5

[0144] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 1 kg / h and the initial activation time is replaced with 10 h; the flow rate of carbon dioxide is replaced with 0.25 kg / h and the reactivation time is replaced with 6 h.

[0145] Example 6

[0146] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 0.25 kg / h and the initial activation time is replaced with 6 h.

[0147] Example 7

[0148] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 1 kg / h and the initial activation time is replaced with 12 h.

[0149] Comparative Example 1

[0150] The preparation process is basically the same as that in Example 1, except that only water vapor is used for initial activation in step (S1), that is, carbon dioxide is not used for secondary activation.

[0151] Comparative Example 2

[0152] The preparation process is basically the same as in Example 1, except that the flow rate of carbon dioxide in step (S1) is replaced with 4 kg / h and the reactivation time is replaced with 16 h.

[0153] The calculated mass ratio of phenolic resin to carbon dioxide is 0.12:1.

[0154] Comparative Example 3

[0155] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 1.5 kg / h, the initial activation time is replaced with 12 h, the flow rate of carbon dioxide is replaced with 1 kg / h, and the reactivation time is replaced with 10 h.

[0156] The calculated mass ratio of phenolic resin to water vapor is 0.42:1.

[0157] The mass ratio of phenolic resin to carbon dioxide is 0.75:1.

[0158] Comparative Example 4

[0159] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 1.5 kg / h and the initial activation time is replaced with 16 h; the flow rate of carbon dioxide is replaced with 0.25 kg / h and the reactivation time is replaced with 6 h.

[0160] The calculated mass ratio of phenolic resin to water vapor is 0.31:1.

[0161] The mass ratio of phenolic resin to carbon dioxide is 5:1.

[0162] Comparative Example 5

[0163] The preparation process is basically the same as in Example 1, except that the flow rate of water vapor in step (S1) is replaced with 0.02 kg / h and the initial activation time is replaced with 4 h.

[0164] The calculated mass ratio of phenolic resin to water vapor is 93.75:1.

[0165] Comparative Example 6

[0166] The preparation process is basically the same as in Example 1, except that in step (S1), only water vapor is used for initial activation, the flow rate of water vapor is replaced with 4 kg / h, the initial activation time is replaced with 24 h, and carbon dioxide is not used for reactivation.

[0167] Comparative Example 7

[0168] The preparation process is basically the same as in Example 1, except that in step (S1), only water vapor is used for initial activation, the flow rate of water vapor is replaced with 6 kg / h, the initial activation time is replaced with 32 h, and carbon dioxide is not used for reactivation.

[0169] The porous carbon prepared in Examples 1-7 and Comparative Examples 1-7 were tested for specific surface area and pore size distribution parameters using a JW-BK300C surface analyzer and a pore size analyzer, and for particle size analysis using a Malvern 3000 laser particle size analyzer. The results are shown in Table 1.

[0170] Table 1

[0171]

[0172]

[0173] Application examples

[0174] The electrochemical performance of the silicon-carbon anode materials prepared in Examples 1-7 and Comparative Examples 1-8 was tested, and the results are shown in Table 2.

[0175] A slurry was prepared by mixing silicon-carbon anode material with carboxymethyl cellulose (CMC), acrylonitrile (LA133), single-walled carbon nanotubes (SWCNT), and carbon black (SP) in a mass ratio of 90:3.5:3.5:0.2:2.8. The slurry was uniformly coated on copper foil and dried to form a negative electrode sheet. The thickness of the electrode sheet was measured. The electrode sheet was then assembled into a coin cell with a negative electrode shell, electrolyte, separator, lithium sheet, nickel foam, and positive electrode shell in an argon atmosphere glove box.

[0176] The 15 sets of batteries were tested using the Blue Battery Testing System. At 25°C, the batteries were first discharged at 0.05C to 0.005V and left to stand for 10 minutes, then discharged at 0.02C to 0.001V and left to stand for 30 minutes. Then, they were charged at 0.1C to 1.5V and left to stand for 10 minutes. The initial charge capacity was recorded, and the initial coulombic efficiency was calculated. Afterward, the button cells were disassembled in an argon atmosphere glove box, the negative electrode was dried, and the thickness of the electrode was measured again to calculate the expansion rate.

[0177] The above 15 groups of batteries were tested using the Blue Battery Testing System in the manner described above. After 500 cycles, the charge and discharge capacity after 500 cycles was recorded, and the capacity retention rate after 500 cycles was calculated.

[0178] Table 2

[0179]

[0180] As can be seen from Table 2, the secondary batteries assembled in each embodiment prepared by the present invention have a low expansion rate and a high initial efficiency and capacity retention rate. Among them, the secondary battery assembled with the negative electrode material prepared in Example 1 has the best overall electrical performance.

[0181] Comparing Example 1 and Comparative Example 1 in Table 2, it can be seen that the secondary battery assembled in Comparative Example 1 has too low initial efficiency and cycle stability, and too high expansion rate. This may be because carbon dioxide gas was not reactivated, the X value in the prepared porous carbon was too low, and the proportion of pores that can be used for lithium-ion transport was too low, resulting in too low initial efficiency, reduced space to alleviate volume change, which is not conducive to alleviating volume expansion, leading to decreased cycle stability and too high expansion rate.

