Silicon-carbon negative electrode material and its manufacturing method, negative electrode plate, and electrochemical device

Abstract

The present application relates to the technical field of battery anode materials, and more particularly to a silicon-carbon anode material and its manufacturing method, an anode plate, and an electrochemical device. The silicon-carbon anode material includes carbon and modified particles dispersed in the carbon, the modified particles including silicon carbide and silicon, the silicon being at least partially bonded to the carbon through the silicon carbide, and the mass ratio of the silicon carbide to the silicon is from 1:1 to 1:50.

Description

[Technical Field]

[0001] Priority information This application claims priority to Chinese Patent Application No. 202310145325.8, entitled "SILICON-CARBON NEGATIVE ELECTRODE MATERIAL AND PREPARATION METHOD THEREFOR, NEGATIVE ELECTRODE, AND ELECTROCHEMICAL APPARATUS," filed with the State Intellectual Property Office of China on January 31, 2023, which is incorporated herein by reference in its entirety.

[0002] The present application relates to the technical field of battery anode materials, and in particular to silicon-carbon anode materials and methods for producing the same, anode plates, and electrochemical devices. [Background technology]

[0003] Silicon-carbon materials have attracted widespread attention as anode materials for high-capacity lithium-ion batteries. However, the volume expansion and structural crushing of silicon during charge-discharge cycles in silicon-carbon materials can lead to the loss of electrical contact between silicon and carbon, resulting in the continuous consumption of electrolyte, ultimately affecting the cycling performance of lithium-ion batteries.

[0004] Therefore, there is an urgent need to provide silicon-carbon materials that have low volume expansion, good structural stability, and long cycle life. Summary of the Invention

[0005] The purpose of the present application is to solve the above technical problems and provide a silicon-carbon negative electrode material and a manufacturing method thereof, a negative electrode plate, and an electrochemical device.

[0006] To achieve the above object, a first aspect of the present application provides a silicon-carbon negative electrode material comprising carbon and modified particles dispersed in the carbon, wherein the modified particles comprise silicon carbide and silicon, the silicon being at least partially bonded to the carbon via the silicon carbide, and the mass ratio of silicon carbide to silicon is from 1:1 to 1:50.

[0007] A second aspect of the present application provides a method for producing a silicon-carbon anode material, the method comprising: subjecting a silicon-carbon feedstock to a heat treatment under oxygen-isolated conditions to obtain the silicon-carbon anode material, the silicon-carbon feedstock comprising a dispersed silicon-carbon material, the dispersed silicon-carbon material comprising a substrate carbon and silicon particles dispersed in the substrate carbon.

[0008] A third aspect of the present application provides a negative electrode plate comprising a current collector and a dressing layer coated on the current collector, wherein the dressing layer comprises a silicon-carbon negative electrode material, and the silicon-carbon negative electrode material is the silicon-carbon negative electrode material described in the first aspect of the present application or a silicon-carbon negative electrode material produced using the method described in the second aspect of the present application.

[0009] A fourth aspect of the present application provides an electrochemical device including the negative electrode plate according to the third aspect of the present application.

[0010] Through the above technical solutions, the beneficial technical effects achieved by the present application are as follows:

[0011] (1) The silicon-carbon anode material provided in the present application bonds silicon and carbon via silicon carbide, thereby improving the structural stability of the silicon-carbon anode material and avoiding or reducing the separation of the bonding interface between silicon and carbon caused by silicon expansion during the charge-discharge process. This not only effectively solves the problem of short battery cycle life caused by silicon expansion, but also effectively reduces the potential barrier for lithium ion permeation at the silicon-carbon interface, reduces the ion diffusion impedance of lithium ion migration at the silicon-carbon interface, and facilitates lithium ion migration during the charge-discharge process.

[0012] (2) In the silicon-carbon anode material provided in the present application, silicon carbide has excellent mechanical strength. The silicon carbide is distributed on the surface of the silicon, which can better suppress the volume change of the inner silicon layer caused by expansion during the charge and discharge process, reduce the expansion of the electrode plate and battery cell, and improve the cycle capacity retention rate.

[0013] (3) According to the method for producing a silicon-carbon negative electrode material provided in the present application, heat treatment of the dispersed silicon-carbon material can cause the carbon and silicon atoms on the contact surface between the substrate carbon and the silicon particles to undergo appropriate atomic rearrangement, thereby producing silicon carbide. The produced silicon carbide can be combined with silicon to form modified particles with silicon carbide on the outside and silicon on the inside, which structure can improve the mechanical strength of the silicon-carbon negative electrode material and reduce the expansion volume of the silicon material.

