Nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, and its manufacturing method

Abstract

The present invention relates to a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on the surface and a method for producing the same, which is mainly produced by mass % from 4-10wt.% aluminum metaphosphate, 10wt.% pitch decomposition carbon, 15wt.% spherical nanosilicon powder, and 71-65wt.% graphite powder, and the nanosilicon powder is added to deionized water and ultrasonically dispersed, and then graphite powder is added and uniformly ultrasonically stirred, and then aqueous asphalt is added and uniformly stirred and mixed, and then spray dried, and the dried powder is combined with metaphosphate and mechanically fused, and finally transferred to a vacuum furnace for high-temperature carbonization. The present invention discloses a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer, and the composite modified layer on the surface can effectively inhibit the corrosion of the nanosilicon material by the electrolyte, mitigate the volume expansion, improve the electrical conductivity, and improve the cycle life.

Description

[Technical Field]

[0001] The present invention relates to the technical field of electrochemical power supplies, and more particularly to a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, and a method for manufacturing the same. [Background technology]

[0002] Silicon absorbs lithium by forming a lithium-silicon alloy with lithium. However, the lithium absorption process involves a large volume expansion, and the de-lithiation / de-alloying process also involves a significant volume contraction. This volume change can be as large as 300%, which is highly likely to cause silicon material pulverization and seriously affect cycle stability. While the problem of silicon material pulverization during electrochemical cycling can be effectively solved by producing nanosilicon powder with the appropriate particle size, the large volume change effect still exists after lithium absorption into nanosilicon material. When the electrode undergoes repeated volume expansion and contraction, the particles still lose electrical contact and pulverize, resulting in capacity loss and a decrease in cycle life. Composite nanosilicon material based on conventional, mature, commercially available graphite-based anode materials is an effective, viable, and cost-effective way to overcome the inherent shortcomings of silicon-based materials and obtain a new composite anode material whose specific capacity and cycle life meet the demands of lithium-ion battery anode materials.

[0003] However, when nanosilicon and graphite are composited, the expansion and contraction rates of the two materials during lithium absorption and release are inconsistent, leading to loss of electrical contact between the nanosilicon particles and capacity loss. The SEI film formed on the surface becomes unstable, resulting in constant consumption of electrolyte and impeding the transmission of lithium ions in the battery, thereby reducing the material's cycle life. Furthermore, currently, the main method for improving cycle life is to nanosize silicon materials and composite them with other materials. However, nanosized silicon materials have a large specific surface area, making them susceptible to erosion by electrolyte. Furthermore, even when nanosized, the silicon material still expands upon lithium absorption, necessitating further surface modification. The present invention provides a nanosilicon-graphite composite anode material with long cycle life by simply coating the material surface with carbon and modifying it with metaphosphate. Summary of the Invention

[0004] In view of this, an object of the present invention is to provide a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, and a method for producing the same.

[0005] In order to achieve the above object, the present invention adopts the following technical solution.

[0006] A nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, the negative electrode material mainly comprising: It is produced from the following components in mass percentages: 4-10 wt.% aluminum metaphosphate, 10 wt.% pitch decomposition carbon, 15 wt.% spherical nanosilicon powder, and 71-65 wt.% graphite powder.

[0007] Another technical object of the present invention is to provide a method for producing the above-mentioned nanosilicon-graphite composite anode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, including a method and steps for producing the surface carbon coating and the aluminum metaphosphate composite modified layer, and using the nanosilicon-graphite composite material as a silicon carbon composite material for lithium ion batteries, wherein the production method of the present invention is as follows:

[0008] First, nanosilicon powder is added to deionized water and ultrasonically dispersed to obtain a uniform dispersion, then graphite powder is added and uniformly ultrasonically stirred, then aqueous asphalt is added and uniformly stirred and mixed, and then spray-dried. The dried powder is combined with metaphosphate and mechanically fused, and finally transferred to a vacuum furnace for high-temperature carbonization to obtain a nanosilicon-graphite composite negative electrode material with a carbon coating and an aluminum metaphosphate composite modified layer on the surface.

