Silicon-carbon composite material, preparation method, silicon-based negative electrode and lithium ion battery
By designing a core, a carbon coating layer, and an aluminum compound coating layer in a silicon-carbon composite material, the problem of poor high-temperature cycling and high-temperature storage performance of silicon-based anode lithium-ion batteries was solved, achieving high capacity and stable cycling performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 广东省豪鹏新能源科技有限公司
- Filing Date
- 2023-06-06
- Publication Date
- 2026-06-23
Smart Images
Figure CN116565174B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon-carbon composite material, a preparation method, a silicon-based negative electrode, and a lithium-ion battery. Background Technology
[0002] Silicon is considered a novel high-performance anode material for lithium-ion batteries due to its advantages such as high specific capacity, good safety and low-temperature performance, and abundant raw material sources. However, during charge and discharge, silicon undergoes significant volume expansion due to lithium alloying, which can induce irreversible and continuous capacity loss. (SiO) x When silicon-based oxides are used as anode materials, the active material silicon is uniformly dispersed in the inert materials Li2O and Li4SiO4 during the initial lithium insertion, which alleviates the volume change of lithium-silicon alloying and can reduce the volume expansion to half that of pure silicon, thereby improving cycle performance.
[0003] But SiO x The material still suffers from significant volume expansion, resulting in poor high-temperature cycling and storage performance of lithium-ion batteries using silicon-based anodes. The industry is working to further reduce SiO2 levels. x The problem of volume expansion in materials has been addressed in silicon-based anode research, which mainly focuses on the design of silicon bulk nanoparticle structures, porous three-dimensional structures, and interface and surface structures. However, the current research has not been able to completely solve the problem of poor high-temperature cycling and high-temperature storage performance of existing silicon-based anode lithium-ion batteries. Summary of the Invention
[0004] The purpose of this invention is to provide a silicon-carbon composite material, a preparation method, a silicon-based anode, and a lithium-ion battery, thereby improving the high-temperature cycling and high-temperature storage performance of silicon-based anode lithium-ion batteries.
[0005] The present invention discloses a silicon-carbon composite material, which includes a core, a carbon coating layer and an aluminum compound coating layer; the core material is elemental silicon and silicon oxide compound, the core includes a solid part and a porous layer formed on the surface of the solid part, the carbon coating layer is wrapped on the porous layer, and the aluminum compound coating layer is wrapped on the carbon coating layer.
[0006] Optionally, the aluminum compound coating is LiFPA.
[0007] Optionally, the specific surface area of the core is 1.5–7.5 m². 2 / g.
[0008] Optionally, the specific surface area of the silicon-carbon composite material is 170–300 m². 2 / g; and / or the tap density of silicon-carbon composites is 0.5–0.85 g / cm³. 3 .
[0009] Optionally, the oxygen content of the silicon-carbon composite material is 1-10% by mass.
[0010] Optionally, the pore size of the porous layer is 3-10 nm.
[0011] This invention also discloses a method for preparing a silicon-carbon composite material, applicable to the preparation of silicon-carbon composite materials as described above, comprising:
[0012] Silicon oxides are added to a carbon source, heated to dissolve, stirred until homogeneous, cooled, and then pulverized to obtain the core precursor.
[0013] The heat-treated core precursor was cooled to room temperature and stirred evenly with a dispersant solution. Hydrofluoric acid aqueous solution was added for etching to obtain a core with a porous layer on the surface.
[0014] The core is placed in a reactor, and a gaseous carbon source is introduced for gas-phase coating, resulting in C-SiO with a porous surface coated with a carbon layer. y Precursor;
[0015] C-SiO y The precursor is dispersed in deionized water, stirred and mixed, then an aluminum-containing compound is added and stirred and mixed, heated to dryness, dried, ground and sintered to obtain a silicon-carbon composite material with an aluminum compound coating layer encapsulated in a carbon coating layer.
[0016] Optionally, in the step of heat-treating the core precursor, the heat treatment temperature is 900-1150℃ and the heat treatment time is 1-10h.
[0017] The present invention also discloses a silicon-based anode, comprising the silicon-carbon composite material as described above.
[0018] The present invention also discloses a lithium-ion battery, comprising a silicon-based negative electrode as described above.
