Negative electrode composite material, preparation method thereof and battery
By introducing a composite structure of nano-silicon particles and MgSiO3 layers into silicon-based anode materials, the problems of volume expansion and low initial cycle efficiency of silicon-based anode materials during charge and discharge processes are solved, achieving better cycle performance and coulombic efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-11
- Publication Date
- 2026-04-03
AI Technical Summary
Silicon-based anode materials are prone to expansion during charge and discharge and have low initial cycle efficiency, which limits their application in lithium batteries.
The negative electrode composite material consists of core particles and a carbon coating layer. The core particles are composed of nano-silicon particles and a partially coated MgSiO3 layer. The carbon coating layer and MgSiO3 layer are formed through a two-stage calcination process, which buffers volume expansion and improves cycle performance.
It effectively improves the cycle life and initial coulombic efficiency of silicon anode materials, thereby enhancing the overall performance of the battery.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium batteries, specifically to a negative electrode composite material, its preparation method, and a battery. Background Technology
[0002] With the development of technology, the energy density and safety of lithium batteries are constantly improving. However, the energy density of traditional graphite anodes has approached its theoretical limit, which restricts further development.
[0003] To address this issue, silicon-based anodes have become a key research focus. Silicon's theoretical specific capacity is significantly higher than graphite, reaching 4200 mAh / g, which can substantially improve overall battery performance. However, silicon undergoes a volume expansion of up to 300% during charge and discharge. This large volume expansion can lead to the cracking of the anode material and electrolyte penetration, resulting in a decline in cycle performance. Furthermore, silicon's initial cycle efficiency is typically lower than that of graphite, which also limits its commercial application. Summary of the Invention
[0004] In view of this, the present invention aims to provide a negative electrode composite material, its preparation method and battery, to solve the problems of easy expansion of silicon materials during charging and discharging and low initial cycle efficiency in the prior art.
[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: A first aspect of the present invention provides a negative electrode composite material, the negative electrode composite material comprising core particles and a carbon coating layer covering the surface of the core particles, the core particles comprising nano-silicon particles and a MgSiO3 layer at least partially covering the surface of the nano-silicon particles.
[0006] Optionally, based on the total mass of the negative electrode composite material, the content of the MgSiO3 layer is 4~20wt%, preferably 5~10wt%.
[0007] Optionally, the Dv50 of the nano-silicon particles is 100~300nm, preferably 150~250nm.
[0008] Optionally, the thickness of the carbon coating layer is 5~30nm, preferably 10~20nm.
[0009] A second aspect of the present invention provides a method for preparing a negative electrode composite material, the method comprising the following steps: S1. Magnesium powder is placed in an alkaline solution for a first impregnation treatment, and after filtration and washing, a first magnesium powder is obtained; the first magnesium powder is placed in a solution containing dopamine monomer for a second impregnation treatment, and after filtration, washing and drying, a second magnesium powder is obtained. S2. Grind and mix the second magnesium powder with silicon particles to obtain a mixture, and mix the mixture with an organic medium to obtain a slurry; subject the slurry to sand milling and drying to obtain magnesium silicon powder; S3. The silicon-magnesium powder is calcined. The calcination process includes a first stage of calcination and a second stage of calcination. The first stage of calcination is carried out in an atmosphere containing carbon dioxide at a temperature of 500-600°C; the second stage of calcination is carried out in an inert atmosphere at a temperature of 800-1200°C.
[0010] Optionally, the mass ratio of the first magnesium powder to the dopamine monomer is (13~16):1; and / or, the mass ratio of the second magnesium powder to the silicon particles is 1~5wt%; and / or, the Dv50 of the silicon particles is 1~20μm; and / or, the solid content of the mixed slurry is 5~30wt%.
[0011] Optionally, the alkaline solution includes at least one of NaOH solution, Na2CO3 solution, Na2SiO3 solution, Ca(OH)2 solution, and NH4OH; the molar concentration of the alkaline solution is 0.1~1 mol / L; and / or, the organic medium includes at least one of ethanol, isopropanol, ethylene glycol, and acetone.
[0012] Optionally, the atmosphere containing carbon dioxide is a carbon dioxide atmosphere, or the atmosphere containing carbon dioxide is an inert mixed atmosphere with a carbon dioxide volume concentration of not less than 10%.
