A pre-lithiated silicon-carbon negative electrode material and a preparation method thereof, and a lithium ion battery

Abstract

The application discloses a pre-lithium silicon-carbon negative electrode material and a preparation method and lithium ion battery thereof, and belongs to the technical field of lithium ion battery negative electrode materials. The preparation method comprises the following steps: sequentially performing silicon deposition and carbon coating on the surface of porous carbon to obtain a first precursor; pressing the first precursor into a cake-shaped to obtain a cake-shaped precursor; alternately stacking the cake-shaped precursor and metal lithium particles to form a stack, performing heat treatment on the stack after pressing, and then heating the stack to 500-600 DEG C, cooling to 300-400 DEG C, annealing at constant temperature, and then cooling and crushing to obtain a second precursor; mixing and dispersing the second precursor, a fast ion conductor and pitch in a solvent, drying, and then carbonizing to obtain the pre-lithium silicon-carbon negative electrode material. The application can effectively reduce the lithium intercalation capacity, improve the initial coulomb efficiency, and the assembled battery has low direct current internal resistance and good rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a pre-lithium silicon-carbon anode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Silicon-based anode materials have become a research hotspot in the field of lithium-ion batteries and have achieved commercial applications due to their extremely high theoretical specific capacity (up to 4200 mAh / g for pure silicon) and low lithium intercalation potential. However, silicon-based materials undergo drastic volume changes during charge and discharge (expansion rate can reach 300-400%), leading to material structure collapse, electrode pulverization, and decreased interface stability, severely restricting the cycle performance of the battery. To solve this problem, the industry has developed third-generation silicon-carbon materials (III-generation silicon-carbon) using porous carbon as a carrier—depositing elemental silicon into the porous carbon channels through high-temperature pyrolysis of silane, followed by carbon coating to form a composite structure. This design utilizes the buffer space and structural support of porous carbon to significantly alleviate the cycle decay problem caused by volume expansion, increasing the specific capacity to over 1800 mAh / g, and achieving an initial coulombic efficiency (first efficiency) of approximately 92% at a lithium delithiation cutoff potential of 1.5V.

[0004] However, in practical applications, the working delithiation potential of lithium-ion battery anodes is typically controlled at around 0.8V, at which point the initial efficiency of third-generation silicon-carbon anodes drops to around 80%. Although the specific capacity of silicon-carbon materials is significantly higher than that of traditional graphite anodes, their lower initial efficiency leads to a substantial decrease in the overall energy density of the battery, becoming a key bottleneck restricting their industrial application. To improve initial efficiency, existing technologies generally employ a pre-lithiation strategy, which involves introducing a lithium source during the preparation of silicon-carbon materials to compensate for the loss of active lithium and improve initial efficiency. Currently, the mainstream approach is to pre-lithiate porous carbon precursors before silicon deposition and carbon coating.

[0005] However, existing pre-lithiation technologies suffer from three prominent problems: First, the pre-lithiation process often employs liquid-phase treatment of porous carbon, resulting in highly active lithium sources that can easily pose safety risks during subsequent silicon deposition or material transfer. Second, pre-lithiation components tend to deposit within the porous carbon channels, causing blockage and limiting the uniform deposition and loading of elemental silicon. Third, liquid-phase pre-lithiation reagents are expensive, and some are highly corrosive or toxic, posing a problem of poor environmental friendliness. These shortcomings make it difficult for existing pre-lithiated silicon-carbon materials to simultaneously achieve safety, performance stability, and production cost. Therefore, there is an urgent need to develop new pre-lithiation technologies to overcome industrialization barriers. Summary of the Invention

[0006] In view of this, the present invention provides a pre-lithiation silicon-carbon anode material and its preparation method, and a lithium-ion battery. The present invention adopts a pre-lithiation process in which lithium metal particles and silicon-carbon anode materials are compositely pressed and then subjected to high-temperature treatment. The resulting pre-lithiation silicon-carbon anode material can achieve an initial efficiency of more than 83% at a delithiation potential of 0.8V, and also has good rate performance and cycle stability.

[0007] In a first aspect, the present invention provides a method for preparing a pre-lithium silicon-carbon anode material, comprising the following steps: Silicon deposition and carbon coating were performed sequentially on a porous carbon surface to obtain the first precursor. The first precursor is pressed into a disc shape to obtain a disc-shaped precursor; The cake-shaped precursor and lithium metal particles are alternately stacked to form a stack. The stack is pressurized and heated to 500~600℃ for heat treatment, then cooled to 300~400℃ and annealed at a constant temperature. Finally, it is cooled and crushed to obtain the second precursor. The second precursor is mixed and dispersed with fast ion conductor and pitch in a solvent, dried and then carbonized to obtain the pre-lithium silicon-carbon anode material.

[0008] Preferably, the specific steps of sequentially performing silicon deposition and carbon coating on the porous carbon surface are as follows: a gaseous silicon source is introduced into the porous carbon surface, and a chemical vapor deposition reaction is carried out at 500~600℃. After the reaction is completed, an unsaturated hydrocarbon compound is introduced to carry out the reaction.

[0009] Furthermore, the gaseous silicon source is selected from one or more of silane, silane, dichlorosilane, trichlorosilane, or silicon tetrachloride; the unsaturated hydrocarbon is selected from one or more of ethylene, acetylene, propyne, or propylene petroleum gas.