[0014] (4) According to the method for producing silicon-carbon negative electrode materials provided in the present application, the production efficiency and processing effect of silicon-carbon negative electrode materials can be balanced by optimizing the heat treatment process.

[0015] (5) The manufacturing process used in this application is simple, easy to mass-produce, and does not significantly increase material costs.

[0016] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of this specification. In conjunction with the following specific implementations, they are used to explain the present disclosure but do not impose limitations on the disclosure. In the accompanying drawings: [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an XRD diagram of a silicon-carbon negative electrode material according to Example 1 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following is a detailed description of specific implementations of the present application with reference to the accompanying drawings. It should be understood that the specific implementations described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0019] A first aspect of the present application provides a silicon-carbon anode material comprising carbon and modified particles dispersed in the carbon, wherein the modified particles comprise silicon carbide and silicon, the silicon being at least partially bonded to the carbon through the silicon carbide, and the mass ratio of silicon carbide to silicon is from 1:1 to 1:50.

[0020] In this application, the mass ratio of silicon carbide to silicon is measured using an XPS-Si spectrum. The characteristic peaks of silicon carbide and silicon can be separated through the Si spectrum, and the ratio of silicon carbide to silicon can be determined based on the area ratio of the characteristic peak of silicon carbide to the characteristic peak of silicon. In this application, the mass ratio of silicon carbide to silicon in the silicon-carbon negative electrode material is controlled to be 1:1 to 1:50. Silicon carbide can more firmly hold silicon, thereby reducing the expansion coefficient of silicon and increasing the specific capacity of the silicon-carbon negative electrode material. In this application, the modified particles may be a composite material containing silicon and silicon carbide. The modified particles are fixed and dispersed on carbon. The surface of the modified particles is silicon carbide, and the interior is silicon. Silicon carbide can bond silicon and carbon, thereby improving the structural stability of silicon-carbon anode materials and preventing the separation of the bonding interface between silicon and carbon during charge-discharge processes. It also effectively reduces the potential barrier for lithium ion permeation at the interface, reduces the ion diffusion impedance for lithium ion migration at the interface, and facilitates lithium ion migration during charge-discharge processes.

[0021] In some implementations, the carbon includes amorphous carbon. The carbon in the crystalline structure of amorphous carbon is randomly arranged over short distances. In one aspect, this contributes to multidirectional insertion / extraction of lithium ions and improves the rate capability during high-current charging and discharging. In addition, the interstices between the carbon layers in the amorphous carbon crystal are relatively large, which ensures structural stability of the carbon skeleton during lithium ion insertion. In another aspect, this slows down the silicon breakdown process, delaying battery cell failure and further improving the cycling performance of lithium-ion batteries.

[0022] In some implementations, the present application does not impose any particular constraints on the distribution of the modifying particles in the carbon, for example, the modifying particles may be uniformly or non-uniformly distributed in the carbon.

[0023] In some implementations, the silicon comprises silicon crystal grains, and the silicon crystal grains have an average size of 0.2 nm to 10 nm. In some other implementations, the silicon crystal grains have an average size of 1 nm to 3 nm.

[0024] In the present application, the average size of the silicon crystal grains may be measured using XRD spectra and calculated using the Scherrer equation. The average size of the silicon crystal grains may be 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2 nm, 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, 3 nm, 3.2 nm, 3.4 nm, 3.6 nm, 3.8 nm, 4 nm, 4.2 nm, 4.4 nm, 4.6 nm, 4.8 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, and any value within the range formed by any two of these values. When the average diameter of silicon crystal grains is between 1 and 3 nm, the specific surface area of ​​the silicon crystal grains is large, resulting in high interfacial activity, which significantly increases the number of reactive sites for lithium ions, thereby increasing the specific capacity and rate performance of silicon-carbon anode materials.In addition, the volume expansion rate of silicon crystal grains within this particle size range is small, making them suitable for storing lithium ions.

[0025] In some implementations, the silicon further comprises amorphous silicon, which undergoes fewer phase changes during lithiation reactions and has greater stability, which is beneficial for enhancing the cycling performance of the silicon-carbon negative electrode material.

[0026] In some implementations, the carbon content is 20 wt% to 85 wt%, for example, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 85 wt%, and any value within a range formed by any two of these values, based on the total mass of the silicon-carbon negative electrode material. The modified particle content is 15 wt% to 80 wt%, for example, 15 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, and any value within a range formed by any two of these values. In some other implementations, the carbon content is 30 wt% to 48 wt%, and the modified particle content is 52 wt% to 72 wt%, based on the total mass of the silicon-carbon negative electrode material.

