Silicon / carbon composite material, preparation and use thereof
By combining pre-lithiated silicon materials with carbon materials and performing secondary heat transfer gradient heat treatment, the problem of unsatisfactory electrochemical performance of silicon-carbon composite materials in lithium-ion batteries was solved, and the high conductivity and good cycle performance of the materials were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 湖南宸宇富基新能源科技有限公司
- Filing Date
- 2022-05-17
- Publication Date
- 2026-06-12
Smart Images
Figure CN117012913B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery materials, specifically relating to battery anode materials. Background Technology
[0002] With the rapid rise and development of new energy technologies, various new energy devices have gradually entered people's lives, among which lithium-ion batteries have seen the fastest and widest adoption, thanks to their advantages such as high energy density, high voltage, and no memory effect. The lithium-ion battery industry has now matured, and its performance has gradually stabilized. However, the explosive growth of new energy vehicles and digital products has placed higher demands on the performance of lithium-ion batteries.
[0003] The performance of lithium-ion batteries is primarily determined by the cathode and anode materials. Currently, commercially available cathode materials include lithium iron phosphate, lithium cobalt oxide, and ternary materials, while anode materials are mainly carbon-based materials such as graphite. Given the current state of research, significant breakthroughs in cathode capacity are unlikely. However, silicon is one of the most promising next-generation high-capacity lithium-ion battery anode materials. Silicon has a theoretical capacity of up to 4200 mAh / g, is abundant in the Earth's crust, and has a suitable lithium insertion / extraction potential, which could greatly improve the performance of current lithium-ion batteries. However, silicon also has some drawbacks as a lithium-ion battery anode material: firstly, as a semiconductor, silicon has poor conductivity, resulting in poor rate performance; secondly, the lithium insertion / extraction process in silicon involves alloying / dealloying reactions, causing significant volume changes in the entire anode system, leading to material pulverization and even detachment from the current collector, resulting in poor cycle performance.
[0004] Current research focuses on the aforementioned problems of silicon, primarily employing methods such as nanostructuring, porous structures, and material composites to effectively address these issues. Carbon, as a mature anode material, is often used in combination with silicon to neutralize the advantages of both and mitigate their shortcomings. Thanks to the versatility of carbon's properties, numerous silicon-carbon composite materials have been developed, exhibiting varying performance characteristics. However, few mature silicon-carbon composite materials have been commercialized to date. This is primarily due to their complex preparation processes, high costs, unstable performance, and tendency to form silicon carbide. Therefore, research addressing these limiting factors is of significant importance. Summary of the Invention
[0005] To address the problem of unsatisfactory electrochemical performance of existing silicon-carbon materials, the primary objective of this invention is to provide a novel method for preparing silicon / carbon composite materials, aiming to improve the electrochemical properties of the prepared materials, such as energy density, cycle performance, coulombic efficiency, and rate performance.
[0006] The second objective of this invention is to provide a silicon / carbon composite material prepared by the aforementioned method and its application in batteries.
[0007] A third objective of the present invention is to provide a battery comprising the aforementioned silicon / carbon composite material.
[0008] There are already a few cases in the industry where silicon / carbon composite anode materials have been applied to commercial lithium-ion batteries. The main approach involves combining high-purity nano-silicon powder prepared by chemical vapor deposition or ball milling with a large amount of graphite or other carbon materials through simple physical mixing to create a silicon-carbon composite material with slightly better performance than traditional carbon anode materials. However, there have been no reports of the commercialization of pre-lithiated silicon-carbon composite materials to date, and even fewer ideas and technical solutions have been found to fundamentally change the properties of silicon-carbon composite materials using special heat treatment processes and apply them to lithium-ion batteries. This invention aims to provide a high-value, high-performance pre-lithiation silicon / carbon composite anode material for lithium-ion batteries prepared using a special heat treatment process. However, research shows that pre-lithiation technology is difficult to stably apply to improve the performance of lithium-ion battery anode materials, and the composite ratio and method of silicon-carbon composite materials also profoundly affect their final performance. Furthermore, the heat treatment process is unlikely to alter the electrochemical properties of the material, making it difficult for the above technologies to achieve the desired effects when applied to lithium-ion batteries. Moreover, it is difficult to integrate and innovate these technologies to achieve a greater impact. Therefore, in the early stages of technology development, it is difficult to obtain pre-lithiation silicon / carbon composite anode materials with ideal electrochemical performance. Through continuous research, this invention provides the following improved method:
[0009] A method for preparing a silicon / carbon composite material involves pre-lithiation of silicon raw materials and lithium salt at a temperature of 400–800°C.
[0010] Pre-lithiated silicon and carbon materials are mixed, filled and sealed in a heat-conducting container, and then the heat-conducting container is subjected to a secondary heat transfer gradient heat treatment. Subsequently, while still hot, it is placed in a cooling medium system for rapid cooling treatment to obtain nano-silicon / carbon composite material.
[0011] The gradient heat treatment process includes 2 to 5 insulation platforms, wherein the temperature of the initial insulation platform is 200 to 400°C, and the temperature of the final insulation platform is 800 to 1350°C.
[0012] The wall material of the heat-conducting container has a melting point temperature greater than or equal to 1400℃ and a thermal conductivity greater than or equal to 100W / m·K.
[0013] This invention has discovered that by pre-lithiating silicon materials and then combining them with carbon materials, followed by a secondary heat transfer gradient heat treatment process using a heat-conducting container and a rapid cooling process, the degradation of materials during the processing can be effectively overcome. This process helps to synergistically improve the phase structure and crystal occurrence mode of the product, and can unexpectedly and significantly improve the electrochemical performance of the composite material.
