Composite negative electrode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the field of negative electrode materials, and provides a composite negative electrode material, a preparation method thereof and a lithium ion battery, wherein the composite negative electrode material comprises a silicon material and a carbon material; the silicon material comprises main pores and auxiliary pores; and at least part of the carbon material is arranged on the pore wall surface of the main pores, and at least part of the carbon material is filled in the auxiliary pores and connected with the carbon material on the pore wall surface of the main pores. The composite negative electrode material provided by the application can reduce volume expansion and improve cycle stability.

Description

Technical Field

[0001] This application relates to the field of anode material technology, specifically to a composite anode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronics products due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution.

[0003] Silicon, as a negative electrode material for lithium-ion batteries, has a very high theoretical capacity (about 4200 mA h / g) and has great potential in energy storage. Therefore, adding silicon to lithium-ion negative electrode materials is one of the most effective ways to improve the energy density of the cell. However, compared with graphite, silicon has poor conductivity and large volume expansion, which ultimately leads to a much lower cycle stability than graphite.

[0004] Currently, improvements in cycle performance are mainly achieved through silicon material structural design, composite with carbon materials, electrolyte optimization, and binder selection. However, current silicon-carbon composites are prone to inhomogeneity and weak bonding between the silicon and carbon materials. Therefore, improving the contact stability between carbon and silicon materials and suppressing the volume expansion of silicon remains a pressing issue. Summary of the Invention

[0005] In view of this, this application proposes a composite anode material that can reduce volume expansion and improve cycle stability, a method for preparing the same, and a lithium-ion battery.

[0006] A composite negative electrode material, comprising a silicon material, the silicon material including a main channel penetrating the silicon material and auxiliary channels communicating with the main channel; and

[0007] The carbon material, at least a portion of which is located on the surface of the main channel wall, and at least a portion of which is filled in the auxiliary channel and connected to the carbon material on the surface of the main channel wall.

[0008] In some embodiments, the aperture of the main channel is 100nm to 2000nm.

[0009] In some embodiments, the length of the main channel is 100 nm to 15000 nm.

[0010] In some embodiments, the aperture of the auxiliary channel is 10 nm to 100 nm.

[0011] In some embodiments, the length of the auxiliary channel is 10 nm to 1000 nm.

[0012] In some embodiments, the aperture ratio of the main channel to the auxiliary channel is (5-20):1.

[0013] In some embodiments, the length ratio of the main channel to the auxiliary channel is (10-100):1.

[0014] In some embodiments, the silicon material is in the form of primary particles.

[0015] In some embodiments, the auxiliary channel is a blind hole.

[0016] In some embodiments, the pore volume of the main channel accounts for 50% to 80% of the total pore volume of the composite negative electrode material.

[0017] In some embodiments, the pore volume of the auxiliary channel accounts for 20% to 50% of the total pore volume of the composite negative electrode material.

[0018] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon.

[0019] In some embodiments, the carbon material includes amorphous carbon, and the thickness of the amorphous carbon material located on the pore wall surface of the main channel is 10 nm to 200 nm.

[0020] In some embodiments, the carbon material comprises amorphous carbon, and the peak intensity I of the amorphous carbon in the composite anode material is determined by Raman spectroscopy. D With peak intensity I G The ratio of I D / I G >0.8.

[0021] In some embodiments, the carbon material includes amorphous carbon and graphitized carbon, and the thickness of the carbon material located on the pore wall surface of the main channel is 5 nm to 100 nm.

[0022] In some embodiments, the carbon material includes amorphous carbon and graphitized carbon. The peak intensity I of the carbon material in the composite anode material is determined by Raman spectroscopy. D With peak intensity I G The strength ratio is 0.3≤I D / I G ≤0.8.

[0023] In some embodiments, the pore volume of the auxiliary channel is filled to 40% to 100%.

[0024] In some embodiments, the thickness of the carbon material on the surface of the main channel wall accounts for 0.25%-25% of the main channel diameter.

[0025] In some embodiments, the composite anode material further includes a coating carbon layer present on the surface of the silicon material and connected to the carbon material within the main channel.

[0026] In some embodiments, the carbon content in the composite anode material is 5% to 80% by mass.

[0027] In some embodiments, the powder tap density of the composite negative electrode material is 0.2 g / cm³. 3 ~1.2g / cm 3 .

[0028] In some embodiments, the powder compaction density of the composite negative electrode material is 1.2 g / cm³. 3 ~1.8g / cm 3 .

[0029] In some embodiments, the median particle size of the composite anode material is 0.2 μm to 20 μm.

[0030] In some embodiments, the specific surface area of ​​the composite negative electrode material is 1.0 m². 2 / g~50m 2 / g.

[0031] In some embodiments, the oxygen content in the composite negative electrode material is <20% by mass.

[0032] In some embodiments, the porosity of the composite negative electrode material is 20% to 70%.

[0033] A method for preparing a composite anode material includes the following steps:

[0034] A silicon raw material containing silicon material and a pore-forming agent is prepared, and the silicon raw material is etched once to obtain a first precursor with main channels;

[0035] After surface oxidation of the first precursor, a second etching process is performed to obtain a second precursor with main channels and auxiliary channels.

[0036] The second precursor is coated to form a carbon material or polymer on the surface of the pore wall of the main channel, thus obtaining a third precursor; and

[0037] The third precursor is subjected to a pressurized carbon-filling process to fill the auxiliary channels with carbon material, thereby obtaining a composite anode material.

[0038] In some embodiments, the step of preparing the silicon raw material specifically includes: ball milling the silicon raw material containing silicon material and pore-forming agent.

[0039] In some embodiments, the pore-forming agent comprises at least one of an oxide of M, a chloride of M, and an element of M, wherein M comprises at least one of Fe, Cu, Al, B, P, Mg, Ti, and Cr.

[0040] In some embodiments, the purity of the silicon material is >99%.

[0041] In some embodiments, the median particle size of the silicon material is 0.2 μm to 100 μm.

[0042] In some embodiments, the pore-forming agent includes at least one of an oxide of M, a chloride of M, and an element of M, wherein M includes Cu and / or P, and the mass percentage of M in the silicon raw material is 0-2%.

[0043] In some embodiments, the pore-forming agent includes at least one of an oxide of M, a chloride of M, and an element of M, wherein M includes Ti and / or Cr, and the mass percentage of M in the silicon raw material is 0-10%.

[0044] In some embodiments, the pore-forming agent includes at least one of an oxide of M, a chloride of M, and an element of M, wherein M includes Al and / or B, and the mass percentage of M in the silicon raw material is 0-5%.

[0045] In some embodiments, the pore-forming agent includes at least one of an oxide of M, a chloride of M, and an element of M, wherein M includes Fe, and the mass percentage of M in the silicon raw material is 0-3%.

[0046] In some embodiments, the pore-forming agent includes at least one of an oxide of M, a chloride of M, and an element of M, wherein M includes Mg, and the mass percentage of M in the silicon raw material is 0-50%.

[0047] In some embodiments, the step of preparing the silicon raw material specifically includes: ball milling the silicon raw material containing silicon material and pore-forming agent, wherein the median particle size of the silicon raw material obtained by ball milling is 0.2 μm to 20 μm.

[0048] In some embodiments, the step of performing a primary etching process on the silicon material includes: performing a primary etching process on the silicon material using an etching solution containing hydrofluoric acid and an oxidant.

[0049] In some embodiments, the concentration of hydrofluoric acid in the corrosive solution is 1 mol / L to 30 mol / L;

[0050] In some embodiments, the oxidant includes at least one of nitric acid, sulfuric acid, and phosphoric acid.

[0051] In some embodiments, the oxidant includes nitric acid, and the concentration of nitric acid in the corrosive solution is 0.1 mol / L to 10 mol / L.

[0052] In some embodiments, the oxidant includes sulfuric acid, and the concentration of sulfuric acid in the corrosive solution is 0.5 mol / L to 15 mol / L.

[0053] In some embodiments, the oxidant includes phosphoric acid, and the concentration of phosphoric acid in the corrosive solution is 0.05 mol / L to 5 mol / L.

[0054] In some embodiments, the corrosive liquid further includes an auxiliary agent, which includes nitrates, nitrites, sulfates, and phosphates. Preferably, at least one of copper nitrate, sodium nitrate, potassium nitrate, ferric nitrate, ferrous nitrite, sodium nitrite, potassium nitrite, copper sulfate, ferric sulfate, sodium sulfate, potassium sulfate, sodium phosphate, potassium phosphate, ferric phosphate, and copper phosphate is used.

[0055] In some embodiments, the etching solution further includes an auxiliary agent, the concentration of which is 0.01 mol / L to 1 mol / L.

[0056] In some embodiments, the etching process takes 0.5 h to 48 h.

[0057] In some embodiments, the step of performing a primary etching process on the silicon raw material includes: placing the silicon raw material as the anode and graphite or platinum metal as the cathode in an electrolyte containing hydrofluoric acid and ethanol for a primary electrochemical etching process.

[0058] In some embodiments, the electrolyte contains 10% to 49% hydrofluoric acid by mass, and / or the electrolyte contains 1% to 50% ethanol by mass.

[0059] In some embodiments, the stable current of the electrochemical etching process is controlled to be 1 mA / cm. 2 ~20mA / cm 2 The oxidation time of the anode is 5 min to 2 h.

[0060] In some embodiments, after the silicon raw material undergoes one etching process, the method further includes: cleaning and drying the first precursor obtained after the first etching process.

[0061] In some embodiments, the step of surface oxidation of the first precursor includes: heat-treating the first precursor in an oxygen-containing atmosphere to form a silicon dioxide layer on the surface of the first precursor.

[0062] In some embodiments, the heat treatment temperature is 100°C to 600°C, and the heat treatment time is 5 min to 6 h.

[0063] In some embodiments, the oxygen-containing atmosphere includes at least one of air, oxygen and an inert gas mixture, and / or the oxygen content in the oxygen-containing atmosphere is 5% to 50%.

[0064] In some embodiments, the step of surface oxidation of the first precursor includes: placing the first precursor in an acid solution for oxidation treatment, thereby forming a silicon dioxide layer on the surface of the first precursor.

[0065] In some embodiments, the acid solution includes at least one selected from nitric acid, sulfuric acid, perchloric acid, permanganic acid, hypochlorous acid, and nitrous acid.