[0027] Both silicon and carbon can be used as supports for storing lithium ions to achieve the capacity of lithium-ion batteries. Silicon theoretically has a higher specific capacity but poor electrical conductivity and cycle stability, while carbon has a lower specific capacity than silicon but good electrical conductivity and cycle stability. In this application, the specific capacity and cycle stability of silicon-carbon anode materials can be further improved by controlling the content of carbon and modified particles. When the content of carbon and modified particles is within the above range, the performance of the silicon-carbon anode material is better.

[0028] In some implementations, the mass ratio of silicon carbide to silicon in the silicon-carbon negative electrode material is from 1:1 to 1:50. For example, the mass ratio of silicon carbide to silicon in the silicon-carbon negative electrode material can be 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, etc. In some other implementations, the mass ratio of silicon carbide to silicon in the silicon-carbon negative electrode material is from 1:1 to 1:20. Furthermore, the mass ratio of silicon carbide to silicon in the silicon-carbon negative electrode material is from 1:8 to 1:12.

[0029] In some implementations, the average particle size of the silicon-carbon negative electrode material is from 0.5 μm to 40 μm, such as 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, and any value within a range formed by any two of these values. In some other implementations, the average particle size of the silicon-carbon negative electrode material is from 1 μm to 20 μm, and even from 5 μm to 10 μm.

[0030] A second aspect of the present application provides a method for producing a silicon-carbon anode material, the method comprising: subjecting a silicon-carbon feedstock to a heat treatment under oxygen-isolated conditions to obtain the silicon-carbon anode material, the silicon-carbon feedstock comprising a dispersed silicon-carbon material, the dispersed silicon-carbon material comprising a substrate carbon and silicon particles dispersed in the substrate carbon.

[0031] In this application, the inventors have found through research that heat treatment of dispersed silicon-carbon materials can cause appropriate atomic rearrangement of carbon and silicon atoms on the contact surface between the substrate carbon and silicon particles to produce silicon carbide, which can bond the substrate carbon and silicon particles together, thereby improving the mechanical strength of the silicon-carbon composite material and reducing its volume expansion coefficient.

[0032] In some implementations, oxygen isolation means that the heat treatment is performed under conditions where the volumetric oxygen content is 5% or less. In the present application, the method of oxygen isolation may be evacuation and / or filling with an inert gas. The inert gas may be one or more of nitrogen, argon, helium, and neon. By performing the heat treatment under oxygen isolation, the surface structure of the silicon-carbon negative electrode material can be optimized, the material impedance can be reduced, and no adverse effects on the battery occur.

[0033] In some implementations, the present application does not specifically limit the dispersed silicon-carbon material, and it may be a commercially available dispersed silicon-carbon material or may be manufactured using known methods. For example, silicon precursors and carbon precursors may be used for manufacturing according to well-known one-step or multi-step high-temperature deposition methods. The silicon precursor may include silane and / or trichlorosilane, and the carbon precursor may include one or more of hard carbon, porous carbon, mesoporous carbon, activated carbon, soft carbon, porous graphite, methane, ethane, ethylene, and acetylene.

[0034] In some implementations, the present application does not impose any particular limitations on the method of dispersing the silicon particles in the substrate carbon, and the silicon particles may be uniformly or non-uniformly dispersed in the substrate carbon.

[0035] In some implementations, the substrate carbon comprises amorphous carbon, and the silicon particles comprise amorphous silicon. In this application, the inventors have found through research that during the heat treatment process, silicon atoms are rearranged, which leads to the transformation of the amorphous silicon in the silicon particles into silicon crystalline grains. This transformation process is also related to the increase in silicon crystalline grain size.

[0036] Amorphous silicon is less likely to undergo a phase change when reacting with lithium ions, has a relatively stable structure, and has a low volume expansion coefficient, which is beneficial for extending the cycle life of lithium ion batteries. Compared to amorphous silicon, silicon crystalline grains have a relatively large volume expansion coefficient. Therefore, the present application can inhibit or reduce the volume expansion of silicon crystalline grains during the lithiation reaction by controlling the size of the silicon crystalline grains.

[0037] In the present application, the inventors have found that by optimizing the temperature range and holding time during heat treatment of the dispersed silicon-carbon material, the amount of silicon carbide produced and the size of the silicon crystal grains can be balanced, thereby resulting in a silicon-carbon negative electrode material with better performance.

[0038] In some implementations, the substrate carbon content is from 22 wt% to 88 wt%, based on the total mass of the dispersed silicon-carbon material, for example, 22 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 82 wt%, 85 wt%, 88 wt%, and any two of these values. In some implementations, the substrate carbon content is from 32 wt% to 52 wt% and the silicon particle content is from 48 wt% to 68 wt%, based on the total mass of the dispersed silicon-carbon material.