[0014] In this invention, (1) a novel approach is proposed to utilize lithium salt pre-lithiated silicon material, coating its surface with a layer of lithium salt to separate the carbon material subsequently composited with it. This avoids the formation of silicon carbide during subsequent high-temperature heat treatment and enhances the conductivity and mechanical properties of the material, significantly improving the performance of the silicon-carbon composite material and making a major leap forward in the preparation process. (2) A special heat treatment and rapid cooling combined process with secondary indirect heat conduction is used to treat the pre-lithiated silicon / carbon composite anode material. This solves the problem of irreversible material degradation that occurs during traditional heat treatment and rapid cooling processes, and also adjusts the composite, nucleation, and morphological characteristics, which is beneficial to improving the electrochemical performance of the composite material. (3) Combining the silicon pre-lithiated-carbon composite process with the secondary conduction heat treatment and rapid cooling process can achieve synergy and further improve the electrochemical performance of the obtained material. (4) Under the innovative process, further combined control of parameters such as the pre-lithiated process and the secondary conduction heat treatment process can further improve the process synergy and unexpectedly obtain lithium-ion battery pre-lithiated silicon / carbon composite anode material with better performance. This invention features a simple process, low preparation cost, large-scale production capability, and promising commercial application prospects. It is applicable to various types of silicon raw materials and can produce good results, making it an ideal production solution for high-performance pre-lithiated silicon / carbon composite anode materials for lithium-ion batteries.
[0015] In this invention, the silicon raw material is at least one of micron-sized silicon powder and nano-sized silicon powder. The particle size of the micron-sized silicon powder is preferably 1–5 μm. The particle size of the nano-sized silicon powder is less than or equal to 500 nm; preferably less than or equal to 300 nm; more preferably 50–300 nm; and even more preferably 50–100 nm.
[0016] In this invention, the silicon raw material is at least one of amorphous silicon, monocrystalline silicon, and polycrystalline silicon;
[0017] Preferably, the lithium salt is organic lithium and / or inorganic lithium;
[0018] Preferably, the inorganic lithium is at least one selected from lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium oxide, lithium sulfate, and lithium phosphate.
[0019] Preferably, the organolithium is at least one of C1-C6 lithium alkoxides and C1-C10 lithium carboxylate salts;
[0020] Further preferably, the lithium salt comprises two or more lithium salts; more preferably, it comprises two or more lithium hydroxide, lithium carbonate, lithium oxide, and lithium acetate. Research has found that using composite salts can unexpectedly synergize with subsequent secondary conductive heat treatment and quenching processes, further improving the composite morphology and structure of the carbon-silicon composite material and enhancing the electrochemical performance of the prepared material.
[0021] Preferably, the weight ratio of silicon raw material to lithium salt is 10 to 50:1; more preferably, it is 10 to 25:1.
[0022] Preferably, the atmosphere during the pre-lithiation stage is one or more of hydrogen, argon, helium, carbon dioxide, and nitrogen.
[0023] Preferably, the heating rate during the pre-lithiation stage is 1-10℃ / min, more preferably 2-5℃ / min; the heating rate is the rate at which the temperature rises from the initial temperature (e.g., room temperature) to the temperature during the pre-lithiation holding stage.
[0024] Preferably, the pre-lithiation time is 1 to 10 hours, and more preferably 1 to 3 hours.
[0025] In this invention, pre-lithiated silicon raw materials and carbon materials are mixed, and then filled and sealed in a heat-conducting container.
[0026] In this invention, the carbon material is at least one of carbonaceous materials and carbon-source organic matter;
[0027] In this invention, the carbonaceous material is a material with carbon element as the main component. Preferably, the carbon element is at least one of natural graphite, artificial graphite, carbon nanotubes, carbon nanowires, and graphene.
[0028] Preferably, the carbon source organic matter is at least one of asphalt, polymer, small molecule carbon source, etc., and more preferably at least one of asphalt, glucose, sucrose, starch, polyvinylidene fluoride, polyacrylic acid;
[0029] Preferably, the mass ratio of pre-lithiated silicon to carbon material is 1:1 to 20, more preferably 1:5 to 15; and even more preferably 1:5 to 6.
[0030] In this invention, the pre-lithiated silicon and carbon materials can be mixed using existing methods, such as ball milling.
[0031] In this invention, a mixture of pre-lithiated silicon and carbon materials (also referred to as the mixture in this invention) is pre-sealed in a heat-conducting container, and heat treatment and quenching treatment conducted by the wall of the heat-conducting container are used to unexpectedly control the phase and morphology of the composite material, thereby unexpectedly improving the electrochemical performance of the composite material.
[0032] In this invention, the secondary heat transfer heat treatment refers to heat treatment mediated by the wall gap of the heat-conducting container.
[0033] In this invention, the heat-conducting container is a heat-conducting container resistant to high / low temperatures.
[0034] In this invention, the wall material of the heat-conducting container is an alloy material, and more preferably one of stainless steel, aluminum alloy, copper alloy, molybdenum alloy, tungsten alloy, niobium alloy, and nickel alloy.
[0035] Preferably, the wall material of the heat-conducting container does not undergo brittle fracture at -200°C;
[0036] In this invention, the wall material of the heat-conducting container is preferably at least one of 310S, 304, and US366.
[0037] The mixture is filled into the heat-conducting container chamber under a protective atmosphere and then sealed.
[0038] Preferably, the protective gas is at least one of nitrogen, helium, carbon dioxide, and argon.
[0039] Preferably, the filling capacity of the mixture (a mixture of lithium-ionized silicon and carbon materials) is greater than or equal to 50%, more preferably 50-95%, and even more preferably 80-90%.
[0040] In this invention, a heat-conducting container encapsulating a mixture is placed inside a heating furnace chamber, and the mixture inside the heat-conducting container chamber is modified and reformed through secondary heat conduction via the heat-conducting container wall. In this invention, the heat-conducting container can be placed in an inert gas atmosphere (at least one of nitrogen, helium, argon, carbon dioxide, etc.) for heating treatment. In this invention, by utilizing the protective gas combined with the secondary heat conduction of the heat-conducting container, the structure and phase composition of the silicon-carbon composite material can be unexpectedly further improved, the ionic and electronic conductivity network can be improved, the structural stability can be improved, and the electrochemical performance of the silicon-carbon composite material can be improved.