[0010] Preferably, the D50 particle size of the lithium metal particles is 0.1~20mm; the mass ratio of the lithium metal particles to the total mass of the two disc-shaped precursors is 1:(4~55); the top and bottom layers of the stack are both disc-shaped precursors; and the stack has 3 or more layers.

[0011] Preferably, the pressing pressure in the step of pressing the first precursor into a cake shape is 5~20MPa, and the thickness of the cake-shaped precursor is 5~300mm; the pressure applied to the stack is 1~10MPa.

[0012] Preferably, the heat treatment is carried out in an inert atmosphere for 6 to 15 hours; the isothermal annealing takes 12 to 36 hours; and the pressure during the heat treatment and isothermal annealing processes is 1 to 10 MPa.

[0013] Preferably, the mass ratio of the second precursor, the fast ion conductor, and the pitch is (95~100):(0.5~2):(1~5); the solvent is selected from one or more of pyridine, benzene, toluene, xylene, chloroform, naphthalene, tetrahydrofuran, N-methylpyrrolidone, or petroleum ether; the fast ion conductor is selected from H3BO3, Li2ZrS3, Li2O-AlO-SiO2, Li3V2(PO4)3, Li3Ti2(PO4)3, Li3Zr2(PO4)3, Li2O-mB2O3, and Li7La3Zr2O. 12 Li6La3BiSnO 12 One or more of LiAlF4, LiSbF6, LiInF4, Li3PO4, or LiGaF4.

[0014] Preferably, the carbonization temperature is 550~800℃; the carbonization process includes a first carbonization stage and a second carbonization stage, the first carbonization stage is carried out in an oxygen-containing atmosphere with an oxygen volume fraction of 3~15%; the first carbonization stage lasts for 15~30 min; the second carbonization stage is carried out in an inert atmosphere; the second carbonization stage lasts for 1.5~10 h.

[0015] Preferably, in the pre-lithium silicon-carbon anode material, the mass fraction of silicon is 45~62wt% and the mass fraction of lithium is 1~20wt%.

[0016] Secondly, the present invention provides a pre-lithium silicon-carbon anode material prepared by the above preparation method.

[0017] Thirdly, the present invention provides a lithium-ion battery comprising the aforementioned pre-lithium silicon-carbon anode material.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The present invention uses lithium metal particles as lithium source, which significantly reduces the cost compared with liquid phase pre-lithiation. The pre-lithiated silicon-carbon material is aged at high temperature to form a silicon-lithium alloy, and the material has good stability after being coated with fast ion conductor and soft carbon. By alternately stacking the pie-shaped precursor and lithium metal particles to form a stack and then heat-treating it under pressure, the alloying reaction of silicon and lithium is realized, which effectively reduces the lithium intercalation capacity and improves the first coulombic efficiency. The first efficiency of the half cell at 0.8V is higher than 83%, and can reach more than 90%.

[0019] (2) The present invention uses fast ion conductors and soft carbon formed by pitch carbonization for dual-function coating, which greatly improves the performance shortcomings of silicon-carbon materials in terms of ionic and electronic conductivity; the synergistic effect of fast ion conductors and soft carbon not only improves the material kinetic properties, but also helps to reduce the DC internal resistance (DCR) of the full cell and improve the rate performance and cycle performance of the full cell. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 These are scanning electron microscope images of the pre-lithium silicon-carbon anode material of Embodiment 3 of the present invention; Figure 2 These are X-ray diffraction patterns of the pre-lithium silicon-carbon anode material of Example 3 and the silicon-carbon anode material of Comparative Example 1. Figure 3 These are the first charge-discharge curves of the half-cell assembled from the pre-lithium silicon-carbon anode material of Example 3 and the silicon-carbon anode material of Comparative Example 1. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] In half-cell testing, to accurately evaluate the electrochemical performance of silicon-carbon anode materials, lithium metal sheets are typically used as both the counter and reference electrodes. In this case, a high delithiation cutoff potential (e.g., 1.5V) can be set to ensure complete delithiation of the anode material—that is, to allow lithium ions to be extracted from the crystal lattice and migrate to the counter electrode to the maximum extent possible, reducing capacity loss due to lithium residue. Under this idealized testing environment, anode materials typically achieve high initial charge-discharge efficiency (first-time efficiency). The first-time efficiency of third-generation silicon-carbon anodes can reach approximately 92%, reflecting the intrinsic electrochemical activity and reversibility of the material.

[0024] In practical full-cell applications, silicon-carbon anodes need to be used in conjunction with cathode materials (such as ternary cathode materials or lithium iron phosphate cathode materials). Therefore, the operating voltage window during use needs to be determined in conjunction with the electrochemical stability range of the cathode and anode and the battery capacity utilization rate. Among them, the discharge cutoff voltage directly affects the delithiation potential and capacity of the silicon anode. Currently, the discharge voltage of ternary batteries and lithium iron phosphate batteries is generally set at around 2.8V and 2.5V, respectively. Through three-electrode testing, the actual delithiation point of the anode can be detected at around 0.8V. At this potential, lithium ions in the silicon-based anode are difficult to completely deintercalate and intercalate, thus leading to a significant reduction in the first-stage efficiency of the full cell. The reduction in the first-stage efficiency of the battery will essentially lead to a decrease in the utilization efficiency of lithium ions in the battery, which will seriously deteriorate the battery energy density and cost. Although pre-lithiation with silicon-based materials cannot completely change the problem of incomplete lithium ion deintercalation and intercalation caused by the low delithiation potential of the anode during full-cell use, it can effectively reduce the initial lithium intercalation capacity, thereby improving the initial efficiency of the full cell.

