Silicon-carbon composite material and preparation method thereof, negative pole piece and secondary battery

Abstract

The invention relates to the technical field of electrochemistry, in particular to a silicon-carbon composite material and a preparation method thereof, a negative pole piece and a secondary battery. The preparation method of the silicon-carbon composite material provided by the invention comprises the following steps: carrying out etching treatment on petroleum coke by adopting an organic potassium compound to prepare petroleum coke porous carbon; carrying out heteroatom gas deposition doping, silane gas deposition doping and metal gas deposition doping on the petroleum coke porous carbon to prepare a metal doped silicon carbon precursor material; carrying out passivating treatment on the metal-doped silicon carbon precursor material to prepare an intermediate material; and mixing the intermediate material and an inorganic lithium compound in a solvent, and drying to prepare the silicon-carbon composite material. When the silicon-carbon composite material prepared by the preparation method is used as a negative electrode material, the silicon-carbon composite material has relatively high conductivity and excellent structural stability, and expansion can be reduced, so that the rate capability and the cycle performance of a battery can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, specifically to silicon-carbon composite materials and their preparation methods, negative electrode sheets, and secondary batteries. Background Technology

[0002] Secondary batteries are widely used in power devices and energy storage equipment due to their advantages such as rechargeability, high energy density, and environmental friendliness. The negative electrode material is a crucial component of secondary batteries, and its performance directly affects the electrochemical performance of the battery.

[0003] Currently, the most widely used anode materials are graphite and silicon-carbon. Graphite materials have advantages such as relatively low specific capacity, low charge / discharge plateau, and low cost. However, the two-dimensional lithium intercalation / deintercalation structure of graphite results in a slow ion intercalation / deintercalation rate, reducing its rate performance. Silicon-carbon materials have advantages such as high energy density, wide availability of materials, and a three-dimensional lithium intercalation / deintercalation structure. Currently, silicon-carbon materials are mainly composed of porous carbon and deposited nano-silicon. However, due to the poor conductivity of porous carbon and the poor isotropy of carbon-based materials, significant impedance is generated, which is also detrimental to improving the rate performance and cycle performance of secondary batteries. Summary of the Invention

[0004] Based on this, this application provides a silicon-carbon composite material and its preparation method, a negative electrode sheet, and a secondary battery. When used as a negative electrode material, the silicon-carbon composite material provided in this application exhibits high conductivity and excellent structural stability, reducing expansion and thus effectively improving the rate performance and cycle performance of the battery.

[0005] A first aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0006] Petroleum coke porous carbon was prepared by etching petroleum coke with organopotassium compounds.

[0007] Metal-doped silicon-carbon precursor materials were prepared by performing heteroatom gas deposition doping, silane gas deposition doping, and metal gas deposition doping on the porous carbon from petroleum coke.

[0008] The metal-doped silicon-carbon precursor material is passivated to prepare an intermediate material;

[0009] The intermediate material and the inorganic lithium compound were mixed in a solvent and dried to prepare a silicon-carbon composite material.

[0010] In one embodiment, the step of etching petroleum coke using an organopotassium compound includes:

[0011] The petroleum coke and the organopotassium compound are mixed in a dispersion, and after etching, the filter residue is collected.

[0012] The filter residue is activated and washed to prepare the petroleum coke porous carbon.

[0013] In one embodiment, the organopotassium compound includes one or more of potassium 2,4-hexadienoate, potassium citrate, potassium humate, potassium cinnamate, potassium hydrogen 1,2-phthalate, and potassium salt of 2-ethylhexanoate.

[0014] In one embodiment, the dispersion comprises one or more of dichloromethane, ethyl acetate, glycerol, and propylene glycol.

[0015] In one embodiment, the mass ratio of the organopotassium compound to the dispersion is (5~30):(70~95).

[0016] In one embodiment, the etching process parameters include a temperature of 150°C to 300°C.

[0017] In one embodiment, the process parameters for the activation treatment include a temperature of 600°C to 1000°C.

[0018] In one embodiment, the washing step includes: sequentially performing acid washing and water washing.

[0019] In one embodiment, the inorganic lithium compound includes one or more of lithium phosphate, lithium fluoride, lithium titanate, and lithium sulfonate.

[0020] In one embodiment, the mass ratio of the intermediate material to the inorganic lithium compound is 100:(1~5).

[0021] In one embodiment, the mass ratio of the inorganic lithium compound to the solvent is (1~10):(90~99).

[0022] In one embodiment, the metal gas used in the metal gas deposition doping process has a boiling point of 900°C to 1350°C.

[0023] In one embodiment, the metal gas deposition doping step includes: introducing metal gas at a flow rate of 10 sccm to 100 sccm under conditions of temperature 900℃ to 1350℃, vacuum degree ≤10pa, and pressure 1Mpa to 5Mpa to perform deposition doping.

[0024] In one embodiment, the heteroatom gas used in the heteroatom gas deposition doping includes one or more of diborane, methaneborane, phosphine, hydrogen fluoride, and hydrogen chloride.

[0025] In one embodiment, the process parameters for heteroatom gas deposition doping include: vacuum degree ≤10pa, temperature 300℃~500℃, heteroatom gas flow rate 10sccm~100sccm, and pressure 1MPa~5MPa.

[0026] In one embodiment, the silane gas used in the silane gas deposition doping includes one or more of tetrachlorosilane, trichlorosilane, trimethylchlorosilane, tetrafluorosilane, and trimethylfluorosilane.

