A pre-lithiated silicon-carbon negative electrode, negative electrode sheet, secondary battery and preparation method thereof

Abstract

The application discloses a pre-lithiated silicon-carbon negative electrode material, which comprises a porous carbon base, silicon elements distributed in the channels of the porous carbon base, and carbon coated on the outer surfaces of the porous carbon base and the silicon elements, wherein the porous carbon base is a pre-lithiated porous carbon base, and the pre-lithiated porous carbon base further comprises lithium-carbon compounds LiC6 and / or LiC 24 ; and a preparation method thereof comprises the following steps: sequentially performing carbonization treatment and activation treatment on a carbon source to obtain porous carbon; mixing the porous carbon, a lithium source and a solvent to obtain a dispersion liquid, and performing spray drying to obtain a pre-lithiated precursor; and performing three-step high-temperature treatment on the pre-lithiated precursor, and then performing silicon deposition and carbon coating to obtain the pre-lithiated silicon-carbon negative electrode material. The pre-lithiated silicon-carbon negative electrode material prepared by the specific process has high capacity, high initial efficiency, long cycle stability and high rate performance.

Description

Technical Field

[0001] This invention belongs to the technical field of secondary batteries, and particularly relates to a pre-lithiated silicon-carbon anode, anode sheet, secondary battery, and its preparation method. Background Technology

[0002] Anode materials play a crucial role in lithium-ion batteries. Currently, commercially available graphite anodes have almost reached their theoretical capacity limit, failing to meet the demands of future high-performance lithium-ion batteries. Therefore, exploring and developing high-energy-density anode materials with potential is imperative. Silicon, due to its unique advantages such as ultra-high theoretical capacity, low lithium intercalation potential, and abundant reserves, is widely recognized as the best choice for next-generation high-performance lithium-ion battery anode materials. For example, Tesla electric vehicles can easily achieve an industry-leading energy density of 300Wh / kg using only graphite anodes doped with 5-10% silicon, fully demonstrating the enormous potential of silicon anodes. However, the significant volume expansion of silicon anodes during lithium intercalation causes a series of problems, and its inherent low conductivity results in disappointing rate and cycle performance. If these obstacles are not effectively addressed, silicon anodes can only be used as trace additives, making it difficult to achieve a qualitative leap in lithium-ion battery energy density. How to obtain high-performance silicon-based anode materials through low-cost and simple routes is key to realizing the practical application of silicon-based anodes.

[0003] To address the inherent limitations of silicon anode materials, and given the need for rapid charging and discharging in many lithium-ion battery applications, the assembly and design of silicon material structures are crucial to effectively constrain and limit silicon volume expansion, thereby improving performance. Carbon materials offer structural stability, exhibit relatively small volume changes during charging and discharging, and demonstrate good cycle stability. Furthermore, their chemical properties are similar to silicon. Combining silicon and carbon through pre-lithiation processes can partially alleviate the aforementioned problems, but defects such as uneven lithium distribution, insufficient pore structure control, and poor conductivity still exist. For example, traditional physical pre-lithiation processes are prone to localized overlithiation, while chemical pre-lithiation processes are complex and costly.

[0004] Chinese patent application CN118684215A discloses a method for preparing silicon-carbon anode materials by pre-lithiation through lithium vapor embedding in pores. The method includes: Step 1, preparing porous carbon anode materials by high-temperature carbonization and activation of biomass powder; Step 2, introducing lithium vapor into the porous carbon anode materials under vacuum and high-temperature conditions to obtain pre-lithiated carbon materials; Step 3, coating the surface of the pre-lithiated carbon materials with hard carbon under high-temperature conditions using a carbon source gas and a protective gas to obtain carbon-coated pre-lithiated carbon materials; Step 4, mixing the carbon-coated pre-lithiated carbon materials with nanocrystalline silicon powder, a coating agent, and a solvent, evacuating the vacuum, granulating through vacuum liquid-phase coating, and finally carbonizing to obtain silicon-carbon anode materials. In this technical solution, lithium source deposition in porous carbon can lead to the occupation of pores, affecting silane deposition; furthermore, lithium metal is highly reactive, and excessive lithium metal in porous carbon can cause spontaneous combustion and partial formation of lithium oxide. The experimental process requires extremely strict control, resulting in low experimental safety.

[0005] Chinese patent document CN118173769A discloses silicon-carbon composite anode materials, their preparation methods, and applications. The silicon-carbon composite anode material includes lithium-rich porous carbon spheres with silicon dispersed within the pores and carbon coated on the surface. The preparation method includes: spheroidization, where a lithium-rich suspension containing a lithium source, a soft template agent, and a carbon source is spheroidized to obtain lithium-rich carbon spheres; carbonization, where the lithium-rich carbon spheres are carbonized in a containing atmosphere to obtain lithium-rich porous carbon spheres; and silicon deposition and carbon coating to obtain the silicon-carbon composite anode material. This technical solution uses lithium carbonate or lithium hydroxide as the lithium source, which allows for lithium replenishment. Furthermore, the thermal decomposition characteristics of lithium carbonate or lithium hydroxide ensure a rich pore structure around the lithium source. However, analysis of the data in Table 2 shows that the silicon-carbon composite anode material prepared by this process only improves the initial coulombic efficiency of the anode material and has no significant impact on other electrochemical properties such as capacity and rate capability.

[0006] Therefore, it is of great significance to develop a method for preparing silicon-carbon anode materials that combines high capacity, long cycle stability, high rate performance, and low cost.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] To address the aforementioned issues, this invention discloses a pre-lithiated silicon-carbon anode material that combines high capacity, high initial efficiency, long cycle stability, and high rate performance.

[0009] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0010] In a first aspect, the present invention provides a pre-lithiated silicon-carbon anode material, comprising a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coating the outer surfaces of the porous carbon substrate and the silicon elements, wherein the porous carbon substrate is a pre-lithiated porous carbon substrate, and the pre-lithiated porous carbon substrate further comprises a lithium-carbon compound.

[0011] The lithium-carbon compound includes LiC6 and / or LiC. 24 .

[0012] In an optional embodiment, the lithium-carbon compound satisfies at least one of the following three conditions:

[0013] a. The total mass percentage of lithium-carbon compounds is 1.5 to 10.0 wt% based on the mass of the pre-lithiated porous carbon substrate; optionally, the total mass percentage of lithium-carbon compounds is 1.5 to 6.5 wt%.

[0014] b. Lithium-carbon compounds include LiC6 and LiC 24 ;

[0015] c, LiC6 and LiC 24 The mass ratio of the two is 1:(0.5 to 5.0); alternatively, the mass ratio of the two is 1:(1.5 to 3.0).

[0016] In an optional embodiment, the average pore size D50 of the pre-lithiated silicon-carbon anode material is 3–15 μm;

[0017] In an optional embodiment, the specific surface area of ​​the pre-lithiated silicon-carbon anode material is less than 10 m². 2 / g;

[0018] In an optional embodiment, the tap density of the pre-lithiated silicon-carbon anode material is 0.6–1.3 g / cm³. 3 ;

[0019] In an optional embodiment, the powder resistivity of the pre-lithiated silicon-carbon anode material at 20 MPa is not higher than 30 Ω·cm; optionally, not higher than 5 Ω·cm; more preferably, not higher than 3 Ω·cm.