[0041] This invention has discovered that by coupling the gradient heat treatment process with the aforementioned secondary heat transfer process and the aforementioned quenching process, it is possible to successfully link the heat treatment and quenching processes of nanoscale materials. Moreover, it is possible to unexpectedly control the structure and morphology of composite materials and unexpectedly further improve their electrochemical performance.
[0042] Preferably, the gradient heat treatment process includes three holding stages, wherein the temperature of the first holding stage is 200–400℃, preferably 200–300℃; the temperature of the second holding stage is 500–700℃, preferably 600–700℃; and the temperature of the third holding stage is 900–1200℃, preferably 1000–1200℃. Preferably, the heating rate to the first holding temperature is 10–20℃ / min; the heating rate from the first holding temperature to the second holding temperature is 5–10℃ / min; and the heating rate from the second holding temperature to the third holding temperature is 1–5℃ / min. Preferably, the holding time for the first stage is 1–3 hours; the holding time for the second stage is 2–5 hours; and the holding time for the third stage is 1–5 hours.
[0043] The gradient heat treatment described in this invention preferably includes a four-stage heat preservation process: the first stage heat preservation temperature is 200–400℃; the second stage heat preservation temperature is 500–600℃; the third stage heat preservation temperature is 700–800℃; and the fourth stage heat preservation temperature is 1100–1200℃. The heat preservation time for the first and second stages is 1–3 hours; and the heat preservation time for the third and fourth stages is 2–5 hours.
[0044] In this invention, at the end of the gradient heat treatment, the heat-conducting container, while still sealed, is placed in a cooling medium for rapid cooling. In this invention, "while still hot" refers to the heat-conducting container being placed in a cooling medium for rapid cooling after the gradient heat treatment, where the temperature drop is less than or equal to 100°C compared to the temperature at the time of heat treatment. More preferably, when the temperature drop is less than or equal to 50°C, the container is placed directly in the cooling medium for rapid cooling.
[0045] The sealed state described in this invention is a state that isolates gases, liquids, and solids.
[0046] Preferably, the cooling medium is a liquid cooling medium or a gaseous cooling medium;
[0047] Preferably, the cooling medium is one or more of anhydrous ethanol, polyethylene glycol, deionized water, liquid nitrogen, dry ice, air, argon, and nitrogen.
[0048] Preferably, the temperature difference between the heat-conducting container and the initial cooling medium is greater than or equal to 700°C.
[0049] Preferably, the cooling rate is 10-10000℃ / min.
[0050] A preferred method of the present invention includes the following steps:
[0051] Step 1: Mix the silicon raw material and lithium salt evenly:
[0052] Nano-silicon powder and lithium oxalate are mixed in a mixer at a certain mass ratio for 5-10 hours to ensure uniform mixing, and then the mixture is taken out to obtain the final mixture.
[0053] Step 2: The mixture obtained in Step 1 is pretreated under a protective atmosphere to achieve prelithiation of nano-silicon powder. The prelithiation temperature is 600-800℃, the time is 1-10h, and the heating rate is 2-10℃ / min. After the heat treatment is completed, the prelithiation nano-silicon powder is obtained by cooling it in the furnace.
[0054] Step 3: Mix the pre-lithiated nano-silicon powder obtained in step 2 with natural graphite and asphalt in a mixer at a certain mass ratio for 10-24 hours to make them evenly mixed, and then take them out to obtain silicon-carbon composite material.
[0055] Step 4: The silicon-carbon mixture obtained in Step 3 is filled into a heat-conducting container under a protective atmosphere, and the heat-conducting container is placed in the heating chamber of a tube furnace. A protective atmosphere is introduced into the heating chamber for three-stage heat treatment. The first stage of heat treatment is held at a temperature of 200–400°C, the second stage at a temperature of 500–700°C, and the third stage at a temperature of 900–1200°C.
[0056] Step 5: Place the heat-conducting container after heat treatment in step 4 directly into the cooling medium under sealed high temperature conditions, so that it is fully wrapped by the cooling medium and subjected to rapid cooling treatment. Stir continuously during the process. After rapid cooling, open the heat-conducting container to obtain silicon / carbon composite anode material.
[0057] The present invention also provides a silicon / carbon composite material prepared by the method described above.
[0058] The special preparation method described in this invention can endow the material with a special microstructure and physicochemical properties, and the material prepared by this method can exhibit better electrochemical performance.
[0059] The silicon / carbon composite material of the present invention has 5-100 nm pre-reserved pores and numerous defects. The silicon / carbon composite material of the present invention is a multilayer micro / nano composite material with a particle size of less than or equal to 30 μm; more preferably less than or equal to 10 μm.
[0060] The present invention also discloses an application of the aforementioned silicon / carbon composite material in the preparation of batteries.
[0061] A preferred application of this invention is the preparation of the negative electrode for a battery. This invention allows for the preparation of a negative electrode from the aforementioned silicon / carbon composite material using existing methods. For example, the silicon / carbon composite material obtained by the method is slurried with a conductive agent and a binder, coated onto the surface of a current collector, and dried to obtain the battery negative electrode. The conductive agent, binder, and slurry solvent can all be materials well-known in the industry, and the methods for slurry preparation, coating, and drying to obtain the negative electrode can also be well-known in the industry.
[0062] In the application described in this invention, the battery is a lithium secondary battery, preferably a lithium metal battery or a lithium-ion battery.
[0063] The present invention also provides a lithium secondary battery comprising the silicon / carbon composite material obtained by the preparation method described above;
[0064] Preferably, the negative electrode contains the silicon / carbon composite material;
[0065] The lithium secondary battery is a lithium metal battery or a lithium-ion battery.