[0027] In one embodiment, the silane gas deposition doping step includes: introducing silane gas at a flow rate of 10 sccm to 100 sccm under conditions of temperature 450°C to 550°C, vacuum degree ≤ 10 Pa, and pressure 1 MPa to 5 MPa to perform deposition doping.

[0028] In one embodiment, the passivation process includes:

[0029] With a dew point of ≤-60℃, the metal-doped silicon-carbon precursor material is heated to 100℃~200℃ and passivated by introducing an oxidizing gas at a flow rate of 10sccm~100sccm.

[0030] In one embodiment, the oxidizing gas includes one or more of oxygen, nitrous oxide, nitrogen dioxide, chlorine dioxide, and ozone.

[0031] A second aspect of this application provides a silicon-carbon composite material.

[0032] The silicon-carbon composite material includes a metal-doped silicon-carbon precursor material and an inorganic lithium compound layer coating the surface of the metal-doped silicon-carbon precursor material.

[0033] The metal-doped silicon-carbon precursor material includes a petroleum coke porous carbon matrix and heteroatom compounds, nano-silicon, and metals deposited in the pores and / or surface of the petroleum coke porous carbon matrix.

[0034] A third aspect of this application provides a negative electrode sheet, comprising a negative current collector and a negative active material layer disposed on the surface of the negative current collector, wherein the negative active material layer comprises a silicon-carbon composite material prepared by any of the preparation methods of the first aspect of this application, or a silicon-carbon composite material as described in the second aspect of this application.

[0035] A fourth aspect of this application provides a secondary battery, including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode; wherein the negative electrode is the negative electrode sheet described in the third aspect of this application.

[0036] The method for preparing silicon-carbon composite materials provided in this application has at least the following beneficial effects:

[0037] In the preparation method provided in this application, petroleum coke is etched using an organopotassium compound, which forms porous carbon with a rich pore structure. When the porous carbon is doped with heteroatom gas deposition, heteroatoms are deposited on the channels or surface of the porous carbon, which helps to change the electronic structure of the porous carbon, increase active sites, and reduce the impedance of the silicon-carbon composite material. The silicon-carbon produced by silane gas deposition combines the advantages of high silicon specific capacity and carbon's ability to buffer volume changes during charge and discharge, resulting in a high-specific-capacity composite material. Further doping and depositing metals on the channels or surface of the porous carbon, which synergize with the nano-silicon formed by silane gas deposition, produces an alloy that improves the structural stability of the material, thereby reducing its expansion; simultaneously, metal doping also improves the ionic conductivity of the material. Furthermore, after passivation treatment of the metal-doped silicon-carbon precursor material, an inorganic lithium compound coating layer is applied, which further improves the lithium-ion insertion / extraction rate and reduces gas generation during charge and discharge.

[0038] Therefore, the silicon-carbon composite material of this application, through the deposition and doping of porous carbon, heteroatoms, nano-silicon and metals from petroleum coke, and the coating of inorganic lithium compounds, can effectively improve conductivity and structural stability, thereby effectively improving the rate performance and cycle performance of the battery. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The image shows a SEM image of the silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0041] The following detailed description, in conjunction with specific embodiments, provides a more complete and clear account of the silicon-carbon composite material, its preparation method, the negative electrode sheet, and the secondary battery of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0042] A first aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0043] S10: Prepare metal-doped silicon-carbon precursor materials by heteroatom gas deposition doping, silane gas deposition doping, and metal gas deposition doping of porous carbon from petroleum coke.

[0044] S20: Passivate the metal-doped silicon-carbon precursor material to prepare the intermediate material.

[0045] S30: Prepare silicon-carbon composite material by mixing intermediate materials and inorganic lithium compounds in a solvent and drying them.

[0046] Porous carbon materials are key materials for silicon-carbon materials. Petroleum coke has attracted widespread attention due to its low impedance. However, creating pores in petroleum coke is challenging. Currently, the main method involves activating petroleum coke with strong alkaline pore-forming agents to form a porous structure. However, this method suffers from drawbacks such as high corrosiveness to equipment by inorganic alkaline pore-forming agents, high impurity content, and poor consistency of the porous structure. Therefore, the petroleum coke porous carbon prepared by the above methods offers limited improvement to the storage performance of secondary batteries.

[0047] In one example, porous carbon from petroleum coke was prepared by etching petroleum coke with an organopotassium compound.

[0048] In one example, the steps for preparing porous carbon from petroleum coke include:

[0049] a1: Petroleum coke and organopotassium compounds are mixed in a dispersion, and after etching, the filter residue is collected.

[0050] a2: The filter residue is activated and washed to prepare porous carbon from petroleum coke.

[0051] In one example, the organopotassium compound includes one or more of potassium 2,4-hexadienoate, potassium citrate, potassium humate, potassium cinnamate, potassium hydrogen 1,2-phthalate, and potassium salt of 2-ethylhexanoate.

[0052] The potassium ions in the aforementioned specific types of organopotassium compounds can electrostatically attract and interact with electronegative groups or defect sites on the surface of petroleum coke, thereby breaking the C-C bonds and other chemical bonds in the petroleum coke and optimizing its pore structure. Simultaneously, the organic groups of these organopotassium compounds can insert into the interstices of the microcrystalline structure of the petroleum coke, thereby reducing the interaction forces in the crystal structure, making the petroleum coke easier to etch, and the organic groups easier to wash off. Therefore, this application uses organopotassium compounds to etch petroleum coke, which not only has the advantage of introducing low impurity content but also exhibits low corrosivity to equipment.