[0019] The silicon-carbon composite material of this invention is applied to the preparation of silicon-based anodes and their lithium-ion batteries. The core of the silicon-carbon composite material comprises a solid portion and a porous layer from the inside out. The porous layer provides space for the volume expansion of silicon oxide during charging and discharging. The porous layer and carbon coating layer not only improve the conductivity of the silicon-carbon composite material, but also, because the porous layer forms before the carbon coating layer, the carbon coating layer is not damaged during the formation of the porous layer, thus improving conductivity. The carbon coating layer also reduces the specific surface area after etching the porous layer, reducing the generation of side reactions in the subsequent lithium-ion battery. This results in the silicon-carbon composite material having high capacity, stable cycle performance, and excellent high-temperature cycling and high-temperature storage performance. The aluminum compound coating layer provides aluminum-containing compounds. On the lithium anode side, the aluminum-containing compounds are reduced, forming a protective material inside the SEI layer, further improving the capacity, cycle performance, high-temperature cycling, and high-temperature storage performance of the silicon-carbon composite material. Attached Figure Description
[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of the invention and illustrate implementation methods, and together with the textual description, explain the principles of the invention. Obviously, the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings:
[0021] Figure 1 This is a partial cross-sectional view of the silicon-carbon composite material according to an embodiment of the present invention;
[0022] Figure 2 This is a schematic diagram of the kernel of an embodiment of the present invention.
[0023] Among them, 1. Core; 11. Solid part; 12. Porous layer; 2. Carbon coating layer; 3. Aluminum compound coating layer. Detailed Implementation
[0024] It should be understood that the terminology, specific structural and functional details used herein are merely for describing particular embodiments and are representative. However, the invention can be implemented in many alternative forms and should not be construed as being limited to the embodiments set forth herein.
[0025] The present invention will now be described in detail with reference to the accompanying drawings and optional embodiments.
[0026] like Figure 1 and Figure 2 As shown, as an embodiment of the present invention, a silicon-carbon composite material is disclosed. The silicon-carbon composite material includes a core 1, a carbon coating layer 2, and an aluminum compound coating layer 3. The core 1 is made of elemental silicon and silicon oxide. The core 1 includes a solid part 11 and a porous layer 12 formed on the surface of the solid part 11. The carbon coating layer 2 is wrapped on the porous layer 12, and the aluminum compound coating layer 3 is wrapped on the carbon coating layer 2.
[0027] The silicon-carbon composite material of this invention is applied to the preparation of silicon-based anodes and their lithium-ion batteries. The core 1 of the silicon-carbon composite material comprises, from the inside out, a solid portion 11 and a porous layer 12. The porous layer 12 provides space for the volume expansion of silicon oxides during charging and discharging. The porous layer 12 and the carbon coating layer 2 not only improve the conductivity of the silicon-carbon composite material, but also, because the porous layer 12 forms before the carbon coating layer 2, the carbon coating layer 2 is not damaged during the formation of the porous layer 12, thus improving conductivity. The coating of the carbon coating layer 2 also reduces the specific surface area of the porous layer 12 after etching, reducing the generation of side reactions in the subsequent lithium-ion battery. This results in the silicon-carbon composite material having high capacity, stable cycle performance, and excellent high-temperature cycling and high-temperature storage performance. The aluminum compound coating layer 3 provides aluminum-containing compounds. On the lithium anode side, the aluminum-containing compounds are reduced, forming a protective material inside the SEI layer, further improving the capacity, cycle performance, high-temperature cycling, and high-temperature storage performance of the silicon-carbon composite material.
[0028] Specifically, the residual carbon content of the core 1 of this invention is 0.5-5%. If the residual carbon content is too high, it will reduce the compaction density of the silicon-carbon composite material and increase the etching difficulty of the porous layer 12. If the residual carbon content is too low, the kinetic performance of the lithium-ion battery will be poor and the expected performance effect will not be achieved.