[0020] Secondly, the present invention also provides a method for preparing the aforementioned pre-lithiated silicon-carbon anode material, comprising:

[0021] S1. Carbonize the carbon source to obtain a carbon source precursor; activate the carbon source precursor to obtain porous carbon.

[0022] S2. The porous carbon and lithium source prepared in step S1 are mixed with a solvent to obtain a dispersion, which is then spray-dried to obtain a prelithiated precursor.

[0023] S3. The prelithiated precursor prepared in step S2 is subjected to three high-temperature treatments and then cooled to room temperature to obtain a prelithiated porous carbon substrate.

[0024] The three-step high-temperature treatment includes:

[0025] The first step is high-temperature treatment, in which the reactor is heated to 500-1200℃ under a nitrogen and / or inert gas atmosphere and held at that temperature for 2-8 hours;

[0026] The second step involves high-temperature treatment, in which the reactor is heated to 500–1300°C under a reducing atmosphere and held at that temperature for 2–10 hours.

[0027] The third step involves high-temperature treatment, in which the reactor is heated to 500–1200°C under an inert gas atmosphere and held at that temperature for 1–10 hours.

[0028] S4. The pre-lithiated porous carbon substrate prepared in step S3 is subjected to silicon deposition and carbon coating in sequence to obtain the pre-lithiated silicon-carbon anode material.

[0029] In an optional implementation, step S1 satisfies at least one of the following (1) to (8):

[0030] (1) The carbon source is selected from one or more of the following: biomass, polymer, coal-based, and petroleum-based;

[0031] In an optional implementation, the biomass is selected from common types such as coconut shells, rice, straw, and bamboo;

[0032] In an optional embodiment, the polymer is selected from common types such as phenolic resin and epoxy resin.

[0033] (2) The activation treatment methods include physical activation and / or chemical activation;

[0034] (3) The physical activation uses an activator selected from one or more of water vapor, carbon dioxide, and carbon monoxide;

[0035] (4) The physical activation is carried out at a temperature of 500 to 1500°C and the pressure is controlled to be 0.1 to 15 kPa during activation;

[0036] Optionally, the activation temperature is 700–1200℃;

[0037] Optionally, the activation pressure is controlled to be 2–10 kPa;

[0038] In an optional implementation, the activation time is 1 to 30 hours, which can be adjusted adaptively according to the activation temperature;

[0039] (5) The physical activation involves an activator flow rate of 1–50 kg / h;

[0040] Optionally, the flow rate of the activator is 1–10 kg / h;

[0041] (6) The chemical activation used is selected from one or more of potassium hydroxide, sodium hydroxide, phosphoric acid, hydrochloric acid, and sulfuric acid;

[0042] (7) In the chemical activation, the mass ratio of the activator to the carbon source precursor is 1:(0.5-6.0);

[0043] Optionally, the mass ratio of activator to carbon source precursor is 1:(1-4);

[0044] (8) The chemical activation is performed at a temperature of 600–1200°C;

[0045] Optionally, the activation temperature is 700–1000℃.

[0046] In an optional implementation, step S2 satisfies at least one of the following (a) to (v):

[0047] (i) The lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, lithium fluoride, lithium nitrate, and lithium phosphate;

[0048] (ii) The solvent is selected from one or more of water, methanol, ethanol, and tetrahydrofuran;

[0049] (iii) The mass ratio of porous carbon to lithium source is (0.5~20):1;

[0050] Optionally, the mass ratio of porous carbon to lithium source is (0.5–5.0):1;

[0051] Alternatively, the mass ratio of porous carbon to lithium source is (0.8–3.0):1;

[0052] (iv) The concentration of lithium salt in the dispersion is (1-30) wt%;

[0053] (v) The spray dryer has an inlet temperature of 60-180℃ and an outlet temperature of 60-150℃;

[0054] Optionally, the inlet temperature is 80–150℃ and the outlet temperature is 80–120℃.

[0055] Step S3 employs a three-step high-temperature processing technology. The first step, high-temperature processing, decomposes the lithium source. When a nitrogen atmosphere is used, the main decomposition products are lithium nitride and lithium oxide; when an inert gas atmosphere is used, the main decomposition product is lithium oxide. The second and third steps, high-temperature processing, convert the decomposition products from the first step into lithium-carbon compounds. Appropriate processing conditions ensure the formation of a high and suitable content of lithium-carbon compounds, ultimately yielding a negative electrode material with excellent overall electrochemical performance. Therefore, the three-step high-temperature processing technology is indispensable and mutually influential.

[0056] In an optional implementation, step S3 satisfies at least one of the following (A) to (C):

[0057] (A) The inert gas used in the first high-temperature treatment is selected from argon and / or helium;

[0058] In an optional embodiment, in the first high-temperature treatment, the flow rate of nitrogen and / or inert gas is 1 to 20 L / min;

[0059] Optionally, the flow rate is 1–10 L / min;

[0060] In an optional embodiment, in the first high-temperature treatment, the reactor is heated to 600-1000°C;

[0061] In an optional implementation, the first high-temperature treatment is performed by holding the temperature for 3 to 5 hours.

[0062] (B) The reducing atmosphere used in the second step of high-temperature treatment is selected from one or more of carbon monoxide, hydrogen, hydrogen sulfide, and methane.

[0063] In an optional embodiment, in the second high-temperature treatment, the flow rate of the reducing gas is 1-20 L / min;

[0064] Optionally, the flow rate is 1–10 L / min;

[0065] In an optional embodiment, in the second high-temperature treatment, the reactor is heated to 700–1200°C;

[0066] In an optional implementation, the second high-temperature treatment is carried out for 3 to 9 hours;

[0067] (C) The inert gas used in the third step of high-temperature treatment is selected from argon and / or helium;

[0068] In an optional embodiment, in the third step of high-temperature treatment, the flow rate of the inert gas is 1 to 20 L / min;

[0069] Optionally, the flow rate is 1–10 L / min;

[0070] In an optional embodiment, in the third high-temperature treatment, the reactor is heated to 600–1000°C;

[0071] In an optional implementation, the third high-temperature treatment involves holding the temperature for 3 to 5 hours.

[0072] In an optional implementation, in step S4:

[0073] The gas source used for silicon deposition includes silicon source gas, inert gas, and a second gas source that can be selectively added;

[0074] In an optional embodiment, the silicon source gas is selected from one or more of silane, silane, monochlorosilane, dichlorosilane, and trichlorosilane;

[0075] In an optional embodiment, the inert gas is selected from nitrogen, argon, helium, etc.

[0076] In an optional embodiment, the second gas source is selected from one or more of carbon source gas, nitrogen source gas, sulfur source gas, and phosphorus source gas;

[0077] Optionally, the carbon source gas is selected from alkane gases whose pyrolysis temperature is within the carbon deposition temperature range, specifically common types such as ethylene and acetylene;

[0078] Optionally, the nitrogen source gas is selected from ammonia;

[0079] Optionally, the sulfur source gas is selected from one or more of hydrogen sulfide, sulfur dioxide, and sulfur hexafluoride;

[0080] Optionally, the phosphorus source gas is selected from one or more of phosphine, phosphorus chloride, and phosphorus fluoride;

[0081] In an optional embodiment, the second gas source is co-deposited after being mixed with the silicon source gas, or it is deposited alternately with the silicon source gas.