[0053] In one example, the pore size of the micropores in the porous carbon of petroleum coke is 1 nm to 10 nm.

[0054] In one example, the dispersion includes one or more of dichloromethane, ethyl acetate, glycerol, and propylene glycol.

[0055] In one example, the mass ratio of the organopotassium compound to the dispersion is (5~30):(70~95). For example, the mass ratio of the organopotassium compound to the dispersion includes, but is not limited to, 5:95, 8:92, 10:90, 12:88, 15:85, 20:80, 25:75, 28:72, or 30:70, or any two of the above values ​​as endpoints. Understandably, the mixture obtained by mixing petroleum coke and the organopotassium compound in the dispersion has a mass concentration of the organopotassium compound of 5%~30%. For example, the mass concentration of the organopotassium compound in the resulting mixture includes, but is not limited to, 5%, 8%, 10%, 12%, 15%, 20%, 25%, 28%, or 30%.

[0056] In one example, the etching process parameters include a temperature of 150°C to 300°C. This application uses an organopotassium compound as the etching substrate, and with a properly formulated dispersion and a suitable type of organopotassium compound, the etching conditions are relatively mild, effectively reducing energy consumption and making it suitable for industrial production. For example, the etching temperature includes, but is not limited to, 150°C, 180°C, 190°C, 200°C, 210°C, 280°C, or 300°C, or any two of the above values ​​as endpoints.

[0057] Furthermore, the etching process takes 0.5 h to 2 h. For example, the etching process takes, but is not limited to, 0.5 h, 0.8 h, 1 h, 1.5 h, 1.8 h or 2 h.

[0058] In one example, in step a1, the mass ratio of petroleum coke to organopotassium compound is 100:(5~150). Specifying the mass ratio of petroleum coke to organopotassium compound plays a crucial role in ensuring etching efficiency. Examples of such mass ratios include, but are not limited to, 100:5, 100:20, 100:30, 100:50, 100:100, 100:130, 100:140, or 100:150.

[0059] To re-expose the active sites after etching and to repair and optimize irregularities or defects on the surface after etching, resulting in a more uniform and stable surface structure, and to increase the number of pores in the material for the deposition of nano-silicon, the activation process parameters in one example include a temperature of 600°C to 1000°C. For example, the activation temperature may include, but is not limited to, 600°C, 700°C, 800°C, 900°C, or 1000°C.

[0060] Furthermore, the activation treatment time is 1 hour to 6 hours. The activation treatment time includes, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0061] In one example, the washing steps include: acid washing and water washing in sequence.

[0062] As a further example, the pickling solution used in the pickling step is hydrochloric acid with a molar concentration of 0.08 mol / L to 0.12 mol / L.

[0063] In one example, after the washing step a2, vacuum drying is also included.

[0064] In one specific example, the steps for preparing porous carbon from petroleum coke include:

[0065] Petroleum coke and organopotassium compounds are mixed in a dispersion, and after etching at 150℃~300℃ for 0.5h~2h, the filter residue is collected.

[0066] The filter residue was activated at 600℃~1000℃ for 1h~6h, then acid-washed with hydrochloric acid with a molar concentration of 0.08mol / L~0.12mol / L, washed with water, and vacuum dried to prepare porous carbon from petroleum coke.

[0067] In one example, the heteroatom gas used in the heteroatom gas deposition doping includes one or more of diborane, methaneborane, phosphine, hydrogen fluoride, and hydrogen chloride.

[0068] During the deposition and doping process, the aforementioned heteroatom gases can improve the conductivity of the porous carbon material by altering its electronic structure, increasing carrier concentration, or improving its crystal structure, thereby reducing impedance.

[0069] In one example, the process parameters for heteroatom gas deposition doping include: vacuum degree ≤10 Pa, temperature 300℃~500℃, heteroatom gas flow rate 10 sccm~100 sccm, and pressure 1 MPa~5 MPa. These process parameters are defined to ensure effective heteroatom gas deposition and doping, achieving target performance such as impedance reduction, while also ensuring process stability and repeatability, and reducing product quality variations caused by parameter fluctuations. Furthermore, the vacuum degree for heteroatom gas deposition doping includes, but is not limited to, 2 Pa, 3 Pa, 5 Pa, 7 Pa, 9 Pa, or 10 Pa. The temperature for heteroatom gas deposition doping includes, but is not limited to, 300℃, 350℃, 380℃, 400℃, 420℃, 450℃, 480℃, or 500℃. The heteroatom gas flow rate includes, but is not limited to, 10 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm, 80 sccm, or 100 sccm. The pressure of heteroatom gases includes, but is not limited to, 1 MPa, 2 MPa, 3 MPa, 4 MPa or 5 MPa.

[0070] Furthermore, the heteroatom gas deposition doping time is 30 min to 300 min. For example, the heteroatom gas deposition doping time includes, but is not limited to, 30 min, 50 min, 70 min, 90 min, 100 min, 150 min, 180 min, 200 min, 220 min, 240 min, 280 min, or 300 min.