[0013] Optionally, in step S1, the conditions for the first impregnation treatment include: a temperature of 60~80℃ and a time of 10~20 min; and / or, the conditions for the second impregnation treatment include: a pH of 8~9, a temperature of 35~40℃, and a time of 5~7 h; and / or, in step S2, the time for the sand milling treatment is 5~20 h; and / or, the temperature for the drying treatment is 40~80℃; and / or, in step S3, the time for the first calcination stage is 2~24 h; and the time for the second calcination stage is 2~5 h.
[0014] A third aspect of the present invention provides a battery comprising a negative electrode material, the negative electrode material comprising the above-described negative electrode composite material and / or a negative electrode composite material prepared according to the above-described method.
[0015] The beneficial technical effects of the present invention through the above technical solution are as follows: (1) The negative electrode composite material of the present invention includes core particles and carbon coating layer. The core particles include nano-silicon particles and at least part of the MgSiO3 layer coating the surface of the nano-silicon particles. MgSiO3 can act as a buffer for the volume expansion of silicon material during the charging and discharging process of silicon negative electrode material, thereby improving the cycle performance of silicon negative electrode material. The combined effect of the MgSiO3 layer and the carbon coating layer can effectively improve the cycle life of silicon negative electrode material.
[0016] (2) In the preparation method of the present invention, magnesium powder is first immersed in an alkaline solution to obtain magnesium powder with dense magnesium hydroxide coating on the surface (i.e., first magnesium powder); then the first magnesium powder is immersed in a solution containing dopamine monomer to obtain magnesium powder with polydopamine on the surface (i.e., second magnesium powder). This step can introduce active functional groups, enhance the dispersibility of magnesium powder, and make it more fully bonded to the oxide layer on the surface of silicon material during subsequent grinding, which is more conducive to the formation of silicate phase. This invention involves mixing a second layer of magnesium powder with silicon particles and then with an organic medium. The resulting slurry is then milled and dried. During this process, the silicon particles react with the organic medium to produce silicon dioxide, thus yielding magnesium-silicon powder. Finally, the magnesium-silicon powder undergoes a two-stage calcination. The first stage calcination is performed at 500-600°C using carbon dioxide as the carbon source. During this reaction, pre-treated magnesium powder directly coats the silicon material with a carbon layer, improving the cycle performance of the silicon anode material. The second stage calcination is performed at 800-1200°C, utilizing the byproduct MgO from the first heating stage. This process pre-consumes the oxide layer formed on the silicon material surface during milling, reducing the dead lithium phase formed during the initial charge-discharge cycle and improving the initial coulombic efficiency of the silicon anode material. Furthermore, the final product of the two-stage heating, silicate MgSiO3, acts as a buffer for the volume expansion of the silicon anode, further enhancing the cycle performance of the silicon anode material.
[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation
[0018] This invention discloses a negative electrode composite material, its preparation method, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.
[0019] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.
[0020] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges or individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0021] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.
[0022] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.
[0023] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.
[0024] To address the problems of silicon materials easily expanding during charging and discharging and having low initial cycle efficiency in existing technologies, the present invention adopts the following technical solution: A first aspect of the present invention provides a negative electrode composite material, the negative electrode composite material comprising core particles and a carbon coating layer covering the surface of the core particles, the core particles comprising nano-silicon particles and a MgSiO3 layer at least partially covering the surface of the nano-silicon particles.
[0025] The anode composite material of the present invention includes core particles and a carbon coating layer. The core particles include nano-silicon particles and a MgSiO3 layer at least partially coating the surface of the nano-silicon particles. MgSiO3 can act as a buffer for the volume expansion of silicon materials during the charging and discharging process, thereby improving the cycle performance of silicon anode materials. The combined effect of the MgSiO3 layer and the carbon coating layer can effectively improve the cycle life of silicon anode materials.