[0082] In an optional embodiment, the total flow rate of the gas source for silicon deposition is 1–100 L / min;

[0083] Optionally, the total flow rate of the gas source is 1 to 30 L / min.

[0084] In an optional embodiment, the silicon deposition process involves a silicon source gas comprising 30–99 vol% of the gas source.

[0085] Optionally, the silicon source gas accounts for 50-90 vol% of the gas source;

[0086] In an optional embodiment, the silicon deposition is performed at a temperature of 400–1000°C for a time of 1–50 hours.

[0087] In an optional embodiment, the gas source used for carbon coating includes carbon source gas and carrier gas;

[0088] Optionally, the carbon source gas is selected from alkane gases whose pyrolysis temperature is within the carbon deposition temperature range; specifically, ethylene, acetylene, etc.

[0089] In an optional embodiment, the carbon coating is performed with the carbon source gas accounting for 30-90 vol%.

[0090] Optionally, the carbon source gas accounts for 50–90 vol%.

[0091] In an optional embodiment, the carbon coating is performed at a temperature of 300–1200°C for 2–20 hours.

[0092] Thirdly, the present invention also provides a negative electrode sheet, comprising the aforementioned pre-lithiated silicon-carbon negative electrode material.

[0093] Fourthly, the present invention also provides a secondary battery, including the aforementioned negative electrode sheet.

[0094] Compared with the prior art, the present invention has the following advantages:

[0095] This invention discloses a pre-lithiated silicon-carbon anode material and its preparation method. Pre-lithiated porous carbon is prepared using a specific process, and then silicon deposition and carbon coating are performed on this carbon as a substrate to obtain the pre-lithiated silicon-carbon anode material. The pre-lithiated porous carbon also includes lithium-carbon compounds, specifically LiC6 and / or LiC. 24 .

[0096] This invention provides a pre-lithiated silicon-carbon anode material prepared through a specific pre-lithiation process. The lithium-carbon compounds generated in the substrate can provide a lithium source for the anode in advance, compensating for irreversible lithium loss during the first charge-discharge cycle caused by the formation of the solid electrolyte interphase (SEI) film and side reactions. Furthermore, it reduces the kinetic resistance of the initial lithium intercalation process and optimizes the initial coulombic efficiency. The generated lithium-carbon compounds can pre-form a stable SEI film during electrochemical processes, reducing the continuous decomposition of the electrolyte in subsequent cycles and lowering lithium inventory losses. The lithium-carbon compounds LiC6 and LiC... 24 The corresponding lithium intercalation degree is lower, the lithium ion diffusion path is shorter, and the interface impedance is smaller, which is conducive to rapid charging and discharging. Constructing a lithium-carbon conductive network reduces electrode polarization and enhances conductivity, thereby significantly improving the rate performance of the anode material. In addition, this lithium-carbon compound can make lithium distribution more uniform, reduce local stress concentration, and improve the mechanical stability of the material, which helps to improve stability. After pre-lithiation, its high lithium content can be directly used to improve the overall energy density of the battery. Attached Figure Description

[0097] Figure 1 The elemental distribution maps (SEM-EDS) of lithium and carbon in the pre-lithiated porous carbon substrate prepared in Example 1 are shown.

[0098] Figure 2 The XRD patterns of the pre-lithiated porous carbon substrates prepared in Examples 1, 7 and 8 are shown. Detailed Implementation

[0099] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0100] In the description of this invention, it should be noted that those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. The embodiments of this invention are described below based on its overall structure. Unless otherwise specified, the raw materials used in the embodiments of this invention were all purchased commercially.

[0101] In a first aspect, the present invention provides a pre-lithiated silicon-carbon anode material, comprising a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coating the outer surfaces of the porous carbon substrate and the silicon elements, wherein the porous carbon substrate is a pre-lithiated porous carbon substrate, and the pre-lithiated porous carbon substrate further comprises a lithium-carbon compound.

[0102] The lithium-carbon compound includes LiC6 and / or LiC. 24 .

[0103] In an optional embodiment, the lithium-carbon compound satisfies at least one of the following three conditions:

[0104] a. Based on the mass of the pre-lithiated porous carbon substrate, the total mass percentage of lithium-carbon compounds is 1.5–10.0 wt%; specifically, it can be 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, 10.0 wt%, or any value within the above range; optionally, the total mass percentage of lithium-carbon compounds is 1.5–6.5 wt%.

[0105] b. Lithium-carbon compounds include LiC6 and LiC24 ;

[0106] c, LiC6 and LiC 24 The mass ratio of the two is 1:(0.5 to 5.0); 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or any ratio within the above range; optionally, the mass ratio of the two is 1:(1.5 to 3.0).

[0107] In an optional embodiment, the average pore size D50 of the pre-lithiated silicon-carbon anode material is 3 to 15 μm; specifically, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any value within the above range;

[0108] In an optional embodiment, the specific surface area of ​​the pre-lithiated silicon-carbon anode material is less than 10 m². 2 / g;

[0109] In an optional embodiment, the tap density of the pre-lithiated silicon-carbon anode material is 0.6–1.3 g / cm³. 3 Specifically, it can be 0.6 g / cm³. 3 0.65g / cm 3 0.7g / cm 3 0.75g / cm 3 0.8g / cm 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.05g / cm 3 1.1g / cm 3 1.15g / cm 3 1.2g / cm 3 1.25g / cm 3 1.3g / cm 3 Or any value within the above range;

[0110] In an optional embodiment, the powder resistivity of the pre-lithiated silicon-carbon anode material at 20 MPa is <30 Ω·cm; specifically, it can be 0.1 Ω·cm, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 8 Ω·cm, 10 Ω·cm, 12 Ω·cm, 15 Ω·cm, 18 Ω·cm, 20 Ω·cm, 22 Ω·cm, 25 Ω·cm, 28 Ω·cm, 30 Ω·cm or any value within the above range; optionally, it is not higher than 5 Ω·cm; more preferably, it is not higher than 3 Ω·cm.

[0111] Secondly, the present invention also provides a method for preparing the aforementioned pre-lithiated silicon-carbon anode material, comprising:

[0112] S1. Carbonize the carbon source to obtain a carbon source precursor; activate the carbon source precursor to obtain porous carbon.

[0113] S2. The porous carbon and lithium source prepared in step S1 are mixed with a solvent to obtain a dispersion, which is then spray-dried to obtain a prelithiated precursor.

[0114] S3. The prelithiated precursor prepared in step S2 is subjected to three high-temperature treatments and then cooled to room temperature to obtain a prelithiated porous carbon substrate.

[0115] The three-step high-temperature treatment includes:

[0116] The first step is high-temperature treatment, in which the reactor is heated to 500-1200°C under a nitrogen and / or inert gas atmosphere. Specifically, it can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C or any value within the above range; optionally, the reactor is heated to 600-1000°C.

[0117] In an optional embodiment, the heat is maintained for 2 to 8 hours; specifically, it can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or any value within the above range; optionally, the heat is maintained for 3 to 5 hours.

[0118] The second step involves high-temperature treatment, in a reducing atmosphere, heating the reactor to 500–1300°C, specifically 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, or any value within the above range; optionally, the reactor is heated to 700–1200°C.