[0066] This invention innovatively employs the aforementioned pre-lithiation-secondary conduction heat treatment-cooling process, combined with the synergistic control of various parameters, to obtain a pre-lithiated silicon / carbon composite anode active material with excellent morphology, uniform composite structure, good crystallinity, and stable internal microstructure. This material can reduce the generation of "dead lithium" during the electrochemical reaction, alleviate the huge stress changes during charge and discharge, improve the coulombic efficiency during charge and discharge, and ensure its good cycle performance. Furthermore, this process eliminates the generation of byproducts such as silicon carbide through pre-lithiation technology, while simultaneously improving the conductivity and mechanical properties of the material, playing a crucial role in the complete release of the final material performance. The pre-lithiated silicon / carbon composite anode material prepared using this invention can be perfectly matched with all high-performance cathode materials, including lithium-free sulfur cathodes and fluoride cathodes, to fabricate higher-performance lithium-ion battery devices.
[0067] Compared with the prior art, the present invention has the following advantages:
[0068] (1) The present invention uses a pre-lithiation technology that is simple, efficient and flexible. It can not only provide an additional lithium source for silicon / carbon composite anode and improve its coulombic efficiency, but also serve as a buffer layer between silicon and carbon materials to prevent direct contact between the two, prevent the generation of unfavorable products such as silicon carbide in subsequent processing, and improve the mechanical properties of the material, making silicon less prone to breakage when volume expansion and contraction occurs, and greatly improving the cycle performance of the material.
[0069] (2) The present invention achieves heat treatment and rapid cooling through secondary conduction. In addition, the combined control of heat treatment gradient process can effectively overcome the preparation degradation problem of traditional process. Moreover, it can also adjust the phase, composite mode and morphology, and can synergistically improve the electrochemical performance of the prepared material.
[0070] (3) Combining the pre-lithiated silicon with carbon materials and then combining it with a secondary conduction heat treatment-quenching process can further achieve synergy and help to further improve the electrochemical performance of the prepared materials.
[0071] (4) Under the innovative process described above, the present invention further synergizes with the pre-lithiation process, heat treatment modification temperature and unique cooling method, which helps to further improve the electrochemical performance of the obtained pre-lithiation silicon / carbon composite anode active material. Attached Figure Description
[0072] Appendix Figure 1 The image shows the SEM image of the high-performance lithium-ion battery pre-lithiated silicon / carbon composite anode material finally prepared in Example 1.
[0073] Appendix Figure 2 The image shows the XRD pattern of the high-performance lithium-ion battery pre-lithiated silicon / carbon composite anode material finally prepared in Example 1.
[0074] From the appendix Figure 1 It can be seen that the high-performance lithium-ion battery pre-lithiated silicon / carbon composite anode material prepared in Example 1 of this invention has a uniform morphology, consisting of near-spherical particles with a size of 1–10 μm. The pre-lithiated nano-silicon particles are tightly bonded to the surface of the spherical graphite, and the nano-silicon particles are invisible due to their small size. Figure 2 It can be seen that the high-performance lithium-ion battery pre-lithiated silicon / carbon composite anode material obtained after processing in Example 1 of the present invention has Si and C as its main phases. The content of the pre-lithiated product is low and does not reach the XRD detection response limit. Detailed Implementation
[0075] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments.
[0076] In this invention, the heat-conducting containers are all made of metal, especially alloy pressure- and temperature-resistant containers, for example, their thermal conductivity is greater than 100 W / m·K; for example, in the following cases, unless otherwise stated, the heat-conducting containers are high / low temperature resistant chromium-nickel stainless steel containers, and the material type is 304. High / low temperature resistant nickel-based stainless steel containers, and the material type is 310S.
[0077] Example 1:
[0078] ① Take 10g of silicon nanopowder (D50 is 300nm) and 0.5g of lithium oxalate and mix them in a mixer for 6 hours to make them evenly mixed. Then take them out to obtain the mixture.
[0079] ② The mixture from step ① is subjected to high-temperature heat treatment under an argon atmosphere to achieve pre-lithiation of nano-silicon powder. The pre-lithiation temperature is 600℃, the time is 3h, and the heating rate is 2℃ / min. After the heat treatment is completed, the pre-lithiated nano-silicon powder is obtained by cooling it in the furnace.
[0080] ③ The pre-lithiated nano-silicon powder obtained in step ② is mixed with spherical graphite and high-temperature asphalt in a mixer at a mass ratio of 1:10:2 for 20 hours to make the mixture uniform, and then the silicon-carbon composite material is obtained.
[0081] ④ The silicon-carbon mixture obtained in step ③ is sealed in an argon-filled glove box in a 304φ50*100mm high / low temperature chromium-nickel stainless steel container with a filling capacity of 90%. Then it is placed in the heating chamber of a tube furnace, and an argon atmosphere (calcination atmosphere) is introduced into the heating chamber for step-by-step secondary conduction high-temperature heat treatment. The heat treatment procedure is as follows: first, the temperature is raised from room temperature to 300℃ at a heating rate of 10℃ / min and held for 1 hour; then, the temperature is raised to 600℃ at a heating rate of 5℃ / min and held for 3 hours; finally, the temperature is raised to 1000℃ at a heating rate of 2℃ / min and held for 2 hours.
[0082] ⑤ Immediately after completing the stepped high-temperature heat treatment, open the tube furnace from step ④ and quickly transfer the entire high / low temperature resistant chromium-nickel stainless steel container (while maintaining a sealed state) into 10L of 10℃ cooling water, ensuring it is fully enveloped by the cooling water. Continuously stir to accelerate cooling, achieving rapid, instantaneous temperature reduction. After 3 hours of stabilization, place it in a 100℃ oven for drying. After drying, disassemble the high / low temperature resistant chromium-nickel stainless steel container and remove the high-performance pre-lithiated silicon / carbon composite anode material for lithium-ion batteries. SEM and XRD results are shown in [reference needed]. Figure 1 and 2 .