[0025] To further improve the initial efficiency of silicon-based anode materials at a lower cost, this invention provides a method for preparing a pre-lithium silicon-carbon anode material, comprising the following steps: Silicon deposition and carbon coating were performed sequentially on a porous carbon surface to obtain the first precursor. The first precursor is pressed into a disc shape to obtain a disc-shaped precursor; The cake-shaped precursor and lithium metal particles are stacked alternately, pressed, and then heat-treated at 500-600°C. Then, the temperature is lowered to 300-400°C and annealed at a constant temperature. Finally, the precursor is cooled and pulverized to obtain the second precursor. The second precursor is mixed and dispersed with fast ion conductor and pitch in a solvent, dried and then carbonized to obtain the pre-lithium silicon-carbon anode material.

[0026] This invention firstly forms a first precursor by sequentially depositing silicon and coating carbon on a porous carbon surface. The porous carbon serves as a substrate, providing structural support and buffer space. The silicon particles formed by silicon deposition work synergistically with the carbon coating layer to initially alleviate the volume expansion problem of silicon during lithium intercalation. The first precursor is then pressed into a disc shape, and the disc-shaped precursor is alternately stacked with metallic lithium particles to form a multi-layered "sandwich" structure. This increases the structural density of the material, ensuring that the metallic lithium particles diffuse uniformly into the upper or lower layers of the first precursor.

[0027] Placing lithium metal particles between two disc-shaped precursors and pressing them together physically creates a tight contact between the lithium particles and the precursor surfaces, reducing interfacial voids and providing a continuous diffusion path for subsequent lithium melting, penetration, and chemical reactions. During the heating process after pressing, when the temperature reaches above the melting point of lithium metal (approximately 180°C), the lithium particles gradually melt into a liquid state. As the temperature continues to rise to 500-600°C, the fluidity and diffusion activity of the liquid lithium significantly increase, allowing it to penetrate into the material through the porous structure of the precursors. There, it undergoes an alloying reaction with silicon to form a lithium-silicon alloy phase with high lithium storage capacity. Simultaneously, it reacts with the carbon components in the precursors to form lithium-carbon compounds. This temperature range ensures sufficient melting of lithium to promote its uniform distribution in the precursors while activating the diffusion capabilities of silicon and carbon atoms through a high-temperature environment. The silicon-lithium alloying reaction is the most kinetic and is the primary reaction process at this stage, while the lithium-carbon reaction occurs concurrently as a secondary competing reaction.

[0028] The temperature is then lowered to 300-400℃ for isothermal annealing. This stage, with temperatures below the boiling point of lithium (approximately 1342℃), avoids significant lithium volatilization loss and allows sufficient time for further lithium atom diffusion through slow cooling. Driven by the temperature gradient, liquid lithium migrates to incompletely reacted silicon and carbon regions, eliminating localized lithium concentration differences and ensuring more thorough and uniform lithium-silicon and lithium-carbon alloying reactions. Under isothermal conditions, the crystal structures of lithium-silicon and lithium-carbon alloys gradually relax, reducing lattice defects, improving phase stability, and preventing stress concentration caused by rapid cooling.

[0029] After annealing, the material gradually solidifies during cooling, stabilizing the structures of the lithium-silicon alloy phase, lithium-carbon alloy phase, and other reaction products. Finally, through a crushing operation, the blocky material is broken into granular secondary precursors, in which the silicon has been converted into lithium-silicon alloy, and the carbon component partially forms lithium-carbon alloy. The granular structure is beneficial for dispersion and shaping in subsequent processes.

[0030] Finally, the second precursor is mixed with a fast ion conductor and pitch and carbonized. After carbonization, the pitch forms a soft carbon coating layer, which improves the material's structural stability, electronic conductivity, and lithium-ion insertion window. The fast ion conductor promotes the rapid conduction of lithium ions. The two work synergistically to improve the material's ionic and electronic conductivity, further enhancing the electrochemical performance of the silicon-carbon anode material.

[0031] In this invention, the specific steps of sequentially depositing silicon and coating carbon on a porous carbon surface are as follows: a vapor-phase silicon source is introduced into the porous carbon surface, and a chemical vapor deposition reaction is carried out at 500-600°C. This process utilizes a thermal decomposition reaction to uniformly deposit silicon atoms into the pores and surface of the porous carbon, forming nano-silicon particles. After the reaction is complete, an unsaturated hydrocarbon is introduced to react, and a carbon coating layer is formed on the silicon surface through a pyrolysis reaction.

[0032] In this invention, the gaseous silicon source is selected from one or more of silane, silane, dichlorosilane, trichlorosilane, or silicon tetrachloride; the unsaturated hydrocarbon is selected from one or more of ethylene, acetylene, propyne, or propylene petroleum gas.