[0026] In this invention, if the MgSiO3 content in the negative electrode composite material is too low, the silicon negative electrode material may lack buffer material for volume expansion, resulting in severe capacity retention degradation during battery charging and discharging. If the MgSiO3 content in the negative electrode composite material is too high, the battery energy density may decrease, and the effective lithium intercalation sites of the silicon negative electrode material may be covered, leading to a reduction in the reversible capacity of the battery. According to this invention, based on the total mass of the negative electrode composite material, the content of the MgSiO3 layer can be 4~20wt%. Exemplarily, based on the total mass of the negative electrode composite material, the content of the MgSiO3 layer can be any value from 4 wt%, 8 wt%, 12 wt%, 16 wt%, and 20 wt%, or any value within the range of any two of the above values. As a preferred embodiment of this invention, based on the total mass of the negative electrode composite material, the content of the MgSiO3 layer is 5~10wt%.
[0027] In this invention, if the Dv50 of the silicon nanoparticles is too small, it may lead to silicon particle agglomeration; if the Dv50 of the silicon nanoparticles is too large, it may lead to increased volume expansion stress, damaging the structure of the negative electrode material. According to this invention, the Dv50 of the silicon nanoparticles can be 100~300 nm. Exemplarily, the Dv50 of the silicon nanoparticles can be any value selected from 100 nm, 150 nm, 200 nm, 250 nm, and 300 nm, or any value within the range formed by any two of the above values. As a preferred embodiment of this invention, the Dv50 of the silicon nanoparticles is 150~250 nm.
[0028] In this invention, a suitable carbon coating thickness improves the conductivity of the negative electrode material and the cycle life of the battery. If the carbon coating is too thick, it may reduce the specific capacity of the negative electrode material; if the carbon coating is too thin, it may cause uncontrollable volume expansion of the silicon particles. According to this invention, the thickness of the carbon coating can be 5-30 nm. Exemplarily, the thickness of the carbon coating can be any value selected from 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, and 30 nm, or any value within the range formed by any two of the above values. Preferably, the thickness of the carbon coating is 10-20 nm.
[0029] A second aspect of the present invention provides a method for preparing a negative electrode composite material, the method comprising the following steps: S1. Magnesium powder is placed in an alkaline solution for a first impregnation treatment, and after filtration and washing, a first magnesium powder is obtained; the first magnesium powder is placed in a solution containing dopamine monomer for a second impregnation treatment, and after filtration, washing and drying, a second magnesium powder is obtained. S2. Grind and mix the second magnesium powder with silicon particles to obtain a mixture, and mix the mixture with an organic medium to obtain a slurry; subject the slurry to sand milling and drying to obtain magnesium silicon powder; S3. The silicon-magnesium powder is calcined. The calcination process includes a first stage of calcination and a second stage of calcination. The first stage of calcination is carried out in an atmosphere containing carbon dioxide at a temperature of 500-600°C; the second stage of calcination is carried out in an inert atmosphere at a temperature of 800-1200°C.
[0030] In the preparation method of the present invention, magnesium powder is first immersed in an alkaline solution to obtain magnesium powder with a dense magnesium hydroxide coating on the surface (i.e., first magnesium powder); then the first magnesium powder is immersed in a solution containing dopamine monomer to obtain magnesium powder with polydopamine on the surface (i.e., second magnesium powder). This step can introduce active functional groups, enhance the dispersibility of magnesium powder, and make it more fully bonded to the oxide layer on the surface of silicon material during subsequent grinding, which is more conducive to the formation of silicate phase. This invention involves mixing a second magnesium powder with silicon particles and then mixing it with an organic medium. The mixture is then milled and dried. During this process, the silicon particles react with the organic medium to produce silicon dioxide, resulting in magnesium-silicon powder. Finally, the magnesium-silicon powder is subjected to a two-stage calcination. The first stage of calcination is carried out at a temperature of 500-600°C, using carbon dioxide as the carbon source. The chemical formula of the reaction is shown in formula (1). During the reaction, the pretreated magnesium powder is used to directly coat the silicon material with a carbon layer, thereby improving the cycle performance of the silicon anode material. The second stage of calcination is carried out at a temperature of 800-1200°C, using the byproduct MgO from the first heating stage. The chemical formula of the reaction is shown in formula (2). During this process, the oxide layer formed on the surface of the silicon material during milling is consumed in advance. This not only reduces the dead lithium phase formed during the first charge and discharge, thus improving the first coulombic efficiency of the silicon anode material, but also fully utilizes the final product MgSiO3 from the two-step heating stage as a buffer for the volume expansion of the silicon anode, thereby improving the cycle performance of the silicon anode material a second time.