[0182] Comparing Example 1 and Comparative Example 2 in Table 2, it can be seen that the secondary battery assembled in Comparative Example 2 exhibits significant cycle degradation and excessive expansion rate. This may be due to the excessive amount of carbon dioxide used during reactivation, resulting in an excessively high X value in the prepared porous carbon, a high proportion of ineffective pores (pores that silane molecules cannot enter), and an easy deposition of silicon on the surface of the porous carbon, which can easily lead to silicon floating phenomenon.

[0183] Comparing Example 1 and Comparative Example 3 in Table 2, it can be seen that the secondary battery assembled in Comparative Example 3 exhibits significant cycle degradation and excessive expansion rate. This may be due to the excessive amount of activator used in both the primary and secondary activation processes, resulting in a low Y value and a high proportion of X and Z values ​​in the prepared porous carbon, which easily leads to silicon floating phenomenon.

[0184] Comparing Example 1 and Comparative Example 4 in Table 2, it can be seen that the secondary battery assembled in Comparative Example 4 exhibits significant cycle degradation and excessive expansion rate. This may be due to the excessive amount of activator used during the first activation and the insufficient amount of activator used during the second activation, resulting in an excessively high Z value and a large average pore size in the prepared porous carbon. This is not conducive to the effective pores (pores that can accommodate 2 to 3 silane molecules, i.e., pores represented by the Y value) of the confined silicon nanoparticles, which account for a low proportion and easily leads to silicon floating phenomenon.

[0185] Comparing Example 1 and Comparative Example 5 in Table 2, it can be seen that the secondary battery assembled in Comparative Example 5 showed significant deterioration in both initial efficiency and cycle life. This may be due to the insufficient amount of activator used during the first activation, resulting in a low Z value in the prepared porous carbon: the average pore size is too small, which is not conducive to the transport of lithium ions.

[0186] Comparing Example 1 with Comparative Examples 6 and 7 in Table 2, it can be seen that the secondary batteries assembled in Comparative Examples 6 and 7 showed significant deterioration in both initial efficiency and cycle life, and excessively high expansion rates. This may be due to the lack of reactivation with carbon dioxide, and the excessively low amount of activator used in the first activation, resulting in an excessively high average pore size in the prepared porous carbon (greater than the total size of 2-3 silane molecules), exceeding 5 nm. As a result, silicon is prone to homogeneous nucleation growth, i.e., silicon floating phenomenon is likely to occur.

[0187] The above-described embodiments are preferred embodiments, but the scope of protection of the present invention is not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that, Based on porous carbon material, it also includes nano-silicon particles distributed in the pores of the porous carbon material, and an outermost carbon coating layer. The porous carbon material has micropores accounting for ≥95% of the total pore volume, and the micropores have a diameter ≤2nm. The proportion of micropores with a pore size of 0~0.44nm is denoted as X%, where 0.5≤X≤1.5; The percentage of micropores with a pore size of 0.44~1.32nm is denoted as Y%, and 69≤Y≤80; The proportion of micropores with a pore size of 1.32~2nm is denoted as Z%, 19≤Z≤30; Furthermore, X+Y+Z=100.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (a) Dv50 is 7.0 ± 1.0 μm; (b) Specific surface area is 3±2m² 2 / g; (c) Powder resistivity <10Ω-cm at 20MPa; (d) Tap density is 0.9 ± 0.05 g / cm³ 3 .

3. The negative electrode material according to claim 1, characterized in that, The average pore size of the porous carbon material is 1.5 ± 0.3 nm.

4. The negative electrode material according to claim 1, characterized in that, The porous carbon material satisfies at least one of the following conditions: (1) Specific surface area is 1500~2200 m² 2 / g; (2) The pore volume is 0.7~1.3cm 3 / g; (3) The particle size Dv50 is 7.0±1.0μm.

5. A method for preparing a negative electrode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: (S1) The carbon source precursor is subjected to high-temperature carbonization treatment, and then two activation treatments are performed to obtain porous carbon material; The two activation treatments are as follows: the first activation uses water vapor as the activating agent, and the second activation uses carbon dioxide as the activating agent. During the initial activation, the mass ratio of carbon source precursor to water vapor is (0.5~5.0):1; The steam flow rate is 0.05~1 kg / h; the activation temperature is 700~900℃; The reactivation process involves a carbon source precursor to carbon dioxide mass ratio of (0.3~5.0):

1. The flow rate of carbon dioxide is 0.05~2 kg / h; the activation temperature is 900~1200℃; The initial activation time is 6-12 hours. The reactivation process takes 6-12 hours. (S2) Using the porous carbon material as a substrate, silicon deposition is performed to obtain a porous carbon substrate loaded with nano-silicon particles; (S3) Carbon coating treatment is performed to obtain the negative electrode material.

6. The method for preparing the negative electrode material according to claim 5, characterized in that: In step (S1): The carbon source precursor is selected from polymeric carbon sources and / or biomass carbon sources; The high-temperature carbonization treatment is performed at a temperature of 700~900℃. In step (S2): The silicon deposition temperature is 400~600℃; In step (S3): The carbon coating process is carried out at a temperature of 500~700℃.

7. A negative electrode sheet, characterized in that, Includes the negative electrode material as described in any one of claims 1 to 4.

8. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 7.

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