[0033] This invention does not impose special restrictions on the selection of porous carbon; commonly used porous carbon in the art can be used. Preferably, the specific surface area is 1700~2700 m². 2 / g, pore volume 0.7~1.4cm 3 / g, porous carbon with a D50 particle size of 2~8µm.

[0034] The D50 particle size of the lithium metal particles described in this invention is 0.1~20mm, more preferably 1~10mm, and even more preferably 1~5mm. The mass ratio of the lithium metal particles to the cake-shaped precursor is 1:(4~55), more preferably 1:(5~20), and even more preferably 1:(8~15). The amount of pre-lithiation is controlled by the mass ratio of the two. The higher the amount of pre-lithiation, the higher the initial efficiency. However, if the amount is too high, some active lithium will not be able to participate in alloying, forming floating lithium on the material surface, which seriously deteriorates the material's storage stability and processing performance. In this invention, the top and bottom layers of the stack formed by alternately stacking the cake-shaped precursor and the lithium metal particles are both cake-shaped precursors. The number of alternating stacked layers is 3 or more, more preferably 3~21 layers, and even more preferably 5~13 layers. Multi-layer stacking is more conducive to the uniform diffusion of lithium metal into the first precursor, shortening the subsequent heat treatment time and isothermal annealing time.

[0035] In this invention, the pressing pressure in the step of pressing the first precursor into a cake shape is 5~20MPa, more preferably 10~15MPa; the pressing time is not particularly limited, but is preferably 0.5~2h. The thickness of the cake-shaped precursor is 5~300mm, more preferably 10~100mm.

[0036] In this invention, the heat treatment is carried out under an inert atmosphere, with the inert gas selected from nitrogen or argon, to prevent lithium from reacting with oxygen and water vapor, and to promote the melting and penetration of metallic lithium to form a lithium-silicon alloy with silicon. The heat treatment time is 6-15 hours, more preferably 6-10 hours. The isothermal annealing time is 12-36 hours, which allows lithium to diffuse at the atomic level, eliminating the concentration gradient and making its distribution more uniform. The pressure applied to the stack is 1-10 MPa, more preferably 3-7 MPa. Maintaining the pressurized state of the stack during the heat treatment and isothermal annealing processes helps maintain the material's density, suppress lithium vapor volatilization, and improve pre-lithiation uniformity. This invention does not impose special restrictions on the pressurization method; for example, it can be achieved by using an inert pressure plate connected to an external cylinder for pressure control.

[0037] In this invention, the mass ratio of the second precursor, the fast ion conductor, and the pitch is (95~100):(0.5~2):(1~5); the solvent is selected from one or more of pyridine, benzene, toluene, xylene, chloroform, naphthalene, tetrahydrofuran, N-methylpyrrolidone, or petroleum ether; the fast ion conductor is selected from H3BO3, Li2ZrS3, Li2O-AlO-SiO2, Li3V2(PO4)3, Li3Ti2(PO4)3, Li3Zr2(PO4)3, Li2O-mB2O3, and Li7La3Zr2O. 12 Li6La3BiSnO 12 The solvent is one or more of LiAlF4, LiSbF6, LiInF4, Li3PO4, or LiGaF4. This invention does not impose special limitations on the equipment and process for mixing and dispersion, as long as the second precursor, fast ion conductor, and pitch are uniformly dispersed. This invention also does not impose special limitations on the drying process, as long as the solvent can be removed.

[0038] In this invention, the carbonization temperature is 550~800℃, more preferably 600~700℃; the carbonization includes a first carbonization stage and a second carbonization stage. The first carbonization stage is carried out in an oxygen-containing atmosphere, with an oxygen volume fraction of 3~15%, more preferably 8~12%; the duration of the first carbonization stage is 15~30 min. Appropriate oxidation is used to regulate the carbon interlayer spacing to improve the rate performance of the material. Excessive time will cause structural damage to the pre-lithiated silicon-lithium alloy and silicon-carbon alloy. The oxygen-containing atmosphere in the first carbonization stage includes oxygen and an inert gas, which can be selected from nitrogen, argon, etc. The second carbonization stage is carried out in an inert atmosphere, which can be nitrogen, argon, etc. The duration of the second carbonization stage is 1.5~10 h, more preferably 1.5~3.5 h. The temperatures of the first and second carbonization stages can be the same or different; preferably, they are carried out at the same temperature.

[0039] In the pre-lithiated silicon-carbon anode material of the present invention, the silicon mass fraction is 45-62 wt%, and the silicon content can be controlled by the pore volume of the porous carbon, the silane introduction time, and the flow rate; excessive silicon content will lead to increased volume expansion, thereby reducing cycle stability. The lithium mass fraction is 1-20 wt%, more preferably 2-15 wt%, and the lithium content is controlled by the mass ratio of lithium metal particles to the first precursor.

[0040] After obtaining the pre-lithium silicon-carbon anode material by carbonization, the present invention also includes a pulverization step, and the final pre-lithium silicon-carbon anode material has a D50 particle size of 3~10µm.

[0041] The present invention also provides a pre-lithium silicon-carbon anode material prepared by the above preparation method.

[0042] The present invention also provides a lithium-ion battery comprising the above-mentioned pre-lithium silicon-carbon anode material.