[0119] In an optional embodiment, the heat preservation time is 2 to 10 hours; specifically, it can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or any value within the above range; optionally, the heat preservation time is 3 to 9 hours.

[0120] The third step involves high-temperature treatment, in an inert gas atmosphere, heating the reactor to 500–1200°C, specifically 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, or any value within the above range; optionally, the reactor is heated to 600–1000°C.

[0121] In an optional embodiment, the heat preservation time is 1 to 10 hours; specifically, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or any value within the above range; optionally, the heat preservation time is 3 to 5 hours.

[0122] S4. The pre-lithiated porous carbon substrate prepared in step S3 is subjected to silicon deposition and carbon coating in sequence to obtain the pre-lithiated silicon-carbon anode material.

[0123] In an optional implementation, step S1 satisfies at least one of the following (1) to (8):

[0124] (1) The carbon source is selected from one or more of the following: biomass, polymer, coal-based, and petroleum-based;

[0125] In an optional implementation, the biomass is selected from common types such as coconut shells, rice, straw, and bamboo;

[0126] In an optional embodiment, the polymer is selected from common types such as phenolic resin and epoxy resin.

[0127] (2) The activation treatment methods include physical activation and / or chemical activation;

[0128] (3) The physical activation uses an activator selected from one or more of water vapor, carbon dioxide, and carbon monoxide;

[0129] (4) The physical activation temperature is 500-1500℃; specifically, it can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃ or any value within the above range; optionally, the activation temperature is 700-1200℃.

[0130] The physical activation is controlled at a pressure of 0.1–15 kPa; specifically, it can be 0.1 kPa, 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 5 kPa, 8 kPa, 10 kPa, 12 kPa, 15 kPa or any value within the above range; optionally, the activation pressure is controlled at 2–10 kPa.

[0131] In an optional implementation, the activation time is 1 to 30 hours, which can be adjusted adaptively according to the activation temperature;

[0132] (5) The physical activation involves an activator flow rate of 1–50 kg / h; specifically, it can be 1 kg / h, 2 kg / h, 5 kg / h, 10 kg / h, 12 kg / h, 15 kg / h, 20 kg / h, 22 kg / h, 25 kg / h, 30 kg / h, 32 kg / h, 35 kg / h, 40 kg / h, 42 kg / h, 45 kg / h, 50 kg / h, or any value within the above range; optionally, the activator flow rate is 1–10 kg / h.

[0133] (6) The chemical activation used is selected from one or more of potassium hydroxide, sodium hydroxide, phosphoric acid, hydrochloric acid, and sulfuric acid;

[0134] (7) In the chemical activation, the mass ratio of the activator to the carbon source precursor is 1:(0.5 to 6.0); specifically, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6 or any ratio within the above range; optionally, the mass ratio of the activator to the carbon source precursor is 1:(1 to 4).

[0135] (8) The chemical activation temperature is 600 to 1200℃; specifically, it can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or any value within the above range; optionally, the activation temperature is 700 to 1000℃.

[0136] In an optional implementation, step S2 satisfies at least one of the following (a) to (v):

[0137] (i) The lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, lithium fluoride, lithium nitrate, and lithium phosphate;

[0138] (ii) The solvent is selected from one or more of water, methanol, ethanol, and tetrahydrofuran;

[0139] (iii) The mass ratio of porous carbon to lithium source is (0.5 to 20):1; specifically, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 15:1, 18:1, 20:1 or any ratio within the above range; optionally, the mass ratio of porous carbon to lithium source is (0.5 to 5.0):1; more preferably, the mass ratio of porous carbon to lithium source is (0.8 to 3.0):1;

[0140] (iv) The concentration of lithium salt in the dispersion is (1-30) wt%; specifically, it can be 1 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, 28 wt%, 30 wt%, or any value within the above range;

[0141] (v) The spray drying process has an inlet temperature of 60–180°C; specifically, it can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C or any value within the above range; optionally, the inlet temperature is 80–150°C.

[0142] The spray drying process has an outlet temperature of 60–150°C; specifically, it can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or any value within the above range; optionally, the outlet temperature is 80–120°C.

[0143] Step S3 employs a three-step high-temperature processing technology. The first step, high-temperature processing, decomposes the lithium source. When a nitrogen atmosphere is used, the main decomposition products are lithium nitride and lithium oxide; when an inert gas atmosphere is used, the main decomposition product is lithium oxide. The second and third steps, high-temperature processing, convert the decomposition products from the first step into lithium-carbon compounds. Appropriate processing conditions ensure the formation of a high and suitable content of lithium-carbon compounds, ultimately yielding a negative electrode material with excellent overall electrochemical performance. Therefore, the three-step high-temperature processing technology is indispensable and mutually influential.

[0144] In an optional implementation, step S3 satisfies at least one of the following (A) to (C):

[0145] (A) The inert gas used in the first high-temperature treatment is selected from argon and / or helium;

[0146] In an optional embodiment, during the first high-temperature treatment, the flow rate of nitrogen and / or inert gas is 1 to 20 L / min; specifically, it can be 1 L / min, 2 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min or any value within the above range; optionally, the flow rate is 1 to 10 L / min.

[0147] (B) The reducing atmosphere used in the second step of high-temperature treatment is selected from one or more of carbon monoxide, hydrogen, hydrogen sulfide, and methane.

[0148] In an optional embodiment, in the second high-temperature treatment, the flow rate of the reducing gas is 1 to 20 L / min; specifically, it can be 1 L / min, 2 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min or any value within the above range; optionally, the flow rate is 1 to 10 L / min.

[0149] (C) The inert gas used in the third step of high-temperature treatment is selected from argon and / or helium;

[0150] In an optional embodiment, in the third step of high-temperature treatment, the flow rate of the inert gas is 1 to 20 L / min; specifically, it can be 1 L / min, 2 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min or any value within the above range; optionally, the flow rate is 1 to 10 L / min.

[0151] In an optional implementation, in step S4:

[0152] The gas source used for silicon deposition includes silicon source gas, inert gas, and a second gas source that can be selectively added;

[0153] In an optional embodiment, the silicon source gas is selected from one or more of silane, silane, monochlorosilane, dichlorosilane, and trichlorosilane;

[0154] In an optional embodiment, the inert gas is selected from nitrogen, argon, helium, etc.

[0155] In an optional embodiment, the second gas source is selected from one or more of carbon source gas, nitrogen source gas, sulfur source gas, and phosphorus source gas;

[0156] Optionally, the carbon source gas is selected from alkane gases whose pyrolysis temperature is within the carbon deposition temperature range, specifically common types such as ethylene and acetylene;

[0157] Optionally, the nitrogen source gas is selected from ammonia;

[0158] Optionally, the sulfur source gas is selected from one or more of hydrogen sulfide, sulfur dioxide, and sulfur hexafluoride;

[0159] Optionally, the phosphorus source gas is selected from one or more of phosphine, phosphorus chloride, and phosphorus fluoride;

[0160] In an optional embodiment, the second gas source is co-deposited after being mixed with the silicon source gas, or it is deposited alternately with the silicon source gas.

[0161] In an optional embodiment, the total flow rate of the gas source for silicon deposition is 1 to 100 L / min; specifically, it can be 1 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, 55 L / min, 60 L / min, 65 L / min, 70 L / min, 75 L / min, 80 L / min, 85 L / min, 90 L / min, 95 L / min, 100 L / min or any value within the above range; optionally, the total flow rate of the gas source is 1 to 30 L / min.