[0031] 2Mg + CO2 = 2MgO + C Equation (1) MgO+SiO2=MgSiO3 Formula (2) According to the present invention, the mass ratio of the first magnesium powder to the dopamine monomer can be (13~16):1; for example, the mass ratio of the first magnesium powder to the dopamine monomer can be any value among 13:1, 14:1, 15:1 and 16:1 or any value within the range of any two of the above values.
[0032] According to the present invention, the mass ratio of the second magnesium powder to the silicon particles can be 1 to 5 wt%; for example, the mass ratio of the second magnesium powder to the silicon particles can be any value among 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%, or any value within the range of any two of the above values.
[0033] According to the present invention, the Dv50 of the silicon particle can be 1~20μm; for example, the Dv50 of the silicon particle can be any value among 1μm, 5μm, 10μm, 15μm and 20μm or any value within the range of any two of the above values.
[0034] According to the present invention, the solid content of the mixed slurry can be 5 to 30 wt%. Exemplarily, the solid content of the mixed slurry can be any value selected from 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt%, or any value within the range formed by any pair of the above values.
[0035] For example, the alkaline solution may include at least one of NaOH solution, Na2CO3 solution, Na2SiO3 solution, Ca(OH)2 solution and NH4OH; the molar concentration of the alkaline solution may be 0.1~1 mol / L.
[0036] For example, the organic medium includes at least one of ethanol, isopropanol, ethylene glycol and acetone.
[0037] In this invention, the atmosphere containing carbon dioxide is a carbon dioxide atmosphere, or the atmosphere containing carbon dioxide is an inert mixed atmosphere with a carbon dioxide volume concentration of not less than 10%.
[0038] In an embodiment of the present invention, in step S1, the conditions for the first impregnation treatment may include: a temperature of 60~80°C and a time of 10~20 min; and / or, the conditions for the second impregnation treatment may include: a pH of 8~9, a temperature of 35~40°C, and a time of 5~7 h.
[0039] In an embodiment of the present invention, in step S2, the sand milling time can be 5 to 20 hours; and / or, the drying temperature can be 40 to 80°C.
[0040] In an embodiment of the present invention, in step S3, the calcination time of the first stage can be 2 to 24 hours; the calcination time of the second stage can be 2 to 5 hours.
[0041] A third aspect of the present invention provides a battery comprising a negative electrode material, the negative electrode material comprising the above-described negative electrode composite material and / or a negative electrode composite material prepared according to the above-described method.
[0042] In some embodiments of the present invention, the battery further includes a positive electrode, an electrolyte, and a separator. That is, the battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.
[0043] In this embodiment, the materials and structures of the positive electrode current collector, the conductive agent and the binder in the positive electrode active material layer are not limited, and the positive electrode structure and composition known in the art that can be used in secondary batteries can be selected.
[0044] In this embodiment, the specific material or type of the separator is not limited, and any separator known in the art that can be used in secondary batteries can be selected.
[0045] It should also be noted that the battery of the present invention does not limit the specific material or type of electrolyte, and can use any components and types known in the art that can be used in secondary batteries, as long as the purpose of the present invention can be achieved.
[0046] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.
[0047] The present invention will be specifically described below with reference to examples, but the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present invention and are not intended to limit the present invention.
[0048] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.
[0049] Example 1 150g of untreated magnesium powder was soaked in 0.1M NaOH solution at 80℃ for the first impregnation treatment. After 10 minutes, it was filtered and washed to obtain the first magnesium powder. Under ice-water bath conditions, the first magnesium powder was soaked in 1L of solution containing 10g of dopamine. The mixture was stirred for 1 hour, then heated to 37°C, the pH was controlled at 8.5, and it was stirred again for 6 hours. After filtration, washing and drying, the second magnesium powder was obtained.
