A silicon-based negative electrode material and its preparation method and application

Abstract

The present invention provides a silicon-based anode material, its preparation method, and its application. The silicon-based anode material comprises a nano-silicon core and a vanadium nitride coating layer and a nitrogen-doped reduced graphene oxide coating layer sequentially stacked on the surface of the nano-silicon core. The silicon-based anode material of the present invention can enhance the conductivity and structural stability of the silicon-based anode during long-term cycling, thereby extending the battery life. Lithium-ion batteries made using the silicon-based anode material of the present invention exhibit both good long-term cycling performance and rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a silicon-based negative electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in a variety of applications, including mobile electronic devices, hybrid electric vehicles, and electric vehicles, due to their stable cycling performance, high volumetric / gravimetric energy density, and high power density. However, lithium-ion vehicles typically require several hours to fully charge to 80% state of charge (SOC), compared to just a few minutes for conventional fuel-powered vehicles. This means that higher power energy density and faster charging performance are two key parameters in the development of lithium-ion batteries. Therefore, developing new electrode materials with high energy density is key to achieving high-energy density systems.

[0003] Silicon (Si) has a high theoretical capacity of 4200mAh / g, which is 10 times that of commercial graphite anodes, making it the most promising alternative to commercial graphite anodes in the future. However, the silicon anode faces a huge volume expansion (>300%) during the lithium insertion / extraction process, which causes cracks on the particle surface and triggers the uncontrolled and continuous formation of the solid electrolyte interface (SEI), resulting in the failure of the conductive contacts between the active particles and the collapse of the electrode structure, which leads to a rapid deterioration of the battery capacity and even safety issues. In addition, silicon material is a common semiconductor material. Its poor intrinsic conductivity causes a large internal resistance of the battery and cannot withstand high-rate cycling. The above shortcomings seriously limit its commercial application.

[0004] CN112164779A discloses a carbon-coated silicon-based negative electrode material and its preparation method. The preparation method comprises the following steps: uniformly mixing a lithium source and a silicon source, heating the mixture under an inert atmosphere to perform a pre-lithiation reaction, then adding an organic carbon source, and continuing to heat the mixture to perform high-temperature calcination. The temperature does not drop during the pre-lithiation reaction to the high-temperature calcination, thereby obtaining a carbon-coated silicon-based negative electrode material.

[0005] CN108091848A discloses a carbon-coated mesoporous silicon-based negative electrode material and a preparation method thereof. The mesoporous silicon-based negative electrode material is prepared by directly coating a carbon source on the surface of a silicon source through a double template method and then calcining the carbon source.

[0006] The above scheme uses a carbon coating layer to improve the conductivity of the silicon negative electrode, buffer volume expansion and stabilize the SEI film. During the actual electrochemical cycle, the carbon layer is difficult to withstand the volume changes of silicon in long cycles. In addition, due to the uneven distribution of carbon, it will also aggravate the decline in silicon utilization. Summary of the Invention

[0007] The present invention aims to provide a silicon-based anode material, its preparation method, and its application. This silicon-based anode material can enhance the conductivity and structural stability of silicon-based anodes during long-term cycling, thereby extending battery life. Lithium-ion batteries fabricated using this silicon-based anode material exhibit both excellent long-term cycling performance and rate capability.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a silicon-based negative electrode material, comprising a nano-silicon core and a vanadium nitride coating layer and a nitrogen-doped reduced graphene oxide coating layer sequentially stacked on the surface of the nano-silicon core.

