Silicon-carbon composite material, preparation method thereof and negative electrode sheet containing same

Abstract

This disclosure relates to a silicon-carbon composite material, its preparation method, and a negative electrode sheet comprising the same. The preparation method includes the following steps: oxidizing a silicon surface; mixing the oxidized silicon with a silane coupling agent to obtain modified silicon; mixing the modified silicon with a liquid carbon source and sintering to obtain the silicon-carbon composite material. This disclosure, by oxidizing and modifying the silicon surface, can significantly improve the bonding strength between silicon and carbon layers, effectively improve the interfacial state between silicon and carbon, and enhance the cycle stability of the silicon-carbon composite material, thereby enabling lithium-ion batteries using this silicon-carbon composite material to exhibit excellent cycle stability.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery material preparation technology, and in particular to a silicon-carbon composite material and its preparation method, and a negative electrode sheet containing the same. Background Technology

[0002] Silicon has become an important anode material for high-energy-density lithium-ion batteries due to its advantages such as high theoretical specific capacity, low lithiation potential, and abundant reserves. However, the large volume expansion effect and low conductivity of silicon anodes limit their further application and commercialization.

[0003] To address the problems associated with silicon materials, domestic and international research has mainly focused on the following aspects: ① Nanostructuring, which reduces the size of silicon materials to alleviate the volume effect caused by expansion, such as nanoparticles, nanowires, and nanotubes; ② Porosity, which utilizes the well-developed pore structure inside the material to alleviate volume expansion during charging and discharging; ③ Preparation of composite materials, which combines silicon and carbon. Carbon materials have certain mechanical strength and high conductivity, which can both alleviate the expansion of silicon materials and increase the conductivity of composite materials.

[0004] Preparing composite materials by combining silicon and carbon is an effective way to solve the above problems. Coating the surface of silicon particles with carbon materials such as amorphous carbon, graphene, and carbon nanotubes can alleviate the volume expansion effect of silicon and solve problems such as the low conductivity of silicon materials. However, the surface of pure silicon is very inert and cannot chemically react with the coated carbon materials. The two are only connected by van der Waals forces. During battery cycling, silicon is prone to detach from the surface carbon layer, affecting the cycling stability of the material. Summary of the Invention

[0005] To address the aforementioned technical problems, this disclosure provides a silicon-carbon composite material, a method for preparing the same, and a negative electrode sheet comprising the same.

[0006] In a first aspect, this disclosure provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0007] Oxidize the silicon surface;

[0008] The oxidized silicon was mixed with a silane coupling agent and reacted to obtain modified silicon.

[0009] The modified silicon was mixed with a liquid carbon source and sintered to obtain the silicon-carbon composite material.

[0010] In this disclosure, the silicon surface is oxidized to form a modifiable surface, and then the oxidized surface is modified to ensure excellent bonding between the subsequent carbon coating layer and the silicon core, effectively improving the interface state between silicon and carbon. Ultimately, when the obtained silicon-carbon composite material is used as the lithium anode of a lithium-ion battery, the battery exhibits excellent cycle stability.

[0011] As a preferred embodiment of this disclosure, the mass ratio of the oxidized silicon to the silane coupling agent is (30-200):1, for example, 50:1, 80:1, 100:1, 120:1, 150:1, 180:1, etc., and more preferably (50-150):1.

[0012] This disclosure utilizes a silane coupling agent to modify the surface of oxidized silicon. Under acidic or alkaline conditions, the silane coupling agent can hydrolyze and undergo a hydrolysis-condensation reaction with the hydroxyl groups on the oxidized silicon surface to introduce the silane coupling agent. The introduction of the silane coupling agent can significantly improve the bonding strength between silicon and carbon layers, effectively improve the interfacial state between silicon and carbon, and thus improve the cycle stability of silicon-carbon composite materials.

[0013] When the amount of silane coupling agent added is too small, it cannot effectively improve the bonding strength between the silicon surface and the carbon layer. When the amount of silane coupling agent added is too large, due to the introduction of too many oxygen atoms, the residual oxygen value in the resulting silicon-carbon composite material is too high, which will have a great adverse effect on the first coulombic efficiency of the lithium-ion battery using it.

[0014] As a preferred embodiment of this disclosure, the modification is carried out under acidic conditions.

[0015] As a preferred embodiment of this disclosure, the silane coupling agent is selected from silane coupling agents containing epoxy groups and / or silane coupling agents containing hydroxyl groups.