[0050] Silicon particles with a Dv50 of 10 μm were ground and mixed with magnesium powder comprising 1 wt% of the silicon particles to obtain a mixture. The mixture was then mixed with ethanol to prepare a slurry with a solid content of 5 wt%. The slurry was sand-milled for 12 h and then dried at 60 °C to obtain silicon-magnesium powder. The prepared nano-silicon had a Dv50 of 200 nm, a carbon coating thickness of 15 nm, and a MgSiO3 layer content of 4 wt%.
[0051] The silicon-magnesium powder was placed in a tube furnace and heated at 600°C for 3 hours in a carbon dioxide atmosphere with a gas flow rate of 50 mL / min. Then, it was switched to an inert atmosphere and heated at 1000°C for 2 hours. After natural cooling, the negative electrode composite material of this embodiment was obtained.
[0052] Example 2 150g of untreated magnesium powder was soaked in 0.1M NaOH solution at 80°C for the first impregnation treatment. After 10 minutes, it was filtered and washed to obtain the first magnesium powder. Under ice-water bath conditions, the first magnesium powder was soaked in 1L of solution containing 10g of dopamine. The mixture was stirred for 1 hour, then heated to 37°C, the pH was controlled at 8.5, and it was stirred again for 6 hours. After filtration, washing and drying, the second magnesium powder was obtained.
[0053] Silicon particles with a Dv50 of 10 μm were ground and mixed with magnesium powder comprising 3 wt% of the silicon particles to obtain a mixture. The mixture was then mixed with ethanol to prepare a slurry with a solid content of 5 wt%. The slurry was sand-milled for 12 h and then dried at 60 °C to obtain silicon-magnesium powder. The prepared nano-silicon had a Dv50 of 200 nm, a carbon coating thickness of 15 nm, and a MgSiO3 layer content of 12.5 wt%.
[0054] The silicon-magnesium powder was placed in a tube furnace and heated at 600°C for 3 hours in a carbon dioxide atmosphere with a gas flow rate of 50 mL / min. Then, it was switched to an inert atmosphere and heated at 1000°C for 2 hours. After natural cooling, the negative electrode composite material of this embodiment was obtained.
[0055] Example 3 150g of untreated magnesium powder was soaked in 0.1M NaOH solution at 80℃ for the first impregnation treatment. After 10 minutes, it was filtered and washed to obtain the first magnesium powder. Under ice-water bath conditions, the first magnesium powder was soaked in 1L of solution containing 10g of dopamine. The mixture was stirred for 1 hour, then heated to 37°C, the pH was controlled at 8.5, and it was stirred again for 6 hours. After filtration, washing and drying, the second magnesium powder was obtained.
[0056] Silicon particles with a Dv50 of 10 μm were ground and mixed with magnesium powder comprising 5 wt% of the silicon particles to obtain a mixture. The mixture was then mixed with ethanol to prepare a slurry with a solid content of 5 wt%. The slurry was milled for 12 h and then dried at 60 °C to obtain silicon-magnesium powder. The prepared nano-silicon had a Dv50 of 200 nm, a carbon coating thickness of 15 nm, and a MgSiO3 layer content of 20 wt%.
[0057] The silicon-magnesium powder was placed in a tube furnace and heated at 600°C for 3 hours in a carbon dioxide atmosphere with a gas flow rate of 50 mL / min. Then, it was switched to an inert atmosphere and heated at 1000°C for 2 hours. After natural cooling, the negative electrode composite material of this embodiment was obtained.
[0058] Comparative Example 1 Silicon particles with a Dv50 of 10 μm were mixed with ethanol to prepare a slurry with a solid content of 5 wt%. The slurry was milled for 12 h and then dried at 60 °C to obtain the negative electrode composite material of this comparative example.
[0059] Comparative Example 2 150g of untreated magnesium powder was immersed in 0.1M NaOH solution at 80℃ for the first immersion treatment. After 10 minutes, the powder was filtered and washed to obtain the first magnesium powder.
[0060] Silicon particles with a Dv50 of 10 μm were ground and mixed with first magnesium powder accounting for 1 wt% of the silicon particles to obtain a mixture. The mixture was then mixed with ethanol to prepare a slurry with a solid content of 5 wt%. The slurry was sand-milled for 12 h and then dried at 60 °C to obtain a mixture of first magnesium powder and nano-silicon oxide.