[0039] In this application, by controlling the content of silicon and carbon in the dispersed silicon-carbon material, the mass ratio of carbon to modified particles in the silicon-carbon negative electrode material produced after heat treatment can be balanced, thereby increasing the specific capacity and improving the cycle stability of the silicon-carbon negative electrode material. When the content of substrate carbon and silicon particles in the dispersed silicon-carbon material is within the above specified range, the cycle performance of the produced silicon-carbon negative electrode material is better.

[0040] In some implementations, the average particle size of the dispersed silicon-carbon material is from 0.5 μm to 40 μm, such as 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, and any value within a range formed by any two of these values. In some other implementations, the average particle size of the dispersed silicon-carbon material is from 1 μm to 20 μm, and even from 5 μm to 10 μm. In the present application, the average particle size of the dispersed silicon-carbon material and the average particle size of the produced silicon-carbon negative electrode material are substantially the same.

[0041] In some implementations, the heating rate of the thermal treatment is from 0.5°C / min to 50°C / min, e.g., the heating rate is 0.5°C / min, 1°C / min, 5°C / min, 10°C / min, 20°C / min, 30°C / min, 40°C / min, 50°C / min, and any value within a range formed by any two of these values, and the processing temperature is from 400°C to 900°C, e.g., the processing temperature is 400°C, 450°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1200°C, 1400°C, 1600°C, 1800°C, 1900°C, 2000°C, 2200°C, 2400°C, 2600°C, 2800°C, 2900°C, 3000°C, 3100°C, 3200°C, 3300°C, 3400°C, 3500°C, 3600°C, 3700°C, 3800°C, 3900°C, 4000°C, 4100°C, 4200°C, 4300°C, 4400°C, 4500°C, 4600°C, 4700°C, 4800°C, 4900°C, 5000°C, 5100°C, 5200°C, 5300°C, 5400°C, 5500°C, 5600°C, 570 and the treatment time is from 30 to 240 minutes, for example, 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes, 210 minutes, 240 minutes, and any value within the range formed by any two of these values.

[0042] In some other implementations, the heating rate of the heat treatment is from 2°C / min to 30°C / min, or even from 5°C / min to 20°C / min, the treatment temperature of the heat treatment is from 600°C to 800°C, or even from 650°C to 750°C, and the treatment time of the heat treatment is from 30 minutes to 150 minutes, or even from 60 minutes to 90 minutes.

[0043] The heat treatment process is mainly related to the elemental rearrangement at the interface between carbon atoms and silicon atoms to produce silicon carbide. The amount of silicon carbide produced can be controlled by controlling the heating rate, treatment temperature, and treatment time. The heat treatment process also affects the growth of silicon crystal grains. In this application, excessively large silicon crystal grains adversely affect the performance of the material. When the heat treatment conditions are within the specified ranges, the silicon-carbon negative electrode material produced has the best performance.

[0044] A third aspect of the present application provides a negative electrode plate comprising a current collector and a dressing layer coated on the current collector, wherein the dressing layer comprises a silicon-carbon negative electrode material, and the silicon-carbon negative electrode material is the silicon-carbon negative electrode material described in the first aspect of the present application or a silicon-carbon negative electrode material produced using the method described in the second aspect of the present application.

[0045] In some implementations, the dressing layer further comprises at least one of graphite, a conductive agent, and a binder.

[0046] In some implementations, the current collector comprises copper foil or foamed copper.

[0047] In some implementations, the dressing layer includes 1 part by weight of silicon-carbon negative electrode material, 0 to 100 parts by weight of graphite, 0.1 to 1 part by weight of a conductive agent, and 0.5 to 1.5 parts by weight of a binder, for example, graphite including 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 parts by weight, and any value within a range formed by any two of these values; conductive agent including 0.1, 0.2, 0.5, 0.7, 1 part by weight, and any value within a range formed by any two of these values; and binder including 0.5, 0.7, 1, 1.2, 1.5 parts by weight, and any value within a range formed by any two of these values.

[0048] In some other implementations, the dressing layer includes 1 part by weight of silicon-carbon anode material, 8 to 30 parts by weight of graphite, 0.4 to 0.6 parts by weight of a conductive agent, and 0.8 to 1.2 parts by weight of a binder.

[0049] In some implementations, the binder includes, but is not limited to, polyacrylic acid, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate, and modifications thereof, as well as mixed binders in which the above-mentioned various binders are mixed in various proportions, and the conductive agent includes, but is not limited to, carbon nanotubes, carbon fiber, activated carbon, amorphous carbon, conductive carbon black, and acetylene black, as well as mixed conductive agents in which the above-mentioned various conductive agents are mixed in various proportions.