[0016] In this disclosure, by adding a specific amount of silane coupling agent containing epoxy groups or hydroxyl groups, uniformly distributed epoxy groups or hydroxyl groups can be formed on the silicon surface. Through hydrogen bonding and electronegativity between the epoxy groups or hydroxyl groups and the liquid carbon source, the modified silicon can be uniformly dispersed in the liquid carbon source, forming a uniform liquid film on the silicon surface and thus achieving uniform carbon layer deposition. At the same time, the hydrogen bonds can form covalent bonds after subsequent sintering, thereby significantly improving the bonding strength between silicon and the carbon layer.

[0017] As a preferred embodiment of this disclosure, the silane coupling agent is selected from any one or a combination of at least two of 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, or glycidyl oxypropyltrimethoxysilane.

[0018] As a preferred technical solution of this disclosure, the silicon in step (1) is selected from any one or a combination of two or more of the following: silicon nanoparticles, silicon nanowires, silicon nanowafers or porous silicon nanoparticles.

[0019] As a preferred technical solution of this disclosure, the silicon in step (1) has a size of 10-500nm, such as 20nm, 50nm, 100nm, 200nm, 300nm, 400nm, etc., preferably 50-200nm.

[0020] This disclosure enables the production of silicon-carbon composite materials with extremely excellent interfacial stability by selecting nano-silicon of a specific size and combining it with a specific amount of silane coupling agent.

[0021] As a preferred technical solution of this disclosure, the oxidation method in step (1) includes oxidation using an oxidizing agent.

[0022] This disclosure utilizes an oxidant to oxidize the silicon surface. Under acidic conditions, the alkoxy groups in the silane coupling agent hydrolyze into hydroxyl groups, which then hydrolyze and condense with the hydroxyl groups on the oxidized silicon surface. This allows the silane coupling agent to bind to the silicon surface. Simultaneously, the introduced silane coupling agent and the liquid nitrogen source have hydrogen bonding interactions, which can form covalent bonds after sintering. This significantly improves the bonding strength between silicon and carbon layers, enhances the interfacial state between silicon and carbon, and improves the cycle stability of silicon-carbon composite materials.

[0023] As a preferred embodiment of this disclosure, the oxidant is selected from hydrogen peroxide or piranha solution.

[0024] The piranha solution is a mixture of concentrated sulfuric acid and 30% hydrogen peroxide.

[0025] As a preferred technical solution of this disclosure, the liquid carbon source in step (3) is selected from any one or a combination of at least two of pyridine, pyrrole, aniline, piperidine, pyrimidine, pyran or wash oil.

[0026] As a preferred technical solution of this disclosure, the liquid carbon source is selected from any one or a combination of at least two of pyridine, pyrrole, aniline or wash oil.

[0027] The liquid carbon source selected in this disclosure can form hydrogen bonds and other interactions with the modified silicon, enabling the liquid carbon source to form a uniform liquid film on the silicon surface, thereby ensuring the formation of a uniformly coated carbon layer during subsequent sintering. Furthermore, during sintering, the hydrogen bonds can be transformed into covalent bonds, increasing the interfacial bonding force between silicon and carbon, ensuring that the silicon and the surface carbon layer will not separate during subsequent applications, thus ensuring the cycle stability of the lithium-ion battery.

[0028] This disclosure does not impose any particular limitation on the mixing method. Any mixing method that can make the modified silicon and the liquid carbon source evenly mixed is applicable to this disclosure. Preferably, ultrasonic dispersion is performed for 15-60 min, such as 20 min, 30 min, 40 min, 50 min, etc., followed by stirring for 6-12 h, such as 7 h, 8 h, 9 h, 10 h, 11 h, etc.

[0029] As a preferred technical solution of this disclosure, the mass-volume ratio of the modified silicon to the liquid carbon source in step (3) is 0.5g:(2-10)mL, for example 0.5g:3mL, 0.5g:4mL, 0.5g:5mL, 0.5g:6mL, 0.5g:7mL, etc. The mass-volume ratio of silicon to liquid carbon source means that the ratio between silicon and liquid carbon source is 0.5g of silicon to 2-10mL of liquid carbon source.

[0030] As a preferred technical solution of this disclosure, the mass-to-volume ratio of the modified silicon to the liquid carbon source in step (3) is 0.5 g:(2-5) mL.

[0031] This disclosure allows for the control of the thickness of the carbon layer in the prepared silicon-carbon composite material particles by adjusting the amount of liquid carbon source added.

[0032] As a preferred technical solution of this disclosure, the sintering temperature in step (3) is 900-1100℃, such as 950℃, 1000℃, 1050℃, etc.