[0009] in particular, Step 1) weighing nanosilicon powder according to the formula, adding it to deionized water, and dispersing it by ultrasonic stirring to obtain a nanosilicon powder dispersion; Step 2) is to stir the suspension of step 1 at high speed, add graphite powder according to the blending ratio, and after stirring and mixing for a certain period of time, add water-based asphalt and stir uniformly at high speed while adding deionized water to control the solid content of the suspension within the range of 10 to 15 wt.%. Step 3) spray-drying the suspension of step 2) in a spray dryer, controlling the spray inlet temperature at 200-220°C and the feed rate at 20-30 kg / h to obtain a dry powder; Step 4) weighing aluminum metaphosphate powder according to the blending ratio, adding it to the dry powder of step 3), mixing it uniformly, and then adding it to a mechanical blender for blending to obtain a precursor whose surface is coated with asphalt and an aluminum metaphosphate modified layer; Step 5) involves transferring the precursor from step 4) to a vacuum furnace and subjecting it to high-temperature carbonization at 800-1200°C for 3-6 hours, followed by removing it, crushing it, and sieving it to obtain a nanosilicon-graphite composite anode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface.

[0010] It should be noted that the present invention modifies the surface of a nanosilicon-graphite composite anode material with a carbon coating layer, which effectively improves the bonding strength between the nanosilicon and graphite and improves the conductivity of the silicon material, and the surface modification with aluminum metaphosphate effectively mitigates volume expansion and stabilizes the SEI film formed on the surface of the material. The present invention combines nanosilicon and graphite to produce a nanosilicon-graphite composite anode material, and then uses the surface carbon coating and aluminum metaphosphate composite modification layer to reinforce the conductivity of the nanosilicon particles, stabilize the SEI film, and mitigate volume changes in the material, resulting in a composite anode material with a longer cycle life.

[0011] Compared with the prior art, the present invention discloses a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface and a manufacturing method thereof, which has the following beneficial effects:

[0012] 1) The presence of the composite modification layer not only has the same effects as conventional carbon coatings, such as improving the conductivity of the silicon material, blocking erosion of the silicon material by the electrolyte, and mitigating volume expansion, but the dispersion of aluminum metaphosphate in the coating layer also strengthens the peel strength of the coating layer and allows it to better adapt to volume changes in the material.

[0013] 2) The presence of aluminum metaphosphate forms a stable SEI film on the surface of the material, reducing electrolyte consumption and contributing to a higher cycle life. [Brief explanation of the drawings]

[0014] In order to more clearly explain the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings that need to be used in the description of the embodiments or the prior art. It is obvious that the drawings in the following description are only the embodiments of the present invention, and those skilled in the art can derive other drawings from the provided drawings without exerting any creative effort. [Figure 1]1 is an energy spectrum analysis of a nanosilicon-graphite composite negative electrode material having aluminum metaphosphate modification on its surface prepared according to the present invention. [Figure 2] FIG. 2 is a capacity retention curve obtained by assembling the silicon carbon composite materials prepared in Example 1 and Comparative Example 1 of the present invention into a 2032 button battery as a negative electrode plate and then testing the battery. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following clearly and completely describes the technical solutions in the embodiments of the present invention in conjunction with the specification and drawings, and it is obvious that the described embodiments are only some of the embodiments of the present invention, not all of the embodiments, and all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative efforts are all within the protection scope of the present invention.

[0016] The present invention discloses and protects a method for preparing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modification layer on its surface.

[0017] The technical solution of the present invention will be further described below in conjunction with specific examples, but the content of the present invention is not limited to the following examples. [Example]

[0018] A method for producing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, specifically, Step 1) weighing 450 g of nanosilicon powder and adding it to 27 kg of deionized water and dispersing it with ultrasonic stirring to obtain a suspension of nanosilicon powder; Step 2) is performed by adding 1950 g of graphite powder to the suspension of step 1 while stirring at high speed, stirring thoroughly to mix uniformly, and then adding 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon content 50 wt.%) and mixing uniformly to obtain a uniform slurry with a solid content of about 10 wt.%. Step 3) spray-drying the uniform slurry obtained in step 2) while ultrasonically stirring, controlling the atomizer inlet temperature at 220°C and the feed rate at 30 kg / h to obtain a dry powder; Step 4) weighs out 300 g of aluminum metaphosphate powder and adds it to a mechanical fusion machine together with the dry powder obtained in step 3), and extrudes it at high speed for 20 minutes to fuse it, thereby obtaining a precursor whose surface is coated with asphalt and an aluminum metaphosphate modified layer; Step 5) includes transferring the precursor from step 4) to a vacuum furnace and subjecting it to carbonization treatment under vacuum conditions at 800°C for 3 hours, thereby carbonizing the pitch at high temperature and obtaining a nanosilicon-graphite composite negative electrode material having a surface with about 10 wt.% of pitch decomposition carbon and 10 wt.% of aluminum metaphosphate composite modification layer; The nanosilicon-graphite composite negative electrode material prepared in this example was used as a negative electrode plate, which was then assembled into a 2032 button battery and subjected to a cycle life test. The material performance data is shown in Table 1, and the cycle life curve is shown in Figure 2.