[0029] In this invention, the silicon-carbon composite material is first etched to obtain a porous layer 12 to improve the lithium-ion migration rate. However, the etched core 1 has a large specific surface area. Therefore, a carbon coating layer 2 is then formed through vapor phase coating to modify the surface, reduce the specific surface area, and decrease side reactions with the electrolyte. If the carbon coating layer 2 is formed through vapor phase coating first, and then the porous layer 12 is etched, it is difficult to achieve the above advantages, and the carbon coating layer 2 may also be etched away during the etching of the porous layer 12. Finally, an aluminum compound coating layer 3 is added to further strengthen the inner structure of the silicon-carbon composite material.
[0030] Specifically, the aluminum compound coating layer 3 is LiFPA. LiFPA is a lithium salt of perfluorinated pinacol aluminate (LiFPA) centered on highly fluorinated (8-CF3) aluminum (Al). On the lithium anode side, LiFPA will be reduced to form protective substances such as LiF, Li2O and aluminum-containing compounds inside the SEI layer, which further improves the capacity and cycle performance of the silicon-carbon composite material, and enhances its high-temperature cycling and high-temperature storage performance.
[0031] Specifically, the specific surface area of core 1 is 1.5–7.5 m². 2 With a surface area of / g and a smaller specific surface area, there are fewer side reactions with the electrolyte, which is beneficial for improving the initial coulombic efficiency. Specifically, the specific surface area of core 1 can be 1.5m². 2 / g, 2.2m 2 / g, 2.51m 2 / g, 3.21m2 / g, 3.5m 2 / g, 3.8m 2 / g、4m 2 / g, 4.3m 2 / g, 4.5m 2 / g, 4.8m 2 / g、5m 2 / g, 5.3m 2 / g, 5.5m 2 / g, 5.8m 2 / g、6m 2 / g、6.3m 2 / g, 6.5m 2 / g, 6.8m 2 / g、7m 2 / g, 7.3m 2 / g, 7.5m 2 / g, etc. The specific surface area of silicon-carbon composite materials is 1.5–7.5 m². 2 / g, its surface is not too smooth, ranging from 1.5 to 7.5m 2 Within a specific surface area range of / g, a smaller specific surface area results in fewer side reactions with the electrolyte, which is beneficial for improving the initial coulombic efficiency. More specifically, the specific surface area of the silicon-carbon composite material is 170–300 m² / g. 2 / g, specifically 170m 2 / g、186m 2 / g、190m 2 / g、200m 2 / g、210m 2 / g、220m 2 / g、230m 2 / g、240m 2 / g、250m 2 / g、260m 2 / g、270m 2 / g、280m 2 / g、290m 2 / g、300m 2 / g etc.
[0032] Specifically, the tap density of the silicon-carbon composite material is 0.5–0.85 g / cm³. 3 Specifically, it can be 0.5g / cm 3 0.55g / cm 3 0.6g / cm 3 0.65g / cm 3 0.7g / cm 3 0.75g / cm 3 0.8g / cm3 Or 0.85g / cm 3 wait.
[0033] Specifically, the mass percentage of oxygen in the silicon-carbon composite material is 1-10%, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 9.5%, 9.8%, 9.9%, or 10%. The mass percentage of oxygen in the silicon-carbon composite material reflects the degree of carbon source substitution; the lower the mass percentage of oxygen, the higher the degree of carbon source substitution. Specifically, the pore size of the porous layer 12 is 3-10 nm, specifically 3 nm, 4 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, 9.9 nm, or 10 nm. Pores that are too small cannot achieve rapid lithium ion migration, while pores that are too large result in a large specific surface area, exacerbating side reactions with the electrolyte. This scheme controls the pore size of the porous layer 12 to 3-10 nm, enabling rapid lithium ion migration and minimizing side reactions with the electrolyte. Specifically, the pore size of the porous layer 12 can be controlled by adjusting the acidity of the etching solution, the carbonization temperature, and the gas evaporation rate during etching.
[0034] Specifically, the conductivity of silicon-based anode materials is 0.55–0.94 S / mm, specifically 0.55 S / mm, 0.6 S / mm, 0.7 S / mm, 0.73 S / mm, 0.75 S / mm, 0.78 S / mm, 0.8 S / mm, 0.83 S / mm, 0.85 S / mm, 0.88 S / mm, 0.9 S / mm, or 0.92 S / mm, 0.94 S / mm, etc.