[0050] The battery manufactured using the negative plate provided in the present application has the advantages of high specific capacity, low cycle fade, and small cycle volume expansion.

[0051] A fourth aspect of the present application provides an electrochemical device including the negative electrode plate according to the third aspect of the present application.

[0052] The present application does not impose any particular limitation on the electrochemical device, and any electrochemical device capable of employing the negative electrode of the present application, such as any type of primary battery or secondary battery, may be used in the present application. In some examples, the electrochemical device is a lithium secondary battery. The electrochemical device provided in the present application has the advantages of high energy density, excellent cycle performance, and small cycle expansion.

[0053] The present application is explained in detail below through examples and comparative examples.

[0054] Dispersed silicon-carbon material I was purchased from Group 14 technologies, Inc., USA. The substrate carbon was amorphous carbon with a content of 48 wt%, the silicon particles were amorphous silicon with a content of 52 wt%, and the average particle size of the dispersed silicon-carbon material was 7 μm.

[0055] Dispersed silicon-carbon material II was produced using the following method: a porous carbon material (purchased from Shanghai Danyuan New Material Technology Co., Ltd.) was placed in a tubular furnace, silane was introduced under nitrogen protection, and the reaction was carried out at 550°C for 180 minutes to deposit silicon, obtaining dispersed silicon-carbon material II. The substrate carbon in dispersed silicon-carbon material II was amorphous porous carbon with a content of 85 wt%, the silicon particles were amorphous silicon with a content of 15 wt%, and the average particle size of the dispersed silicon-carbon material was 7 μm. [Example]

[0056] 2 kg of dispersed silicon material I was placed in a crucible with a lid, which was then placed in a high-temperature furnace. After sealing, the furnace chamber was evacuated using a vacuum pump and filled with nitrogen for protection. The vacuum-nitrogen filling operation was repeated several times until the oxygen content in the furnace chamber was lower than 0.5 v%, and then the temperature was increased to 700 °C at a heating rate of 5 °C / min and held for 60 minutes. After that, nitrogen was filled several times to quickly cool the high-temperature furnace, and after the temperature had dropped to room temperature, a silicon-carbon negative electrode material was obtained. [Example]

[0057] Same as Example 1 except the heating rate was 8°C / min. [Example]

[0058] Same as Example 1 except the heating rate was 20°C / min. [Example]

[0059] The same as in Example 1 except that the heat treatment temperature was 600°C. [Example]

[0060] The same as in Example 1 except that the heat treatment temperature was 800°C. [Example]

[0061] The same as Example 1 was performed except that the heat treatment time was 120 minutes. [Example]

[0062] The same as Example 1 was performed except that the heat treatment time was 30 minutes. [Example]

[0063] Same as Example 1 except that the dispersed silicon-carbon material was II. [Example]

[0064] The same as in Example 1 was used except that the heat treatment temperature was 900° C. and the heat treatment time was 90 minutes.

[0065] Comparative Example 1 The silicon-carbon anode material was not subjected to heat treatment, and the dispersed silicon-carbon material I was directly used as the silicon-carbon anode material.

[0066] Comparative Example 2 The same as Example 1 was performed except that the heat treatment time was 20 minutes.

[0067] Comparative Example 3 The same as in Example 1 was used except that the heat treatment temperature was 1000° C. and the heat treatment time was 300 minutes.

[0068] Test Example 1 The silicon-carbon negative electrode material prepared in Example 1 was characterized by XRD, and the results are shown in FIG.

[0069] As can be seen from Figure 1, there is no peak with a half-width of less than 3° at 2θ = 26 ± 1°, indicating that the carbon in the silicon-carbon negative electrode material produced in Example 1 was amorphous carbon. There is a diffraction peak at 2θ = 28.5 ± 1°, indicating that the silicon-carbon negative electrode material produced in Example 1 contained silicon. There is a diffraction peak at 2θ = 35.7 ± 1°, indicating that the silicon-carbon negative electrode material produced in Example 1 contained silicon carbide.

[0070] From the manufacturing method of Example 1, it can be seen that during the heat treatment process, silicon and carbon react on the contact surface between silicon and carbon to produce silicon carbide, and the silicon carbide is distributed on the silicon and can form modified particles together with silicon. The silicon carbide distributed on the surface of the modified particles can firmly bond silicon and carbon together.

[0071] The results of XRD characterization of the silicon-carbon negative electrode materials prepared in Examples 2 to 9 were essentially the same as those in FIG.