[0071] In one example, the silane gas used in the silane gas deposition doping includes one or more of tetrachlorosilane, trichlorosilane, trimethylchlorosilane, tetrafluorosilane, and trimethylfluorosilane.

[0072] The process parameters in the silane gas deposition step play an important role in promoting the uniform decomposition and deposition of silane gas on the porous carbon surface of petroleum coke, improving the crystallinity and purity of nano-silicon, and thus increasing the specific capacity of the composite material.

[0073] In one example, the silane gas deposition doping step includes: introducing silane gas at a flow rate of 10 sccm to 100 sccm under conditions of temperature 450℃~550℃, vacuum degree ≤10 Pa, and pressure 1 MPa~5 MPa for deposition doping. The vacuum degree for silane gas deposition doping includes, but is not limited to, 2 Pa, 3 Pa, 5 Pa, 7 Pa, 9 Pa, or 10 Pa. The temperature for silane gas deposition doping includes, but is not limited to, 400℃, 420℃, 450℃, 480℃, 500℃, 520℃, or 550℃. The flow rate of silane gas includes, but is not limited to, 10 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm, 80 sccm, or 100 sccm. The pressure of the silane gas includes, but is not limited to, 1 MPa, 2 MPa, 3 MPa, 4 MPa, or 5 MPa.

[0074] Understandably, silane gas deposition doping can be performed in the same apparatus after the heteroatom gas deposition doping step.

[0075] Furthermore, the silane gas deposition doping time is 30 min to 300 min. For example, the silane gas deposition doping time includes, but is not limited to, 30 min, 50 min, 70 min, 90 min, 100 min, 150 min, 180 min, 200 min, 220 min, 240 min, 280 min, or 300 min.

[0076] In one example, the metal gas used in the metal gas deposition doping process has a boiling point of 900°C to 1350°C. This boiling point range allows the metal to vaporize and deposit under relatively moderate temperature conditions. It avoids the problem of the metal being too reactive and difficult to control due to a boiling point that is too low, or the need for excessive energy consumption and complex processes to achieve deposition due to a boiling point that is too high. This facilitates precise control of the deposition rate and the quality of the metal deposition.

[0077] In one example, the metal gas deposition doping step includes: introducing metal gas at a flow rate of 10 sccm to 100 sccm under conditions of temperature 900°C to 1350°C, vacuum degree ≤10 Pa, and pressure 1 MPa to 5 MPa for deposition doping. For example, the vacuum degree for metal gas deposition doping includes, but is not limited to, 2 Pa, 3 Pa, 5 Pa, 7 Pa, 9 Pa, or 10 Pa. The temperature for metal gas deposition doping includes, but is not limited to, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, or 1350°C. The flow rate of the metal gas includes, but is not limited to, 10 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm, 80 sccm, or 100 sccm. The pressure of the metal gas includes, but is not limited to, 1 MPa, 2 MPa, 3 MPa, 4 MPa, or 5 MPa.

[0078] Furthermore, the metal gas deposition doping time is 30 min to 300 min. For example, the metal gas deposition doping time includes, but is not limited to, 30 min, 50 min, 70 min, 90 min, 100 min, 150 min, 180 min, 200 min, 220 min, 240 min, 280 min, or 300 min.

[0079] Understandably, metal gas deposition doping can be performed in the same apparatus after the silane gas deposition doping step.

[0080] In one example, the passivation process includes the following steps:

[0081] With a dew point ≤ -60℃, the metal-doped silicon-carbon precursor material is heated to 100℃~200℃, and passivation treatment is performed by introducing an oxidizing gas at a flow rate of 10 sccm~100 sccm. The passivation temperature includes, but is not limited to, 100℃, 120℃, 150℃, 170℃, 180℃, or 200℃. The flow rate of the oxidizing gas includes, but is not limited to, 10 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm, 80 sccm, or 100 sccm.

[0082] In one example, the oxidizing gas includes one or more of oxygen, nitrous oxide, nitrogen dioxide, chlorine dioxide, and ozone.

[0083] Furthermore, the passivation treatment time is 30 min to 300 min. For example, the passivation treatment time includes, but is not limited to, 30 min, 50 min, 70 min, 90 min, 100 min, 150 min, 180 min, 200 min, 220 min, 240 min, 280 min, or 300 min.

[0084] Following deposition and doping, passivation is performed in an oxidizing gas. During this process, the oxidizing gas reacts with the material surface to form a dense passivation film. This helps prevent further oxidation or other chemical reactions, thereby improving the material's stability and corrosion resistance. Simultaneously, passivation also improves the surface properties of the material, reducing defects and active sites. Furthermore, it optimizes the interfacial contact between the material and subsequent inorganic lithium compounds, lowering the interfacial resistance.

[0085] In one example, the inorganic lithium compound includes one or more of lithium phosphate, lithium fluoride, lithium titanate, and lithium sulfonate.

[0086] In one example, the mass ratio of the intermediate material to the inorganic lithium compound is 100:(1~5). Specifying this mass ratio is crucial for ensuring the quality of the inorganic lithium compound coating in the silicon-carbon composite material and further enhancing the lithium-ion intercalation / deintercalation rate during charging and discharging. For example, the mass ratio of the intermediate material to the inorganic lithium compound includes, but is not limited to, 100:1, 100:2, 100:3, 100:4, or 100:5.