[0035] This invention also discloses a method for preparing a silicon-carbon composite material, applicable to the preparation of the silicon-carbon composite material as described above, comprising:
[0036] S100: Silicon oxides are added to a carbon source, heated to dissolve, stirred evenly, cooled, and then pulverized to obtain the core precursor;
[0037] S200: A heat-treated core precursor, cooled to room temperature and stirred evenly with a dispersant solution, then etched with hydrofluoric acid aqueous solution to obtain a core (C-SiO2) with a porous surface layer. x );
[0038] S300: The core is placed in a reactor, and a gaseous carbon source is introduced for gas-phase coating to obtain a porous C-SiO2 layer with a carbon coating on its surface. y Precursor;
[0039] S400: C-SiO yThe precursor is dispersed in deionized water, stirred and mixed, then an aluminum-containing compound is added and stirred and mixed, heated to dryness, dried, ground and sintered to obtain a silicon-carbon composite material with an aluminum compound coating layer encapsulated in a carbon coating layer.
[0040] The aforementioned silicon-carbon composite material was prepared using the above preparation method. In step S100, the silicon oxide compound and the carbon source were heated, dissolved, and mixed to obtain the core precursor. The carbon source served as a carbon donor and also as a reducing agent, reacting with the silicon oxide compound in a redox reaction.
[0041] In step S200, the purpose of heat-treating the core precursor is to increase its graphitization degree. The heat treatment process is a high-temperature carbonization process, which is a process in which the structure of carbon fibers further transforms into a disordered graphite structure or a graphite structure. This process will expel elements other than carbon, producing carbon fibers with a carbon content of over 90%, removing impurities, improving purity, increasing true specific gravity, reducing resistivity, and improving electrical conductivity. After heat treatment, the core precursor is dispersed by a dispersant, and then etched with hydrofluoric acid aqueous solution to create a porous structure on the surface of the core precursor, thereby forming a porous layer on the core surface. The core portion enclosed by the porous layer is a solid part.
[0042] In step S300, the porous core is further coated with a carbon source vapor phase to form a carbon coating layer on the surface of the porous layer. This carbon source vapor phase coating results in a carbon coating layer with high uniformity and a small specific surface area. In step S400, an aluminum-containing compound is added, and after stirring, mixing, heating to dryness, drying, grinding, and sintering, an aluminum compound coating layer is formed. This aluminum compound coating layer coats the carbon coating layer, further strengthening the inner structure of the silicon-carbon composite material. On the lithium anode side, LiFPA will be reduced, forming protective materials such as LiF, Li2O, and aluminum-containing compounds inside the SEI layer, further improving the capacity, cycle performance, high-temperature cycling, and high-temperature storage performance of the silicon-carbon composite material.
[0043] Further, in step S100, a silicon oxide compound is added to a carbon source, and the silicon oxide compound and carbon source are dissolved by heating under an inert atmosphere and at a high temperature of 300-600°C. The silicon oxide compound can be silicon dioxide, silicon suboxide, etc. After a redox reaction, the silicon oxide compound partially generates elemental silicon. The carbon source can be asphalt, resin, etc. Preferably, the carbon source is asphalt. More preferably, the carbon source is asphalt with high isotropy, which can reduce expansion and improve the performance of silicon-carbon composite materials.
[0044] In step S200, the heat treatment temperature of the core precursor is 900-1150℃. This temperature range allows for sufficient graphitization of the core precursor, effectively removing elements other than carbon and ensuring the carbon content of the carbon fiber exceeds 90%. The heat treatment time for the core precursor is 1-10 hours. A shorter heat treatment time results in a lower degree of graphitization, while a longer time wastes time and increases energy consumption. Hydrofluoric acid aqueous solution is added, and the etching reaction is carried out at 500-2500 r / min for 10 hours to obtain a core with a porous layer. The core (C-SiO₂) contains... x The weight ratio of ) and hydrofluoric acid is (1:8) to (1:1). Step S200 further includes the step of washing the core (C-SiO) with deionized water. x At least twice, vacuum dry at pH 3–7 for 1–20 h at 60–150 °C, then sieve to obtain a porous core (C-SiO₂). x ), where 0 <x<2。
[0045] In step S300, the gaseous carbon source can be carbon monoxide, carbon dioxide, or a mixture of both. In step S400, the aluminum compound is 0.1 mol of LiFPA.