[0066] In some embodiments, the concentration of the acid solution is 1 mol / L to 18 mol / L, and the acid washing time is 1 h to 48 h.

[0067] In some embodiments, the oxygen content of the first precursor after oxidation treatment is 5% to 20% by mass.

[0068] In some embodiments, the first precursor is subjected to surface oxidation treatment to form a silicon dioxide layer on the surface of the first precursor, the thickness of the silicon dioxide layer being 20 nm to 500 nm.

[0069] In some embodiments, the secondary etching process includes: placing the surface-oxidized product in an etching solution containing a metal salt solution for secondary etching to obtain a second precursor having a main channel and an auxiliary channel.

[0070] In some embodiments, the metal salt in the metal salt solution includes at least one of nitrates, nitrites, and halide salts.

[0071] In some embodiments, the metal element in the metal salt includes at least one selected from Ag, Pt, Cu, Fe, and Au.

[0072] In some embodiments, the concentration of the metal salt solution is 0.01 mol / L to 1 mol / L.

[0073] In some embodiments, the temperature of the secondary etching process is 10°C to 100°C, and the etching time is 0.5h to 12h.

[0074] In some embodiments, the etching solution includes hydrogen peroxide, ethanol, and hydrofluoric acid, wherein the concentration of hydrogen peroxide in the etching solution is 0.1 mol / L to 5 mol / L, the concentration of hydrofluoric acid in the etching solution is 1 mol / L to 10 mol / L, and the mass content of ethanol in the etching solution is 1% to 15%.

[0075] In some embodiments, the step of coating the second precursor includes: heating the second precursor under a protective atmosphere, then introducing a carbon source gas for carbon coating treatment to obtain a third precursor.

[0076] In some implementations, the heating rate is 1°C / min to 20°C / min.

[0077] In some embodiments, the heating temperature is 600℃~1000℃, and the holding time is 1h~48h.

[0078] In some embodiments, the carbon source gas includes at least one selected from acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0079] In some embodiments, the concentration of the carbon source gas is 0.1 L / min to 10 L / min.

[0080] In some embodiments, the step of coating the second precursor includes: dispersing the second precursor in a coating liquid containing a polymer and spray drying to obtain a third precursor.

[0081] In some embodiments, the solid content of the second precursor in the coating liquid is 5% to 50%.

[0082] In some embodiments, the coating liquid further includes a polar solvent.

[0083] In some embodiments, the mass ratio of the second precursor to the polymer is 10:(0.1 to 5).

[0084] In some embodiments, the spray drying temperature is 60°C to 200°C.

[0085] In some embodiments, the polymer includes at least one selected from polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylacetylene, polyaniline, polyacetylene, and tannic acid.

[0086] In some embodiments, the step of pressurizing and carbon-filling the third precursor includes: mixing the organic carbon source with the third precursor under a protective atmosphere and then placing it under pressure for stepwise heating heat treatment, so that the liquefied organic carbon source fills the auxiliary channels of the third precursor under capillary action.

[0087] In some embodiments, the organic carbon source includes at least one of humic acid, asphalt, resin, amino acid, tar, fatty acid, cellulose and starch, and / or the mass ratio of the organic carbon source to the third precursor is (0.1 to 6):10.

[0088] In some embodiments, the pressure of the pressurized environment is 0.1 MPa to 2 MPa;

[0089] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0090] In some embodiments, the step of pressurizing and carbon-filling the third precursor includes: mixing the organic carbon source with the third precursor under a protective atmosphere and placing it under pressure, first heating it to 150°C to 500°C and holding it at that temperature for 0.5h to 24h, and then continuing to heat it to 600°C to 1100°C and holding it at that temperature for 1h to 12h.

[0091] A lithium-ion battery, the lithium-ion battery comprising the composite negative electrode material described above or a negative electrode material prepared by the method for preparing the composite negative electrode material.

[0092] The technical solution of this application has at least the following beneficial effects:

[0093] First, the composite anode material provided in this application has a main channel and an auxiliary channel within the silicon material. The main channel penetrates the silicon material and is connected to the auxiliary channel. On the one hand, the porous silicon material can improve lithium storage performance while mitigating the volume expansion of the silicon material and improving structural stability. On the other hand, the carbon material located on the surface of the pore wall of the main channel can mitigate the volume expansion of the silicon material and improve its conductivity. The carbon material in the claw-shaped extended auxiliary channel can enhance the bonding strength with the silicon material, ensuring that the silicon material can maintain stable electrical contact with the carbon material even when it expands and contracts in volume. This allows the anode material to have excellent cycle stability and a low expansion rate.

[0094] Secondly, the method for preparing the negative electrode material provided in this application involves etching silicon material once to form a through-hole main channel, followed by a second etching. Since the silicon material surface is oxidized to form a silicon dioxide passivation layer, the second etching mainly occurs inside the silicon material particles, resulting in a second precursor with main and auxiliary channels. The auxiliary channels extend into the silicon material along the surface of the main channel wall, which can effectively suppress the volume expansion of the silicon material. Then, carbon material is coated on the pore wall of the main channel of the silicon material, which can alleviate the volume expansion of the silicon material and improve the conductivity of the silicon material. Furthermore, under the capillary effect and pressure difference of the auxiliary channels, the carbon material can fill into the auxiliary channels. The carbon material in the claw-shaped extended auxiliary channels can enhance the bonding strength with the silicon material, ensuring that the silicon material can still maintain stable electrical contact with the carbon material when the volume expands and contracts, so that the negative electrode material can have excellent cycle stability and low expansion rate.

[0095] The method for preparing composite anode materials provided in this application not only improves the electrochemical performance of the materials and is suitable for large-scale production, but also effectively improves the rate performance and cycle stability of lithium batteries. Attached Figure Description

[0096] Figure 1a and Figure 1b These are schematic diagrams of the composite negative electrode material provided in this embodiment;

[0097] Figure 2 This is a schematic diagram of the preparation method of the composite negative electrode material provided in this embodiment;

[0098] Figure 3 Scanning electron microscope (SEM) image of the composite anode material provided in Example 1;

[0099] Figure 4 Raman diagram of the composite negative electrode material provided in Example 1;

[0100] Figure 5 The cycling performance curve of the composite negative electrode material provided in Example 1 is shown. Detailed Implementation

[0101] The following are preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention.

[0102] Currently, in lithium-ion batteries, the anode material is one of the key materials affecting its charge-discharge performance. To improve battery energy density, the research and development of high-capacity anode materials is becoming increasingly mature. However, these anode materials experience significant volume expansion during the lithium alloying process, and they can pulverize and fall off the current collector during charge-discharge, causing a loss of electrical contact between the anode material and the current collector. This results in deteriorated electrochemical performance, capacity decay, and decreased cycle stability, hindering commercial application. To improve the cycle stability of lithium-ion batteries, this application provides a composite anode material with low expansion and good stability.

[0103] Specifically, this application provides a composite anode material, such as Figure 1a and Figure 1b As shown, the composite anode material includes silicon material;

[0104] The silicon material includes a main channel 10 penetrating the silicon material and an auxiliary channel 11 communicating with the main channel 10; and

[0105] Carbon material 20, at least a portion of which is located on the surface of the main channel 10, and at least a portion of which is filled in the auxiliary channel 11 and connected to the carbon material on the surface of the main channel.

[0106] The silicon material in this composite anode material has a main channel and an auxiliary channel. The main channel runs through the silicon material and is connected to the auxiliary channel. On the one hand, the porous silicon material can improve lithium storage performance while mitigating the volume expansion of the silicon material and improving structural stability. On the other hand, the carbon material located on the surface of the pore wall of the main channel can mitigate the volume expansion of the silicon material and improve its conductivity. The carbon material in the claw-shaped auxiliary channel can enhance the bonding strength with the silicon material, ensuring that the silicon material can maintain stable electrical contact with the carbon material even when it expands and contracts in volume. This allows the anode material to have excellent cycle stability and a low expansion rate.

[0107] It should be noted that the main channel and the auxiliary channel can extend in a straight line or in a winding manner.

[0108] The carbon material filling the auxiliary channels is connected to the carbon material on the surface of the main channel walls. Specifically, when the carbon material includes amorphous carbon and graphitized carbon, a clear interface exists between the carbon materials in the main and auxiliary channels; when the carbon material contains only amorphous carbon, there is no clear interface between the carbon materials in the main and auxiliary channels. In practical applications, the presence of interfaces should be avoided, as this is more conducive to enhancing the bonding strength between the carbon materials in the main and auxiliary channels, helping the carbon material to firmly hold the silicon material, and better mitigating volume expansion.

[0109] In some embodiments, the main channel is a through-hole with a diameter of 100nm to 2000nm; the diameter refers to the diameter of the hole, which can be 100nm, 150nm, 200nm, 500nm, 700nm, 1000nm, 1500nm, or 2000nm, and is not limited here. The main channel helps to alleviate stress concentration caused by the volume expansion of silicon material, prevents silicon material structure pulverization, and improves the structural stability of the anode material.

[0110] In some embodiments, the length of the main channel is 100nm to 15000nm, specifically it can be 100nm, 500nm, 1000nm, 2000nm, 5000nm, 10000nm or 15000nm, etc., and is not limited here.

[0111] In some embodiments, the auxiliary channel is a blind via with a diameter of 10 nm to 100 nm. The diameter refers to the pore size, which can be 10 nm, 30 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, and is not limited here. The auxiliary channel helps increase the number of active sites in the silicon material, improves the electron transport rate, and enhances the rate capability of the anode material. Furthermore, the combination of the main channel and the auxiliary channel can form a claw-like structure, resulting in a strong bond between the silicon-based material and the carbon material, making it less prone to detachment.

[0112] In some embodiments, the length of the auxiliary channel is 10nm to 1000nm, specifically it can be 10nm, 50nm, 100nm, 200nm, 300nm, 500nm, 700nm, 800nm ​​or 100nm, etc., and is not limited here.

[0113] In some embodiments, the diameter ratio of the main channel to the auxiliary channel is (5-20):1, specifically it can be 5:1, 10:1, 12:1, 15:1, 18:1 or 20:1, etc., and is not limited here. The length ratio of the main channel to the auxiliary channel is (10-100):1, specifically it can be 10:1, 20:1, 30:1, 50:1, 70:1, 80:1 or 100:1, etc., and is not limited here.