[0162] In an optional embodiment, the silicon deposition process involves a silicon source gas concentration of 30–99 vol% in the gas source; specifically, it can be 30 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 80 vol%, 90 vol%, 99 vol%, or any value within the above range; optionally, the silicon source gas concentration in the gas source is 50–90 vol%.

[0163] In an optional embodiment, the silicon deposition temperature is 400 to 1000°C, specifically 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C or any value within the above range;

[0164] The silicon deposition time is 1 to 50 hours; it can be adjusted according to the silicon deposition temperature.

[0165] In an optional embodiment, the gas source used for carbon coating includes carbon source gas and carrier gas;

[0166] Optionally, the carbon source gas is selected from alkane gases whose pyrolysis temperature is within the carbon deposition temperature range; specifically, ethylene, acetylene, etc.

[0167] In an optional embodiment, the carbon coating is achieved by having a carbon source gas content of 30–90 vol% in the gas source; specifically, it can be 30 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 80 vol%, 90 vol%, 99 vol%, or any value within the above range; optionally, the carbon source gas content in the gas source is 50–90 vol%.

[0168] In an optional embodiment, the carbon coating temperature is 300–1200°C, specifically 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, or any value within the above range;

[0169] The carbon coating time is 2 to 20 hours; it can be adjusted according to the carbon coating temperature.

[0170] Thirdly, the present invention also provides a negative electrode sheet, comprising the aforementioned pre-lithiated silicon-carbon negative electrode material.

[0171] Fourthly, the present invention also provides a secondary battery, including the aforementioned negative electrode sheet.

[0172] Example 1

[0173] (1) Phenolic resin was used as a carbon source and carbonized at 800℃ for 5h under nitrogen protection, with a heating rate of 5℃ / min, to obtain a carbon precursor.

[0174] (2) Place the above 10kg carbon precursor in a rotary kiln, evacuate it, and backfill it with nitrogen to keep the kiln in an inert atmosphere. Control the oxygen content in the kiln to be below 500ppm, adjust the rotary kiln speed to 5r / min, and heat the carbon precursor to 800℃ at 5℃ / min for physical activation. The activation process gas is water vapor, the flow rate is 2kg / h, the activation time is 10h, and the kiln pressure is kept below 5KPa during the activation process to obtain porous carbon particles. Then, after coarse crushing, gas crushing, and classification, porous carbon is obtained.

[0175] The specific surface area of ​​porous carbon was measured to be 2030 m². 2 / g, pore volume 0.95cm 3 / g, D50=7.0μm;

[0176] (3) Dissolve 5 kg of lithium acetate in 35 kg of water (12.5 wt%), stir until it is completely dissolved, add 10 kg of porous carbon obtained in step (2), and then spray dry the above dispersion to obtain a pre-lithiation precursor. The spray drying inlet temperature is 120°C and the outlet temperature is 110°C.

[0177] (4) The prelithiated precursor obtained in step (3) is placed in a rotary kiln, vacuumed, and then backfilled with nitrogen to maintain an inert atmosphere in the kiln. The rotary kiln speed is adjusted to 1 r / min, and the temperature is raised to 900℃ at 5℃ / min. Nitrogen is continuously introduced at a flow rate of 4 L / min and held for 3 h. Then, CO gas is introduced for reduction at a flow rate of 4 L / min and held for 6 h. Then, argon gas is introduced at a flow rate of 4 L / min and held for 3 h. Finally, argon gas is introduced to cool down and a prelithiated porous carbon substrate is obtained.

[0178] (5) Add 10 kg of the pre-lithiated porous carbon substrate obtained in step (4) into a rotary kiln. Maintain an inert atmosphere inside the kiln and control the oxygen content inside the kiln to be below 500 ppm. Then, purge with nitrogen gas at a flow rate of 4 L / min and heat to 475 °C. Purge with a gas source consisting of 80 vol% silane and 20 vol% nitrogen at a flow rate of 5 L / min. The volume of silane in the gas source is 9800 L. Control the kiln rotation speed to 1.5 r / min. Silane deposition is then performed. Subsequently, nitrogen is introduced into the rotary kiln again at a flow rate of 8 L / min. After heating to 600°C, a gas source consisting of 80 vol% acetylene and 20 vol% nitrogen is introduced at a flow rate of 8 L / min. The volume of acetylene gas in the gas source is 3500 L. The kiln speed is controlled at 1.5 r / min. The carbon source gas is decomposed through high-temperature pyrolysis, and carbon atoms are coated on the porous carbon surface of the deposited silicon. After carbon coating is completed, a pre-lithiated silicon-carbon anode material is obtained.

[0179] EDS analysis revealed that in the pre-lithiated porous carbon substrate prepared in step (4) of this embodiment, LiC6 and LiC... 24 The total mass of the pre-lithiated porous carbon substrate accounts for 2.4% of the total mass. According to the XRD pattern, LiC6 and LiC... 24 The mass ratio of the two is 1:2.04.

[0180] Figure 1 The image shows a scanning electron microscope (SEM) image of the pre-lithiated porous carbon substrate prepared in step (4) of this embodiment. It is observed that the C and Li elements are uniformly distributed in the pre-lithiated porous carbon substrate.

[0181] The actual silicon content in the pre-lithiated silicon-carbon anode material prepared in this embodiment was 48.13% (Mettler-Toledo TG-A2, 30–1000 °C) as determined by the TG method.

[0182] Example 2

[0183] The preparation process is basically the same as in Example 1, except that the mass of lithium acetate in step (3) is replaced with 3.5 kg.

[0184] Example 3

[0185] The preparation process is basically the same as in Example 1, except that the mass of lithium acetate in step (3) is replaced with 8.75 kg.

[0186] Example 4

[0187] The preparation process is basically the same as in Example 1, except that the mass of lithium acetate in step (3) is replaced with 12 kg.

[0188] Comparative Example 1

[0189] The preparation process is basically the same as in Example 1, except that the mass of lithium acetate in step (3) is replaced with 0.4 kg.

[0190] Example 5

[0191] The preparation process is basically the same as in Example 1, except that the time of the first high-temperature treatment in step (4) is different, specifically:

[0192] The temperature was increased to 900℃ at a rate of 5℃ / min, and nitrogen gas was continuously introduced at a flow rate of 4L / min. The temperature was maintained for 5 hours.

[0193] Example 6

[0194] The preparation process is basically the same as in Example 1, except that the time of the first high-temperature treatment in step (4) is different, specifically:

[0195] The temperature was increased to 900℃ at a rate of 5℃ / min, and nitrogen gas was continuously introduced at a flow rate of 4L / min. The temperature was maintained for 2 hours.

[0196] Comparative Example 2

[0197] The preparation process is basically the same as in Example 1, except that the time of the first high-temperature treatment in step (4) is different, specifically:

[0198] The temperature was increased to 900℃ at a rate of 5℃ / min, and nitrogen gas was continuously introduced at a flow rate of 4L / min. The temperature was maintained for 1 hour.

[0199] Example 7

[0200] The preparation process is basically the same as in Example 1, except that the time of the second high-temperature treatment in step (4) is different, specifically:

[0201] CO gas was introduced for reduction at a flow rate of 4 L / min, and the temperature was maintained for 3 hours.