[0046] This invention also discloses a silicon-based anode, comprising the silicon-carbon composite material described above. The silicon-based anode, made using the silicon-carbon composite material of this invention, exhibits excellent high-temperature cycling and high-temperature storage performance.
[0047] The present invention also discloses a lithium-ion battery, comprising a silicon-based negative electrode as described above. Specifically, the lithium-ion battery further comprises a positive electrode sheet, a lithium battery separator, and an electrolyte. The positive electrode sheet comprises a positive current collector and a positive active slurry layer located on the positive current collector, wherein the positive active slurry layer comprises a positive active material; the negative electrode sheet comprises a negative current collector and a negative active slurry layer located on the negative current collector, wherein the negative active slurry layer comprises a negative active material, and the negative active material is the silicon-carbon composite material of the present invention.
[0048] Preferably, the positive electrode active material is one or more selected from lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials, lithium iron phosphate (LiFePO4), and lithium manganese oxide (LiMn2O4).
[0049] The technical solution of the present invention will be further illustrated below through specific embodiments and comparative examples.
[0050] Example 1
[0051] Silica was heated and dissolved under an argon atmosphere at a high temperature of 450°C, and stirred until homogeneous. Pitch was then added, with a silica to pitch weight ratio of 1:20. After cooling and pulverizing, the resulting core precursor was obtained, and its carbon content was measured to be 3.5%.
[0052] The obtained core precursor was heat-treated at 1000℃ for 10h in an argon atmosphere and then cooled to room temperature in the furnace to obtain the heat-treated product.
[0053] Add 10% PVP dispersant to deionized water in a reaction vessel and stir for 30 minutes. Then add the heat-treated product and stir at 600 rpm for 1 hour. Next, add a 20% hydrofluoric acid aqueous solution and etch at 500 rpm for 5 hours to obtain a core with a porous layer. Wash the core with deionized water until pH=7.
[0054] The core was placed in a reactor, and carbon dioxide was introduced for gas-phase coating to obtain a porous C-SiO2 layer with a carbon coating on its surface. y Precursor.
[0055] The above-mentioned core is then dispersed in deionized water, the mixed solution is stirred, and 0.1 mol of LiFPA is added to the mixed solution and stirred. The mixture is then heated to dryness, dried, ground, and sintered to obtain a silicon-carbon composite material.
[0056] Example 2
[0057] Silica was heated and dissolved under an argon atmosphere at a high temperature of 700°C, and stirred until homogeneous. Pitch was then added, with a silica to pitch weight ratio of 1:20. After cooling and pulverizing, the resulting core precursor was obtained, and its carbon content was measured to be 2.8%.
[0058] The obtained core precursor was heat-treated at 1000℃ for 10h in an argon atmosphere and then cooled to room temperature in the furnace to obtain the heat-treated product.
[0059] Add 10% PVP dispersant to deionized water in a reaction vessel and stir for 30 minutes. Then add the heat-treated product and stir at 600 rpm for 1 hour. Next, add a 20% hydrofluoric acid aqueous solution and etch at 500 rpm for 5 hours to obtain a core with a porous layer. Wash the core with deionized water until pH=7.
[0060] The core was placed in a reactor, and carbon dioxide was introduced for gas-phase coating to obtain a porous C-SiO2 layer with a carbon coating on its surface. y Precursor.
[0061] The above-mentioned core is then dispersed in deionized water, the mixed solution is stirred, and 0.1 mol of LiFPA is added to the mixed solution and stirred. The mixture is then heated to dryness, dried, ground, and sintered to obtain a silicon-carbon composite material.
[0062] Comparative Example 1
[0063] Silica was heated and dissolved under an argon atmosphere at a high temperature of 450°C, and stirred until homogeneous. Pitch was then added, with a silica to pitch weight ratio of 1:20. After cooling and pulverizing, the resulting core precursor was obtained, and its carbon content was measured to be 3.5%.
[0064] The obtained core precursor was heat-treated at 1000℃ for 10h in an argon atmosphere and then cooled to room temperature in the furnace to obtain the heat-treated product.