[0114] Understandably, the diameter and length of the main channel are both greater than those of the auxiliary channel. The auxiliary channel extends along the wall of the larger main channel, facilitating the penetration of carbon material into the silicon material through capillary action. This allows the carbon material to bond tightly with the silicon, maintaining stable electrical contact during silicon expansion and contraction. A diameter ratio of (5–20):1 between the main and auxiliary channels ensures the main channel effectively mitigates volume expansion while maintaining stability after lithium insertion. This results in excellent stability of the carbon material in the auxiliary channel, firmly "holding" the silicon and preventing pulverization. If the ratio is less than 5:1, the main channel diameter is too small, and the reserved space is insufficient to adequately mitigate the volume expansion after complete lithium insertion. If the ratio is greater than 20:1, the carbon content in the auxiliary channel is low, and its strength is reduced, decreasing the volume expansion mitigation effect. Furthermore, the anode material is prone to structural damage as silicon expands.

[0115] In some implementations, the silicon material is in the form of primary particles.

[0116] In some embodiments, the volume of the main channel accounts for 50% to 80% of the total pore volume of the composite negative electrode material. Specifically, it can be 50%, 55%, 60%, 65%, 70%, 75%, or 80%, etc., and is not limited here.

[0117] In some embodiments, the volume of the auxiliary channel accounts for 50% to 80% of the total pore volume of the composite negative electrode material, specifically 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc., and is not limited here.

[0118] In some embodiments, the carbon material includes at least one of amorphous carbon and graphitized carbon.

[0119] In some embodiments, the carbon material includes amorphous carbon, and the thickness of the amorphous carbon material located on the pore wall surface of the main channel is 10nm to 200nm, specifically 10nm, 20nm, 40nm, 50nm, 80nm, 100nm, 150nm, 180nm or 200nm, etc., which are not limited here.

[0120] Raman spectroscopy analysis of the composite anode material revealed that amorphous carbon exhibits carbon characteristic peaks D and G, with the peak intensity I of peak D being... D The peak intensity I of the carbon characteristic peak G G Strength ratio of I D / I G >0.8; specifically, it can be 0.85, 0.9, 0.95, or 0.99, etc.

[0121] In some embodiments, the carbon material includes amorphous carbon and graphitized carbon, and the thickness of the carbon material located on the pore wall surface of the main channel is 5nm to 100nm; specifically, it can be 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 70nm, 80nm or 100nm, etc., without limitation. It is understood that if the thickness of the graphitized carbon is too small, the material conductivity will decrease and the bonding with the silicon material will not be strong. If the thickness is too large, it will prevent the lithium-ion battery from entering and affect the material capacity.

[0122] In some embodiments, the thickness of the carbon material on the surface of the main channel wall accounts for 0.25%-25% of the main channel diameter, specifically 0.25%, 0.5%, 1%, 5%, 10%, 15%, 20%, or 25%, etc., and is not limited here. This ensures sufficient conductivity and bonding strength while also leaving enough space to mitigate expansion.

[0123] Raman spectroscopy was used to determine the composite anode material. The carbon material exhibited carbon characteristic peaks D and G, and the peak intensity I of carbon characteristic peak D was... D The peak intensity I of the carbon characteristic peak G G The strength ratio is 0.3≤I D / I G ≤0.8; specifically, it can be 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8, etc.

[0124] In some embodiments, a portion of the carbon material is filled in the auxiliary channel and connected to the carbon material in the main channel. The filling rate of the pore volume of the auxiliary channel is 40% to 100%, specifically 40%, 45%, 50%, 60%, 70%, 80%, 90%, or 100%, etc., which is not limited here.

[0125] In some embodiments, the composite anode material further includes a coated carbon layer present on the surface of the silicon material and connected to the carbon material within the main channel.

[0126] In some embodiments, the porosity of the composite negative electrode material is 20% to 70%, specifically 20%, 35%, 40%, 42%, 45%, 50%, 58%, 62%, 68%, 70%, etc., and is not limited here.

[0127] In some embodiments, the tap density of the composite negative electrode material is 0.2 g / cm³. 3 ~1.2g / cm 3 For example, 0.2g / cm 3 0.3g / cm 3 0.5g / cm 3 0.6g / cm 30.7g / cm 3 0.8g / cm 3 1.0g / cm 3 1.2g / cm 3 Etc. Preferably 0.5 g / cm³ 3 ~0.8g / cm 3 .

[0128] In some embodiments, the powder compaction density of the composite negative electrode material is 1.2 g / cm³. 3 ~1.8g / cm 3 For example, 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 Or 1.8g / cm 3 The preferred value is 1.45 g / cm³. 3 ~1.75g / cm 3 .

[0129] In some embodiments, the median particle size of the composite anode material is 0.2 μm to 20 μm. Optionally, the median particle size of the composite anode material can specifically be 0.2 μm, 0.5 μm, 1 μm, 3 μm, 4 μm, 5 μm, 7 μm, 10 μm, 13 μm, 15 μm, or 20 μm, etc., and is not limited thereto. The median particle size of the composite anode material is preferably 0.5 μm to 10 μm, and more preferably 1 μm to 5 μm.

[0130] The specific surface area ratio of the composite negative electrode material is 1m² 2 / g~50m 2 / g. Optionally, the specific surface area ratio of the composite negative electrode material can be 1m². 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g or 50m 2 / g, etc., are not limited here; understandably, the smaller the specific surface area, the better. An excessively large specific surface area can easily lead to the formation of an SEI film, consuming too much irreversible lithium salt and reducing the initial efficiency of the battery. Considering the cost of the preparation process, the specific surface area is controlled at 2m². 2 / g~15m2 / g.

[0131] In some embodiments, the carbon content in the composite anode material is 5% to 80% by mass. Specifically, it can be 5%, 8%, 10%, 15%, 20%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, or 80%, etc., and is not limited here. It should be noted that the carbon in the composite anode material is derived from carbon materials.

[0132] In some embodiments, the mass content of oxygen in the composite negative electrode material is less than 20%. Specifically, it can be 5%, 6%, 8%, 10%, 12%, 15%, 18%, 19%, etc., and is not limited here.

[0133] This application also provides a method for preparing a composite anode material, such as... Figure 2 As shown, the method includes the following steps S100 to S400:

[0134] S100. Prepare a silicon raw material containing silicon material and a pore-forming agent, and perform an etching process on the silicon raw material to obtain a first precursor with main channels.

[0135] S200. After surface oxidation treatment of the first precursor, a second etching treatment is performed to obtain a second precursor with main channels and auxiliary channels.

[0136] S300, the second precursor is coated to form carbon material or polymer on the surface of the pore wall of the main channel, thus obtaining the third precursor.

[0137] S400. The third precursor is subjected to a pressurized carbon filling process to fill the auxiliary channel with carbon material, thereby obtaining a composite negative electrode material.

[0138] The composite negative electrode material prepared by the above method includes: a silicon material, the silicon material including a main channel penetrating the silicon material and an auxiliary channel communicating with the main channel; and a carbon material, at least a portion of the carbon material being located on the surface of the pore wall of the main channel, and at least a portion of the carbon material filling the auxiliary channel and being connected to the carbon material on the surface of the pore wall of the main channel.

[0139] In this scheme, silicon material is etched once to form a through-hole main channel, and then etched a second time. Since the silicon material surface is oxidized to form a silicon dioxide passivation layer, the second etching mainly occurs inside the silicon material particles, resulting in a second precursor with main and auxiliary channels. The auxiliary channels extend into the silicon material along the surface of the main channel, which can effectively suppress the volume expansion of the silicon material. Then, carbon material is coated on the pore wall of the main channel of the silicon material to alleviate the volume expansion of the silicon material and improve the conductivity of the silicon material. Furthermore, under the action of capillary effect and pressure difference of the auxiliary channel, the carbon material can fill into the auxiliary channel. The carbon material in the claw-shaped extended auxiliary channel can enhance the bonding strength with the silicon material, which can ensure that the silicon material can still maintain stable electrical contact with the carbon material when the silicon material expands and contracts, so that the negative electrode material can have excellent cycle stability and low expansion rate.

[0140] The following is a detailed introduction to this plan:

[0141] S100. Prepare a silicon raw material containing silicon material and a pore-forming agent, and perform an etching process on the silicon raw material to obtain a first precursor with main channels.

[0142] In some embodiments, the step of preparing the silicon raw material specifically includes: ball milling the silicon raw material containing silicon material and a pore-forming agent. In some specific embodiments, the silicon material can be placed in a ball milling apparatus with a protective gas atmosphere, and after adding the pore-forming agent, suitable milling beads can be added. The mixture can then be ball-milled for a certain period of time at a certain milling speed. In other embodiments, the silicon material can also be doped with the pore-forming agent through a high-temperature heat treatment method.

[0143] In some embodiments, the median particle size of the silicon raw material obtained by ball milling is 0.2 μm to 20 μm, specifically it can be 0.2 μm, 1 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, etc., and is not limited thereto. Preferably, the median particle size of the silicon raw material obtained by ball milling is 0.5 μm to 10 μm, more preferably, the median particle size of the silicon raw material obtained by ball milling is 1 μm to 5 μm.

[0144] In some embodiments, the pore-forming agent comprises at least one of an oxide of M, a chloride of M, and an element of M, wherein M comprises at least one of Fe, Cu, Al, B, P, Mg, Ti, and Cr.

[0145] When M includes Cu and / or P, the mass percentage of M in the silicon raw material is 0-2%, excluding zero. When M includes Ti and / or Cr, the mass percentage of M in the silicon raw material is 0-10%, excluding zero. When M includes Al and / or B, the mass percentage of M in the silicon raw material is 0-5%, excluding zero. When M includes Fe, the mass percentage of M in the silicon raw material is 0-3%, excluding zero. When M includes Mg, the mass percentage of M in the silicon raw material is 0-50%, excluding zero.

[0146] In some embodiments, the purity of the silicon material is >99%.

[0147] In some embodiments, the silicon material includes at least one of crystalline silicon and amorphous silicon.

[0148] In some embodiments, the median particle size of the silicon material is 0.2 μm to 100 μm, specifically it can be 0.2 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 50 μm or 100 μm, etc., and is not limited here.