[0061] The mixture of magnesium powder and nano-silicon oxide was placed in a tube furnace and heated at 600°C for 3 hours in a carbon dioxide atmosphere with a gas flow rate of 50 mL / min. Then, it was switched to an inert atmosphere and heated at 1000°C for 2 hours. After natural cooling, the negative electrode composite material of this comparative example was obtained.
[0062] Comparative Example 3 150g of untreated magnesium powder was soaked in 0.1M NaOH solution at 80℃ for the first impregnation treatment. After 10 minutes, it was filtered and washed to obtain the first magnesium powder. Under ice-water bath conditions, the first magnesium powder was soaked in 1L of solution containing 10g of dopamine. The mixture was stirred for 1 hour, then heated to 37°C, the pH was controlled at 8.5, and it was stirred again for 6 hours. After filtration, washing and drying, the second magnesium powder was obtained.
[0063] Silicon particles with a Dv50 of 10 μm were ground and mixed with a second magnesium powder accounting for 1 wt% of the silicon particles to obtain a mixture of the second magnesium powder and silicon particles.
[0064] The mixture of second magnesium powder and silicon particles was placed in a tube furnace and heated at 600°C for 3 hours in a carbon dioxide atmosphere with a gas flow rate of 50 mL / min. Then, it was switched to an inert atmosphere and heated at 1000°C for 2 hours. After natural cooling, the negative electrode composite material of this comparative example was obtained.
[0065] Comparative Example 4 150g of untreated magnesium powder was soaked in 0.1M NaOH solution at 80°C for the first impregnation treatment. After 10 minutes, it was filtered and washed to obtain the first magnesium powder. Under ice-water bath conditions, the first magnesium powder was soaked in 1L of solution containing 10g of dopamine. The mixture was stirred for 1 hour, then heated to 37°C, the pH was controlled at 8.5, and it was stirred again for 6 hours. After filtration, washing and drying, the second magnesium powder was obtained.
[0066] Silicon particles with a Dv50 of 10 μm were ground and mixed with magnesium powder comprising 3 wt% of the silicon particles to obtain a mixture. The mixture was then mixed with ethanol to prepare a slurry with a solid content of 5 wt%. The slurry was sand-milled for 12 h and then dried at 60 °C to obtain silicon-magnesium powder. The prepared nano-silicon had a Dv50 of 200 nm, a carbon coating thickness of 15 nm, and a MgSiO3 layer content of 12.5 wt%.
[0067] The silicon-magnesium powder was placed in a tube furnace and heated at 1000℃ for 5 hours in an inert atmosphere with a gas flow rate of 50 mL / min. After natural cooling, the negative electrode composite material of this comparative example was obtained.
[0068] Test Example 1 The negative electrode composite materials prepared in Examples 1-3 and Comparative Examples 1-4 were used as negative electrode materials for coin cells, and lithium sheets were used as positive electrode materials for coin cells. 1M LiPF6 solution (EC:DMC:EMC=1:1:1) was used as electrolyte to prepare coin cells.
[0069] The prepared coin cells were left to stand at room temperature for 8 hours before capacity testing. Specifically, a constant current charge-discharge experiment of 0.005~2V was conducted on the coin cells with a constant current of 180mA / g. The capacity retention rate of the cells after 300 cycles was calculated. The test results are shown in Table 1.
[0070] The test method for the first charge specific capacity is as follows: discharge at a constant current density of 180mA / g to 0.005V and record the first discharge specific capacity; then charge at a constant current density of 180mA / g to 2V to obtain the first charge specific capacity.
[0071] The test method for initial coulombic efficiency is: initial charge specific capacity / initial discharge specific capacity × 100%.
[0072] The test method for the specific capacity after 300 charge cycles is the same as the specific capacity test for the first charge.
[0073] The test method for capacity retention rate is: specific capacity after 300 charge cycles / specific capacity after the first charge × 100%.