[0019] Here, the battery cycle performance test method involves first discharging to 0.01 V at a current density of 100 mA / g, then discharging to 0.005 V at a current of 10 mA / g, leaving it to stand for 3 minutes, and then charging to 1.5 V at a current density of 100 mA / g, which constitutes one cycle.

[0020] The nanosilicon-graphite composite anode material with aluminum metaphosphate modification on the surface produced by the present invention was subjected to energy spectrum analysis, specifically as shown in Figure 1. As can be seen from the energy spectrum diagram, nanosilicon particles are dispersed on the surfaces of the graphite particles in the composite material, and the particles are bound into a single whole by the carbon coating on the surface and the aluminum metaphosphate modification layer. [Example]

[0021] A method for producing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, specifically, Step 1) weighing 450 g of nanosilicon powder and adding it to 27 kg of deionized water and dispersing it with ultrasonic stirring to obtain a suspension of nanosilicon powder; Step 2) is performed by adding 2130 g of graphite powder to the suspension of step 1) while stirring at high speed, stirring thoroughly to mix uniformly, and then adding 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon content 50 wt.%) and mixing uniformly to obtain a uniform slurry with a solid content of approximately 10 wt.%. Step 3) spray-drying the uniform slurry obtained in step 2) while ultrasonically stirring, controlling the atomizer inlet temperature at 200°C and the feed rate at 30 kg / h to obtain a dry powder; Step 4) weighs out 120 g of aluminum metaphosphate powder and adds it to a mechanical fusion machine together with the dry powder obtained in step 3), and extrudes it at high speed for 20 minutes to fuse it, thereby obtaining a precursor whose surface is coated with asphalt and an aluminum metaphosphate modified layer; The precursor from step 4) is transferred to a vacuum furnace and carbonized at 800°C under vacuum conditions for 6 hours, and step 5) carbonizes the pitch at high temperature to obtain a nanosilicon-graphite composite negative electrode material having a surface with approximately 10 wt.% pitch decomposition carbon and 4 wt.% aluminum metaphosphate composite modification layer. [Example]

[0022] A method for producing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, specifically, Step 1) weighing 450 g of nanosilicon powder and adding it to 17 kg of deionized water and dispersing it with ultrasonic stirring to obtain a suspension of nanosilicon powder; Step 2) is performed by adding 1950 g of graphite powder to the suspension of step 1) while stirring at high speed, and mixing thoroughly to mix uniformly. 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon amount 50 wt.%) is then added and mixed uniformly to obtain a uniform slurry with a solid content of about 15 wt.%. Step 3) spray-drying the uniform slurry obtained in step 2) while ultrasonically stirring, controlling the atomizer inlet temperature at 200°C and the feed rate at 30 kg / h to obtain a dry powder; Step 4) weighs out 300 g of aluminum metaphosphate powder and adds it to a mechanical fusion machine together with the dry powder obtained in step 3), and extrudes it at high speed for 20 minutes to fuse it, thereby obtaining a precursor whose surface is coated with asphalt and an aluminum metaphosphate modified layer; The precursor from step 4) is transferred to a vacuum furnace and carbonized at 1000°C under vacuum conditions for 6 hours, and step 5) carbonizes the pitch at high temperature to obtain a nanosilicon-graphite composite negative electrode material having a surface layer of approximately 10 wt.% pitch decomposition carbon and 10 wt.% aluminum metaphosphate composite modification layer. [Example]