[0033] As a preferred technical solution of this disclosure, the sintering time in step (3) is 0.5-3h, for example 1h, 1.5h, 2h, 2.5h, etc.

[0034] In one specific embodiment of this disclosure, the sintering is carried out in an inert atmosphere in a vertical carbonization furnace, preferably N2 or Ar.

[0035] This disclosure also allows for the control of the thickness of the carbon layer in the silicon-carbon composite material particles by controlling the sintering temperature.

[0036] Secondly, this disclosure provides a silicon-carbon composite material prepared by the preparation method described in the first aspect.

[0037] The silicon-carbon composite material disclosed herein can effectively suppress the volume expansion of silicon during the lithiation process, and has excellent interfacial bonding stability between silicon and carbon, preventing silicon-carbon separation during application. Therefore, when used as a negative electrode material for lithium-ion batteries, it enables the batteries to have stable cycle performance.

[0038] Thirdly, this disclosure provides the application of the silicon-carbon composite material described in the second aspect in lithium-ion battery anode materials.

[0039] Fourthly, this disclosure provides a negative electrode comprising the silicon-carbon composite material described in the second aspect.

[0040] Fifthly, this disclosure provides an electrochemical device comprising the silicon-carbon composite material described in the second aspect or the negative electrode sheet described in the fourth aspect.

[0041] The technical solution provided in this disclosure has the following advantages compared with the prior art:

[0042] (1) This disclosure improves the bonding strength between silicon and carbon by oxidizing the silicon surface and then modifying the oxidized surface, thereby effectively improving the interface state between silicon and carbon, and finally making the silicon-carbon composite material used as the lithium anode of lithium-ion battery, so that the battery has excellent cycle stability.

[0043] (2) The preparation method of silicon-carbon composite material provided in this disclosure is simple. The silicon-carbon material is wrapped by graphite material, which has high uniformity and bonding strength. It can effectively suppress the volume expansion of silicon during the lithiation process and is suitable for industrial production. Detailed Implementation

[0044] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0045] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0046] Preparation Example 1

[0047] This preparation example provides a method for preparing a silicon-carbon composite material, including the following steps:

[0048] (1) Weigh 1g of 100nm diameter silicon nanoparticles and place them in a three-necked flask equipped with a magnetic stirrer and N2 protection. Add 20mL of anhydrous ethanol and mix well. Then add 40mL of 30wt% H2O2 aqueous solution and stir at 75℃ for 48h. Centrifuge at 10000rpm for 30min to obtain silicon oxide nanoparticles.

[0049] (2) Weigh 1g of silicon oxide nanoparticles and place them in a three-necked flask equipped with a magnetic stirrer and N2 protection. Add 40g of a mixture of deionized water and ethanol in a mass ratio of 1:3. After uniform dispersion, add concentrated hydrochloric acid to adjust the pH of the mixture to approximately 4. Then, add a total of 15mg of 3-glycidyl etheroxypropyltrimethoxysilane to the mixture. Stir and reflux at 70℃ for 10h to allow the hydrolyzed 3-glycidyl etheroxypropyltrimethoxysilane to undergo a dehydration condensation reaction with the silicon oxide nanoparticles. After the reaction is complete, centrifuge at 10000rpm for 30min and wash with ethanol at least three times. Dry under vacuum at 60℃ for 12h to obtain modified silicon nanoparticles.

[0050] (3) Disperse 500 mg of modified nano-silicon particles in 3 mL of pyridine, sonicate for 30 min, stir for 12 h to obtain a suspension, and gradually sinter and carbonize the suspension at 1000 °C for 1 h under a nitrogen atmosphere with a heating rate of 10 °C / min to obtain a silicon-carbon composite material.

[0051] Preparation Example 2

[0052] This preparation example provides a method for preparing a silicon-carbon composite material, including the following steps:

[0053] (1) Weigh 1g of silicon nanowires with a length of 200nm and place them in a three-necked flask equipped with magnetic stirring and N2 protection. Add 20mL of anhydrous ethanol and mix well. Then add 40mL of piranha solution and stir at 75℃ for 48h. Centrifuge at 10000rpm for 30min to obtain silicon oxide nanowires.