[0083] The obtained high-performance pre-lithiated silicon / carbon composite anode material has a particle size of 1-10 μm, no other impurity phases, a tight composite structure, and a uniform morphology.
[0084] The electrochemical performance of this material was tested using a 2025-type lithium-ion half-cell:
[0085] Using Super P as a conductive agent, CMC as a binder, and deionized water as a solvent, a slurry was prepared and uniformly coated on copper foil according to a mass ratio of active material: conductive agent: binder = 90:5:5. After drying, the slurry was cut into electrode sheets and assembled into a 2025 type coin cell with lithium sheet as the counter electrode. The electrolyte used was a silicon-based negative electrode electrolyte (1mol / L LiPF6, EC:DEC = 1:1, 10% FEC), and the separator was made of PP / PE / PP material.
[0086] The half-cell was charged and discharged using a CT2001A battery testing system manufactured by Wuhan Landian Electronics Co., Ltd. The test range was 0.01V to 1.2V, and the test temperature was 25℃.
[0087] After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge-discharge was 96.30%, and the reversible capacity after 500 cycles was 586.4 mAh / g.
[0088] Example 2:
[0089] ① Take 10g of silicon nanopowder (D50 is 200nm) and 0.5g of lithium hydroxide and mix them in a mixer for 5 hours to make them evenly mixed. Then take them out to obtain the mixture.
[0090] ② The mixture from step ① is subjected to high-temperature heat treatment under an argon atmosphere to achieve pre-lithiation of nano-silicon powder. The pre-lithiation temperature is 700℃, the time is 2h, and the heating rate is 4℃ / min. After the heat treatment is completed, the pre-lithiated nano-silicon powder is obtained by cooling it in the furnace.
[0091] ③ The pre-lithiated nano-silicon powder obtained in step ② is mixed with carbon nanotubes and starch in a mixer at a mass ratio of 1:10:2 for 24 hours to make the mixture uniform, and then the silicon-carbon composite material is obtained.
[0092] ④ The silicon-carbon mixture obtained in step ③ is sealed in a 304φ50*100mm high / low temperature chromium-nickel stainless steel container in an argon-filled glove box, with a filling capacity of 90%. Then it is taken out and placed in the heating chamber of a tube furnace. Argon atmosphere is introduced into the heating chamber and a stepped secondary conduction high temperature heat treatment is performed. The heat treatment procedure is as follows: first, the temperature is raised from room temperature to 300℃ at a heating rate of 10℃ / min and held for 2 hours; then the temperature is raised to 600℃ at a heating rate of 10℃ / min and held for 3 hours; finally, the temperature is raised to 1100℃ at a heating rate of 5℃ / min and held for 2 hours.
[0093] ⑤ The same post-processing as in Example 1 was performed to obtain a high-performance pre-lithiated silicon / carbon composite anode material for lithium-ion batteries;
[0094] The obtained high-performance pre-lithiated silicon / carbon composite anode material has a particle size of 5-20 μm, no other impurity phases, tight composite structure, and uniform morphology. After being assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge-discharge is 95.25%, and the reversible capacity after 500 cycles is 575.4 mAh / g.
[0095] Example 3:
[0096] ① Take 20g of silicon nanopowder (D50 is 200nm), 0.4g of lithium hydroxide and 0.4g of lithium carbonate and mix them in a mixer for 6 hours to make them evenly mixed. Then take them out to obtain the mixture.
[0097] ② The mixture from step ① is subjected to high-temperature heat treatment under a nitrogen atmosphere to achieve pre-lithiation of nano-silicon powder. The pre-lithiation temperature is 800℃, the time is 3h, and the heating rate is 5℃ / min. After the heat treatment is completed, the pre-lithiated nano-silicon powder is obtained by cooling it in the furnace.
[0098] ③ The pre-lithiated nano-silicon powder obtained in step ② is mixed with artificial graphite and polyacrylic acid in a mixer at a mass ratio of 1:5:1 for 24 hours to make the mixture uniform, and then the silicon-carbon composite material is obtained.
[0099] ④ The silicon-carbon mixture obtained in step ③ is sealed in an argon-filled glove box into a 310Sφ60*120mm high / low temperature resistant nickel-based stainless steel container (310S), with a filling capacity of 80%. Then it is taken out and placed in the heating chamber of a tube furnace. Argon atmosphere is introduced into the heating chamber and a stepped secondary conduction high temperature heat treatment is performed. The heat treatment procedure is as follows: first, the temperature is raised from room temperature to 250℃ at a heating rate of 20℃ / min and held for 1 hour; then, the temperature is raised to 700℃ at a heating rate of 10℃ / min and held for 4 hours; finally, the temperature is raised to 1200℃ at a heating rate of 2℃ / min and held for 1 hour.
[0100] ⑤ At the moment the stepped high-temperature heat treatment is completed, the tube furnace in step ④ is opened, and the entire high / low temperature resistant nickel-based stainless steel container (keeping it sealed) is quickly transferred to 5L-196℃ liquid nitrogen, so that it is fully wrapped by liquid nitrogen, and the mixture is continuously stirred to accelerate cooling and achieve instantaneous rapid cooling. After 3 hours of temperature stabilization, it is placed in a 100℃ oven for drying. After drying, the high / low temperature resistant nickel-based stainless steel container is disassembled and the high-performance pre-lithiated silicon / carbon composite anode material for lithium-ion batteries is obtained.
[0101] The obtained high-performance pre-lithiated silicon / carbon composite anode material has a particle size of 5-10 μm, no other impurity phases, tight composite structure, and uniform morphology. After being assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge-discharge is 95.42%, and the reversible capacity after 500 cycles is 783.2 mAh / g.