[0043] This invention does not impose any special limitations on the preparation method of lithium-ion batteries; commonly used lithium-ion battery preparation methods in the field can be used. The half-cell assembled with the pre-lithiated silicon-carbon anode material of this invention exhibits high initial delithiation capacity and initial efficiency, with an initial delithiation capacity exceeding 1590 mAh / g at 0.8V and an initial efficiency exceeding 83% at 0.8V, reaching a maximum of over 90%. Furthermore, the full cell assembled with the pre-lithiated silicon-carbon anode material of this invention exhibits good cycle stability and rate performance.

[0044] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not have any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used. In the following embodiments, the D50 particle size of the porous carbon is 7 μm, and the pore volume is 1 cm³. 3 / g, specific surface area is 2050m² 2 / g. The D50 particle size of the lithium metal particles is 0.3mm.

[0045] In the following examples, EMC represents ethyl methyl carbonate, EC represents ethylene carbonate, PS represents propylene sulfate, and DTD represents ethylene sulfate.

[0046] Example 1 This embodiment provides a pre-lithium silicon-carbon anode material and its preparation method.

[0047] (1) Preparation of the first precursor: Porous carbon was placed in a 20 kg fluidized bed and heated under an inert atmosphere. A mixture of silane and nitrogen (volume ratio 1:2) was introduced at a flow rate of 0.5 L / min, and the internal temperature of the fluidized bed was increased to 550 °C at a rate of 5 °C / min. Deposition was carried out for 60 min. After the silane was fully reduced, acetylene was introduced while maintaining a constant temperature and a flow rate of 0.2 L / min. The reaction was allowed to proceed for 10 min to obtain the first precursor.

[0048] (2) Preparation of the second precursor: The first precursor was pressed into a cake-shaped precursor under 10 MPa pressure for 1 hour, with the cake thickness controlled at 80 mm. A layer of lithium metal particles was spread evenly on the surface of the cake-shaped precursor, and then another layer of cake-shaped precursor was placed on top, controlling the mass ratio of lithium metal particles to cake-shaped precursor at 1:50. The cake-shaped precursor and lithium metal particle layers were arranged in an "ABABA" structure, with a total of 9 stacked layers. The top and bottom layers of the stack were both cake-shaped precursors. The stack was pressurized to 5 MPa and kept at a constant pressure during heat treatment. Nitrogen gas was introduced to maintain a slight positive pressure, and the temperature was heated to 600℃ and held for 8 hours. Then, the temperature was lowered to 320℃ and annealed at a constant temperature for 24 hours. After cooling and pulverizing, the second precursor was obtained after sieving.

[0049] (3) Preparation of pre-lithium silicon-carbon anode material: Coal pitch with a carbonization rate of 50% was dissolved in N-methylpyrrolidone at a mass fraction of 5 wt%, and then a second precursor and Li7La3Zr2O were added. 12 Controlling the second precursor, Li7La3Zr2O 12 The mass ratio of the carbon to coal tar pitch is 97:1:2. After drying, a mixture of nitrogen and oxygen with a volume ratio of 9:1 is introduced, and the temperature is raised to 650℃ at 5℃ / min and held for 30 min. Then, the temperature is kept constant and pure nitrogen is introduced for 2.5 h. After cooling, the material is crushed and screened to obtain the pre-lithium silicon-carbon anode material.

[0050] According to atomic absorption spectrometry, the mass fraction of silicon in the pre-lithiated silicon-carbon anode material obtained in this embodiment is 49.2 wt%, and the mass fraction of lithium is 1.6 wt%.

[0051] Example 2 The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass ratio of lithium metal particles to the cake precursor is controlled to be 1:25.

[0052] According to atomic absorption spectrometry, the mass fraction of silicon in the pre-lithiated silicon-carbon anode material obtained in this embodiment is 48.1 wt%, and the mass fraction of lithium is 3.3 wt%.

[0053] Example 3 The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass ratio of lithium metal particles to the cake precursor is controlled to be 1:12.5.

[0054] Atomic absorption spectrometry analysis revealed that the pre-lithiated silicon-carbon anode material obtained in this embodiment contained 46.8 wt% silicon and 6.8 wt% lithium. A scanning electron microscope (SEM) image of the pre-lithiated silicon-carbon anode material obtained in this embodiment is shown below. Figure 1 As shown in the figure, the particle size distribution is between 5 and 10 μm.

[0055] Example 4 Compared with Example 3, the difference in this embodiment is that in step (3) of this embodiment, the second precursor, Li7La3Zr2O is controlled. 12 The mass ratio of the tar pitch to coal is 97.5:0.5:2.

[0056] According to atomic absorption spectrometry, the mass fraction of silicon in the pre-lithiated silicon-carbon anode material obtained in this embodiment is 46.9 wt%, and the mass fraction of lithium is 6.87 wt%.

[0057] Example 5 Compared with Example 3, the difference in this embodiment is that in step (3) of this embodiment, the second precursor, Li7La3Zr2O is controlled. 12 The mass ratio of the tar pitch to coal is 96.5:1.5:2.

[0058] According to atomic absorption spectrometry, the pre-lithium silicon-carbon anode material obtained in this embodiment has a silicon mass fraction of 46.2 wt% and a lithium mass fraction of 6.74 wt%.