[0074] Table 1 As can be seen from the data in Table 1, the examples show a significant improvement in first-charge efficiency and cycle capacity retention compared to the comparative examples. Specifically, with the increase in the amount of second magnesium powder added in the examples, the proportion of MgSiO3 phase in the prepared negative electrode composite material also increases, resulting in a more significant improvement in first-charge efficiency and cycle capacity retention. In Comparative Example 2, the first magnesium powder, which has not undergone dopamine polymerization, is difficult to disperse uniformly on the surface of silicon particles, leading to a poor effect in improving first-charge efficiency. In Comparative Example 3, silicon particles that have not undergone sand milling are used directly. On the one hand, the natural oxide layer distribution on the surface of the silicon particles is relatively random, which is unfavorable for the formation of the MgSiO3 phase; on the other hand, the cycle performance difference between large silicon particles and nano-silicon is significant, resulting in a severe deterioration in both capacity retention and first-charge efficiency. In Comparative Example 4, magnesium powder that has not been oxidized by carbon dioxide will directly reduce silicon oxide at high temperatures. Although the resulting nano-silicon improves the first-charge specific capacity, its stability decreases significantly.
[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A negative electrode composite material, characterized in that, The negative electrode composite material includes core particles and a carbon coating layer covering the surface of the core particles. The core particles include nano-silicon particles and a MgSiO3 layer that at least partially covers the surface of the nano-silicon particles.
2. The negative electrode composite material according to claim 1, characterized in that, Based on the total mass of the negative electrode composite material, the content of the MgSiO3 layer is 4~20wt%, preferably 5~10wt%.
3. The negative electrode composite material according to claim 1, characterized in that, The Dv50 of the nano-silicon particles is 100~300nm, preferably 150~250nm.
4. The negative electrode composite material according to claim 1, characterized in that, The thickness of the carbon coating layer is 5~30nm, preferably 10~20nm.
5. A method for preparing a negative electrode composite material, characterized in that, The preparation method includes the following steps: S1. Magnesium powder is placed in an alkaline solution for a first impregnation treatment, and after filtration and washing, a first magnesium powder is obtained; the first magnesium powder is placed in a solution containing dopamine monomer for a second impregnation treatment, and after filtration, washing and drying, a second magnesium powder is obtained. S2. Grind and mix the second magnesium powder with silicon particles to obtain a mixture, and mix the mixture with an organic medium to obtain a slurry; subject the slurry to sand milling and drying to obtain magnesium silicon powder; S3. The silicon-magnesium powder is calcined. The calcination process includes a first stage of calcination and a second stage of calcination. The first stage of calcination is carried out in an atmosphere containing carbon dioxide at a temperature of 500-600°C; the second stage of calcination is carried out in an inert atmosphere at a temperature of 800-1200°C.
6. The preparation method according to claim 5, characterized in that, The mass ratio of the first magnesium powder to the dopamine monomer is (13~16):1; and / or, The second magnesium powder accounts for 1-5 wt% of the mass of the silicon particles; and / or, The Dv50 of the silicon particles is 1~20μm; and / or, The solid content of the mixed slurry is 5~30wt%.
7. The preparation method according to claim 5, characterized in that, The alkaline solution includes at least one selected from NaOH solution, Na₂CO₃ solution, Na₂SiO₃ solution, Ca(OH)₂ solution, and NH₄OH; the molar concentration of the alkaline solution is 0.1~1 mol / L; and / or, The organic medium includes at least one of ethanol, isopropanol, ethylene glycol, and acetone.
8. The preparation method according to claim 5, characterized in that, The atmosphere containing carbon dioxide is a carbon dioxide atmosphere, or the atmosphere containing carbon dioxide is an inert mixed atmosphere with a carbon dioxide volume concentration of not less than 10%.
9. The preparation method according to claim 5, characterized in that, In step S1, the conditions for the first impregnation treatment include: a temperature of 60-80°C and a time of 10-20 min; and / or, the conditions for the second impregnation treatment include: a pH of 8-9, a temperature of 35-40°C, and a time of 5-7 h; and / or, In step S2, the sand milling process takes 5-20 hours; and / or, the drying process takes 40-80°C; and / or, In step S3, the calcination time for the first stage is 2-24 hours; the calcination time for the second stage is 2-5 hours.
10. A battery, characterized in that, The battery includes a negative electrode material, which includes the negative electrode composite material according to any one of claims 1 to 4 and / or the negative electrode composite material prepared by the method according to any one of claims 5 to 9.