[0065] Add 10% PVP dispersant to deionized water in a reaction vessel and stir for 30 minutes. Then add the heat-treated product and stir at 600 rpm for 1 hour. Next, add a 20% hydrofluoric acid aqueous solution and etch at 500 rpm for 5 hours to obtain a core with a porous layer. Wash the core with deionized water until pH=7.
[0066] The above-mentioned core is then dispersed in deionized water, the mixed solution is stirred, and 0.1 mol of LiFPA is added to the mixed solution and stirred. The mixture is then heated to dryness, dried, ground, and sintered to obtain a silicon-carbon composite material.
[0067] Comparative Example 2
[0068] Silica was heated and dissolved under an argon atmosphere at a high temperature of 450°C, and stirred until homogeneous. Pitch was then added, with a silica to pitch weight ratio of 1:20. After cooling and pulverizing, the resulting core precursor was obtained, and its carbon content was measured to be 3.5%.
[0069] The obtained core precursor was heat-treated at 1000℃ for 10h in an argon atmosphere and then cooled to room temperature in the furnace to obtain the heat-treated product.
[0070] Add 10% PVP dispersant to deionized water in a reaction vessel and stir for 30 minutes. Then add the heat-treated product and stir at 600 rpm for 1 hour. Next, add a 20% hydrofluoric acid aqueous solution and etch at 500 rpm for 5 hours to obtain a core with a porous layer. Wash the core with deionized water until pH=7.
[0071] The core is placed in a reactor and carbon dioxide is introduced for gas-phase coating, resulting in a silicon-carbon composite material with a porous surface coated with a carbon coating.
[0072] Comparative Example 3
[0073] Silica was heated and dissolved under an argon atmosphere at a high temperature of 450°C, and stirred until homogeneous. Pitch was then added, with a silica to pitch weight ratio of 1:20. After cooling and pulverizing, the resulting core precursor was obtained, and its carbon content was measured to be 3.5%.
[0074] The obtained core precursor was heat-treated at 1000℃ for 10h in an argon atmosphere and then cooled to room temperature in the furnace to obtain the heat-treated product.
[0075] Add 10% PVP dispersant to deionized water in a reaction vessel and stir for 30 minutes. Then add the heat-treated product and stir at 600 rpm for 1 hour. Next, add a 20% hydrofluoric acid aqueous solution and etch at 500 rpm for 5 hours to obtain a core with a porous layer. Wash the core with deionized water until pH=7.
[0076] The above-mentioned core was dispersed in deionized water, the mixed solution was stirred, and then 0.1 mol of LiFPA was added to the mixed solution and stirred. The mixture was heated to dryness, dried, ground, and sintered to obtain a core with a porous surface coated with LiFPA.
[0077] The core is then placed in a reactor and carbon dioxide is introduced for gas-phase coating, resulting in a silicon-carbon composite material with a carbon coating layer encapsulating a LiFPA coating layer.
[0078] The difference between Example 2 and Example 1 is that the heating temperatures of silica and asphalt are different; the difference between Comparative Example 1 and Example 1 is that no vapor phase encapsulation was performed and no carbon encapsulation layer was formed; the difference between Comparative Example 2 and Example 1 is that no LiFPA encapsulation was performed and no LiFPA encapsulation layer was formed; the difference between Comparative Example 3 and Example 1 is that Comparative Example 3 was first encapsulated with LiFPA and then encapsulated with a carbon encapsulation layer.
[0079] The silicon-carbon composite materials obtained in the above embodiments and comparative examples were used to prepare lithium-ion batteries. The method for manufacturing lithium-ion batteries is as follows:
[0080] Preparation of the positive electrode sheet: The positive electrode active material LCO, conductive agent CNT, and binder polyvinylidene fluoride are thoroughly mixed in N-methylpyrrolidone solvent at a weight ratio of 97:1.5:1.5 to form a uniform positive electrode slurry. This slurry is then coated onto the positive electrode current collector Al foil, dried, and cold-pressed to obtain the positive electrode sheet.
[0081] Fabrication of the negative electrode sheet: The silicon-carbon composite material, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose from the above examples and comparative examples are thoroughly mixed in an appropriate amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. This slurry is coated onto the negative electrode current collector Cu foil, dried, and cold-pressed to obtain the negative electrode sheet.