[0059] Comparative Example 1 Compared with Example 1, this comparative example does not perform steps (2) and (3), and directly uses the first precursor as the silicon-carbon anode material.

[0060] According to atomic absorption spectrometry, the silicon mass fraction of the silicon-carbon anode material obtained in this comparative example is 50.9 wt%.

[0061] Comparative Example 2 The difference between this comparative example and Example 1 is that step (2) is omitted in this comparative example. The specific steps are as follows: (1) Preparation of the first precursor: Porous carbon was placed in a 20 kg fluidized bed and heated under an inert atmosphere. A mixture of silane and nitrogen (volume ratio 1:2) was introduced at a flow rate of 0.5 L / min, and the internal temperature of the fluidized bed was increased to 550 °C at a rate of 5 °C / min. Deposition was carried out for 60 min. After the silane was fully reduced, acetylene was introduced while maintaining a constant temperature and a flow rate of 0.2 L / min. The reaction was allowed to proceed for 10 min to obtain the first precursor.

[0062] (2) Preparation of silicon-carbon anode materials: Coal pitch with a carbonization rate of 50% was dissolved in N-methylpyrrolidone at a mass fraction of 5 wt%, and then the first precursor and Li7La3Zr2O were added. 12 Controlling the first precursor, Li7La3Zr2O 12 The mass ratio of the carbon dioxide to coal tar pitch is 97:1:2. After drying, a mixture of nitrogen and oxygen in a volume ratio of 9:1 is introduced, and the temperature is increased to 650℃ at 5℃ / min for 3 hours for carbonization. After cooling, the carbon dioxide is crushed and screened to obtain silicon-carbon anode material.

[0063] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (3) of this comparative example, carbonization in an oxygen-containing atmosphere is not performed; instead, carbonization is carried out only in an inert atmosphere. Step (3) of this comparative example is as follows: Coal pitch with a carbonization rate of 50% was dissolved in N-methylpyrrolidone at a mass fraction of 5 wt%, and then a second precursor and Li7La3Zr2O were added. 12 Controlling the second precursor, Li7La3Zr2O 12 The mass ratio of the carbon dioxide to coal tar pitch is 97:1:2. After drying, high-purity nitrogen gas is introduced, and the temperature is increased to 650℃ at 5℃ / min and maintained for 3 hours. After cooling, the carbon dioxide is crushed and screened to obtain the pre-lithium silicon-carbon anode material.

[0064] According to atomic absorption spectrometry, the mass fraction of silicon in the pre-lithiated silicon-carbon anode material obtained in this embodiment is 49.1 wt%, and the mass fraction of lithium is 1.58 wt%.

[0065] Comparative Example 4 The difference between this comparative example and Example 1 is that annealing is not performed in step (2) of this comparative example. Step (2) of this comparative example is as follows: The first precursor was pressed into a cake-shaped precursor under a pressure of 10 MPa for 1 hour, with the cake thickness controlled at 80 mm. A layer of lithium metal particles was spread evenly on the surface of the cake-shaped precursor, and then another layer of cake-shaped precursor was placed on top, with the mass ratio of lithium metal particles to cake-shaped precursor controlled at 1:50. The cake-shaped precursor and lithium metal particle layers were arranged in an "ABABA" structure, with a total of 9 stacked layers. The top and bottom layers of the stack were both cake-shaped precursors. Then, it was heated to 600℃ under a nitrogen atmosphere at a pressure of 5 MPa and held for 8 hours, then cooled, pulverized, and sieved to obtain the second precursor.

[0066] After the product was crushed, it was found that there was obvious lithium metal on the surface of the particles at the contact position of the sandwich structure. After removing these particles, step (3) was carried out.

[0067] According to atomic absorption spectrometry, the mass fraction of silicon in the pre-lithiated silicon-carbon anode material obtained in this embodiment is 49.5 wt%, and the mass fraction of lithium is 1.48 wt%.

[0068] Test case 1. X-ray diffraction (XRD) test XRD tests were performed on the negative electrode material powders of Example 3 and Comparative Example 1 at a scan rate of 10° / min. The test results are as follows: Figure 2 As shown in the figure. XRD test results show that, compared with Comparative Example 1, the peak shape of the pre-lithiated silicon-carbon anode material prepared in Example 3 did not change, but the peak positions shifted slightly to the left, with the standard peak shifting from 28.4° to 27.6°. According to the Bragg equation, the interplanar spacing (d) of the material increased after prelithiation, which confirms that the product prepared in Example 3 achieved effective prelithiation.

[0069] 2. Initial lithium insertion capacity and first-efficiency test The silicon-carbon anode materials of Examples 1-5 and Comparative Examples 1-4 were mixed with a conductive agent (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber latex (SBR) in a mass ratio of 90:5:2:3 to prepare a slurry. This slurry was uniformly coated onto a copper foil current collector, dried, rolled, and then cut into circular electrode sheets as working electrodes. A lithium metal sheet was used as the counter electrode and reference electrode to prepare a half-cell. The initial lithium insertion capacity, initial lithium de-lithiation capacity at 0.8V and 1.5V, and initial efficiency were tested, and the results are summarized in Table 1.