[0087] In one example, the mass ratio of the inorganic lithium compound to the solvent is (1~10):(90~99). Understandably, the inorganic lithium compound solution can be prepared by mixing the inorganic lithium compound with the solvent and then mixed with the intermediate material. Examples of such mass ratios include, but are not limited to, 1:99, 2:98, 5:95, 8:92, or 10:90.

[0088] In one example, in step S30, the drying method is vacuum drying. Further, the process parameters for vacuum drying include: inlet temperature 190℃~210℃, outlet temperature 70℃~90℃, and flow rate 0.08kg / h~0.12 kg / h.

[0089] A second aspect of this application provides a silicon-carbon composite material.

[0090] Among them, silicon-carbon composite materials include metal-doped silicon-carbon precursor materials and an inorganic lithium compound layer coated on the surface of the metal-doped silicon-carbon precursor materials.

[0091] Among them, the metal-doped silicon-carbon precursor materials include petroleum coke porous carbon matrix and heteroatom compounds, nano-silicon and metals deposited on the pores and / or surface of petroleum coke porous carbon matrix.

[0092] Understandably, heteroatom compounds are prepared by heteroatom gas deposition doping. Nano-silicon is prepared by silane gas deposition doping. Metals are prepared by metal gas deposition doping.

[0093] This application involves forming heteroatom compounds, nano-silicon, and metals on the channels or surface of porous carbon from petroleum coke. The heteroatom compounds alter the electronic structure of the porous carbon, increasing active sites and reducing the impedance of the silicon-carbon composite material. Nano-silicon deposition allows the silicon-carbon formed from petroleum coke compounds to combine the advantages of silicon's high specific capacity and carbon's ability to buffer volume changes during charge and discharge, thereby increasing specific capacity while reducing expansion. Furthermore, metal is deposited and doped onto the channels or surface of the porous carbon from petroleum coke. This metal synergizes with the nano-silicon formed by silane gas deposition, resulting in an alloy that enhances the material's structural stability and reduces its expansion. Simultaneously, metal doping also improves the material's conductivity. In addition, an inorganic lithium compound coating further enhances the lithium-ion insertion / extraction rate during charge and discharge, improving the initial efficiency and rate performance.

[0094] In one example, the tap density of the silicon-carbon composite material was 1 g / cm³. 3 ~1.1 g / cm 3 .

[0095] In one example, the specific surface area of ​​the silicon-carbon composite material is 2.5 m². 2 / g~3.05 m 2 / g.

[0096] In one example, the resistivity of the silicon-carbon composite powder is 0.7 Ω·m to 1.15 Ω·m.

[0097] In one example, the pressure specific surface area of ​​the silicon-carbon composite material is 13.5 m². 2 / g~16.6 m 2 / g.

[0098] A third aspect of this application provides a negative electrode sheet, comprising a negative current collector and a negative active material layer disposed on the surface of the negative current collector, wherein the negative active material layer comprises a silicon-carbon composite material prepared by any of the preparation methods of the first aspect of this application, or a silicon-carbon composite material of the second aspect of this application.

[0099] The silicon-carbon composite material of this application, through the deposition and doping of porous carbon, heteroatoms, nano-silicon and metals from petroleum coke, and the coating of inorganic lithium compounds, can effectively improve conductivity and structural stability, thereby effectively improving the rate performance and cycle performance of the battery.

[0100] A fourth aspect of this application provides a secondary battery, including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode; wherein the negative electrode is the negative electrode sheet of the third aspect of this application.

[0101] The following detailed embodiments illustrate this application in more detail. It should also be understood that the following embodiments are for further explanation only and should not be construed as limiting the scope of protection of this application. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of this application fall within the scope of protection of this application. The specific process parameters, etc., in the following embodiments are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not necessarily limited to the specific values ​​in the embodiments below.

[0102] Example 1

[0103] (1) Preparation of porous carbon from petroleum coke: 100g of petroleum coke (particle size D50=5μm) was added to a 300g solution of 10wt% potassium 2,4-hexadienoate (organopotassium compound) in dichloromethane and dispersed evenly. The solution was then transferred to a high-pressure reactor and etched at 200℃ for 1h. After filtration, the filter residue was collected. The resulting filter residue was activated at 800℃ for 3h. The filter residue was then washed with 0.1mol / L hydrochloric acid and deionized water and dried under vacuum at 80℃ for 24h to obtain porous carbon from petroleum coke.

[0104] (2) Multi-step deposition doping: The porous carbon from petroleum coke is transferred to a rotary kiln. The air in the first-effect exhaust tube is evacuated to ≤10pa. Then the temperature is raised to 400℃, and borane gas is introduced at a flow rate of 50sccm. The pressure of the cavity is maintained at 3MPa. Deposition is carried out for 150min to complete the heteroatom gas deposition doping.

[0105] After that, stop the flow of diborane gas, raise the temperature to 500℃ and switch to tetrachlorosilane gas at a flow rate of 300 sccm for 150 min, and maintain the pressure in the cavity at 3 MPa to complete the silane gas deposition and doping.

[0106] Finally, the temperature was raised to 1100℃, and magnesium gas was introduced at a flow rate of 50 sccm for 150 min. The pressure in the chamber was maintained at 3 MPa to carry out metal deposition, thus obtaining a metal-doped silicon-carbon precursor material.

[0107] (3) Passivation treatment: At a dew point of ≤-60℃, the metal-doped silicon-carbon precursor material is transferred to a tube furnace, heated to 150℃ and nitrous oxide gas is introduced. Passivation is carried out for 150 min at a flow rate of 50 sccm to obtain the intermediate material.