[0149] In some embodiments, in S100, the step of performing a primary etching process on the silicon material includes: performing a primary etching process on the silicon material using an etching solution containing hydrofluoric acid and an oxidant.

[0150] In some embodiments, the concentration of hydrofluoric acid in the corrosive solution is 1 mol / L to 30 mol / L; specifically, it can be 1 mol / L, 5 mol / L, 10 mol / L, 15 mol / L, 20 mol / L, 25 mol / L, or 30 mol / L, etc., and is not limited here.

[0151] In some embodiments, the oxidant includes at least one of nitric acid, sulfuric acid, and phosphoric acid;

[0152] In some embodiments, the oxidant includes nitric acid, and the concentration of nitric acid in the corrosive solution is 0.1 mol / L to 10 mol / L, specifically 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 5 mol / L, 7 mol / L or 10 mol / L, etc., which is not limited here.

[0153] In some embodiments, the oxidant includes sulfuric acid, and the concentration of sulfuric acid in the corrosive solution is 0.5 mol / L to 15 mol / L, specifically 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 5 mol / L, 7 mol / L, 10 mol / L, 12 mol / L or 15 mol / L, etc., which are not limited here.

[0154] In some embodiments, the oxidant includes phosphoric acid, and the concentration of phosphoric acid in the corrosive solution is 0.05 mol / L to 5 mol / L, specifically 0.05 mol / L, 0.5 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3 mol / L or 5 mol / L, etc., which are not limited here.

[0155] In some embodiments, the corrosive liquid further includes an auxiliary agent, which includes nitrates, nitrites, sulfates, and phosphates. Preferably, at least one of copper nitrate, sodium nitrate, potassium nitrate, ferric nitrate, ferrous nitrite, sodium nitrite, potassium nitrite, copper sulfate, ferric sulfate, sodium sulfate, potassium sulfate, sodium phosphate, potassium phosphate, ferric phosphate, and copper phosphate is used.

[0156] In some embodiments, the etching solution further includes an auxiliary agent, the concentration of which is 0.01 mol / L to 1 mol / L, specifically 0.01 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L, etc., and is not limited here.

[0157] In some embodiments, the etching process takes 0.5h to 48h, specifically 0.5h, 1h, 3h, 6h, 12h, 24h, 36h or 48h, etc., and is not limited here.

[0158] In some embodiments, in S100, the step of performing a primary etching process on the silicon raw material includes: placing the silicon raw material as the anode and graphite or platinum metal as the cathode in an electrolyte containing hydrofluoric acid and ethanol for a primary electrochemical etching process.

[0159] In some embodiments, the electrolyte contains 10% to 49% hydrofluoric acid by mass, and / or the electrolyte contains 1% to 50% ethanol by mass.

[0160] In some embodiments, the stable current of the electrochemical etching process is controlled to be 1 mA / cm. 2 ~20mA / cm 2 The oxidation time of the anode is 5 min to 2 h.

[0161] In some embodiments, after the silicon raw material undergoes one etching process, the method further includes: cleaning and drying the first precursor obtained after the first etching process.

[0162] In some implementations, the solvent used for cleaning can be water, and the drying method can be vacuum drying, hot air drying, etc.

[0163] S200. After surface oxidation treatment of the first precursor, a second etching treatment is performed to obtain a second precursor with main channels and auxiliary channels.

[0164] In some embodiments, the step of surface oxidation of the first precursor includes: heat-treating the first precursor in an oxygen-containing atmosphere to form a silicon dioxide layer on the surface of the first precursor.

[0165] In some embodiments, the heat treatment temperature is 100℃ to 600℃, and the heat treatment time is 5 minutes to 6 hours; specifically, the heat treatment temperature can be 100℃, 150℃, 200℃, 250℃, 300℃, 450℃, 550℃, or 600℃. The heat treatment time can be 5 minutes, 0.2 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, and is not limited thereto.

[0166] In some embodiments, the oxygen-containing atmosphere includes at least one of air, oxygen and an inert gas mixture, and / or the oxygen content in the oxygen-containing atmosphere is 5% to 50%.

[0167] In some embodiments, the step of surface oxidation of the first precursor includes: placing the first precursor in an acid solution for oxidation treatment, thereby forming a silicon dioxide layer on the surface of the first precursor.

[0168] In some embodiments, the acid solution includes at least one selected from nitric acid, sulfuric acid, perchloric acid, permanganic acid, hypochlorous acid, and nitrous acid.

[0169] In some embodiments, the concentration of the acid solution is 1 mol / L to 18 mol / L, specifically 1 mol / L, 5 mol / L, 8 mol / L, 10 mol / L, 13 mol / L, 15 mol / L or 18 mol / L, etc., and is not limited here.

[0170] In some embodiments, the pickling treatment time is 1 hour to 48 hours; specifically, it can be 1 hour, 3 hours, 6 hours, 9 hours, 12 hours, 15 hours, 18 hours, 24 hours or 48 hours, and is not limited here.

[0171] In some embodiments, the mass content of oxygen in the first precursor after oxidation treatment is 5% to 20%, specifically 5%, 8%, 10%, 12%, 15%, 18% or 20%, etc., which are not limited here.

[0172] In some embodiments, the thickness of the silicon dioxide layer is 20nm to 500nm, specifically 20nm, 30nm, 50nm, 80nm, 100nm, 200nm, 300nm, 400nm, or 500nm, etc., and is not limited thereto. It is understood that forming a silicon dioxide layer on the surface of the first precursor can protect the surface of the first precursor during subsequent secondary etching, ensuring that the secondary etching occurs inside the silicon material, rather than on the surface.

[0173] In some embodiments, the secondary etching process includes: placing the surface-oxidized product in an etching solution containing a metal salt solution for secondary etching to obtain a second precursor having a main channel and an auxiliary channel.

[0174] In some embodiments, the metal salt in the metal salt solution includes at least one of nitrates, nitrites, and halide salts.

[0175] In some embodiments, the metal element in the metal salt includes at least one selected from Ag, Pt, Cu, Fe, and Au.

[0176] In some embodiments, the concentration of the metal salt solution is 0.01 mol / L to 1 mol / L, specifically 0.01 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, or 1 mol / L, etc., and is not limited here.

[0177] In some embodiments, the temperature of the secondary etching process is 10°C to 100°C, and the etching time is 0.5h to 12h.

[0178] In some embodiments, the etching solution includes hydrogen peroxide, ethanol, and hydrofluoric acid, wherein the concentration of hydrogen peroxide in the etching solution is 0.1 mol / L to 5 mol / L, the concentration of hydrofluoric acid in the etching solution is 1 mol / L to 10 mol / L, and the mass content of ethanol in the etching solution is 1% to 15%.

[0179] S300, the second precursor is coated to form carbon material or polymer on the surface of the pore wall of the main channel, thus obtaining the third precursor.

[0180] In some embodiments, the step of coating the second precursor includes: heating the second precursor under a protective atmosphere, then introducing a carbon source gas for carbon coating treatment to obtain a third precursor.

[0181] In some embodiments, the heating rate is 1℃ / min to 20℃ / min, specifically 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, 15℃ / min or 20℃ / min, etc., and is not limited here.

[0182] In some embodiments, the heating temperature is 600℃~1000℃, and the holding time is 1h~48h; the heating temperature can specifically be 600℃, 700℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, etc., and is not limited here. The holding time can specifically be 1h, 3h, 6h, 12h, 24h, 36h or 48h, etc., and is not limited here.

[0183] In some embodiments, the carbon source gas includes at least one selected from acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0184] In some embodiments, the concentration of the carbon source gas is 0.1 L / min to 10 L / min; specifically, it can be 0.1 L / min, 0.4 L / min, 0.6 L / min, 0.8 L / min, 1.0 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 9 L / min or 10 L / min, etc., and is not limited here. A certain concentration of carbon source gas is introduced as the gas source for the carbon material. After being kept at a certain temperature for a certain period of time, the carbon material is deposited on the surface of the silicon material. Due to the large pore size of the main channel of the silicon material, the pressure difference between the outer surface of the silicon material and the main channel is small, allowing the carbon source gas to penetrate into the main channel and deposit on the pore wall. During the deposition process, in addition to generating amorphous carbon, the carbon source may also generate some graphitized carbon. This is related to factors such as deposition temperature, the carbon source itself, and concentration. Generally speaking, the higher the deposition temperature, the more graphitized carbon is generated. However, it is necessary to control the amount of graphitized carbon generated, because too much graphitized carbon will prevent lithium ion insertion and extraction, affecting the capacity of the material.

[0185] In some embodiments, the step of coating the second precursor includes: dispersing the second precursor in a coating solution containing a polymer, and spray drying to obtain a third precursor. Understandably, a polymer layer is formed on the outer surface of the silicon material and on the pore walls of the main channels during this process.

[0186] In some embodiments, the solid content of the second precursor in the coating liquid is 5% to 50%, specifically it can be 5%, 10%, 15%, 20%, 25%, 30%, 35% or 50%, etc., and is not limited here.

[0187] In some embodiments, the polymer includes at least one selected from polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylacetylene, polyaniline, polyacetylene, and tannic acid.

[0188] In some embodiments, the coating solution further includes a polar solvent, including at least one of water, anhydrous ethanol, and methanol.

[0189] In some embodiments, the mass ratio of the second precursor to the polymer is 10:(0.1 to 5), specifically 10:0.1, 10:0.5, 10:1, 10:2, 10:3, 10:4 or 10:5, etc., which are not limited here.

[0190] In some embodiments, the spray drying temperature is 60℃ to 200℃, specifically 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, or 200℃, etc., and is not limited thereto. By controlling the drying temperature, the adhesion between the polymer layer and the silicon material can be improved.

[0191] S400, the third precursor is subjected to pressurized carbon filling treatment so that carbon material fills the auxiliary channel to obtain a composite negative electrode material.

[0192] In some embodiments, under a protective atmosphere, the organic carbon source is mixed with the third precursor and then subjected to a pressurized environment and a stepped heating heat treatment, so that the liquefied organic carbon source fills the auxiliary channels of the third precursor under capillary action and pressure difference.

[0193] In some embodiments, under a protective atmosphere, the organic carbon source is mixed with the third precursor and placed under pressure. The mixture is first heated to 150°C to 500°C and held for 0.5h to 24h, and then heated to 600°C to 1100°C and held for 1h to 12h.