[0070] Table 1. Initial lithium insertion capacity, initial lithium extraction capacity, and first-efficiency test results.

[0071] Compared with Comparative Examples 1 and 2, the silicon-carbon anode materials of Examples 1-3 showed significant improvements in first-efficiency at both 0.8V and 1.5V. Specifically, the change in delithiation capacity of the silicon-carbon anode material after prelithiation was relatively small, and the contribution to the improvement in first-efficiency mainly came from the decrease in lithium intercalation capacity. This indirectly proves that the prelithiation process in step (2) of Examples 1 was accompanied by an alloying reaction between silicon and lithium. Compared with Comparative Example 1, the prelithiation content in Example 1 was 1.6wt%, corresponding to an increase in first-efficiency of about 3% at a delithiation potential of 0.8V. From the comparison between Examples 1-3, it can be seen that the more prelithiation is done, the more significant the improvement in first-efficiency of the material, and at the same time, the first delithiation capacity is also slightly improved.

[0072] Compared with Example 3, Examples 4 and 5 adjusted the proportion of fast ion conductors in step (3), and it was found that the initial efficiency decreased slightly, but the decrease was not significant.

[0073] Compared with Comparative Example 1, Comparative Example 2 showed a slight improvement in specific capacity and initial efficiency, indicating that coating with soft carbon and fast ion conductor materials improved the kinetic properties of the materials.

[0074] Compared to Example 1, Comparative Example 3 showed comparable lithium intercalation / deintercalation capacity but slightly higher initial efficiency. This is presumably due to the elimination of the asphalt coating oxidation treatment step, resulting in a more regular carbon layer coating on the product surface and a relatively lower interlayer spacing. This suggests that the impedance and charging capability of Comparative Example 3 will deteriorate. Comparative Example 4 showed a higher initial lithium intercalation capacity but a lower initial efficiency, which was due to the elimination of annealing in step (2). This indicates that annealing is a key factor affecting the uniformity of pre-lithiation, and the product state and pre-lithiation amount after this step also corroborate this issue.

[0075] Figure 2 The charge-discharge curves of the half-cells of Comparative Example 1 and Example 3 further corroborate that the main contribution to the improvement of the first efficiency of the material after pre-lithiation comes from the reduction of the lithium intercalation capacity, and the lithium intercalation plateau of the material after pre-lithiation is reduced (the average delithiation potential is reduced by 5.7mV), which is consistent with the lithium intercalation potential under different silicon-lithium ratios.

[0076] 3. Full battery performance test Preparation of the positive electrode: Polyvinylidene fluoride (PVDF), conductive agent SP, and ternary positive electrode material (NCM, Rongbai S85E) are mixed at a mass ratio of 1.5:1:97.5 and then added to N-methylpyrrolidone (NMP). The mixture is stirred evenly to form a slurry. The slurry is then coated onto an aluminum foil current collector. The surface density of the positive electrode on one side is 170±3 g / m². 2 Cold-pressed to 3.55g / m³ 3 After punching, the positive electrode sheet is obtained.

[0077] Preparation of the negative electrode sheet: Sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), conductive agent (SuperP), graphite, and silicon-carbon negative electrode materials of Examples 1-5 and Comparative Examples 1-4 were added to deionized water at a mass ratio of 1.3:2:1:89.7:6. The mixture was stirred thoroughly and mixed evenly. The slurry was coated onto a copper foil current collector. The areal density of the negative electrode was determined according to an N / P ratio of 1.12, and then cold-pressed to 1.65 g / m³. 3 After punching, the negative electrode sheet is formed.

[0078] Battery fabrication: The separator, negative electrode, and positive electrode are stacked in a "Z" shape to obtain the bare cell to be injected with electrolyte. This bare cell is then packaged in aluminum-plastic film to obtain the electrolyte-injected cell. After baking, the electrolyte-injected battery is obtained, with a designed capacity of 2Ah. The electrolyte is prepared according to the mass ratio of LiPF6: EMC: EC: PS: LiPO2F2: DTD of 14: 65.4: 16.6: 1: 1: 2. After electrolyte injection, the battery undergoes formation, secondary sealing, and capacity testing to obtain the battery to be tested.

[0079] The performance testing method is as follows: (1) First-time efficiency of full battery: Place the prepared battery on a pressurized formation device, set the temperature to 45℃, charge it to 3.4V with a current of 0.1, let it stand for 30 minutes, remove the battery and place it at 25℃, charge it to 4.2V with 0.33C, continue constant voltage charging with a cutoff current of 0.05C, let it stand for 30 minutes, discharge it to 2.8V with 0.33C, and record the ratio of the first discharge capacity to the charging capacity.

[0080] (2) DC internal resistance (DCR) test: Charge the battery at 0.5C for 1 hour, i.e. the battery is at 50% SOC. After resting for ≥12 hours and discharging at 2C for 30 seconds, calculate the battery discharge DCR by voltage difference.

[0081] (3) Rate charging performance test: Charge the battery at 3C constant current and constant voltage to 4.2V, cut-off current is 0.05C, discharge at 1C to 2.8V, calculate the constant current charging capacity ratio, i.e. 3C constant current ratio.