[0102] Example 4:
[0103] ① Take 20g of silicon nanopowder (D50 is 200nm), 0.4g of lithium oxide and 0.4g of lithium acetate and mix them in a mixer for 6 hours to make them evenly mixed. Then take them out to obtain the mixture.
[0104] ② The mixture from step ① is subjected to high-temperature heat treatment under a nitrogen atmosphere to achieve pre-lithiation of nano-silicon powder. The pre-lithiation temperature is 700℃, the time is 5h, and the heating rate is 5℃ / min. After the heat treatment is completed, the pre-lithiated nano-silicon powder is obtained by cooling it in the furnace.
[0105] ③ The pre-lithiated nano-silicon powder obtained in step ② is mixed with graphene and sucrose in a mixer at a mass ratio of 1:5:1 for 24 hours to make the mixture uniform, and then the silicon-carbon composite material is obtained.
[0106] ④ The silicon-carbon mixture obtained in step ③ is sealed in an argon-filled glove box in a 310Sφ60*120mm high / low temperature resistant nickel-based stainless steel container with a filling capacity of 80%. Then it is taken out and placed in the heating chamber of a tube furnace. Argon atmosphere is introduced into the heating chamber and a stepped secondary conduction high temperature heat treatment is performed. The heat treatment procedure is as follows: first, the temperature is raised from room temperature to 200℃ at a heating rate of 15℃ / min and held for 1 hour; then the temperature is raised to 500℃ at a heating rate of 10℃ / min and held for 1 hour; then the temperature is raised to 800℃ at a heating rate of 10℃ / min and held for 4 hours; finally, the temperature is raised to 1200℃ at a heating rate of 2℃ / min and held for 2 hours.
[0107] ⑤ The same process as in Example 3 was followed to obtain a high-performance pre-lithiated silicon / carbon composite anode material for lithium-ion batteries;
[0108] The obtained high-performance pre-lithiated silicon / carbon composite anode material has a particle size of 5-15 μm, no other impurity phases, tight composite structure, and uniform morphology. After being assembled into a half-cell according to the method of Example 1, the initial coulombic efficiency at 0.2C charge and discharge is 94.76%, and the reversible capacity after 500 cycles is 748.5 mAh / g.
[0109] Example 5:
[0110] Compared with Example 4, the only difference is that only a single lithium oxide is used as the lithium source, and the total amount added is 0.8g; other preparation parameters are the same as in Example 1.
[0111] The half-cell assembled according to the method in Example 1 showed an initial coulombic efficiency of 92.23% after 0.2C charge-discharge and a reversible capacity of 629.3 mAh / g after 500 cycles. A comparison of Examples 4 and 5 shows that the combined lithium salt and the subsequent secondary conduction heat treatment-cold treatment have a better synergistic effect, resulting in better coulombic efficiency and cycle stability.
[0112] Comparative Example 1:
[0113] Compared with Example 1, the only difference is that steps ① and ② are omitted, and the silicon nanoparticles are directly subjected to step ③ and subsequent operations. The difference in steps is as follows:
[0114] Take 10g of silicon nanopowder raw material (same as in Example 1), and mix it directly with spherical graphite and high-temperature asphalt in a mixer at a mass ratio of 1:10:2 for 20 hours to make it uniformly mixed. Then take it out to obtain silicon-carbon mixed material; the subsequent operation is the same as in Example 1 to obtain the negative electrode material.
[0115] The obtained negative electrode material has a particle size of 1-10 μm. After being assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge-discharge was 59.32%, and the reversible capacity after 100 cycles was 243.8 mAh / g.
[0116] Comparative Example 2:
[0117] Compared with Example 1, the only difference is that step ② is omitted, and the mixture from step ① is directly proceeded to step ③ and subsequent operations. The difference in steps is as follows:
[0118] The lithium salt / nano silicon mixture was obtained according to Example 1. The mixture from step ① was directly mixed with spherical graphite and high-temperature asphalt in a mixer at a mass ratio of 1:10:2 for 20 hours without the high-temperature treatment in step ②, so that the mixture was uniformly mixed. Then the mixture was taken out to obtain silicon-carbon composite material. The subsequent operation was the same as in Example 1 to obtain the negative electrode material.
[0119] The obtained material was assembled into a half-cell according to the method of Example 1. The first coulombic efficiency at 0.2C charge and discharge was less than 50%, and the reversible capacity after 100 cycles was 168.6 mAh / g.
[0120] Comparative Example 3:
[0121] Compared to Example 1, the only difference is that the nano-silicon is not pre-lithiated; instead, it is mixed with carbon materials before undergoing pre-lithiation. The specific operation is as follows:
[0122] ① Take 10g of silicon nanopowder (same as in Example 1), mix it with spherical graphite and high-temperature asphalt in a mixer at a mass ratio of 1:10:2 for 20 hours to make it uniformly mixed, and then take it out to obtain silicon-carbon composite material;
[0123] ② Mix the silicon-carbon mixture from step ① and 0.5g of lithium oxalate in a mixer for 6 hours to ensure uniform mixing, and then remove the mixture to obtain the final product.
[0124] ③ The mixture obtained in step ② is subjected to high-temperature pre-lithiation under an argon atmosphere. The pre-lithiation temperature is 600℃, the time is 3h, and the heating rate is 2℃ / min. After the heat treatment is completed, the material is cooled and taken out with the furnace to obtain the pre-lithiated silicon / carbon material.
[0125] ④ Subsequent operations are the same as in Example 1 to obtain the negative electrode material;
[0126] The obtained material was assembled into a half-cell according to the method of Example 1. The first coulombic efficiency at 0.2C charge and discharge was 72.65%, and the reversible capacity after 200 cycles was 334.8 mAh / g.