[0108] (4) Preparation of inorganic lithium compound coating layer: 3g of lithium phosphate was added to 60g of ethylene carbonate solvent and dispersed evenly to prepare a solution with a mass concentration of 5wt%. Then, 100g of intermediate material was added and dispersed evenly. Spray drying was carried out (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h) to obtain silicon-carbon composite material.

[0109] Example 2

[0110] (1) Preparation of porous carbon from petroleum coke: 100g of petroleum coke (particle size D50=10μm) was added to 300g of ethyl acetate solution of 30wt% potassium citrate (organopotassium compound) and dispersed evenly. The mixture was then transferred to a high-pressure reactor and etched at 150℃ for 2h. After filtration, the filter residue was collected. The resulting filter residue was activated at 600℃ for 6h. The filter residue was then washed with 0.1mol / L hydrochloric acid and deionized water and dried under vacuum at 80℃ for 24h to obtain porous carbon from petroleum coke.

[0111] (2) Multi-step deposition doping: The porous carbon from petroleum coke is transferred to a rotary kiln. The air in the first-effect exhaust tube is evacuated to ≤10 Pa. Then the temperature is raised to 300℃, and borane gas is introduced at a flow rate of 10 sccm. The pressure of the cavity is maintained at 1 MPa. Deposition is carried out for 300 min to complete the heteroatom gas deposition doping.

[0112] Then, stop the flow of borane gas, raise the temperature to 450°C, and switch to trichlorosilane gas at a flow rate of 100 sccm for 300 min, maintaining the pressure in the chamber at 1 MPa to complete the silane gas deposition and doping.

[0113] Finally, the temperature was raised to 900℃, and zinc gas was introduced at a flow rate of 10 sccm for 300 min. The pressure in the chamber was maintained at 1 MPa to carry out metal deposition, thus obtaining a metal-doped silicon-carbon precursor material.

[0114] (3) Passivation treatment: At a dew point of ≤-60℃, the metal-doped silicon-carbon precursor material is transferred to a tube furnace, heated to 100℃ and nitrogen dioxide gas is introduced. Passivation is carried out for 300 minutes at a flow rate of 10 sccm to obtain the intermediate material.

[0115] (4) Preparation of inorganic lithium compound coating layer: 1g of lithium fluoride was added to 100g of dimethyl carbonate solvent and dispersed evenly to prepare a solution with a mass concentration of 1wt%. Then, 100g of intermediate material was added and dispersed evenly. Spray drying was carried out (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h) to obtain silicon-carbon composite material.

[0116] Example 3

[0117] (1) Preparation of porous carbon from petroleum coke: 100g of petroleum coke (particle size D50=10μm) was added to 500g of a glycerol solution containing 30wt% potassium cinnamate (an organopotassium compound) and dispersed evenly. The solution was then transferred to a high-pressure reactor and etched at 300℃ for 0.5h. After filtration, the filter residue was collected. The resulting filter residue was activated at 1000℃ for 1h. The filter residue was then washed with 0.1mol / L hydrochloric acid and deionized water and dried under vacuum at 80℃ for 24h to obtain porous carbon from petroleum coke.

[0118] (2) Multi-step deposition doping: The porous carbon from petroleum coke is transferred to a rotary kiln. The air in the first-effect exhaust tube is evacuated to ≤10pa. Then the temperature is raised to 500℃, and phosphine gas is introduced at a flow rate of 100sccm. The pressure of the cavity is maintained at 5MPa. Deposition is carried out for 30min to complete the heteroatom gas deposition doping.

[0119] Then, stop the flow of phosphine gas, raise the temperature to 550℃ and switch to trimethylchlorosilane gas at a flow rate of 500 sccm for 30 minutes, maintaining the pressure in the chamber at 5 MPa to complete the silane gas deposition and doping.

[0120] Finally, the temperature was raised to 1200℃, and lithium metal gas was introduced at a flow rate of 100 sccm for 30 minutes. The pressure in the chamber was maintained at 5 MPa to perform metal deposition, thus obtaining a metal-doped silicon-carbon precursor material.

[0121] (3) Passivation treatment: At a dew point of ≤-60℃, the metal-doped silicon-carbon precursor material is transferred to a tube furnace, heated to 200℃ and chlorine dioxide gas is introduced. Passivation is carried out for 30 minutes at a flow rate of 100 sccm to obtain the intermediate material.

[0122] (4) Preparation of inorganic lithium compound coating layer: 5g lithium sulfonate compound was added to 50g propylene carbonate solvent and dispersed evenly to prepare a solution with a mass concentration of 10wt%. Then, 100g intermediate material was added and dispersed evenly. Spray drying was carried out (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h) to obtain silicon-carbon composite material.

[0123] Example 4

[0124] Example 4 is basically the same as Example 3. The main difference is that the heteroatom gas used in step (2) of Example 4 is hydrogen fluoride; that is, hydrogen fluoride replaces phosphine in step (2) of Example 3.

[0125] Example 5

[0126] Example 5 is basically the same as Example 3. The main difference is that the silane gas used in step (2) of Example 5 is tetrafluorosilane; that is, tetrafluorosilane replaces the trimethylchlorosilane gas in step (2) of Example 3.