[0194] Through a stepped heating heat treatment, the temperature is maintained at 150℃ to 500℃ for 0.5h to 24h. Specific temperatures can be 150℃, 200℃, 300℃, 400℃, 450℃, or 500℃, and the holding time can be 0.5h, 2h, 3h, 5h, 6h, 12h, 18h, or 24h, etc., without limitation. This first-stage heating treatment facilitates the formation of a liquid organic carbon source. Under the pressure difference between the auxiliary channels and the surface of the silicon material, as well as the capillary action of the auxiliary channels, the liquid organic carbon source flows into the auxiliary channels. Since the main channels are through-holes, only a small amount of organic carbon source remains on the surface of the main channels. Continue heating to 600℃~1100℃ and hold for 1h~12h. Specific temperatures can be 600℃, 700℃, 800℃, 900℃, 1050℃, or 1100℃, and holding times can be 1h, 2h, 3h, 5h, 6h, 8h, 10h, or 12h, etc., without limitation. This process allows for the complete carbonization of organic carbon sources or polymers, forming carbon materials. During carbonization, in addition to amorphous carbon, some graphitized carbon may also be generated. Generally speaking, the higher the deposition temperature, the more graphitized carbon is generated. However, the amount of graphitized carbon generated must be controlled, because excessive graphitized carbon will inhibit lithium-ion insertion / extraction, affecting the capacity of the anode material.

[0195] In some embodiments, the organic carbon source includes at least one of humic acid, bitumen, resin, amino acids, tar, fatty acids, cellulose, and starch.

[0196] In some embodiments, the mass ratio of the organic carbon source to the third precursor is (0.1–6):10; specifically, it can be 0.1:10, 0.5:10, 1:10, 2:10, 3:10, 4:10, 5:10, 5.9:10, or 6:10, etc., and is not limited here. By controlling the mass ratio of the organic carbon source to the third precursor, it is possible to ensure that an appropriate amount of organic carbon source fills the auxiliary channels of the silicon material. If the mass ratio is too large, it may block the main channels of the silicon material.

[0197] In some embodiments, the pressure of the pressurized environment is 0.1 MPa to 2 MPa; specifically, it can be 0.1 MPa, 0.3 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.5 MPa or 2.0 MPa, etc., and is not limited here.

[0198] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0199] This invention also provides a lithium-ion battery, using the composite negative electrode material provided in the above embodiments of this invention or the negative electrode material prepared by the method for preparing the composite negative electrode material provided in the above embodiments of this invention. The lithium-ion battery provided by this invention has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion.

[0200] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0201] Example 1

[0202] A method for preparing a composite anode material includes the following steps:

[0203] (1) Silicon with a median particle size of 2.5 μm was mixed with copper chloride and iron chloride at a mass ratio of 10:1:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain copper and iron doped silicon raw material.

[0204] (2) 100g of silicon raw material was added to the etching solution for etching. The etching solution included 3mol / L hydrofluoric acid solution and 2mol / L nitric acid solution. After mechanical stirring for 1h, 0.5mol / L sodium nitrite was added. After stirring for another 2h, the first precursor was obtained by filtration, washing with water and drying.

[0205] (3) Take 50g of the first precursor and put it into an atmosphere furnace. Heat it to 500℃ at a heating rate of 3℃ / min. Introduce 1.5L / min of argon and 0.1L / min of oxygen as a mixed gas to oxidize the first precursor. The treatment time is 1h. After cooling, take it out to obtain the oxidized first precursor.

[0206] (4) Take out 100g of the oxidized first precursor and put it into a corrosion solution containing metal salt solution for secondary etching treatment. The corrosion solution includes 0.2mol / L copper nitrate solution, 0.2mol / L hydrogen peroxide solution, 4mol / L hydrofluoric acid solution and 5% ethanol. Under 40℃, mechanically stir for 3h, and after cleaning and drying, the second precursor is obtained.

[0207] (5) The second precursor is placed in a rotary atmosphere furnace and heated to 900°C at a heating rate of 3°C / min under the protection of argon atmosphere. Then, acetylene gas is introduced at a rate of 1.5L / min so that the volume ratio of argon to acetylene in the rotary atmosphere furnace is 9:1. After holding at the temperature for 3 hours, the third precursor is obtained by cooling.

[0208] (6) Mix 100g of the third precursor and asphalt at a mass ratio of 10:0.5, place them in a stainless steel reaction vessel, introduce argon gas, and pressurize to a pressure of 1 MPa. Heat the mixture to 300°C at a heating rate of 10°C / min, hold for 2 hours, then heat it to 950°C at a heating rate of 3°C / min, hold for 3 hours, and finally cool to obtain the composite anode material.

[0209] Figure 3 These are scanning electron microscope images of the composite negative electrode material in this embodiment; such as... Figure 3 As shown, the resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0210] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0211] Figure 4 This is the XRD pattern of the silicon-carbon composite anode material in this embodiment; from Figure 4 The XRD pattern shows that the three strong peaks at 28.4°, 47.3° and 56.1° correspond to the three strong peaks of silicon (JCPDS No. 27-1402), indicating that there are basically no impurities.

[0212] Figure 5 In this embodiment, the cycling performance curve of the silicon-carbon composite anode material shows that after 200 cycles at a current of 1000 mA / g, it still has a capacity of 1378 mAh / g, with a capacity retention rate of 81%.

[0213] Example 2

[0214] A method for preparing a composite anode material includes the following steps:

[0215] (1) Silicon with a median particle size of 0.8 μm and ferric chloride were mixed evenly at a mass ratio of 10:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain iron-doped silicon raw material.

[0216] (2) 100g of silicon raw material was added to the etching solution for etching. The etching solution included 3mol / L hydrofluoric acid solution and 2mol / L nitric acid solution. After mechanical stirring for 1h, 0.5mol / L sodium nitrite was added. After stirring for another 2h, the first precursor was obtained by filtration, washing with water and drying.

[0217] (3) Take 50g of the first precursor and put it into an atmosphere furnace. Heat it to 500℃ at a heating rate of 3℃ / min. Introduce 1.5L / min of argon and 0.1L / min of oxygen as a mixed gas to oxidize the first precursor. The treatment time is 1h. After cooling, take it out to obtain the oxidized first precursor.

[0218] (4) Take 100g of the oxidized first precursor and put it into a corrosion solution containing metal salt solution. The corrosion solution includes 0.1mol / L ferric nitrate solution, 0.2mol / L hydrogen peroxide solution, 2mol / L hydrofluoric acid solution and 5% ethanol. Under 40℃, mechanically stir for 3h, and after washing and drying, obtain the second precursor.

[0219] (5) The second precursor is placed in a rotary atmosphere furnace and heated to 600°C at a heating rate of 3°C / min under the protection of argon atmosphere. Then, acetylene gas is introduced at a rate of 0.5L / min so that the volume ratio of argon to acetylene in the rotary atmosphere furnace is 9:1. After holding at the temperature for 3 hours, the third precursor is obtained by cooling.

[0220] (6) Mix 100g of the third precursor and asphalt at a mass ratio of 10:0.5, place them in a stainless steel reaction vessel, introduce argon gas, and pressurize to a pressure of 1 MPa. Heat the mixture to 300°C at a heating rate of 10°C / min, hold for 2 hours, then heat it to 650°C at a heating rate of 3°C / min, hold for 3 hours, and finally cool to obtain the composite anode material.

[0221] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0222] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0223] Example 3

[0224] A method for preparing a composite anode material includes the following steps:

[0225] (1) Silicon with a median particle size of 3.5 μm and ferric chloride were mixed evenly at a mass ratio of 10:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain iron-doped silicon raw material.

[0226] (2) 100g of silicon raw material was added to the etching solution for etching. The etching solution included 4mol / L hydrofluoric acid solution and 3mol / L nitric acid solution. After mechanical stirring for 2h, 1.5mol / L sodium nitrite was added. After stirring for another 2h, the mixture was filtered, washed with water and dried to obtain the first precursor.

[0227] (3) Take 50g of the first precursor and put it into an atmosphere furnace. Heat it to 550℃ at a heating rate of 3℃ / min. Introduce 1.5L / min of argon and 0.2L / min of oxygen as a mixed gas to oxidize the first precursor. The treatment time is 1h. After cooling, take it out to obtain the oxidized first precursor.

[0228] (4) Take 100g of the oxidized first precursor and put it into a corrosion solution containing metal salt solution. The corrosion solution includes 0.2mol / L ferric nitrate solution, 0.2mol / L hydrogen peroxide solution, 3mol / L hydrofluoric acid solution and 5% ethanol. Stir mechanically for 3h at 40℃, and then wash and dry to obtain the second precursor.

[0229] (5) Take 10g of the second precursor and dissolve it in 100g of anhydrous ethanol. Add 3g of tannic acid and stir mechanically for 30 minutes. Then, control the drying temperature at 120℃ by spray drying so that the surface of the second precursor is coated with polymer. Cool to obtain the third precursor.

[0230] (6) Mix 100g of the third precursor and asphalt at a mass ratio of 10:0.8, put them into a stainless steel reaction vessel, introduce argon gas, and pressurize to a pressure of 2 MPa. Heat the mixture to 300°C at a heating rate of 10°C / min, hold for 2 hours, then heat it to 950°C at a heating rate of 3°C / min, hold for 3 hours, and finally cool to obtain the composite negative electrode material.

[0231] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0232] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0233] Example 4

[0234] A method for preparing a composite anode material includes the following steps:

[0235] (1) Silicon with a median particle size of 12 μm and aluminum chloride were mixed evenly at a mass ratio of 10:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain iron-doped silicon raw material.

[0236] (2) 100g of silicon raw material was prepared as an anode and graphite was used as an anode. The anode was added to the electrolyte, which was composed of an aqueous solution of 15% hydrofluoric acid and 5% ethanol. A continuous current of 2mA / cm2 was applied to the electrode and kept for 30min. After cleaning and drying, the first precursor was obtained.

[0237] (3) Take 50g of the first precursor and put it into an atmosphere furnace. Heat it to 500℃ at a heating rate of 3℃ / min. Introduce 1.5L / min of argon and 0.15L / min of oxygen as a mixed gas to oxidize the first precursor. The treatment time is 2h. After cooling, take it out to obtain the oxidized first precursor.