[0010] The silicon-based negative electrode material of the present invention is provided with a vanadium nitride coating layer and a nitrogen-doped reduced graphene oxide coating layer. The introduction of VN, on the one hand, provides a fast electron transmission channel, improves the conductivity of the silicon material, and enhances the rate performance of the silicon negative electrode in long cycles; on the other hand, the high mechanical strength VN particles act as a buffer layer to restrict the local expansion of the silicon material, avoid direct contact between silicon and the electrolyte, effectively reduce the interface side reaction, and further improve the structural stability of the silicon negative electrode in long cycles. There are a large number of vacancies and defects in the structure of the nitrogen-doped reduced graphene oxide coating layer, which promotes the Li + The diffusion rate of the composite material is improved, which improves the electronic conductivity and electrochemical activity of the composite material. At the same time, the three-dimensional graphene matrix can evenly disperse the silicon nanoparticles and prevent their agglomeration, buffering the volume effect of silicon during the lithiation process, and further improving the long-term cycle performance of the composite material.

[0011] Preferably, the thickness of the vanadium nitride coating layer is 8 to 20 nm, for example, 8 nm, 10 nm, 12 nm, 15 nm or 20 nm.

[0012] Preferably, the thickness of the nitrogen-doped reduced graphene oxide coating layer is 5 to 30 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm or 30 nm.

[0013] Preferably, the mass fraction of carbon element in the silicon-based negative electrode material is 20-35%, for example, 20%, 22%, 25%, 30% or 35%.

[0014] Preferably, the median particle size D50 of the silicon-based negative electrode material is 4 to 25 μm, for example, 4 μm, 8 μm, 10 μm, 15 μm or 25 μm.

[0015] Preferably, the resistivity of the silicon-based negative electrode material is 1 to 6 Ω·cm, for example, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm or 6 Ω·cm.

[0016] Preferably, the capacity of the silicon-based negative electrode material is 1400 to 2600 mAh / g, for example, 1400 mAh / g, 1500 mAh / g, 1800 mAh / g, 2000 mAh / g or 2600 mAh / g.

[0017] In a second aspect, the present invention provides a method for preparing the silicon-based negative electrode material according to the first aspect, the preparation method comprising the following steps:

[0018] (1) performing an amino modification treatment on the nano-silicon particles after grafting treatment to obtain modified silicon;

[0019] (2) mixing the vanadium source, the modified silicon and the graphene oxide with a solvent, and performing a solvothermal reaction to obtain a composite material;

[0020] (3) performing an ammonia reduction reaction on the composite material obtained in step (2) to obtain the silicon-based negative electrode material.

[0021] The present invention adopts a solvent-thermal self-assembly method and a one-step nitridation reaction to coat the surface of nano-silicon with a vanadium nitride layer (VN), which is evenly distributed on three-dimensional graphene nanosheets. A vanadium nitride-coated nano-silicon / nitrogen-doped reduced graphene oxide (Si@VN / N-dopedrGO) composite material is successfully prepared.

[0022] Preferably, the grafting treatment in step (1) comprises dispersing silicon nanoparticles in a mixed solution and grafting hydroxyl groups on the surface of the silicon nanoparticles to form silanols.

[0023] Preferably, the mixed solution comprises H2SO4 and H2O2.

[0024] Preferably, the volume ratio of H2SO4 and H2O2 is (2-4):1, for example: 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, etc.

[0025] Preferably, the temperature of the grafting treatment is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C.

[0026] Preferably, the grafting treatment is followed by filtering, washing and drying.

[0027] Preferably, the amino modification treatment comprises mixing the silanol obtained by the grafting treatment with 3-aminopropyltriethoxysilane and performing a stirring treatment.

[0028] Preferably, the vanadium source in step (2) includes sodium metabisulphate.

[0029] Preferably, the mass ratio of the modified silicon to the vanadium source is 1:(0.2-0.4), for example: 1:0.2, 1:0.25, 1:0.3, 1:0.35 or 1:0.4, etc.

[0030] Preferably, the mass ratio of the modified silicon to graphene oxide is 1:(1.5-2), for example: 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc.

[0031] Preferably, the solvent comprises a polar solvent.

[0032] Preferably, the solvent comprises ethanol and / or water.