[0072] Test Example 2 The silicon-carbon negative electrode materials produced in Examples 1 to 9 and Comparative Examples 1 to 3 were characterized for the carbon content, the modified particle content, the mass ratio of silicon carbide to silicon in the modified particle, the average size of the silicon crystal grains, and the particle size of the silicon-carbon negative electrode material, and the results are shown in Table 1.

[0073] The carbon and modified particle content was measured using a high-frequency infrared carbon-sulfur analyzer and a combustion furnace. The test samples were calcined at 1300°C to gasify and decompose the carbon, and the mass of the remaining parts (silicon carbide and silicon) was measured. The mass of the calcined sample was subtracted from the mass of the sample before calcination, and the difference was used as the mass of carbon in the sample. The average silicon grain size was tested by XRD, and the mass ratio of silicon carbide to silicon was characterized by XPS-Si spectroscopy. The particle size of the silicon-carbon anode material was also tested using a Malvern laser particle size analyzer. [Table 1]

[0074] A comparison of Examples 1, 2 and 3 shows that when the heating rate was within the range of 5°C / min to 20°C / min, the average silicon grain size and the amount of silicon carbide produced remained substantially unchanged as the heating rate increased.

[0075] Comparing Examples 1, 4, 5, and 9, it can be seen that within the heat treatment temperature range specified in this application, the average size of silicon crystal grains and the amount of silicon carbide produced increase with the treatment temperature. It can be seen that the reaction temperature has a significant effect on the growth of silicon crystal grains. When the temperature exceeds a certain range, i.e., when the critical point for the transformation of amorphous silicon into silicon crystal grains is reached, the silicon carbide increases rapidly.

[0076] Comparing Examples 1, 6, and 7, it can be seen that within the heat treatment time range specified in this application, as the modification time decreases, the amount of modified particles and silicon carbide produced decreases, and the average size of silicon crystal grains also decreases slightly. Also, as the modification time increases, the amount of silicon carbide produced increases, and the average size of silicon crystal grains also increases, but the rate of increase is relatively slow.

[0077] From the above examples, it can be seen that silicon carbide and silicon grain control in this application was not achieved through a single heat treatment condition, but was the result of a coordination of heating rate, heat treatment temperature, and heat treatment time.

[0078] A comparison of Examples 1 and 8 shows that within the heat treatment time range specified in this application, varying the carbon and silicon composition ratios in the dispersed silicon-carbon feedstock did not significantly change the amount of modified particles and silicon carbide produced, nor the average size of the silicon crystal grains.

[0079] Comparing Example 1 with Comparative Examples 2 and 3, it can be seen that too short or too long a heat treatment time at high temperature did not contribute to controlling the growth of silicon carbide.

[0080] Test Example 3 After 2025-type button batteries were fabricated using the silicon-carbon negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 3, the negative electrode specific capacity of the 2025-type button batteries was tested (Note: the negative electrode specific capacity can be understood as the specific capacity of the active material of the 2025-type button battery, i.e., the specific capacity of the active material formed by the silicon-carbon negative electrode material and optional graphite; the negative electrode referred to here does not represent the actual negative electrode of the 2025-type button battery, but is merely for consistency with the name in soft-pack batteries), and the results are shown in Table 2. Taking Example 1 as an example, the method for measuring the negative electrode specific capacity is as follows.

[0081] The silicon-carbon anode material prepared in Example 1 was mixed with graphite, a conductive agent (a 1:0.1 mass ratio of conductive carbon black to carbon nanotubes), and polyacrylic acid in a mass ratio of 1:9:0.5:1. An appropriate amount of water was added, and the mixture was kneaded for 1 hour at a solids content of approximately 60%. Water was added to adjust the slurry viscosity to 5000 Pa s to prepare anode slurry. The resulting anode slurry was coated onto a copper foil current collector, dried, and cold-pressed to obtain anode plates.

[0082] A 17 mm diameter, 1 mm thick lithium metal sheet was used as the counter electrode. A 25 μm thick polyethylene porous membrane coated with an alumina ceramic layer served as the separator. An equal-weight mixture of vinyl carbonate and dimethyl carbonate containing 1 mol / L lithium hexafluorophosphate was used as the electrolyte. The fabricated negative electrode, separator, lithium metal sheet, and electrolyte were assembled into a 2025-type button cell in an Ar gas glove box with water and oxygen contents both less than 5 ppm. In a NEWARE electrochemical test cabinet, the cell was discharged to 5 mV at a rate of 0.05 C and then charged to 1.5 V at a rate of 0.05 C. The specific capacity of the negative electrode was calculated based on the charge capacity.