[0127] Example 6

[0128] Example 6 is basically the same as Example 3, the main difference being that the multi-step deposition doping process in step (2) is as follows:

[0129] Petroleum coke porous carbon was transferred to a rotary kiln and heated to 1200°C. Lithium metal gas was introduced at a flow rate of 100 sccm for 30 min, and the pressure in the chamber was maintained at 5 MPa to perform metal deposition, resulting in metal-doped porous carbon. Then, the temperature was raised to 550°C and trimethylchlorosilane gas was introduced at a flow rate of 500 sccm for 30 min, while maintaining the pressure in the chamber at 5 MPa to complete the silane gas deposition doping.

[0130] Finally, the air inside the tube was evacuated to a vacuum of ≤10 Pa, then the temperature was raised to 500°C, and phosphine gas was introduced at a flow rate of 100 sccm. The pressure in the chamber was maintained at 5 MPa, and deposition was carried out for 30 minutes to complete the heteroatom metal-doped silicon-carbon precursor material. Other procedures were the same as in Example 3.

[0131] Comparative Example 1

[0132] Comparative Example 1 is basically the same as Example 1, the main difference being that Comparative Example 1 uses commercially available porous carbon (Kuraray Co., Ltd., Japan, model: YP-80F, biomass raw material) instead of petroleum coke porous carbon.

[0133] Comparative Example 2

[0134] Comparative Example 2 is basically the same as Example 1, except that potassium 2,4-hexadienoate in step (1) of Comparative Example 2 is replaced with potassium hydroxide.

[0135] Comparative Example 3

[0136] Comparative Example 3 is basically the same as Example 1, except that Comparative Example 3 does not include step (4), that is, the intermediate material in step (3) is used as the silicon-carbon anode material.

[0137] SEM test

[0138] The silicon-carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown; by Figure 1 As can be seen from the data, the composite material prepared in Example 1 exhibits a granular structure with some microporous structures on the surface and a particle size between 5 μm and 10 μm.

[0139] Physical and chemical performance testing

[0140] The silicon-carbon composite materials prepared in the examples and comparative examples were tested for tap density and specific surface area according to GB / T 38823-2020 "Silicon-Carbon"; the powder resistivity was tested using a four-probe tester; and the pressure specific surface area was tested by adding the silicon-carbon composite material to a tablet press (test pressure 5T). The test results are shown in Table 1.

[0141] Table 1. Results of physicochemical performance tests

[0142]

[0143] Button cell battery test

[0144] The silicon-carbon composite material used in the examples and comparative examples was assembled into a coin cell as a raw material for the negative electrode material of a lithium-ion battery.

[0145] The specific preparation method of the negative electrode sheet is as follows: add binder, conductive agent and solvent to silicon-carbon composite material, stir to make slurry, coat it on copper foil, and then dry and roll it to obtain the negative electrode sheet.

[0146] The adhesive used is LA136D adhesive, conductive agent SP, and solvent is double-distilled water. The mass-volume ratio of silicon-carbon composite material, SP, LA136D, and double-distilled water is 80g:15g:15g:300mL.

[0147] Lithium metal sheets were used as the positive electrode; the electrolyte was LiPF6 / EC+DEC, with 1.1 mol / L LiPF6 as the electrolyte and a 1:1 volume ratio mixture of EC and DEC as the solvent; the separator was a polypropylene (PP) membrane. The coin cells were assembled in an argon-filled glove box. Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The initial discharge capacity, initial efficiency, charge DCR (50% SOC), and cycle performance (0.2C / 0.2C, 100 cycles) of the coin cells were tested. The negative electrode expansion rate was also tested by dissection at 100% SOC after full charge. The test results are shown in Table 2.

[0148] Table 2 Performance test results of button cells

[0149]

[0150] As shown in Tables 1 and 2, the embodiments exhibit better initial discharge capacity, DCR, expansion, and cycle performance compared to the comparative examples. This is because coating the material surface with lithium phosphate compounds results in high ionic conductivity, high strength, reduced DCR and expansion, and improved cycle performance. Comparative Example 1 used porous carbon materials other than petroleum coke porous carbon; Comparative Example 2 used inorganic potassium to etch petroleum coke; and Comparative Example 3 used an intermediate material without inorganic lithium compound coating as the silicon-carbon anode material. All of these factors lead to a decrease in initial discharge capacity, an increase in DCR, and a deterioration in cycle performance.

[0151] Soft-pack battery testing

[0152] Rate performance: The silicon-carbon composite material used in the examples and comparative examples was mixed with 95% artificial graphite as the negative electrode, and the negative electrode sheet was prepared by slurry mixing and coating. The ternary material (LiNi) was used. 1 / 3 Co 1 / 3 Mn 1 / 3 A 2Ah pouch cell was prepared using O2 as the positive electrode, LiPF6 (with EC and DEC in a volume ratio of 1:1 as the electrolyte) at a concentration of 1.3 mol / L, and a Celgard 2400 membrane as the separator.

[0153] The rate performance of the soft-pack battery was tested: the charge and discharge voltage range was 2.5-4.2V, the temperature was 25±3.0℃, the resistance was tested under different SOC conditions (90%, 70%, 50%, 30%, 10%, 5%) by charging at 3C, and the discharge was carried out at 4.0C. The results are shown in Table 3.