[0033] Preferably, the temperature of the solvothermal reaction is 120-180°C, for example, 120°C, 130°C, 140°C, 160°C or 180°C.

[0034] Preferably, the solvent thermal reaction time is 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0035] Preferably, the solvothermal reaction is followed by freeze-drying.

[0036] Preferably, the freeze-drying treatment time is 20 to 30 hours, for example, 20 hours, 22 hours, 25 hours, 28 hours or 30 hours.

[0037] Preferably, the temperature of the ammonia reduction reaction in step (3) is 500-700°C, for example, 500°C, 550°C, 600°C, 650°C or 700°C.

[0038] Preferably, the ammonia reduction reaction time is 0.5 to 1.5 h, for example, 0.5 h, 0.8 h, 1 h, 1.2 h or 1.5 h.

[0039] Preferably, the flow rate of ammonia gas introduced into the ammonia reduction reaction is 100-200 sccm, for example, 100 sccm, 120 sccm, 150 sccm, 180 sccm or 200 sccm.

[0040] The equation for the ammonia reduction reaction of the present invention is as follows:

[0041] 3V2O5+10NH3→6VN+2N2↑+15H2O↑

[0042] In a third aspect, the present invention provides a negative electrode plate, wherein the negative electrode plate comprises the silicon-based negative electrode material as described in the first aspect.

[0043] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the negative electrode sheet as described in the third aspect.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) A vanadium nitride coating layer and a nitrogen-doped reduced graphene oxide coating layer are provided on the surface of the silicon-based negative electrode material of the present invention. The introduction of VN provides a fast electron transmission channel, improves the electrical conductivity of the silicon material, and enhances the rate performance of the silicon negative electrode in long cycles.

[0046] (2) In the silicon-based negative electrode material of the present invention, the VN particles with high mechanical strength act as a buffer layer to restrict the local expansion of the silicon material, avoid direct contact between silicon and the electrolyte, effectively reduce the interface side reaction, and further improve the structural stability of the silicon negative electrode in long cycles. There are a large number of vacancies and defects in the structure of the nitrogen-doped reduced graphene oxide coating layer, which promotes the Li + The diffusion rate of the composite material is improved, which improves the electronic conductivity and electrochemical activity of the composite material.

[0047] (3) In the silicon-based negative electrode material of the present invention, the three-dimensional graphene matrix can evenly disperse silicon nanoparticles and prevent their agglomeration, buffering the volume effect of silicon during the lithiation process, and further improving the long-term cycle performance of the composite material.

[0048] (4) The capacity of the battery made of the silicon-based negative electrode material of the present invention can reach more than 2174mAh / g, 1Ag -1 / 0.1Ag -1 The rate performance can reach more than 82%, the capacity retention rate after 100 cycles at 0.2A / g can reach more than 86%, and the resistivity can reach below 1.6Ω·cm. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic structural diagram of the silicon-based negative electrode material described in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] Example 1

[0052] This embodiment provides a silicon-based negative electrode material, and the preparation method of the silicon-based negative electrode material is as follows:

[0053] (1) 3 g of nano-silicon powder was dispersed in a mixture of 45 mL of sulfuric acid (H2SO4) and 15 mL of hydrogen peroxide (H2O2), stirred in a water bath at 80 ° C for 6 h, then the mixture was filtered, washed, and dried in a 60 ° C forced air oven for 24 h to obtain pretreated Si-OH. Then, 32 mL of 3-aminopropyltriethoxysilane (APTES) and 0.8 g of Si-OH were added to a beaker containing 500 mL of deionized water. After magnetic stirring at room temperature for 12 h, the mixture was centrifuged and washed to remove excess APTES. The product was dried in a 60 ° C forced air oven for 24 h to obtain Si particles modified with -NH2 groups (Si-APTES).