[0238] (4) Take 100g of the oxidized first precursor and put it into a corrosion solution containing metal salt solution. The corrosion solution includes 0.1mol / L copper nitrate solution, 0.3mol / L hydrogen peroxide solution, 2mol / L hydrofluoric acid solution and 5% ethanol. Stir mechanically for 3h at 45℃, and then wash and dry to obtain the second precursor.

[0239] (5) The second precursor is placed in a rotary atmosphere furnace and heated to 800°C at a heating rate of 3°C / min under the protection of argon atmosphere. Then, acetylene gas is introduced at a rate of 1.5L / min so that the volume ratio of argon to acetylene in the rotary atmosphere furnace is 9:1. After holding at the temperature for 3 hours, the third precursor is obtained by cooling.

[0240] (6) Mix 100g of the third precursor and humic acid in a mass ratio of 10:0.5, place them in a stainless steel reaction vessel, introduce argon gas, and pressurize to a pressure of 0.5 MPa. Heat the mixture to 250°C at a heating rate of 10°C / min, hold for 2 hours, then heat the mixture to 900°C at a heating rate of 3°C / min, hold for 3 hours, and finally cool to obtain the composite anode material.

[0241] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0242] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0243] Example 5

[0244] Unlike Example 1:

[0245] (1) Silicon with a median particle size of 15 μm was mixed with copper chloride and iron chloride at a mass ratio of 10:1:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain copper and iron doped silicon raw material.

[0246] (6) Mix 100g of the third precursor and asphalt in a mass ratio of 10:0.1, put them into a stainless steel reaction vessel, introduce argon gas, and pressurize to a pressure of 1 MPa. Heat the mixture to 300°C at a heating rate of 10°C / min, hold for 2 hours, then heat it to 850°C at a heating rate of 3°C / min, hold for 3 hours, and finally cool to obtain the composite negative electrode material.

[0247] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0248] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0249] Example 6

[0250] Unlike Example 1,

[0251] (1) Silicon with a median particle size of 1.5 μm was mixed with copper chloride and iron chloride at a mass ratio of 10:1:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain copper and iron doped silicon raw material.

[0252] (6) Mix 100g of the third precursor and asphalt at a mass ratio of 10:6, put them into a stainless steel reaction vessel, introduce argon gas, pressurize to a pressure of 1 MPa, raise the temperature to 300℃ at a heating rate of 10℃ / min, hold for 2 hours, raise the temperature to 850℃ at a heating rate of 3℃ / min, hold for 3 hours, and then cool to finally obtain the composite negative electrode material.

[0253] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0254] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0255] Example 7

[0256] Unlike Example 1, (6) 100g of the third precursor and asphalt were mixed evenly at a mass ratio of 10:0.5 and placed in a stainless steel reaction vessel. Argon gas was introduced and the pressure was increased by 0.1 MPa. The temperature was raised to 300°C at a heating rate of 10°C / min and held for 2 hours. Then, the temperature was raised to 950°C at a heating rate of 3°C / min and held for 3 hours. Finally, the composite negative electrode material was obtained by cooling.

[0257] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0258] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0259] Example 8

[0260] Unlike Example 1, (6) 100g of the third precursor and asphalt were mixed evenly at a mass ratio of 10:0.5 and placed in a stainless steel reaction vessel. Argon gas was introduced and the pressure was increased to 10 MPa. The temperature was raised to 300°C at a heating rate of 10°C / min and held for 2 hours. Then, the temperature was raised to 950°C at a heating rate of 3°C / min and held for 3 hours. Finally, the composite negative electrode material was obtained by cooling.

[0261] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0262] The auxiliary channels of the obtained composite anode material are blind holes, and the test parameters of the composite anode material are shown in Table 1.

[0263] Example 9

[0264] Unlike Example 1:

[0265] (1) Silicon with a median particle size of 0.2 μm was mixed with copper chloride and iron chloride at a mass ratio of 10:1:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000 r / min for 24 h under argon atmosphere protection to obtain copper and iron doped silicon raw material.

[0266] (4) Take out 100g of the oxidized first precursor and put it into a etching solution containing metal salt solution for secondary etching treatment. The etching solution includes 0.3mol / L silver nitrate solution and 1.2mol / L hydrogen peroxide solution. Under 60℃, mechanically stir for 8h, and after cleaning and drying, the second precursor is obtained.

[0267] The resulting composite anode material includes silicon material, which includes a main channel penetrating the silicon material and an auxiliary channel connected to the main channel; and carbon material, wherein a portion of the carbon material is located on the surface of the pore wall of the main channel and the surface of the silicon material, and a portion of the carbon material fills the auxiliary channel and is connected to the carbon material on the surface of the pore wall of the main channel.

[0268] The auxiliary pores of the obtained composite anode material are through holes, and the test parameters of the composite anode material are shown in Table 1.

[0269] Comparative Example 1

[0270] (1) 2.5μm silicon was mixed with copper chloride and iron chloride at a mass ratio of 10:1:1 and then placed in a ball mill jar. Zirconia ball milling beads were added and the mixture was milled at a speed of 1000r / min for 24h under argon atmosphere protection to obtain copper and iron doped silicon raw material.

[0271] (2) 100g of silicon raw material was added to the etching solution for etching. The etching solution included 3mol / L hydrofluoric acid solution and 2mol / L nitric acid solution. After mechanical stirring for 1h, 0.5mol / L sodium nitrite was added. After stirring for another 2h, the first precursor was obtained by filtration, washing with water and drying.

[0272] (3) The first silicon precursor was placed in a rotary atmosphere furnace and heated to 900°C at a heating rate of 3°C / min under the protection of argon atmosphere. Then, acetylene gas was introduced at a rate of 1.5L / min so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After holding at the temperature for 3 hours, the silicon-carbon composite material was obtained by cooling.

[0273] The resulting composite anode material includes a silicon material, the silicon material including a main channel penetrating the silicon material; and a carbon material, the carbon material forming a carbon layer on the surface of the pore wall of the main channel and the surface of the silicon material.

[0274] The test parameters of the obtained composite anode material are shown in Table 1.

[0275] Comparative Example 2

[0276] Unlike Example 1, steps (2) and (6) were not performed.

[0277] The resulting composite anode material includes a silicon material having a porous structure; and a carbon material having a carbon layer formed on the surface of the silicon material.

[0278] The test parameters of the obtained composite anode material are shown in Table 1.

[0279] Comparative Example 3

[0280] Unlike Example 1, 2.5μm silicon raw material was used directly without the addition of a pore-forming agent.

[0281] The test parameters of the obtained composite anode material are shown in Table 1.

[0282] Test method:

[0283] 1) Particle size of the negative electrode material:

[0284] The particle size testing method refers to GB / T 19077-2016. It can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0285] 2) Test method for specific surface area of ​​negative electrode material:

[0286] After measuring the amount of gas adsorbed on the solid surface at different relative pressures under constant temperature and low temperature, the amount of monolayer adsorption of the sample is obtained based on the Brownnor-Etter-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0287] 3) Test method for tap density:

[0288] The tap density was tested by weighing a certain amount of sample and vibrating it 3000 times at 300 times / min.

[0289] 4) Porosity testing methods:

[0290] The porosity of the material was determined by performing mercury porosimetry using a mercury porosimetry instrument.

[0291] 5) Test methods for oxygen and carbon content:

[0292] The oxygen content was measured using a Fourier transform infrared spectroscopy instrument, and the carbon content was tested using thermogravimetric analysis.

[0293] 6) SEM testing:

[0294] Scanning electron microscopy characterization was performed using a transmission electron microscope at an operating voltage of 200 kV to observe the structure of the negative electrode material and to scale the thickness of the amorphous carbon.

[0295] 7) Aperture testing method:

[0296] The material was sectioned using a FIB-SEM device, and the pore size was measured in the SEM. 8) Method for testing carbon layer thickness:

[0297] The material was sectioned using a FIB-SEM device, and the average thickness of the carbon layer was measured in the SEM.

[0298] 9) Test method for the filling rate of the auxiliary channel's pore volume:

[0299] The pore volume V1 of the auxiliary channel in the composite negative electrode material was measured using a mercury porosimeter. After removing the carbon material in the composite negative electrode material at high temperature in an oxygen atmosphere, the pore volume V2 of the auxiliary channel was measured using a mercury porosimeter. The pore volume filling rate V = (V2 - V1) / V2. When testing V1 and V2, the pore volume statistics of the stage with mercury pressure greater than 172 PSIA were taken.

[0300] 10) I of the carbon layer D / I G Testing methods:

[0301] Raman spectroscopy was used to measure the carbon layer of the composite anode material at 1300 cm⁻¹. -1 ~1400cm -1 Peak intensity I within the range D With at 1580cm -1 ~1620cm -1 Peak intensity I within the range G The ratio I D / I G 11) Test method for the volume of the main channel:

[0302] After removing the carbon material from the composite anode material at high temperature in an oxygen atmosphere, the pore volume of the main channel is tested using a mercury porosimeter. When testing the pore volume of the main channel, statistical data on pore volume are collected for mercury pressures ranging from 0.1 PSIA to 172 PSIA.

[0303] 12) Test method for auxiliary channel volume:

[0304] After removing the carbon material from the composite anode material at high temperature in an oxygen atmosphere, the pore volume of the auxiliary channel is tested using mercury intrusion porosimetry. When testing the pore volume of the auxiliary channel, the pore volume statistics are taken from the stage where the mercury pressure is greater than 172 PSIA.

[0305] After the above tests, the negative electrode materials prepared in Examples 1-9 and Comparative Examples 1-3 are sample numbers S1-S9 and R1-R3, respectively; the performance parameters of the negative electrode materials are shown in Table 1:

[0306] Table 1

[0307]

[0308]

[0309] 11) Electrochemical testing:

[0310] The negative electrode material was mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6), and carbon black (SP) in a ratio of 92:2:2:2:2 to form a slurry. The slurry was then uniformly coated onto copper foil and dried to form a negative electrode sheet. The negative electrode sheet was then assembled into a coin cell in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, and the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixture of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate). The counter electrode used was a lithium metal sheet.