[0202] Example 8

[0203] The preparation process is basically the same as in Example 1, except that the time of the second high-temperature treatment in step (4) is different, specifically:

[0204] CO gas was introduced for reduction at a flow rate of 4 L / min, and the temperature was maintained for 9 hours.

[0205] Comparative Example 3

[0206] The preparation process is basically the same as in Example 1, except that the time of the second high-temperature treatment in step (4) is different, specifically:

[0207] CO gas was introduced for reduction at a flow rate of 4 L / min, and the temperature was maintained for 1 hour.

[0208] Example 9

[0209] The preparation process is basically the same as in Example 1, except that the temperature of the second high-temperature treatment in step (4) is different, specifically:

[0210] First, adjust the furnace temperature to 1000℃ (the first step of high-temperature treatment is 900℃), then introduce CO gas for reduction at a flow rate of 4L / min and hold for 6 hours.

[0211] Example 10

[0212] The preparation process is basically the same as in Example 1, except that the temperature of the second high-temperature treatment in step (4) is different, specifically:

[0213] First, adjust the furnace temperature to 700℃ (the first step of high-temperature treatment is 900℃), then introduce CO gas for reduction at a flow rate of 4L / min and hold for 6 hours.

[0214] Example 11

[0215] The preparation process is basically the same as in Example 1, except that the temperature of the second high-temperature treatment in step (4) is different, specifically:

[0216] First, adjust the furnace temperature to 1200℃ (the first step of high-temperature treatment is 900℃), then introduce CO gas for reduction at a flow rate of 4L / min and hold for 6 hours.

[0217] Example 12

[0218] The preparation process is basically the same as in Example 1, except that the temperature of the second high-temperature treatment in step (4) is different, specifically:

[0219] First, adjust the furnace temperature to 500℃ (the first step of high-temperature treatment is 900℃), then introduce CO gas for reduction at a flow rate of 4L / min and hold for 6 hours.

[0220] Example 13

[0221] The preparation process is basically the same as in Example 1, except that the temperature of the second high-temperature treatment in step (4) is different, specifically:

[0222] First, adjust the furnace temperature to 1300℃ (the first step of high-temperature treatment is 900℃), then introduce CO gas for reduction at a flow rate of 4L / min and hold for 6 hours.

[0223] Comparative Example 4

[0224] The preparation process is basically the same as in Example 1, except that the temperature of the second high-temperature treatment in step (4) is different, specifically:

[0225] First, adjust the furnace temperature to 400℃ (the first step of high-temperature treatment is 900℃), then introduce CO gas for reduction at a flow rate of 4L / min and hold for 6 hours.

[0226] Example 14

[0227] The preparation process is basically the same as in Example 1, except that the time of the high-temperature treatment in the third step (4) is different, specifically:

[0228] Argon gas was introduced at a flow rate of 4 L / min and kept at that temperature for 5 hours. Finally, argon gas was continued to be introduced to cool the temperature.

[0229] Example 15

[0230] The preparation process is basically the same as in Example 1, except that the time of the high-temperature treatment in the third step (4) is different, specifically:

[0231] Introduce argon gas at a flow rate of 4 L / min and maintain the temperature for 1 hour; finally, continue to purge argon gas to cool down.

[0232] Comparative Example 5

[0233] The preparation process is basically the same as in Example 1, except that the third high-temperature treatment is not performed in step (4), specifically:

[0234] After reduction, argon gas is introduced at a flow rate of 4 L / min for direct cooling.

[0235] Comparative Example 6

[0236] The preparation process is basically the same as in Example 1, except that the third high-temperature treatment and cooling under argon gas were not performed in step (4). Specifically:

[0237] The reduction is carried out under a carbon monoxide atmosphere, and then the temperature is directly lowered under a carbon monoxide atmosphere after reduction.

[0238] Comparative Example 7

[0239] The preparation process is basically the same as in Example 1, except that the atmosphere of the high-temperature treatment in the third step (4) is replaced with nitrogen instead of argon.

[0240] Comparative Example 8

[0241] The preparation process is basically the same as in Example 1, except that the high-temperature treatment processes in the second and third steps are not performed in step (4). Specifically:

[0242] After holding the temperature under nitrogen for 3 hours, the temperature was directly lowered under a nitrogen atmosphere.

[0243] Figure 2 The XRD patterns of the pre-lithiated porous carbon substrates prepared in Examples 1, 7, and 8 are shown. It was observed that the pre-lithiated porous carbon substrate prepared by only the first step of high-temperature treatment in Comparative Example 8 had a more complex product, mainly existing in the forms of lithium oxide and lithium nitride. Comparing Examples 1 and 7, both products contained LiC6 and LiC. 24 The lithium-carbon compound is generated, and the content increases with the extension of the second high-temperature treatment time.

[0244] Comparative Example 9

[0245] (1)~(2) The preparation of porous carbon is exactly the same as in Example 1;

[0246] (3) Place porous carbon as a substrate in a vapor deposition furnace, evacuate to -0.01 MPa on the relative vacuum gauge, introduce argon gas until the relative vacuum gauge reads 1 atmosphere, stop introducing argon gas, and evacuate again until the relative vacuum gauge reads -0.01 MPa. Repeat this cycle 3 times to complete the gas exchange. Proceed to 1200℃ and evacuate the furnace until the P / P0 ratio is 10. -4 (P0 is the saturated vapor pressure of lithium), lithium vapor (purity 99.95%) is slowly and intermittently introduced, and P / P0 slowly rises until P / P0 is 0.5, at which point the introduction of lithium vapor is stopped. The lithium vapor in the reactor is adsorbed in the pores of the porous carbon substrate to obtain pre-lithiated carbon material.

[0247] (4) Silicon deposition and carbon coating were performed on the pre-lithiated carbon material prepared in step (3) as a substrate. The specific preparation process was exactly the same as step (5) in Example 1.

[0248] Comparative Example 10

[0249] (1) 10 kg of lithium carbonate and 100 kg of poly(ethylene glycol)-intercalated-poly(propylene glycol)-intercalated-poly(ethylene glycol) (Synperonic F-108) were mixed into 1000 L of polyvinyl alcohol aqueous solution with a solid content of 30 wt% and stirred for 8 h to obtain a lithium-rich suspension; the lithium-rich suspension was then centrifugally spray-dried to obtain lithium-rich carbon balls. The feed temperature for spray drying was 160 °C and the feed rate was 500 L / h.

[0250] (2) The obtained lithium-rich carbon spheres were placed in a rotary kiln and nitrogen was continuously introduced into the kiln as a protective gas. The temperature was raised to 800°C at a heating rate of 5°C / min for carbonization and pore-forming treatment. The carbonization time was 15h. After the carbonization was completed, the temperature was naturally cooled to room temperature to obtain lithium-rich porous carbon spheres.

[0251] (3) Silicon deposition and carbon coating were performed on the lithium-rich porous carbon spheres prepared in step (2) as a substrate. The specific preparation process was exactly the same as step (5) in Example 1.

[0252] Comparative Example 11

[0253] The preparation process is basically the same as that in Example 1, except that steps (3) and (4) are removed, and silicon deposition and carbon coating are performed directly on porous carbon as a substrate.