[0054] (2) 0.33 g Si-APTES, 0.09 g ammonium metavanadate (NH4VO3) and 100 mL GO (5.7 mg / mL) were mixed, ultrasonicated for 30 min, and stirred continuously for 4 h. The mixed liquid was transferred to the lining of a high-temperature reactor and continuously hydrothermally treated at 160 °C for 10 h. After the product was cooled to room temperature, it was centrifuged, washed, and freeze-dried for 24 h to prepare silicon surface-coated V2O5 layer / graphene oxide (Si@V2O5 / GO);

[0055] (3) The Si@V2O5 / GO was heated to 600°C at a heating rate of 5°C / min under the protection of an ammonia atmosphere, 150 sccm NH3 was introduced, and nitridation treatment was performed for 1 hour. After natural cooling, the silicon-based negative electrode material was obtained.

[0056] The structural diagram of the silicon-based negative electrode material is as follows Figure 1 As shown, the XRD test spectrum of the silicon-based negative electrode material of the present invention has plane diffraction peaks such as (111), (220), (311) and (331) corresponding to Si at at least one of 27-29°, 46-48°, 55-57° and 75-77°. The high-resolution V2p spectrum in the XPS test spectrum can be divided into three characteristic peaks at 518, 516 and 514 eV, corresponding to V 5+ , V 4+ and V 3+ Three valence states.

[0057] Example 2

[0058] This embodiment provides a silicon-based negative electrode material, and the preparation method of the silicon-based negative electrode material is as follows:

[0059] (1) 3 g of nano-silicon powder was dispersed in a mixture of 40 mL of sulfuric acid (H2SO4) and 12 mL of hydrogen peroxide (H2O2), stirred in a water bath at 82 ° C for 6 h, then the mixture was filtered, washed, and dried in a 63 ° C forced air oven for 24 h to obtain pretreated Si-OH. Then, 32 mL of 3-aminopropyltriethoxysilane (APTES) and 0.8 g of Si-OH were added to a beaker containing 500 mL of deionized water. After magnetic stirring at room temperature for 12 h, the mixture was centrifuged and washed to remove excess APTES. The product was dried in a 60 ° C forced air oven for 24 h to obtain Si particles modified with -NH2 groups (Si-APTES).

[0060] (2) 0.33 g Si-APTES, 0.08 g ammonium metavanadate (NH4VO3) and 100 mL GO (5.7 mg / mL) were mixed, ultrasonicated for 30 min, and stirred continuously for 4 h. The mixed liquid was transferred to the lining of a high-temperature reactor and continuously hydrothermally treated at 160 °C for 10 h. After the product was cooled to room temperature, it was centrifuged, washed, and freeze-dried for 24 h to prepare silicon surface-coated V2O5 layer / graphene oxide (Si@V2O5 / GO);

[0061] (3) Si@V2O5 / GO was heated to 620°C at a heating rate of 5°C / min under the protection of an ammonia atmosphere, 160 sccm NH3 was introduced, and nitridation treatment was performed for 1 hour. After natural cooling, the silicon-based negative electrode material was obtained.

[0062] Example 3

[0063] The only difference between this embodiment and embodiment 1 is that the amount of ammonium metavanadate added is 0.06 g, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0064] Example 4

[0065] The only difference between this embodiment and embodiment 1 is that the amount of ammonium metavanadate added is 0.12 g, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0066] Example 5

[0067] The only difference between this embodiment and embodiment 1 is that the amount of graphene oxide added is 80 mL (5.7 mg / mL), and the other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 6

[0069] The only difference between this embodiment and embodiment 1 is that the amount of graphene oxide added is 120 mL (5.7 mg / mL), and the other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Comparative Example 1

[0071] The only difference between this comparative example and Example 1 is that graphene oxide is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Comparative Example 2

[0073] The only difference between this comparative example and Example 1 is that no vanadium source is added, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Performance testing:

[0075] The silicon-based negative electrode materials obtained in Examples 1-6 and Comparative Examples 1-2 were weighed in a mass ratio of active material: conductive agent (super-p) and polyacrylic acid (PAA) = 8:1:1. The active material and conductive agent (super-p) were first placed in an agate mortar and dry-ground for 15 minutes to mix the two materials evenly. The mixture was then transferred to a glass bottle, polyacrylic acid (PAA) and an appropriate amount of deionized water were added, and the mixture was sealed and stirred continuously at 800 rpm for 4 hours to form a uniform slurry. The slurry was then coated on a clean copper foil by a doctor blade method with a coating thickness of about 200 μm. The electrode was then placed in a vacuum drying oven at 80°C and vacuum dried for 12 hours. After natural cooling, the electrode was punched into discs with a diameter of 14 mm using a slicer for standby use. The loading amount of active material in the electrode was about 1.8 to 2 mg / cm 2 .

[0076] S2: Assembling the battery

[0077] The assembly of CR2032 button cells was carried out in a glove box filled with Ar gas, where the contents of H2O and O2 were kept below 0.1 ppm, using an electrolyte of 1MLiPF6 (EC:DMC=1:1 vol%) + 6% FEC and a PP separator.

[0078] S3: Electrochemical performance test analysis

[0079] At room temperature, constant current charge and discharge tests were performed using a LANDCT2001A battery test system with a test voltage range of 0.01 to 1.5 V. The resistivity of the silicon-based composite negative electrode material was tested using a four-probe powder conductivity tester. The test results are shown in Table 1:

[0080] Table 1

[0081]

[0082]

[0083] As can be seen from Table 1, according to Examples 1-2, the capacity of the battery made of the silicon-based negative electrode material of the present invention can reach more than 2174 mAh / g, and 1Ag -1 / 0.1Ag -1 The rate performance can reach more than 82%, the capacity retention rate after 100 cycles at 0.2A / g can reach more than 86%, and the resistivity can reach below 1.6Ω·cm.

[0084] By comparing Example 1 with Examples 3-4, it can be seen that in the preparation process of the silicon-based negative electrode material of the present invention, the mass ratio of modified silicon and vanadium source will affect its performance. When the mass ratio of modified silicon and vanadium source is controlled at 1: (0.2-0.4), the performance of the silicon-based negative electrode material obtained is better. If the amount of vanadium source added is too large, the proportion of inactive substances increases, resulting in a decrease in the capacity of the material electrode at the same surface density; if the amount of vanadium source added is too small, not only the mechanical stability of the composite material structure is reduced, but also the internal resistance of the battery is increased, Li + The transmission channel slows down.

[0085] From the comparison between Example 1 and Examples 5-6, it can be seen that in the preparation process of the silicon-based negative electrode material of the present invention, the mass ratio of modified silicon and graphene oxide will affect its performance. When the mass ratio of modified silicon and graphene oxide is controlled at 1: (1.5-2), the performance of the silicon-based negative electrode material is better. If the amount of graphene oxide added is too large, a larger specific surface area and more surface defects will be generated, thereby resulting in excessive consumption of Li in the first discharge. + , resulting in a decrease in the first efficiency of the battery; if the amount of graphene oxide added is too small, it will slow down the Li + De-embedding reduces capacity.

[0086] Comparison of Example 1 and Comparative Example 1 reveals that the introduction of VN, on the one hand, provides a fast electron transport channel, improving the electrical conductivity of the silicon material and enhancing the rate performance of the silicon anode in long cycles. On the other hand, the high-mechanical-strength VN particles act as a buffer layer, restricting the local expansion of the silicon material and preventing direct contact between silicon and the electrolyte, effectively mitigating interfacial side reactions and further improving the structural stability of the silicon anode in long cycles. The presence of numerous vacancies and defects in the nitrogen-doped reduced graphene oxide coating promotes the diffusion rate of Li+ and enhances the electronic conductivity and electrochemical activity of the composite material.