[0311] The discharge specific capacity of the above 12 groups of batteries was tested on the Landian CT2001A battery testing system. The ratio of the discharge capacity to the battery capacity in 1 hour is the discharge specific capacity.

[0312] The first coulombic efficiency test was conducted on the above 12 groups of batteries on the Landian CT2001A battery testing system. The charge and discharge current was 0.05C, and the first coulombic efficiency was measured.

[0313] The above 12 groups of batteries were subjected to a 100-cycle test on the Landian CT2001A battery testing system with a charge / discharge current of 0.2C. After 100 cycles, the battery capacity and capacity retention rate after each cycle were calculated.

[0314] The capacity retention rate after 100 cycles at 0.2C is calculated as: discharge capacity of the 100th cycle / discharge capacity of the first cycle * 100%, as shown in Table 2.

[0315] Table 2 Comparison of Parameters and Performance of Various Batteries

[0316]

[0317]

[0318] The composite anode material of this application has the advantages of low expansion and good cycle stability.

[0319] As shown in Table 2, the negative electrode materials prepared in Examples 1 to 9, through a first etching and a second etching of silicon material, yield a second precursor with main channels and auxiliary channels. The auxiliary channels extend into the silicon material along the surface of the main channel wall, which can effectively suppress the volume expansion of the silicon material. Then, carbon material is formed on the surface of the silicon material and the pore wall of the main channel, which can alleviate the volume expansion of the silicon material and improve the conductivity of the silicon material. Furthermore, under the capillary effect and pressure difference of the auxiliary channels, the carbon material can fill into the auxiliary channels. The carbon material filled in the claw-shaped extended auxiliary channels can enhance the bonding strength with the silicon material, ensuring that the silicon material can still maintain stable electrical contact with the carbon material when the volume expands and contracts. This allows the negative electrode material to have excellent cycle stability and a low expansion rate. In Example 3, the main channel and the auxiliary channel have relatively large pore diameters, while the auxiliary channel pore diameter is relatively small, resulting in a decrease in the bonding strength between the carbon material and the silicon material and a smaller degree of improvement in volume expansion.

[0320] In the preparation process of the negative electrode material of Comparative Example 1, only one etching process was performed. The silicon material formed the main channel, but there was no auxiliary channel. The bonding strength between the carbon material and the silicon material decreased. During cycling, the silicon material experienced severe volume expansion, decreased electrical contact stability, and decreased cycle stability of the battery.

[0321] In Comparative Example 2, the negative electrode material was only etched once during the preparation process and no pressurized carbon filling was performed. As a result, the bonding strength between the carbon material and the silicon material decreased, the silicon material experienced severe volume expansion during cycling, the electrical contact stability decreased, and the cycle stability of the battery decreased.

[0322] In the preparation process of the negative electrode material of Comparative Example 3, no pore-forming agent was added to the silicon raw material. The silicon material could not form a main channel that penetrated through the silicon material, and its porosity was only 5%. During the cycle charge and discharge process, there was not enough space to alleviate the volume expansion of the silicon material, and the expansion rate of the battery increased significantly.

[0323] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A composite negative electrode material, characterized by, The composite negative electrode material comprises: a silicon material, the silicon material comprising a main pore channel and a secondary pore channel in communication with the main pore channel, the secondary pore channel extending along a pore wall surface of the main pore channel, the main pore channel having a pore diameter of 100 nm to 2000 nm, the secondary pore channel having a pore diameter of 10 nm to 100 nm, the secondary pore channel being a blind hole, and a pore diameter ratio of the main pore channel to the secondary pore channel being (5-20):1; and a carbon material, at least part of the carbon material being located on the pore wall surface of the main pore channel, at least part of the carbon material being filled in the secondary pore channel and connected with the carbon material on the pore wall surface of the main pore channel.

2. The composite negative material of claim 1, wherein, At least one of the following features is included: (1) the pore channel length of the main pore channel is 100 nm to 15000 nm; (2) the pore channel length of the secondary pore channel is 10 nm to 1000 nm; (3) the pore channel length ratio of the main pore channel to the secondary pore channel is (10-100):1; (4) the silicon material is a primary particle; (5) the volume ratio of the pore volume of the main pore channel in the total pore volume of the composite negative electrode material is 50% to 80%; (6) the volume ratio of the pore volume of the secondary pore channel in the total pore volume of the composite negative electrode material is 20% to 50%; (7) the carbon material comprises at least one of amorphous carbon and graphitized carbon; (8) the carbon material comprises amorphous carbon, and the thickness of the amorphous carbon material on the pore wall surface of the main pore channel is 10 nm to 200 nm; (9) the carbon material includes amorphous carbon, and a peak intensity I D of the amorphous carbon measured by Raman spectrum of the composite negative electrode material is greater than 0.8 times of a peak intensity I G of the graphite measured by Raman spectrum of the composite negative electrode material. D / I G > 0.

8. (10) the carbon material comprises amorphous carbon and graphitized carbon, and the thickness of the carbon material on the pore wall surface of the main pore channel is 5 nm to 100 nm; (11) The carbon material includes amorphous carbon and graphitized carbon. The peak intensity I of the composite negative electrode material is determined by Raman spectroscopy. D With peak intensity I G The strength ratio is 0.3≤I D / I G ≤0.8; (12) the filling rate of the pore volume of the secondary pore channel is 40% to 100%; (13) the thickness of the carbon material on the pore wall surface of the main pore channel accounts for 0.25%-25% of the pore diameter of the main pore channel; (14) the composite negative electrode material further comprises a coating carbon layer existing on the surface of the silicon material and connected with the carbon material in the main pore channel.

3. The composite negative material according to any one of claims 1-2, characterized in that, At least one of the following features is included: (1) the mass content of carbon in the composite negative electrode material is 5% to 80%; (2) the tap density of the powder of the composite negative electrode material is 0.2 g / cm 3 1.2 g / cm 3 ; (3) the powder compaction density of the composite negative electrode material is 1.2 g / cm 3 1.8 g / cm 3 ; (4) the median particle size of the composite negative electrode material is 0.2 µm to 20 µm; (5) the specific surface area of the composite negative electrode material is 1.0 m 2 / g~50 m 2 / g; (6) the mass content of oxygen in the composite negative electrode material is <20%; (7) the porosity of the composite negative electrode material is 20% to 70%.

4. A method for preparing a composite negative electrode material, characterized by, The following steps are included: preparing a silicon raw material comprising a silicon material and a pore-forming agent, and performing a first etching treatment on the silicon raw material to obtain a first precursor having a main pore channel; performing a surface oxidation treatment on the first precursor and then performing a second etching treatment to obtain a second precursor having a main pore channel and a secondary pore channel; performing a coating treatment on the second precursor to form a carbon material on the pore wall surface of the main pore channel to obtain a third precursor; and performing a pressurized carbon filling treatment on the third precursor to fill the carbon material in the secondary pore channel to obtain a composite negative electrode material. The composite negative electrode material comprises a silicon material, the silicon material comprises a main pore channel and a secondary pore channel connected to the main pore channel, the pore diameter of the main pore channel is 100 nm-2000 nm, and the pore diameter ratio of the main pore channel to the secondary pore channel is (5-20):

1.

5. The method of claim 4, wherein the method further comprises the step of mixing the carbon material and the metal oxide material. The preparation method comprises at least one of the following characteristics: (1) The step of preparing the silicon raw material specifically comprises: ball milling a silicon raw material comprising a silicon material and a pore-forming agent; (2) The pore-forming agent comprises at least one of an oxide of M, a chloride of M and M element, and M comprises at least one of Fe, Cu, Al, B, P, Mg, Ti and Cr; (3) The purity of the silicon material is >99%; (4) The median particle size of the silicon material is 0.2-100 μm; (5) The pore-forming agent comprises at least one of an oxide of M, a chloride of M and M element, M comprises Cu and / or P, and the mass percentage of M in the silicon raw material is 0-2%; (6) The pore-forming agent comprises at least one of an oxide of M, a chloride of M and M element, M comprises Ti and / or Cr, and the mass percentage of M in the silicon raw material is 0-10%; (7) The pore-forming agent comprises at least one of an oxide of M, a chloride of M and M element, M comprises Al and / or B, and the mass percentage of M in the silicon raw material is 0-5%; (8) The pore-forming agent comprises at least one of an oxide of M, a chloride of M and M element, M comprises Fe, and the mass percentage of M in the silicon raw material is 0-3%; (9) The pore-forming agent comprises at least one of an oxide of M, a chloride of M and M element, M comprises Mg, and the mass percentage of M in the silicon raw material is 0-50%; (10) The step of preparing the silicon raw material specifically comprises: ball milling a silicon raw material comprising a silicon material and a pore-forming agent, and the median particle size of the silicon raw material obtained by ball milling is 0.2-20 μm.