[0254] Example 16

[0255] The preparation process is basically the same as in Example 1, except that the phenolic resin in step (1) is replaced with an equal mass of coconut shell.

[0256] Example 17

[0257] The preparation process is basically the same as in Example 1, except that the physical activation conditions in step (2) are adjusted, specifically:

[0258] Replace the activation temperature with 900℃ and the activation time with 7h.

[0259] Example 18

[0260] The preparation process is basically the same as in Example 1, except that the physical activation in step (2) is replaced by chemical activation, specifically:

[0261] The above 10 kg of carbon precursor and 5 kg of KOH were placed in a rotary kiln. After evacuation, nitrogen was backfilled to maintain an inert atmosphere in the kiln. The oxygen content in the kiln was controlled to be below 500 ppm. The rotary kiln speed was adjusted to 5 r / min, and the carbon precursor was chemically activated at 850℃ at a rate of 5℃ / min for 7 hours. During the activation process, the kiln pressure was kept below 5 kPa to obtain porous carbon particles. These particles were then subjected to coarse crushing, gas crushing, and classification to obtain porous carbon.

[0262] Intermediate pre-lithiation porous carbon substrates (total lithium-carbon ratio, LiC6 to LiC6 ratio) prepared for each embodiment and comparative example 24 The mass ratio of the pre-lithiated silicon-carbon anode material and the final product were tested for performance. The specific results are listed in Table 1 below.

[0263]

[0264]

[0265] Observing the data in Table 1 and comparing Examples 1-4 with Comparative Example 1, it can be seen that by adjusting the amount of lithium salt and porous carbon, the total lithium-carbon ratio (LiC6 and LiC6) in the pre-lithiated porous carbon substrate can be adjusted. 24 (total mass ratio of pre-lithiated porous carbon substrate) and LiC6 and LiC 24 The mass ratio; comparing Examples 1, 5, 6 and Comparative Example 2, it can be seen that adjusting the time of the first-step high-temperature treatment can adjust the total lithium-carbon ratio and the ratio of LiC6 to LiC in the pre-lithiated porous carbon substrate. 24 The mass ratio; comparing Examples 1, 7-13 and Comparative Examples 3-4, it can be seen that by adjusting the time and temperature of the second-step high-temperature treatment, the total lithium-carbon ratio and the ratio of LiC6 to LiC in the pre-lithiated porous carbon substrate can be adjusted. 24 The mass ratio; comparing Examples 1, 14, and 15, it can be seen that adjusting the time of the third step of high-temperature treatment can also adjust the total lithium-carbon ratio and the ratio of LiC6 to LiC in the pre-lithiated porous carbon substrate. 24 The mass ratio.

[0266] Performance testing:

[0267] The products prepared in each embodiment and each comparative example were used as negative electrode materials to assemble batteries.

[0268] (1) Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), conductive agent SuperP, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.5:1.5 to prepare a positive electrode slurry (solid content of 70wt%). The slurry is coated on both sides of the current collector aluminum foil, dried at 100℃, and then cold-pressed at room temperature at 4MPa. The slurry is then trimmed, cut into strips, and slit, and the tabs are welded to form the positive electrode sheet.

[0269] (2) Preparation of negative electrode sheet: Under a nitrogen protective atmosphere, the solvent N-methylpyrrolidone (NMP) and binder PVDF are stirred and mixed, then the conductive agent SuperP is added and stirred and mixed, and then the final products prepared in each example and each comparative example are added as negative electrode active materials and stirred and mixed thoroughly to prepare negative electrode slurry (solid content is 50wt%).

[0270] The above-mentioned negative electrode slurry is coated on both sides of the current collector copper foil, dried at 100°C, and then cold-pressed at 4MPa at room temperature. After that, the foil is trimmed, cut into pieces, slit, and the tabs are welded to form the negative electrode sheet.

[0271] (3) Assembly of lithium-ion batteries

[0272] Using a porous PE polymer film as the separator, the prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes, and wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic shell package and dried at 100℃ under a relative vacuum pressure of -0.95×10⁵ Pa until the moisture content is below 100ppm. An electrolyte composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF₆ (1.0M) is injected into the dried bare cell. The process includes encapsulation, settling, formation (0.02C constant current charging for 2 hours, 0.1C constant current charging for 2 hours), shaping, and capacity testing (capacity grading) to produce a soft-pack liquid lithium-ion battery. During battery assembly, five batteries are prepared for each test group, and five sets of data are tested. The final performance is the average of the five sets of data.

[0273] Battery cycle performance was tested on Blue Electric equipment, specifically as follows: at 25℃, the battery was first discharged at 0.1C to 0.005V, then discharged at 0.08C to 0.001V, then at 0.05C to 0.001V, and then at 0.02C to 0.001V, followed by a 10-minute rest period; then charged at 0.1C to 1.5V, followed by a 10-minute rest period. The charge-discharge capacity after the first cycle was recorded, and the initial coulombic efficiency was calculated. The battery was cycled 500 and 1000 times in the same manner, and the charge-discharge capacity after 500 and 1000 cycles was recorded, and the capacity retention rate after 500 and 1000 cycles was calculated. The expansion test was performed after battery cycling, by disassembling the battery and comparing the thickness of the electrode plates with that before cycling. Rate performance testing involved discharging at 1C to 0.001V, resting for 10 minutes, then charging at 5C to 1.5V, resting for 10 minutes, and recording the charge-discharge capacity and initial efficiency after the first cycle. The performance characteristics of the assembled battery are listed in Table 2 below.

[0274] Table 2

[0275]

[0276]

[0277] Observing the data in Table 2, the batteries assembled in Examples 1 to 4 have high capacity, high initial efficiency, long cycle stability and high rate performance, and excellent overall electrical performance; among them, the overall electrical performance of Example 1 is the best; compared with Example 1 and Comparative Example 1, when the amount of lithium source is too low, the improvement in the electrochemical performance of the assembled battery is limited.

[0278] Compared with Comparative Example 1 and Comparative Example 2, when the first-step high-temperature treatment time is too short, the content of lithium-carbon compounds will be reduced, and the electrochemical performance of the assembled battery will be only slightly improved.

[0279] Compared with Comparative Example 1 and Comparative Example 3, when the second-step high-temperature treatment time is too short, the content of lithium-carbon compounds will be reduced, and the electrochemical performance of the assembled battery will be only slightly improved.

[0280] The batteries assembled in Examples 1, 9-13 have high capacity, high initial efficiency, long cycle stability and high rate performance, with excellent overall electrical performance. However, if the temperature of the second high-temperature treatment is too high, the capacity improvement will not be significant or even decrease. This may be because the high temperature will cause the pores in the porous carbon substrate to collapse, reducing the capacity to accommodate nano-silicon. Therefore, the preferred temperature for the second high-temperature treatment is 700-1200℃.

[0281] Compared with Comparative Example 1 and Comparative Example 4, when the temperature of the second high-temperature treatment is too low, the content of lithium-carbon compounds will be reduced, and the electrochemical performance of the assembled battery will be only slightly improved.

[0282] Comparing Example 1 with Comparative Examples 5 and 6, it was found that when the third high-temperature treatment was not performed (Comparative Example 6), or when the inert gas of the third high-temperature treatment was replaced but the temperature was directly lowered without heat preservation (Comparative Example 5), the content of lithium carbon compounds decreased, which in turn affected the electrochemical performance of the final assembled battery.