[0054] (2) Weigh 1g of silicon oxide nanowires and place them in a three-necked flask equipped with a magnetic stirrer and N2 protection. Add 40g of a mixture of deionized water and ethanol in a mass ratio of 1:3. After uniform dispersion, add concentrated hydrochloric acid to adjust the pH of the mixture to approximately 5. Then, add 10mg of 3-glycidyl etheroxypropyltriethoxysilane dropwise to the mixture. Stir and reflux at 70℃ for 10h to allow the hydrolyzed 3-glycidyl etheroxypropyltriethoxysilane to undergo a dehydration condensation reaction with the silicon oxide nanowires. After the reaction is complete, centrifuge at 10000rpm for 30min and wash with ethanol at least three times. Vacuum dry at 60℃ for 12h to obtain modified silicon nanowires.

[0055] (3) 500 mg of modified silicon nanowires were dispersed in 2 mL of pyrrole, sonicated for 15 min, and stirred for 12 h to obtain a suspension. The suspension was gradually sintered and carbonized at 900 °C for 3 h under a nitrogen atmosphere with a heating rate of 10 °C / min to obtain a silicon-carbon composite material.

[0056] Preparation Example 3

[0057] This preparation example provides a method for preparing a silicon-carbon composite material, including the following steps:

[0058] (1) Weigh 1g of silicon nanosheets with a length of 400nm and place them in a three-necked flask equipped with magnetic stirring and N2 protection. Add 20mL of anhydrous ethanol and mix well. Then add 40mL of piranha solution and stir at 75℃ for 48h. Centrifuge at 10000rpm for 30min to obtain silicon nanosheets of oxide.

[0059] (2) Weigh 1g of silicon oxide nanosheets and place them in a three-necked flask equipped with a magnetic stirrer and N2 protection. Add 40g of a mixed solution of deionized water and ethanol in a mass ratio of 1:3. After uniform dispersion, add concentrated hydrochloric acid to adjust the pH of the mixed solution to approximately 3. Then, add a total of 5mg of glycidyltrimethoxysilane dropwise to the mixed solution. Stir and reflux at 70℃ for 10h to allow the hydrolyzed glycidyltrimethoxysilane to undergo a dehydration condensation reaction with the silicon oxide nanosheets. After the reaction is complete, centrifuge at 10000rpm for 30min and wash with ethanol at least 3 times. Vacuum dry at 60℃ for 12h to obtain modified silicon nanosheets.

[0060] (3) Disperse 500mg of modified nano-silicon wafers in 5mL of pyran, sonicate for 15min, stir for 12h to obtain a suspension, and gradually sinter and carbonize the suspension at 1100℃ for 0.5h under a nitrogen atmosphere with a heating rate of 10℃ / min to obtain silicon-carbon composite material.

[0061] Preparation Example 4

[0062] This preparation example provides a method for preparing silicon-carbon composite materials.

[0063] The difference from Preparation Example 1 is that the liquid carbon source in step (3) is pyrimidine.

[0064] Preparation Examples 5-6

[0065] This preparation example provides a method for preparing silicon-carbon composite materials.

[0066] The difference from Preparation Example 1 is that in step (3), the mass-to-volume ratio of modified nano-silicon particles to liquid carbon source pyridine is 0.5 g: 1 mL (Preparation Example 5) and 0.5 g: 15 mL (Preparation Example 6), respectively.

[0067] Comparative Examples 1-2

[0068] This comparative example provides a method for preparing a silicon-carbon composite material. The difference from preparation example 1 is that in step (2), the mass ratio of oxidized silicon nanoparticles to the silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane is 10:1 (Comparative Example 1) and 300:1 (Comparative Example 2), respectively.

[0069] Comparative Example 3

[0070] This comparative example provides a method for preparing a silicon-carbon composite material. The difference from Preparation Example 1 is that the silane coupling agent in step (2) is 3-aminopropyltrimethoxysilane.

[0071] Comparative Example 4

[0072] This comparative example provides a method for preparing a silicon-carbon composite material, which differs from Preparation Example 1 in that no silane coupling agent is added in step (2).

[0073] Example

[0074] This embodiment provides a method for preparing a lithium-ion battery.

[0075] (1) The silicon-carbon composite material, sodium carboxymethyl cellulose, and acetylene black obtained in Preparation Examples 1-6 and Comparative Examples 1-4 were mixed in a mass ratio of 91:6:3. An appropriate amount of water was added to prepare an electrode slurry, which was coated on a copper foil. The copper foil coated with the electrode material was vacuum dried at 120°C for 12 hours. The copper foil coated with the electrode material was cut into circular electrode sheets with a diameter of 12 mm and held under a pressure of 8 MPa for 180 seconds to obtain an electrode sheet as a negative electrode.