[0083] Soft-pack batteries were fabricated using the silicon-carbon anode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 3, and then the cycle life, expansion rate, and impedance of the soft-pack batteries were tested. The results are shown in Table 2. Taking the silicon-carbon anode material prepared in Example 1 as an example, the soft-pack battery was fabricated as follows.

[0084] The silicon-carbon anode material prepared in Example 1 was mixed with graphite, a conductive agent (a 1:0.1 mass ratio of conductive carbon black to carbon nanotubes), and polyacrylic acid in a mass ratio of 1:9:0.5:1. An appropriate amount of water was added, and the mixture was kneaded for 1 hour at a solids content of approximately 60%. Water was added to adjust the slurry viscosity to 5000 Pa s to prepare anode slurry. The resulting anode slurry was coated onto a copper foil current collector, dried, and cold-pressed to obtain anode plates.

[0085] Lithium cobalt oxide, conductive agent (SP), and PVDF were mixed in a 100:1:1 ratio, NMP (N-methylpyrrolidone) was added, and the mixture was stirred for 1 hour at a solids content of approximately 80% to obtain a positive electrode slurry. The resulting positive electrode slurry was then coated onto an aluminum foil current collector, dried, and cold-pressed to obtain a positive electrode plate.

[0086] After the positive and negative electrodes were cut into 50 × 90 mm sheets, a 7 μm-thick porous polyethylene membrane coated with an alumina ceramic layer was used as the separator, and an equal-mass mixture of vinyl carbonate and dimethyl carbonate containing 1 mol / L lithium hexafluorophosphate was used as the electrolyte. The positive electrodes, separator, negative electrodes, and electrolyte were assembled into a laminated soft-pack battery in an Ar gas glove box with water and oxygen contents both less than 5 ppm.

[0087] Cycle Life Test The soft pack battery was subjected to a cycle test at room temperature with a 1C charge and 0.5C discharge, with a cycle voltage range of 3.0V to 4.48V, and the number of cycles at which the capacity of the soft pack battery decreased to 80% was recorded.

[0088] Expansion Rate Test The soft-pack batteries were subjected to a cycle test of 1C charge and 0.5C discharge at room temperature. The battery thickness was recorded using a PPG pressure of 400g and compared with the initial battery thickness. The thickness at 800 cycles was recorded and the expansion ratio was calculated. The formula for thickness expansion ratio is (battery thickness at 800 cycles / initial battery thickness)*100%.

[0089] Battery Impedance Test Method At room temperature, the battery impedance was measured using a HIOKI BT3562A Battery HiTester instrument. [Table 2]

[0090] Comparing Examples 1 to 9 with Comparative Examples 1 to 3, it can be seen that the formation of silicon carbide significantly improves cycle stability, increases the volume expansion rate, and improves the impedance performance of lithium-ion batteries. Silicon carbide can bond silicon and carbon, increasing the structural stability of silicon-carbon anode materials and preventing or reducing the separation of the silicon-carbon bonding interface caused by silicon expansion during charge and discharge. It also effectively reduces the potential barrier to lithium ion permeation at the silicon-carbon interface, reducing the ion diffusion impedance of lithium ion migration at the silicon-carbon interface, ultimately improving the cycle performance of lithium-ion batteries.

[0091] Test Example 4 See Test Example 3. Using the composite anode material in Example 1, a 2025-type button battery and a soft-pack battery were fabricated. The difference was that the mass ratio of the composite anode material to graphite was changed. The specific anode capacity of the 2025-type button battery and the impedance of the soft-pack battery at room temperature, as well as the capacity retention rate after 1000 cycles, were then tested. The test results are shown in Table 3. [Table 3]

[0092] The data in Table 3 show that the more silicon-carbon anode material added, the worse the cycling performance, but the higher the anode specific capacity. Therefore, to balance the trade-off between the two, the current mass ratio of silicon-carbon anode material to graphite is between 1:8 and 1:30, which better balances the trade-off between increasing anode specific capacity and improving cycling performance.

[0093] Preferred implementation forms of the present application have been described in detail above with reference to the accompanying drawings. However, the present application is not limited thereto. Various simple modifications to the technical solutions of the present application may be made, including combining various specific technical features in any suitable manner within the technical concept of the present application. To avoid unnecessary repetition, the present application will not further describe various possible combinations. However, these simple modifications and combinations are also considered to be the contents disclosed by the present application and fall within the protection scope of the present application.

Claims

1. 1. A silicon-carbon anode material comprising: carbon; and modified particles dispersed in the carbon, the modified particles comprising silicon carbide and silicon, the silicon being at least partially bonded to the carbon through the silicon carbide, the mass ratio of the silicon carbide to the silicon being from 1:1 to 1:

50.