[0283] Comparative Examples 1 and 7 and 8 show similar results when the inert atmosphere of the third high-temperature treatment was replaced with nitrogen (Comparative Example 7) and only the first high-temperature treatment was performed (Comparative Example 8). No lithium carbon compounds were detected in the product, which affected the electrochemical performance of the final assembled battery.

[0284] Comparing Example 1 with Comparative Examples 9 and 10, Comparative Examples 9 and 10 represent pre-lithiation processes disclosed in the prior art. In Comparative Example 9, porous carbon is prepared first, followed by pre-lithiation. Comparative Example 10 is similar to that in this application, where the preparation of porous carbon and the pre-lithiation process are carried out simultaneously, but the specific preparation process is significantly different. Comparing the electrochemical performance of the batteries assembled from the three examples, it can be seen that Comparative Examples 9 and 10 can only improve the initial efficiency, but have little to no improvement on capacity, cycle stability, and rate performance. However, the battery assembled using the method of this invention, through special pre-lithiation treatment, not only significantly improves the initial efficiency but also significantly improves its cycle stability and rate performance, resulting in excellent overall electrical performance.

[0285] The above-described embodiments are preferred embodiments, but the scope of protection of the present invention is not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a pre-lithiated silicon-carbon anode material, characterized in that, Comprise: S1, carbon source is treated by carbonization to obtain carbon source precursor; the carbon source precursor is activated to obtain porous carbon; S2, the porous carbon prepared in step S1, lithium source and solvent are mixed to obtain a dispersion liquid, and the dispersion liquid is sprayed and dried to obtain a prelithiation precursor; The mass ratio of porous carbon to lithium source is (0.5-20):1; S3, the prelithiation precursor prepared in step S2 is treated by three-step high temperature treatment and then cooled to room temperature to obtain a prelithiation porous carbon base; The three-step high temperature treatment comprises: The first step of high temperature treatment is to heat the reactor to 500-1200 DEG C under the atmosphere of nitrogen and / or inert gas, and keep the temperature for 2-8h; The second step of high temperature treatment is to heat the reactor to 500-1300 DEG C under the reducing atmosphere, and keep the temperature for 2-10h; The third step of high temperature treatment is to heat the reactor to 500-1200 DEG C under the atmosphere of inert gas, and keep the temperature for 1-10h; S4, the prelithiation porous carbon base prepared in step S3 is sequentially subjected to silicon deposition and carbon coating to obtain the prelithiation silicon-carbon negative electrode material.

2. The method of preparing a prelithiated silicon-carbon negative electrode material according to claim 1, characterized in that, Step S1 meets at least one of the following (1)-(2): (1) the carbon source is selected from one or more of biomass, high molecular polymer, coal-based and petroleum-based; (2) the activation method comprises physical activation and / or chemical activation.

3. The method of preparing a prelithiated silicon-carbon negative electrode material according to claim 2, characterized in that, The physical activation: The adopted activator is selected from one or more of water vapor, carbon dioxide and carbon monoxide; The activation temperature is 500-1500 DEG C, and the pressure during activation is controlled to be 0.1-15 KPa; The flow rate of the activator is 1-50 kg / h.

4. The method of preparing a prelithiated silicon-carbon negative material according to claim 2, characterized in that, The chemical activation: The adopted activator is selected from one or more of potassium hydroxide, sodium hydroxide, phosphoric acid, hydrochloric acid and sulfuric acid; The mass ratio of the activator to the carbon source precursor is 1:(0.5-6.0); The activation temperature is 600-1200 DEG C. 5.The method of preparing a prelithiated silicon-carbon negative material according to claim 1, characterized in that, Step S2 meets at least one of the following (I)-(IV): (I) the lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, lithium fluoride, lithium nitrate and lithium phosphate; (II) the solvent is selected from one or more of water, methanol, ethanol and tetrahydrofuran; (III) the lithium salt concentration in the dispersion liquid is (1-30) wt%; (IV) the spray drying inlet temperature is 60-180 DEG C, and the outlet temperature is 60-150 DEG C.

6. The method of preparing a prelithiated silicon-carbon negative material according to claim 1, wherein, Step S3 meets at least one of the following (A)-(C): (A) the inert gas in the first step of high temperature treatment is selected from argon and / or helium; (B) the reducing atmosphere in the second step of high temperature treatment is selected from one or more of carbon monoxide, hydrogen, hydrogen sulfide and methane; (C) the inert gas in the third step of high temperature treatment is selected from argon and / or helium.

7. The method of preparing a prelithiated silicon-carbon negative material according to claim 1, wherein, In step S4: The gas source for silicon deposition includes silicon source gas and inert gas; And / or, the total flow rate of the gas source for silicon deposition is 1-100 L / min, and the proportion of silicon source gas in the gas source is 30-99 vol%; And / or, the temperature for silicon deposition is 400-1000 DEG C, and the time is 1-50h; The gas source for carbon coating includes carbon source gas and carrier gas; And / or, the carbon-coated, the carbon source gas in the gas source accounts for 30-90vol%; And / or, the carbon-coated, the temperature is 300-1200℃, and the time is 2-20h.

8. The method of preparing a prelithiated silicon-carbon negative electrode material according to claim 7, characterized in that, In step S4: The gas source used for the silicon deposition further includes a second gas source; The second gas source is selected from one or more of carbon source gas, nitrogen source gas, sulfur source gas, and phosphorus source gas; The second gas source is co-deposited after being blended with the silicon source gas, or is alternately deposited with the silicon source gas.

9. A pre-lithiated silicon-carbon anode material prepared according to the method of any one of claims 1 to 8, comprising a porous carbon substrate, silicon elements distributed within the pores of the porous carbon substrate, and carbon coating the outer surfaces of the porous carbon substrate and the silicon elements, characterized in that, The porous carbon substrate is a pre-lithiated porous carbon substrate, and the pre-lithiated porous carbon substrate further includes a lithium-carbon compound; The lithium carbon compound comprises LiC6 and / or LiC 24 .

10. The prelithiated silicon-carbon negative electrode material of claim 9, wherein, The lithium-carbon compound satisfies at least one of the following three conditions: a. The total mass of the lithium-carbon compound accounts for 1.5-10.0wt% of the mass of the pre-lithiated porous carbon substrate; b. Lithium carbon compounds include LiC6and LiC 24 ; c, LiC6 and LiC 24 The mass ratio of the two is 1: (0.5-5).

11. The pre-lithiated silicon-carbon negative electrode material according to claim 9, characterized in that: The average pore diameter D50 of the pre-lithiated silicon-carbon negative electrode material is 3-15μm; and / or the pre-lithiated silicon-carbon anode material has a specific surface area of less than 10 m 2 / g; And / or, the tap density of the pre-lithiated silicon-carbon negative electrode material is 0.6-1.3 g / cm 3 ; And / or, the powder resistivity of the pre-lithiated silicon-carbon negative electrode material under 20MPa is not higher than 30Ω·cm.

12. A negative electrode sheet characterized by comprising: The pre-lithiated silicon-carbon negative electrode material according to any one of claims 9-11.

13. A secondary battery characterized by comprising: The negative electrode sheet according to claim 12.

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