[0023] A method for producing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, specifically, Step 1) weighing 450 g of nanosilicon powder and adding it to 22 kg of deionized water and dispersing it with ultrasonic stirring to obtain a suspension of nanosilicon powder; Step 2) is performed by adding 2010 g of graphite powder to the suspension of step 1 while stirring at high speed, stirring thoroughly to mix uniformly, and then adding 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon content 50 wt.%) and mixing uniformly to obtain a uniform slurry with a solid content of approximately 12.2 wt.%. Step 3) spray-drying the uniform slurry obtained in step 2) while ultrasonically stirring, controlling the atomizer inlet temperature at 210°C and the feed rate at 30 kg / h to obtain a dry powder; Step 4) weighs out 240 g of aluminum metaphosphate powder and adds it to a mechanical fusion machine together with the dry powder obtained in step 3), and extrudes it at high speed for 20 minutes to fuse them together, thereby obtaining a precursor whose surface is coated with asphalt and an aluminum metaphosphate modified layer; The precursor from step 4) is transferred to a vacuum furnace and carbonized at 1200°C under vacuum conditions for 3 hours, and step 5) carbonizes the pitch at high temperature to obtain a nanosilicon-graphite composite negative electrode material having a surface with approximately 10 wt.% pitch decomposition carbon and 8 wt.% aluminum metaphosphate composite modification layer. [Example]

[0024] A method for producing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, specifically, Step 1) weighing 450 g of nanosilicon powder and adding it to 27 kg of deionized water and dispersing it with ultrasonic stirring to obtain a suspension of nanosilicon powder; Step 2) is performed by adding 2070 g of graphite powder to the suspension of step 1) while stirring at high speed, and mixing thoroughly to mix uniformly. 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon amount 50 wt.%) is then added and mixed uniformly to obtain a uniform slurry with a solid content of approximately 10.4 wt.%. Step 3) spray-drying the uniform slurry obtained in step 2) while ultrasonically stirring, controlling the atomizer inlet temperature at 220°C and the feed rate at 30 kg / h to obtain a dry powder; Step 4) weighs out 180 g of aluminum metaphosphate powder and adds it to a mechanical fusion machine together with the dry powder obtained in step 3), and extrudes it at high speed for 20 minutes to fuse them together, thereby obtaining a precursor whose surface is coated with asphalt and an aluminum metaphosphate modified layer; The precursor from step 4) is transferred to a vacuum furnace and carbonized at 1100°C under vacuum conditions for 4 hours, and step 5) carbonizes the pitch at high temperature to obtain a nanosilicon-graphite composite negative electrode material having a surface with approximately 10 wt.% pitch decomposition carbon and 6 wt.% aluminum metaphosphate composite modification layer.

[0025] In order to further verify the superior effects of the present invention compared to the prior art, the inventors have further conducted the following comparative experiments and performance tests, the specific contents of which are as follows: Comparative Example 1

[0026] 1) 450 g of nanosilicon powder was weighed and added to 27 kg of deionized water, and dispersed by ultrasonic stirring to obtain a suspension of nanosilicon powder; 2) While stirring the suspension of step 1) at high speed, add 1950 g of graphite powder and stir thoroughly to mix uniformly. Then, add 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon amount 50 wt.%) and mix uniformly to obtain a uniform slurry with a solid content of about 10 wt.%. 3) The uniform slurry obtained in step 2) is spray-dried under ultrasonic agitation, and the sprayer inlet temperature is controlled at 220°C and the feed rate is controlled at 30 kg / h to obtain a dry powder. 4) The precursor in step 3) is transferred to a vacuum furnace and carbonized under vacuum conditions at 800 ° C for 3 hours to carbonize the pitch at high temperature, obtaining a nanosilicon-graphite composite anode material with only a carbon coating layer on the surface and no aluminum metaphosphate modification; The nanosilicon-graphite composite anode material without surface modification in Comparative Example 1 was assembled into a 2032 button battery and subjected to a cycle life test. The material performance data is shown in Table 1, and the cycle life curve is shown in Figure 2.