2. 10. The silicon-carbon anode material of claim 1, wherein the carbon comprises amorphous carbon.

3. 3. The silicon-carbon negative electrode material of claim 1, wherein the silicon comprises silicon crystal grains, and the silicon crystal grains have an average diameter of 0.2 nm to 10 nm.

4. 4. The silicon-carbon negative electrode material of claim 3, wherein the average diameter of the silicon crystal grains is from 1 nm to 3 nm.

5. 5. The silicon-carbon anode material of claim 3, wherein the silicon further comprises amorphous silicon.

6. 6. The silicon-carbon negative electrode material of claim 1, wherein the carbon content is from 20 wt % to 85 wt % and the modified particles content is from 15 wt % to 80 wt %, based on the total mass of the silicon-carbon negative electrode material.

7. 7. The silicon-carbon negative electrode material of claim 1, wherein the carbon content is from 30 wt % to 48 wt % and the modified particle content is from 52 wt % to 72 wt %, based on the total mass of the silicon-carbon negative electrode material.

8. 8. The silicon-carbon anode material of claim 1, wherein the mass ratio of the silicon carbide to the silicon is from 1:1 to 1:

20.

9. 9. The silicon-carbon anode material of claim 1, wherein the mass ratio of the silicon carbide to the silicon is from 1:8 to 1:

12.

10. 10. The silicon-carbon anode material of claim 1, wherein the silicon-carbon anode material has an average particle size of from 0.5 μm to 40 μm.

11. 11. The silicon-carbon anode material of claim 1, wherein the silicon-carbon anode material has an average particle size of from 1 μm to 20 μm.

12. 12. The silicon-carbon anode material of any one of claims 1 to 11, wherein the silicon-carbon anode material has an average particle size of from 5 μm to 10 μm.

13. 1. A method for producing a silicon-carbon anode material, the method comprising: subjecting a silicon-carbon feedstock to a heat treatment under oxygen-isolated conditions to obtain the silicon-carbon anode material, the silicon-carbon feedstock comprising a dispersed silicon-carbon material, the dispersed silicon-carbon material comprising a substrate carbon and silicon particles dispersed in the substrate carbon.

14. The method of claim 13 , wherein the substrate carbon comprises amorphous carbon and the silicon particles comprise amorphous silicon.

15. 15. The method of claim 13 or 14, wherein the content of the substrate carbon is from 22 wt % to 88 wt % and the content of the silicon particles is from 12 wt % to 78 wt %, based on the total mass of the dispersed silicon-carbon material.

16. 16. The method of any one of claims 13 to 15, wherein the substrate carbon content is from 32 wt% to 52 wt% and the silicon particle content is from 48 wt% to 68 wt%, based on the total mass of the dispersed silicon-carbon material.

17. 17. The method of any one of claims 13 to 16, wherein the dispersed silicon-carbon material has an average particle size of from 0.5 μm to 40 μm.

18. 18. The method of any one of claims 13 to 17, wherein the dispersed silicon-carbon material has an average particle size of from 1 μm to 20 μm.

19. 19. The method of any one of claims 13 to 18, wherein the dispersed silicon-carbon material has an average particle size of from 5 μm to 10 μm.

20. 20. The method of any one of claims 13 to 19, wherein the heat treatment has a heating rate of 0.5°C / min to 50°C / min, a treatment temperature of 400°C to 900°C, and a treatment time of 30 to 240 minutes.

21. 21. A negative electrode plate comprising a current collector and a dressing layer coated on the current collector, wherein the dressing layer comprises a silicon-carbon negative electrode material, the silicon-carbon negative electrode material being the silicon-carbon negative electrode material of any one of claims 1 to 12 or a silicon-carbon negative electrode material produced using the method of any one of claims 13 to 20.

22. 22. The negative plate of claim 21, wherein the dressing layer further comprises at least one of graphite, a conductive agent, and a binder.

23. 23. The negative electrode plate of claim 21 or 22, wherein the current collector comprises copper foil or foamed copper.

24. 24. The negative electrode plate of claim 22 or 23, wherein the dressing layer comprises 1 part by weight of silicon-carbon negative electrode material, 0 to 100 parts by weight of graphite, 0.1 to 1 part by weight of a conductive agent, and 0.5 to 1.5 parts by weight of a binder.

25. 25. The negative electrode plate of any one of claims 22 to 24, wherein the dressing layer comprises 1 part by weight of silicon-carbon negative electrode material, 8 to 30 parts by weight of graphite, 0.4 to 0.6 parts by weight of a conductive agent, and 0.8 to 1.2 parts by weight of a binder.

26. 26. An electrochemical device comprising the negative electrode plate according to any one of claims 21 to 25.

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