[0076] (2) Using NCM622 with a diameter of 12 mm as the positive electrode, Celgard 2400 as the separator, and 1 mol / L lithium hexafluorophosphate as the electrolyte, with a solvent volume ratio of EC (ethylene carbonate):DEC (diethyl carbonate) = 1:1, a CR2032 coin cell was assembled, with 50 μL of electrolyte added. The entire battery assembly was completed in a glove box.

[0077] Performance testing

[0078] Testing: The full cells obtained from Preparation Examples 1-8 and Comparative Examples 1-2 were subjected to charge-discharge tests under the conditions of 500 mA / g and 100 cycles. The results are shown in Table 1.

[0079] Table 1

[0080]

[0081] As shown in Table 1, the silicon-carbon composite anode prepared by silicon oxidation modification in this disclosure enables lithium batteries to have very good capacity retention and cycle stability.

[0082] A comparison of Preparation Example 1 and Preparation Example 4 shows that the cycle stability of the lithium battery is slightly worse when the liquid carbon source is pyran or pyrimidine. A comparison of Preparation Example 1 and Preparation Examples 5-6 shows that when the amount of liquid carbon source added is too small, the initial reversible capacity and initial coulombic efficiency of the electrode are significantly improved, but the cycle stability is significantly reduced. Conversely, when the amount of liquid carbon source added is too large, the results are completely opposite: the initial reversible capacity and initial coulombic efficiency of the electrode decrease, but the cycle stability increases. A comparison of Preparation Example 1 and Comparative Examples 1-2 shows that when the amount of silane coupling agent is too small, the cycle stability of the lithium battery deteriorates; when the amount of silane coupling agent is too large, the initial coulombic efficiency of the lithium battery deteriorates. A comparison of Preparation Example 1 and Comparative Examples 3-4 shows that when no silane coupling agent is added or the silane coupling agent does not contain epoxy groups or hydroxyl groups, the cycle stability of the resulting lithium battery deteriorates.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0084] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily 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 this disclosure. Therefore, this disclosure is not to be limited to the embodiments described 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 silicon-carbon composite material, characterized by, The preparation method includes the following steps: Oxidize the silicon surface; The oxidized silicon was mixed with a silane coupling agent and reacted to obtain modified silicon. The modified silicon was mixed with a liquid carbon source and sintered to obtain the silicon-carbon composite material. The silane coupling agent is selected from silane coupling agents with epoxy groups and / or silane coupling agents with hydroxyl groups. The liquid carbon source is selected from any one or a combination of at least two of pyridine, pyrrole, aniline, piperidine, pyrimidine, pyran, or wash oil.

2. The production method according to claim 1, characterized by, The mass ratio of the oxidized silicon to the silane coupling agent is (30-200):

1.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the oxidized silicon to the silane coupling agent is (50-150):

1.

4. The preparation method according to claim 2 or 3, characterized in that, The silane coupling agent is selected from any one or a combination of at least two of 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, or glycidyl oxypropyltrimethoxysilane.

5. The preparation method according to any one of claims 1-3, characterized in that, The silicon is selected from any one or a combination of two or more of the following: silicon nanoparticles, silicon nanowires, or silicon nanowafers. And / or, the silicon has a size of 10-500 nm.

6. The preparation method according to claim 5, characterized in that, The nano-silicon particles are porous nano-silicon particles.

7. The preparation method according to claim 5, characterized in that, The silicon has a size of 50-200 nm.

8. The preparation method according to any one of claims 1-3, characterized in that, The oxidation method includes oxidation using an oxidizing agent.

9. The preparation method according to claim 8, characterized in that, The oxidant is selected from hydrogen peroxide or piranha solution.

10. The preparation method according to claim 9, characterized in that, The liquid carbon source is selected from any one or a combination of at least two of pyridine, pyrrole, aniline, or wash oil.

11. The preparation method according to any one of claims 1-3, characterized in that, The mass-to-volume ratio of the modified silicon to the liquid carbon source is 0.5 g:(2-10) mL.

12. The preparation method according to claim 11, characterized in that, The mass-to-volume ratio of the modified silicon to the liquid carbon source is 0.5 g:(2-5) mL.

13. The preparation method according to any one of claims 1-3, characterized in that, The sintering temperature is 900-1100℃ and the time is 0.5-3 h.

14. The silicon-carbon composite material prepared by the preparation method according to any one of claims 1-13.

15. The application of the silicon-carbon composite material according to claim 14 in lithium-ion battery anode materials.

16. A negative electrode sheet, characterized in that, It includes the silicon-carbon composite material as described in claim 14.

17. An electrochemical device, characterized in that, It comprises the silicon-carbon composite material of claim 14 or the negative electrode of claim 16.

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