[0082] The manufacturing process of lithium-ion batteries involves stacking the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is followed by winding the cells to form the bare battery cell. The bare cell is then placed in an outer packaging bag, and electrolyte is injected into the dried battery. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery is successfully manufactured.
[0083] High-temperature cycle testing of batteries
[0084] Test method: Place the battery in an environment of 45±2 degrees Celsius and perform standard charge-discharge cycles at a cycle rate of 1C and a charging voltage of 3.0-4.5V. Calculate the capacity retention rate of the battery after each cycle. The calculation formula is as follows: Capacity retention rate (%) after the nth cycle = (Discharge capacity after the nth cycle) / (Discharge capacity after the first cycle) * 100%.
[0085] High-temperature storage test of batteries
[0086] Test method: Charge the fully charged cells to 4.5V at room temperature with a current of 0.5C. Place the fully charged battery in an environment of 85 degrees Celsius for 6 hours and measure the thermal expansion rate. After returning to room temperature, discharge the battery to 3.0V with a current of 0.5C and record the discharge capacity.
[0087] The battery test results are shown in Table 1 below:
[0088] Table 1
[0089]
[0090] As shown in Table 1 above, under high-temperature cycling at 45°C, the capacity retention rate and thickness expansion rate of Examples 1 and 2 are better than those of Comparative Examples 1-3. Under high-temperature storage at 85°C, the capacity retention rate and thickness expansion rate of Examples 1 and 2 are better than those of Comparative Examples 2-3.
[0091] It should be noted that the limitations on each step involved in this solution are not considered as limiting the order of steps, provided that they do not affect the implementation of the specific solution. The steps listed first can be executed first, later, or even simultaneously. As long as this solution can be implemented, it should be considered to fall within the protection scope of this invention.
[0092] The above description, in conjunction with specific optional embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.
Claims
1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes a core, a carbon coating layer, and an aluminum compound coating layer; the core material is elemental silicon and silicon oxide, the core includes a solid part and a porous layer formed on the surface of the solid part, the carbon coating layer is wrapped on the porous layer, and the aluminum compound coating layer is wrapped on the carbon coating layer; the aluminum compound coating layer is LiFPA.
2. The silicon-carbon composite material as described in claim 1, characterized in that, The specific surface area of the core is 1.5 to 7.5 m² / g.
3. The silicon-carbon composite material as described in claim 2, characterized in that, The specific surface area of the silicon-carbon composite material is 170–300 m² / g; and / or the tap density of the silicon-carbon composite material is 0.5–0.85 g / cm³.
4. The silicon-carbon composite material as described in claim 3, characterized in that, The oxygen content of the silicon-carbon composite material is 1-10% by mass.
5. The silicon-carbon composite material as described in claim 1, characterized in that, The pore size of the porous layer is 3-10 nm.
6. A method for preparing a silicon-carbon composite material, applied to the preparation of the silicon-carbon composite material as described in any one of claims 1 to 5, characterized in that, include: Silicon oxides are added to a carbon source, heated to dissolve, stirred until homogeneous, cooled, and then pulverized to obtain the core precursor. The heat-treated core precursor was cooled to room temperature and stirred evenly with a dispersant solution. Hydrofluoric acid aqueous solution was added for etching to obtain a core with a porous layer on the surface. The core is placed in a reactor and a gaseous carbon source is introduced for gas phase coating to obtain a C-SiOy precursor with a porous surface covered with a carbon coating layer. The C-SiOy precursor was dispersed in deionized water, stirred and mixed, and then an aluminum-containing compound was added and stirred and mixed. The mixture was heated to dryness, dried, ground, and sintered to obtain a silicon-carbon composite material with an aluminum compound coating layer encapsulating the carbon coating layer.
7. The preparation method according to claim 6, characterized in that, In the step of heat-treating the core precursor, the heat treatment temperature is 900-1150℃ and the heat treatment time is 1-10h.
8. A silicon-based negative electrode, characterized in that, Including the silicon-carbon composite material as described in any one of claims 1 to 5.
9. A lithium-ion battery, characterized in that, Including the silicon-based anode as described in claim 8.