[0087] From the comparison between Example 1 and Comparative Example 2, it can be seen that the three-dimensional graphene matrix can evenly disperse silicon nanoparticles and prevent their agglomeration, buffer the volume effect of silicon during the lithiation process, and further improve the long-term cycle performance of the composite material.

[0088] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a silicon-based negative electrode material, characterized in that: The silicon-based negative electrode material comprises a nano-silicon core and a vanadium nitride coating layer and a nitrogen-doped reduced graphene oxide coating layer sequentially stacked on the surface of the nano-silicon core; The method for preparing the silicon-based negative electrode material comprises the following steps: (1) performing an amino modification treatment on the nano-silicon particles after grafting treatment to obtain modified silicon; (2) mixing the vanadium source, the modified silicon and the graphene oxide with a solvent, and performing a solvothermal reaction to obtain a composite material; (3) performing an ammonia reduction reaction on the composite material obtained in step (2) to obtain the silicon-based negative electrode material.

2. The preparation method according to claim 1, wherein The thickness of the vanadium nitride coating layer is 8 to 20 nm.

3. The preparation method according to claim 1, wherein The thickness of the nitrogen-doped reduced graphene oxide coating layer is 5 to 30 nm.

4. The preparation method according to claim 1, wherein The mass fraction of carbon element in the silicon-based negative electrode material is 20-35%.

5. The preparation method according to claim 1, wherein The median particle size D50 of the silicon-based negative electrode material is 4 to 25 μm.

6. The preparation method according to claim 1, wherein The resistivity of the silicon-based negative electrode material is 1 to 6 Ω·cm.

7. The preparation method according to claim 1, wherein The capacity of the silicon-based negative electrode material is 1400 to 2600 mAh / g.

8. The preparation method according to claim 1, wherein The grafting treatment in step (1) includes dispersing silicon nanoparticles in a mixed solution and grafting hydroxyl groups on the surface of the silicon nanoparticles to form silanols.

9. The preparation method according to claim 8, wherein The mixed solution includes H2SO4 and H2O2.

10. The preparation method according to claim 9, characterized in that The volume ratio of H2SO4 and H2O2 is (2-4):

1.

11. The preparation method according to claim 1, wherein The temperature of the grafting treatment is 70-90°C.

12. The preparation method according to claim 1, wherein The grafting process is followed by filtering, washing and drying.

13. The preparation method according to claim 1, wherein The amino modification treatment includes mixing the silanol obtained by the grafting treatment and 3-aminopropyltriethoxysilane and performing a stirring treatment.

14. The preparation method according to claim 1, wherein The vanadium source in step (2) includes sodium metavanadate.

15. The preparation method according to claim 1, wherein The mass ratio of the modified silicon to the vanadium source is 1:(0.2-0.4).

16. The preparation method according to claim 1, wherein The mass ratio of the modified silicon to graphene oxide is 1:(1.5-2).

17. The preparation method according to claim 1, wherein The solvent includes a polar solvent.

18. The preparation method according to claim 1, wherein The solvent includes ethanol and / or water.

19. The preparation method according to claim 1, wherein The temperature of the solvent thermal reaction is 120-180°C.

20. The preparation method according to claim 1, wherein The solvent thermal reaction time is 8 to 12 hours.

21. The preparation method according to claim 1, wherein The solvent thermal reaction is followed by freeze drying.

22. The preparation method according to claim 21, wherein The freeze-drying treatment time is 20 to 30 hours.

23. The preparation method according to claim 1, wherein The temperature of the ammonia reduction reaction in step (3) is 500-700°C.

24. The preparation method according to claim 1, wherein The ammonia reduction reaction time is 0.5 to 1.5 hours.

25. The preparation method according to claim 1, wherein The flow rate of ammonia introduced into the ammonia reduction reaction is 100-200 sccm.

26. A negative electrode plate, characterized in that: The negative electrode plate comprises a silicon-based negative electrode material prepared by the preparation method according to any one of claims 1 to 25.

27. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 26.

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