[0127] Comparative Example 4:
[0128] Compared to Example 1, the only difference is that the silicon-carbon hybrid material did not undergo step ④, which involves a stepped secondary conductive high-temperature heat treatment, but instead directly underwent step ⑤, an indirect rapid cooling treatment. The difference lies in the following steps:
[0129] The silicon-carbon hybrid material was obtained according to Example 1;
[0130] The obtained silicon-carbon hybrid material was processed according to Example 1, sealed in a high / low temperature resistant chromium-nickel stainless steel container, and then placed directly in 10L of 10°C cooling water. Subsequent operations were the same as in Example 1 to obtain the negative electrode material. After the obtained material was assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge-discharge was 60.32%, and the reversible capacity after 200 cycles was 238.2mAh / g.
[0131] Comparative Example 5:
[0132] Compared to Example 1, the only difference is that no alloy container was used; instead, a foamed ceramic container with a thermal conductivity of less than 50 W / m·K was used. Specifically:
[0133] The silicon-carbon hybrid material was obtained according to Example 1;
[0134] The obtained silicon-carbon hybrid material was sealed in an argon-filled glove box in a φ50*100mm foamed ceramic container with a filling capacity of 90%. Subsequent operations were the same as in Example 1 to obtain the negative electrode material. After the obtained material was assembled into a half-cell according to the method of Example 1, the first coulombic efficiency of 0.2C charge and discharge was less than 40%, and the reversible capacity after 100 cycles was 85.8 mAh / g.
[0135] Comparative Example 6:
[0136] Compared with Example 1, the only difference is that the secondary conduction high-temperature heat treatment did not involve stepped temperature control, specifically:
[0137] The silicon-carbon hybrid material was obtained according to Example 1;
[0138] The obtained silicon-carbon composite material was sealed in a high / low temperature chromium-nickel stainless steel container according to the operation in Example 1. Then it was taken out and placed in the heating chamber of a tube furnace. Argon atmosphere was introduced into the heating chamber for non-step secondary conduction high temperature heat treatment. The heat treatment procedure was as follows: heating from room temperature to 1000℃ at a heating rate of 5℃ / min and holding for 2h.
[0139] Subsequent operations are the same as in Example 1 to obtain the negative electrode material;
[0140] The obtained material was assembled into a half-cell according to the method of Example 1. The first coulombic efficiency at 0.2C charge and discharge was 79.88%, and the reversible capacity after 200 cycles was 532.9 mAh / g.
[0141] Comparative Example 7:
[0142] Compared with Example 1, the only difference is that no rapid cooling treatment was performed, specifically:
[0143] Follow the procedure in Example 1 until the stepped high-temperature heat treatment is completed; do not perform rapid cooling immediately after the stepped high-temperature heat treatment is completed, allow the stainless steel container to cool with the furnace, and after cooling to room temperature, open the furnace, remove and disassemble the stainless steel container to obtain the negative electrode material; after assembling the obtained material into a half-cell according to the method in Example 1, the first coulombic efficiency of 0.2C charge and discharge is 70.56%, and the reversible capacity after 200 cycles is 334.3 mAh / g.
[0144] Comparative Example 8
[0145] Compared with Example 1, the only difference is that steps ④ and ⑤ do not employ secondary heat treatment and rapid cooling mediated by a heat-conducting container. The difference lies in the following steps:
[0146] The silicon-carbon composite material was not sealed in a high / low temperature resistant chromium-nickel stainless steel container and directly subjected to the aforementioned heat treatment. Subsequently, the heat-treated material was placed in liquid nitrogen for rapid cooling.
[0147] The obtained material, when assembled into a half-cell according to the method of Example 1, showed an initial coulombic efficiency of 22.56% under 0.2C charge-discharge and a reversible capacity of 89.4 mAh / g after 200 cycles.
[0148] Comparative Example 9
[0149] Compared with Example 1, the only difference is that in step ④, the roasting atmosphere is air.
[0150] The obtained material, when assembled into a half-cell according to the method of Example 1, showed an initial coulombic efficiency of 60.52% under 0.2C charge-discharge and a reversible capacity of 256.3 mAh / g after 200 cycles.
[0151] Comparative Example 10
[0152] Compared with Example 1, the only difference is that in step ②, the pre-lithiation temperature is 350°C.
[0153] The obtained material was assembled into a half-cell according to the method of Example 1. The first coulombic efficiency at 0.2C charge and discharge was 77.23%, and the reversible capacity after 200 cycles was 425.3 mAh / g.
[0154] Through examples and comparative examples, it is evident that pre-lithiation technology not only improves the coulombic efficiency and cycle performance of the material but also avoids the formation of silicon carbide and other materials in subsequent processes, significantly impacting the final performance of the material. Staged, special high-temperature heat treatment not only achieves tight composite bonding of silicon and carbon materials but also fundamentally improves the material's performance. A unique cooling process helps stabilize the material's properties, allowing its characteristics to be fully realized. The uniformity of the mixing also directly affects the material's performance; although this step may seem insignificant, it plays a crucial role. Ultimately, the synergistic effect of each process and preparation parameter is essential to maximizing the advantages of this invention and obtaining a high-performance pre-lithiated silicon / carbon composite anode material for lithium-ion batteries.
Claims
1. A method for preparing a silicon / carbon composite material, characterized in that, Silicon raw materials and lithium salts are pre-lithiated at a temperature of 400~800℃; Pre-lithiated silicon and carbon materials are mixed, filled and sealed in a heat-conducting container, and then the heat-conducting container is subjected to a secondary heat transfer gradient heat treatment. Subsequently, while still hot, it is placed in a cooling medium system for rapid cooling treatment to obtain nano-silicon / carbon composite material. The gradient heat treatment process includes 2 to 5 insulation platforms, wherein the temperature of the initial insulation platform is 200 to 400°C, and the temperature of the final insulation platform is 800 to 1350°C. The wall material of the heat-conducting container has a melting point temperature greater than or equal to 1400℃ and a thermal conductivity greater than or equal to 100W / m·K.