[0154] Table 3. Rate performance test results of pouch batteries

[0155]

[0156] As shown in Table 3, the impedance of the pouch cells made of silicon-carbon composite materials prepared in Examples 1-5 is significantly lower than that in Comparative Examples 1-3. The reason for this is that lithium ions migrate during battery charging. The materials in these examples have low powder resistivity, and their outer coating with lithium phosphate helps to increase the lithium ion diffusion rate, reduce impedance, and lower DCR. Example 6 shows a low DCR at high SOC (50%~90%), but an increased DCR at low SOC (5%~30%). This indicates that the sequential deposition order of heteroatom gas deposition doping, silane gas deposition doping, and metal gas deposition doping plays a crucial role in ensuring the performance of the silicon-carbon composite material.

[0157] Cyclic performance: The obtained soft-pack batteries were subjected to cycle performance testing. The test conditions were: charge / discharge current 1C / 1C, voltage range 2.5~4.2V, and 500 cycles. The test results are shown in Table 4.

[0158] Table 4 Cycle performance test results of pouch batteries

[0159]

[0160] As shown in Table 4, the lithium-ion battery prepared using the silicon-carbon composite material obtained in the examples exhibits significantly better cycle performance than the comparative example. The experimental results indicate that this is because the materials in the examples have low expansion and low powder resistivity, reducing the lithium ions consumed during repeated SEI repair during charging and discharging, thus improving cycle performance.

[0161] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0162] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: Petroleum coke porous carbon was prepared by etching petroleum coke with organopotassium compounds. Metal-doped silicon-carbon precursor materials were prepared by performing heteroatom gas deposition doping, silane gas deposition doping, and metal gas deposition doping on the porous carbon from petroleum coke. The metal-doped silicon-carbon precursor material is passivated to prepare an intermediate material; The intermediate material and the inorganic lithium compound were mixed in a solvent and dried to prepare a silicon-carbon composite material.

2. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that, The steps for etching petroleum coke using organopotassium compounds include: The petroleum coke and the organopotassium compound are mixed in a dispersion, and after etching, the filter residue is collected. The filter residue is activated and washed to prepare the petroleum coke porous carbon.

3. The method for preparing silicon-carbon composite material according to claim 2, characterized in that, The preparation steps of the porous carbon from petroleum coke have one or more of the following characteristics: (1) The organopotassium compounds include one or more of potassium 2,4-hexadienoate, potassium citrate, potassium humate, potassium cinnamate, potassium hydrogen 1,2-phthalate and potassium salt of 2-ethylhexanoate; (2) The dispersion comprises one or more of dichloromethane, ethyl acetate, glycerol, and propylene glycol; (3) The mass ratio of the organopotassium compound to the dispersion is (5~30):(70~95); (4) The etching process parameters include: temperature of 150℃~300℃; (5) The process parameters for activation treatment include: temperature of 600℃~1000℃; (6) The washing steps include: acid washing and water washing in sequence.

4. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The inorganic lithium compound includes one or more of lithium phosphate, lithium fluoride, lithium titanate, and lithium sulfonate; And / or, the mass ratio of the intermediate material to the inorganic lithium compound is 100:(1~5); And / or, the mass ratio of the inorganic lithium compound to the solvent is (1~10):(90~99).

5. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, In metal gas deposition doping, the boiling point of the metal gas used is 900℃~1350℃; And / or, the metal gas deposition doping step includes: introducing metal gas at a flow rate of 10 sccm to 100 sccm under conditions of temperature 900℃ to 1350℃, vacuum degree ≤10pa, and pressure 1Mpa to 5Mpa, to perform deposition doping.

6. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, Heteroatom gas deposition doping has one or more of the following characteristics: (1) In heteroatom gas deposition doping, the heteroatom gas used includes one or more of diborane, methaneborane, phosphine, hydrogen fluoride and hydrogen chloride; (2) The process parameters for heteroatom gas deposition doping include: vacuum degree ≤10pa, temperature 300℃~500℃, heteroatom gas flow rate 10sccm~100sccm, and pressure 1Mpa~5Mpa.

7. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, In silane gas deposition doping, the silane gas used includes one or more of tetrachlorosilane, trichlorosilane, trimethylchlorosilane, tetrafluorosilane, and trimethylfluorosilane; And / or, the silane gas deposition doping step includes: introducing silane gas at a flow rate of 10 sccm to 100 sccm under conditions of temperature 450℃~550℃, vacuum degree ≤10pa, and pressure 1Mpa~5Mpa to perform deposition doping; And / or, the passivation treatment step includes: heating the metal-doped silicon-carbon precursor material to 100°C~200°C at a dew point of ≤-60°C, and passing an oxidizing gas through it at a flow rate of 10 sccm~100 sccm for passivation treatment; wherein the oxidizing gas includes one or more of oxygen, nitrous oxide, nitrogen dioxide, chlorine dioxide and ozone.

8. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes a metal-doped silicon-carbon precursor material and an inorganic lithium compound layer coated on the surface of the metal-doped silicon-carbon precursor material. The metal-doped silicon-carbon precursor material includes a petroleum coke porous carbon matrix and heteroatom compounds, nano-silicon, and metals deposited in the pores and / or surface of the petroleum coke porous carbon matrix.

9. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer includes a silicon-carbon composite material prepared by any one of claims 1 to 7, or includes the silicon-carbon composite material as described in claim 8.

10. A secondary battery, characterized in that, It includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode; wherein the negative electrode is the negative electrode sheet according to claim 9.

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