[0027] 1) 450 g of nanosilicon powder was weighed and added to 27 kg of deionized water, and dispersed by ultrasonic stirring to obtain a suspension of nanosilicon powder; 2) While stirring the suspension of step 1) at high speed, add 1950 g of graphite powder and stir thoroughly to mix uniformly. Then, add 1200 g of aqueous asphalt (solid content 50 wt.%, vacuum carbonization residual carbon amount 50 wt.%) and mix uniformly to obtain a uniform slurry with a solid content of about 10 wt.%. 3) The uniform slurry obtained in step 2) is spray-dried under ultrasonic agitation, and the sprayer inlet temperature is controlled at 220°C and the feed rate is controlled at 30 kg / h to obtain a dry powder. 4) The precursor in step 3) is transferred to a vacuum furnace and carbonized under vacuum conditions at 800 ° C for 3 hours, and the pitch is carbonized at high temperature to obtain a nanosilicon-graphite composite anode material with no carbon coating layer on the surface and only aluminum metaphosphate modification; The nanosilicon-graphite composite anode material without surface modification in Comparative Example 2 was assembled into a 2032 button battery and subjected to a cycle life test. The material performance data are shown in Table 1. Comparative Example 3

[0028] 1) 450 g of nanosilicon powder was weighed and added to 27 kg of deionized water, and dispersed by ultrasonic stirring to obtain a suspension of nanosilicon powder; 2) While stirring the suspension of step 1) at high speed, add 1950 g of graphite powder and stir thoroughly to mix uniformly to obtain a uniform slurry with a solid content of about 10 wt. %. 3) The uniform slurry obtained in step 2) is spray-dried under ultrasonic agitation, and the sprayer inlet temperature is controlled at 220°C and the feed rate is controlled at 30 kg / h to obtain a dry powder. 4) The precursor in step 3) is transferred to a vacuum furnace and carbonized under vacuum conditions at 800 °C for 3 hours to obtain a nanosilicon-graphite composite anode material with no carbon coating or aluminum metaphosphate modification on the surface; The nanosilicon-graphite composite anode material without surface modification in Comparative Example 3 was assembled into a 2032 button battery and subjected to a cycle life test. The material performance data are shown in Table 1.

[0029] As can be seen from Table 1, Comparative Example 3, which had no surface modification, had a capacity retention of only 28.4% after 300 cycles; Comparative Example 1, which had only a carbon coating layer modification, had a capacity retention of 70.7% after 300 cycles; and Comparative Example 2, which had only an aluminum metaphosphate modification, had a capacity retention of 46.2% after 300 cycles. However, after the carbon coating and aluminum metaphosphate composite modification, the cycle life of the material was significantly improved, with samples from Examples 1 to 5 having capacity retentions of 103.7%, 87.8%, 104.3%, 102.8%, and 104.4%, respectively, after 300 cycles. Comparative analysis revealed that the carbon coating and aluminum metaphosphate composite modification layer designed in this invention can significantly improve the cycle life of nanosilicon-graphite composite anode materials.

[0030] [Table 1]

[0031] The above description of the disclosed embodiments will enable those skilled in the art to make or use the present invention. Various modifications of these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modified layer on its surface, the negative electrode material having the following component ratios: 4-10 wt. % aluminum metaphosphate, 10 wt. % pitch decomposition carbon, 15 wt. % spherical nano silicon powder, and 71-65 wt. % graphite powder; The manufacturing method includes: Step 1) weighing nanosilicon powder according to the component ratio, adding it to deionized water, and dispersing it by ultrasonic stirring to obtain a nanosilicon powder dispersion; Step 2) of stirring the suspension of step 1) at high speed, adding graphite powder in accordance with the component ratio, stirring and mixing for a certain period of time, adding aqueous asphalt that will be carbonized at high temperature to obtain the pitch decomposition carbon, stirring uniformly at high speed, and adding deionized water to control the solid content of the suspension to within the range of 10 to 15 wt. %; Step 3) spray-drying the suspension of step 2) in a spray dryer to obtain a dry powder; Step 4) weighing aluminum metaphosphate powder according to the component ratio, adding it to the dry powder of step 3), mixing uniformly, and then adding it to a mechanical blender for blending to obtain a precursor having asphalt and an aluminum metaphosphate modified layer coated on its surface; and step 5) subjecting the precursor in step 4) to high-temperature carbonization in a vacuum furnace, and then removing, crushing, and sieving the resulting material to obtain a nanosilicon-graphite composite negative electrode material having a carbon coating and an aluminum metaphosphate composite modification layer on its surface.

2. 2. The method according to claim 1, wherein in step 3), the spray inlet temperature is 200-220°C and the feed rate is 20-30 kg / h.

3. 2. The method of claim 1, wherein in step 5), the high-temperature carbonization temperature is 800-1200°C, and the carbonization time is 3-6 hours.

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