6. The method of claim 4, wherein the method further comprises the step of mixing the carbon material and the metal oxide material. The preparation method comprises at least one of the following characteristics: (1) The step of performing one-time etching treatment on the silicon raw material comprises: using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent to perform one-time etching treatment on the silicon raw material; (2) The step of performing one-time etching treatment on the silicon raw material comprises: using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent to perform one-time etching treatment on the silicon raw material, wherein the concentration of hydrogen fluoride acid in the corrosion liquid is 1-30 mol / L; (3) The step of performing one-time etching treatment on the silicon raw material comprises: using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent to perform one-time etching treatment on the silicon raw material, wherein the oxidizing agent comprises at least one of nitric acid, sulfuric acid and phosphoric acid; (4) The step of performing one-time etching treatment on the silicon raw material comprises: using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent to perform one-time etching treatment on the silicon raw material, wherein the oxidizing agent comprises nitric acid, and the concentration of nitric acid in the corrosion liquid is 0.1-10 mol / L; (5) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent, wherein the oxidizing agent comprises sulfuric acid, and the concentration of the sulfuric acid in the corrosion liquid is 0.5 mol / L-15 mol / L; (6) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent, wherein the oxidizing agent comprises phosphoric acid, and the concentration of the phosphoric acid in the corrosion liquid is 0.05 mol / L-5 mol / L; (7) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent, wherein the corrosion liquid further comprises an auxiliary agent, and the auxiliary agent comprises nitrate, nitrite, sulfate, phosphate; (8) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent, wherein the corrosion liquid further comprises an auxiliary agent, and the auxiliary agent comprises at least one of copper nitrate, sodium nitrate, potassium nitrate, iron nitrate, iron nitrite, sodium nitrite, potassium nitrite, copper sulfate, iron sulfate, sodium sulfate, potassium sulfate, sodium phosphate, potassium phosphate, iron phosphate and copper phosphate; (9) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent, wherein the corrosion liquid further comprises an auxiliary agent, and the concentration of the auxiliary agent in the corrosion liquid is 0.01 mol / L-1 mol / L; (10) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using a corrosion liquid containing hydrogen fluoride acid and an oxidizing agent, and the time of the first etching treatment is 0.5 h-48 h; (11) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using an electrolyte containing hydrogen fluoride acid and ethanol through electrochemistry; (12) the step of performing the first etching treatment on the silicon material comprises: performing the first etching treatment on the silicon material by using an electrolyte containing hydrogen fluoride acid and ethanol through electrochemistry, wherein the mass content of the hydrogen fluoride acid in the electrolyte is 10%-49%, and / or the mass content of the ethanol in the electrolyte is 1%-50%; (13) the step of performing a first etching treatment on the silicon material includes: taking the silicon material as an anode, taking graphite or platinum metal as a cathode, and placing them in an electrolyte containing hydrofluoric acid and ethanol to perform an electrochemical first etching treatment, wherein a stable current of the electrochemical first etching treatment is controlled to be 1 mA / cm 2 20 mA / cm 2 , and an oxidation time of the anode is 5 min to 2 h; (14) after the first etching treatment on the silicon material, the method further comprises: performing cleaning and drying treatment on the first precursor obtained after the first etching treatment.

7. The method of claim 4, wherein the method further comprises the step of mixing the carbon material and the metal oxide material. The preparation method comprises at least one of the following characteristics: (1) the step of performing the surface oxidation treatment on the first precursor comprises: performing heat treatment on the first precursor in an oxygen-containing atmosphere, so as to form a silicon dioxide layer on the surface of the first precursor; (2) the step of surface oxidation treatment of the first precursor includes: placing the first precursor in an oxygen-containing atmosphere for heat treatment, so that a silicon dioxide layer is formed on the surface of the first precursor; wherein the heat treatment temperature is 100-600 DEG C, and the heat treatment time is 5-6 hours; (3) the step of surface oxidation treatment of the first precursor includes: placing the first precursor in an oxygen-containing atmosphere for heat treatment, so that a silicon dioxide layer is formed on the surface of the first precursor; wherein the oxygen-containing atmosphere includes at least one of air, oxygen and a mixture of inert gas, and / or the oxygen content in the oxygen-containing atmosphere is 5-50%; (4) the step of surface oxidation treatment of the first precursor includes: placing the first precursor in an acid solution for oxidation treatment, so that a silicon dioxide layer is formed on the surface of the first precursor; (5) the step of surface oxidation treatment of the first precursor includes: placing the first precursor in an acid solution for oxidation treatment, so that a silicon dioxide layer is formed on the surface of the first precursor, wherein the acid solution includes at least one of nitric acid, sulfuric acid, perchloric acid, permanganic acid, hypochlorous acid and nitrous acid; (6) the step of surface oxidation treatment of the first precursor includes: placing the first precursor in an acid solution for pickling treatment, so that a silicon dioxide layer is formed on the surface of the first precursor, wherein the concentration of the acid solution is 1-18 mol / L, and the pickling treatment time is 1-48 hours; (7) the mass content of oxygen element in the first precursor after oxidation treatment is 5-20%; (8) the step of surface oxidation treatment of the first precursor, so that a silicon dioxide layer is formed on the surface of the first precursor, and the thickness of the silicon dioxide layer is 20-500 nm.

8. The method of claim 4, 5, 6 or 7, wherein the method further comprises the step of: The preparation method comprises at least one of the following features: ​ (1) the step of secondary etching treatment includes: placing the product after surface oxidation treatment in a corrosion liquid containing a metal salt solution for secondary etching treatment, to obtain a second precursor with main channels and auxiliary channels; (2) the step of secondary etching treatment includes: placing the product after surface oxidation treatment in a corrosion liquid containing a metal salt solution for secondary etching treatment, to obtain a second precursor with main channels and auxiliary channels; wherein the metal salt in the metal salt solution includes at least one of nitrate, nitrite and halide; (3) the step of secondary etching treatment includes: placing the product after surface oxidation treatment in a corrosion liquid containing a metal salt solution for secondary etching treatment, to obtain a second precursor with main channels and auxiliary channels; wherein the metal element in the metal salt includes at least one of Ag, Pt, Cu, Fe and Au; (4) the step of secondary etching treatment includes: placing the product after surface oxidation treatment in a corrosion liquid containing a metal salt solution for secondary etching treatment, to obtain a second precursor with main channels and auxiliary channels; wherein the concentration of the metal salt solution is 0.01-1 mol / L; (5) the step of the secondary etching treatment comprises: placing the product after the surface oxidation treatment in an etching solution containing a metal salt solution to perform the secondary etching treatment, so as to obtain a second precursor with main channels and auxiliary channels; wherein the temperature of the secondary etching treatment is 10-100℃, and the etching time is 0.5-12h; (6) the step of the secondary etching treatment comprises: placing the product after the surface oxidation treatment in an etching solution containing a metal salt solution to perform the secondary etching treatment, so as to obtain a second precursor with main channels and auxiliary channels; wherein the etching solution comprises hydrogen peroxide, ethanol and hydrofluoric acid, the concentration of the hydrogen peroxide in the etching solution is 0.1-5mol / L, the concentration of the hydrofluoric acid in the etching solution is 1-10mol / L, and the mass content of the ethanol in the etching solution is 1-15%.

9. The method of claim 4 to 7, wherein the method further comprises the step of mixing the carbon material and the silicon material. The preparation method comprises at least one of the following characteristics: (1) the step of coating the second precursor comprises: after heating the second precursor in a protective atmosphere, carbon source gas is introduced to perform carbon coating treatment, so as to obtain a third precursor; (2) the step of coating the second precursor comprises: after heating the second precursor in a protective atmosphere, carbon source gas is introduced to perform carbon coating treatment, so as to obtain a third precursor, wherein the heating rate is 1-20℃ / min; (3) the step of coating the second precursor comprises: after heating the second precursor in a protective atmosphere, carbon source gas is introduced to perform carbon coating treatment, so as to obtain a third precursor, wherein the heating temperature is 600-1000℃, and the holding time is 1-48h; (4) the step of coating the second precursor comprises: after heating the second precursor in a protective atmosphere, carbon source gas is introduced to perform carbon coating treatment, so as to obtain a third precursor, wherein the carbon source gas comprises at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene and propylene; (5) the step of coating the second precursor comprises: after heating the second precursor in a protective atmosphere, carbon source gas is introduced to perform carbon coating treatment, so as to obtain a third precursor, wherein the concentration of the carbon source gas is 0.1-10L / min; (6) the step of coating the second precursor comprises: dispersing the second precursor in a coating liquid containing a polymer, and performing spray drying to obtain a third precursor; (7) the step of coating the second precursor comprises: dispersing the second precursor in a coating liquid containing a polymer, and performing spray drying to obtain a third precursor, wherein the solid content of the second precursor in the coating liquid is 5-50%; (8) the step of coating the second precursor comprises: dispersing the second precursor in a coating liquid containing a polymer, and performing spray drying to obtain a third precursor, wherein the coating liquid further comprises a polar solvent; (9) The step of coating the second precursor comprises dispersing the second precursor in a coating liquid containing a polymer, and spray drying to obtain a third precursor, wherein the mass ratio of the second precursor to the polymer is 10:(0.1-5); (10) The step of coating the second precursor comprises dispersing the second precursor in a coating liquid containing a polymer, and spray drying to obtain a third precursor, wherein the temperature of the spray drying is 60-200°C; (11) The step of coating the second precursor comprises dispersing the second precursor in a coating liquid containing a polymer, and spray drying to obtain a third precursor, wherein the polymer comprises at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylacetylene, polyaniline, polyacetylene, and tannic acid; (12) The step of pressurized carbon filling of the third precursor comprises mixing an organic carbon source with the third precursor under a protective atmosphere, and then placing the mixture in a pressurized environment, and performing stepwise heating treatment, so that the liquefied organic carbon source is filled into the auxiliary pore channels of the third precursor under capillary action; (13) The step of pressurized carbon filling of the third precursor comprises mixing an organic carbon source with the third precursor under a protective atmosphere, and then placing the mixture in a pressurized environment, and performing stepwise heating treatment, so that the liquefied organic carbon source is filled into the auxiliary pore channels of the third precursor under capillary action, wherein the organic carbon source comprises at least one of humic acid, pitch, resin, amino acid, tar, fatty acid, cellulose, and starch, and / or the mass ratio of the organic carbon source to the third precursor is (0.1-6):10; (14) The step of pressurized carbon filling of the third precursor comprises mixing an organic carbon source with the third precursor under a protective atmosphere, and then placing the mixture in a pressurized environment, and performing stepwise heating treatment, so that the liquefied organic carbon source is filled into the auxiliary pore channels of the third precursor under capillary action, wherein the pressure of the pressurized environment is 0.1-2 MPa; (15) The step of pressurized carbon filling of the third precursor comprises mixing an organic carbon source with the third precursor under a protective atmosphere, and then placing the mixture in a pressurized environment, and performing stepwise heating treatment, so that the liquefied organic carbon source is filled into the auxiliary pore channels of the third precursor under capillary action, wherein the protective atmosphere comprises at least one of helium, neon, argon, krypton, and xenon; (16) The step of pressurized carbon filling of the third precursor comprises mixing an organic carbon source with the third precursor under a protective atmosphere, and then placing the mixture in a pressurized environment, and performing stepwise heating treatment, so that the liquefied organic carbon source is filled into the auxiliary pore channels of the third precursor under capillary action, wherein the temperature is first heated to 150-500°C for 0.5-24 h, and then continuously heated to 600-1100°C for 1-12 h.

10. A lithium-ion battery, characterized by, The negative electrode material includes the composite negative electrode material according to any one of claims 1 to 3 or is prepared by the preparation method of the composite negative electrode material according to any one of claims 4 to 9.

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