[0082] (4) Cyclic performance test: At 25℃, the capacity retention rate after 1000 cycles of 1C charge-discharge was tested. The charge-discharge voltage range was 2.8V~4.2V, and the constant voltage charging cutoff current was 0.05C. The full battery test results are shown in Table 2.

[0083] Table 2. Full Battery Performance Test Results

[0084] Compared with Comparative Examples 1 and 2, the DCR, 3C constant current ratio, and cycle performance of the full cells assembled in Examples 1-3 were significantly improved. This demonstrates that the pre-lithiation of the silicon-carbon anode material in this invention not only improves the low initial efficiency but also significantly enhances other electrochemical performance. Furthermore, within the scope of the examples, the higher the lithium content of the pre-lithiation, the more pronounced the performance advantage. Compared to Comparative Example 1 without pre-lithiation of silicon-carbon, the full cell prepared in Example 3 showed an improvement in initial efficiency of over 2%. The comparison between Examples 4 and 5 and Example 3 shows that the overall battery performance deteriorated after reducing the fast ion conductor content; however, increasing the fast ion conductor content did not significantly alter the overall battery performance, especially since the DCR of the full cell did not show a significant improvement. Considering performance and cost, the fast ion conductor Li7La3Zr2O under these experimental conditions is the best choice. 12 The overall effect is optimal when the content is 1 wt%. Compared with Example 1, the DCR, 3C constant current ratio and cycle performance of the battery in Comparative Example 3 have deteriorated, indicating that the oxidation and carbonization treatment in step (3) has a significant effect on improving the kinetic performance of the material. Compared with Example 1, the overall performance of the battery in Comparative Example 4 has deteriorated (especially the first-efficiency and cycle performance), which is consistent with the verification results of the half-cell, indicating that annealing treatment is beneficial to improving the overall performance of the material.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a pre-lithium silicon-carbon anode material, characterized in that, Includes the following steps: Silicon deposition and carbon coating were performed sequentially on a porous carbon surface to obtain the first precursor. The first precursor is pressed into a disc shape to obtain a disc-shaped precursor; The disc-shaped precursor and lithium metal particles are alternately stacked to form a stack. The stack is pressurized and then heated to 500-600°C for heat treatment. Then it is cooled to 300-400°C and annealed at a constant temperature. After cooling and crushing, a second precursor is obtained. The top and bottom layers of the stack are both disc-shaped precursors. The number of alternating stacks is 3 or more. The second precursor is mixed and dispersed with a fast ion conductor and pitch in a solvent, and after drying, carbonization is performed to obtain a pre-lithiated silicon-carbon negative electrode material; the fast ion conductor is selected from one or more of H3BO3, Li2ZrS3, Li2O-AlO-SiO2, Li3V2(PO4)3, Li3Ti2(PO4)3, Li3Zr2(PO4)3, Li2O-mB2O3, Li7La3Zr2O 12 , Li6La3BiSnO 12 , LiAlF4, LiSbF6, LiBiF4, LiInF4, Li3PO4, or LiGaF4.

2. The preparation method according to claim 1, characterized in that, The specific steps for sequentially depositing silicon and coating carbon on the porous carbon surface are as follows: a gaseous silicon source is introduced into the porous carbon surface, and a chemical vapor deposition reaction is carried out at 500~600℃. After the reaction is completed, an unsaturated hydrocarbon is introduced to carry out the reaction.

3. The preparation method according to claim 2, characterized in that, The gaseous silicon source is selected from one or more of silane, silane, dichlorosilane, trichlorosilane, or silicon tetrachloride; the unsaturated hydrocarbon is selected from one or more of ethylene, acetylene, propyne, or propylene petroleum gas.

4. The preparation method according to claim 1, characterized in that, The particle size of the lithium metal particles is 0.1~20mm; the mass ratio of the lithium metal particles to the total mass of the two cake-shaped precursors is 1:(4~55); the pressing pressure in the step of pressing the first precursor into a cake shape is 5~20MPa, and the thickness of the cake-shaped precursor is 5~300mm; the pressure applied to the stack is 1~10MPa.

5. The preparation method according to claim 1, characterized in that, The heat treatment is carried out in an inert atmosphere for 6 to 15 hours; the isothermal annealing takes 12 to 36 hours; and the pressure during the heat treatment and isothermal annealing processes is 1 to 10 MPa.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the second precursor, fast ion conductor, and pitch is (95~100): (0.5~2): (1~5); the solvent is selected from one or more of pyridine, benzene, toluene, xylene, chloroform, naphthalene, tetrahydrofuran, N-methylpyrrolidone, or petroleum ether.

7. The preparation method according to claim 1, characterized in that, The carbonization temperature is 550~800℃, and the carbonization process includes a first carbonization stage and a second carbonization stage. The first carbonization stage is carried out in an oxygen-containing atmosphere with an oxygen volume fraction of 3~15% and a duration of 15~30 min. The second carbonization stage is carried out in an inert atmosphere and a duration of 1.5~10 h.

8. The preparation method according to claim 1, characterized in that, In the pre-lithiated silicon-carbon anode material, the mass fraction of silicon is 45-52 wt%, and the mass fraction of lithium is 1-10 wt%.

9. The pre-lithium silicon-carbon anode material prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, Including the pre-lithium silicon-carbon anode material as described in claim 9.

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