2. The preparation method according to claim 1, characterized in that, The silicon raw material is at least one of micron-sized silicon powder and nano-sized silicon powder.
3. The preparation method according to claim 2, characterized in that, The silicon raw material is at least one of amorphous silicon, monocrystalline silicon, and polycrystalline silicon.
4. The preparation method according to claim 1, characterized in that, The lithium salt is organic lithium and / or inorganic lithium; The inorganic lithium is at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium oxide, lithium sulfate, and lithium phosphate. The organic lithium is a C1-C6 lithium alkoxide, C1-C6 lithium alkoxide, or C6-C6 lithium alkoxide. 10 At least one of lithium carboxylate salts.
5. The preparation method according to claim 4, characterized in that, The lithium salts mentioned are two or more types of lithium salts.
6. The preparation method according to claim 5, characterized in that, The lithium salt is two or more of lithium hydroxide, lithium carbonate, lithium oxide, and lithium acetate.
7. The preparation method according to claim 1, characterized in that, The weight ratio of silicon raw material to lithium salt is 10~50:
1.
8. The preparation method according to claim 1, characterized in that, The atmosphere during the pre-lithiation stage is one or more of hydrogen, argon, helium, carbon dioxide, and nitrogen. The heating rate during the pre-lithiation stage is 1-10℃ / min; The pre-lithiation temperature is 600~800℃; The pre-lithiation time is 1~10h.
9. The preparation method according to claim 1, characterized in that, The carbon material is at least one of elemental carbon materials and organic carbon sources.
10. The preparation method according to claim 9, characterized in that, The carbon-based material is at least one of natural graphite, artificial graphite, carbon nanotubes, carbon nanowires, and graphene. The carbon source organic matter is at least one of asphalt, polymer, small molecule carbon source, etc.
11. The preparation method according to claim 10, characterized in that, The carbon source organic compound is at least one of asphalt, glucose, sucrose, starch, polyvinylidene fluoride, and polyacrylic acid.
12. The preparation method according to claim 1, characterized in that, The mass ratio of pre-lithiated silicon to carbon materials is 1:1 to 20.
13. The preparation method according to claim 1, characterized in that, The wall material of the heat-conducting container does not undergo brittle fracture at -200℃.
14. The preparation method according to claim 13, characterized in that, The wall material of the heat-conducting container is an alloy material.
15. The preparation method according to claim 14, characterized in that, The wall material of the heat-conducting container is one of stainless steel, aluminum alloy, copper alloy, molybdenum alloy, tungsten alloy, niobium alloy, and nickel alloy.
16. The preparation method according to claim 15, characterized in that, The wall material of the heat-conducting container is at least one of 310S, 304, and US366.
17. The preparation method according to claim 1, characterized in that, The mixture of pre-lithiated silicon and carbon materials is filled into the heat-conducting container chamber under a protective atmosphere and then sealed.
18. The preparation method according to claim 17, characterized in that, The protective atmosphere is at least one of nitrogen, helium, carbon dioxide, and argon. The filling capacity of the mixture is greater than or equal to 50%.
19. The preparation method according to claim 1, characterized in that, The heat-conducting container undergoes a secondary heat transfer gradient heat treatment in a protective atmosphere; wherein the protective atmosphere is at least one of nitrogen, helium, argon, and carbon dioxide.
20. The preparation method according to claim 19, characterized in that, The gradient heat treatment process includes three heat preservation processes: the first heat preservation temperature is 200~400℃, the second heat preservation temperature is 500~700℃, and the third heat preservation temperature is 900~1200℃.
21. The preparation method according to claim 20, characterized in that, The heating rate to the first stage of heat preservation temperature is 10~20℃ / min; the heating rate from the first stage of heat preservation temperature to the second stage of heat preservation temperature is 5~10℃ / min; and the heating rate from the second stage of heat preservation temperature to the third stage of heat preservation temperature is 1~5℃ / min. The first heat preservation time is 1-3 hours; the second heat preservation time is 2-5 hours. The third stage of heat preservation takes 1 to 5 hours.
22. The preparation method according to claim 20, characterized in that, The gradient heat treatment includes four heat preservation processes: the first heat preservation temperature is 200~400℃; the second heat preservation temperature is 500~600℃; the third heat preservation temperature is 700~800℃; and the fourth heat preservation temperature is 1100~1200℃. The insulation time for the first and second stages is 1 to 3 hours; the insulation time for the third and fourth stages is 2 to 5 hours.
23. The preparation method according to claim 1, characterized in that, After gradient heat treatment, the heat-conducting container, which has undergone gradient heat treatment and is kept in a sealed state, is directly placed in a cooling medium for rapid cooling.
24. The preparation method according to claim 23, characterized in that, The cooling medium can be a liquid cooling medium or a gas cooling medium.
25. The preparation method according to claim 24, characterized in that, The cooling medium is one or more of anhydrous ethanol, polyethylene glycol, deionized water, liquid nitrogen, dry ice, air, argon, and nitrogen.
26. The preparation method according to claim 24, characterized in that, The temperature difference between the heat-conducting container and the initial cooling medium is greater than or equal to 800°C.
27. A silicon / carbon composite material prepared by the preparation method according to any one of claims 1 to 26.
28. The application of a silicon / carbon composite material prepared by the preparation method according to any one of claims 1 to 26, characterized in that, Silicon / carbon composite materials are used to prepare batteries.
29. The application as described in claim 28, characterized in that, It is used to prepare the negative electrode of the battery.
30. The application as described in claim 28 or 29, characterized in that, The battery in question is a lithium secondary battery.
31. The application as described in claim 30, characterized in that, The battery is a lithium metal battery or a lithium-ion battery.
32. A lithium secondary battery, characterized in that, The silicon / carbon composite material is prepared by any one of the preparation methods described in claims 1 to 26.
33. The lithium secondary battery as described in claim 32, characterized in that, The negative electrode contains the aforementioned silicon / carbon composite material.