A new silicon-carbon negative electrode material for high-stability and high-capacity lithium-ion battery and its preparation method

Abstract

The present invention provides a novel silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery and a preparation method thereof. The material is prepared by in-situ reaction of a silicon active material surface with a multi-component amorphous layer having a mosaic structure by one-step cracking of a halogen-containing organic carbon source and a lithium salt. The material can interact and tightly connect with the SiOx (1<x<2) layer on the silicon surface to form a strong electron-conducting network and an ion-conducting network, thereby effectively improving the cycle stability of the silicon negative electrode. The implementation process is simple and easy to scale up production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a silicon-carbon negative electrode material and a preparation method thereof. The technical problem to be solved is to improve the cycle performance of the silicon-carbon negative electrode material. Background Art

[0002] As the demand for energy density of lithium-ion batteries increases, the existing graphite anode is unlikely to meet future demand. The theoretical specific capacity of silicon to lithium ranks among the top common anode materials, at 4200mAh / g (Li 22 Si5), also has 3579mAh g at room temperature -1 (Li 15 Si4), and the working potential of silicon is moderate (~0.4V vs Li + / Li) is therefore widely considered to be a potential next-generation lithium-ion battery negative electrode material that can replace graphite. However, the silicon-based negative electrode undergoes a huge volume change (>300%) during the alloying process with lithium. This huge volume expansion and contraction can cause electrode pulverization, active material shedding, and continuous growth of the solid electrolyte interface (SEI) film. This greatly reduces the charge and discharge efficiency, causing the capacity of the lithium-ion battery to decay rapidly and reducing its cycle stability.

[0003] In view of the problems existing in silicon anodes, researchers have proposed a variety of improvement strategies, including nanoscale sizing, material compounding, optimization of composite structure design, and application of new binders and electrolyte additives. By compounding silicon with carbon materials, on the one hand, the overall electronic conductivity of the material is improved, and on the other hand, the composite phase provides a buffer for volume expansion, thereby improving the cycle stability of the silicon anode. However, the current carbon composite strategies that can effectively improve the cycle stability of silicon anodes either result in a silicon capacity of less than 800 mAh / g and a cycle life of no more than 100 cycles due to the relatively high content of the compounded carbon materials (CN112652757 A, CN 110400914A, CN 111977658 A, CN 112768663 A), or the preparation process is complex and difficult to scale up (CN 112331819A, CN 106207177 A). Application No. CN 106207177 A discloses a silicon-carbon anode material with an artificial SEI layer that has both high volumetric specific capacity and cycle performance. It requires complex preparation processes such as ball milling, spray drying, and carbonization, and the capacity after 300 cycles is less than 500 mAh / g. Application No. CN 112331819A discloses a preparation method for a modified silicon-carbon anode. It is prepared by configuring a nano-silicon mixed solution, preparing modified nano-silicon, adding a silane coupling agent to the nano-silicon mixed solution, and compounding with a carbon source. The silicon-carbon anode can reach a capacity of 1585 mAh / g after 100 cycles, but the preparation process is complex, the difficulty of consistent and mass production is high, the cost is high, and it is difficult to scale up production. Application No. CN 112652755 A discloses a silicon-carbon anode material and its preparation method. By mixing a silicon source and a carbon source, then roasting, and then blending with a lithium salt, the reversible capacity is as high as 2500 mAh / g. Since the lithium salt is physically blended rather than in-situ generated in this process, the cycle life may be less than 50 cycles due to uneven mixing. Currently, there are few reports on silicon-carbon anode materials that have both high cycle stability, high specific capacity, and a simple preparation process. Therefore, there is an urgent need to find a preparation technology for high-capacity and high-stability silicon-carbon anode materials. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a preparation method and application of a silicon-carbon composite anode material with both high specific capacity and cycle stability. By pyrolyzing a halogen-containing organic carbon source and a lithium salt in one step to in-situ react and coat a multi-component amorphous layer with a mosaic structure on the surface of silicon active substances, it can interact with the SiO x (1 < x < 2) layer on the silicon surface to form a strong electron conduction network and ion conduction network through close connection, effectively improving the cycle stability of the silicon anode, and the implementation process is simple and easy to scale up production.

[0005] The object of the present invention is achieved by the following technical solution: A method for preparing a silicon-carbon negative electrode material for a lithium-ion battery comprises the following steps:

[0006] (1) mixing a silicon source, a lithium salt, and a halogen-containing organic carbon source in a certain proportion;

[0007] (2) The powder obtained in step (1) is placed in an inert atmosphere or a vacuum environment for high-temperature heat treatment, and then cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0008] As a preferred solution, the silicon source is silicon powder, iron-silicon alloy powder or silicon-calcium alloy powder, and the particle size is 50-5000nm.

[0009] As a preferred embodiment, the lithium salt is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium phosphate, lithium acetate, lithium polyacrylate, lithium acetylacetonate, etc., and the preferred lithium salt is lithium carbonate.

[0010] As a preferred embodiment, the halogen-containing organic carbon source is one of polyvinylidene fluoride, polytetrafluoroethylene, perfluoropolyether, polyvinyl chloride, polyvinylidene chloride, etc., or a mixture of several thereof. The preferred halogen-containing organic carbon source is polyvinylidene fluoride.

[0011] As a preferred solution, the mass ratio of the silicon source to the halogen-containing organic carbon source is 5-50.

[0012] As a preferred solution, the temperature is raised to 400°C to 800°C at a rate of 0.5 to 10°C / min in an inert atmosphere, and carbonization is carried out for 0.5 to 24 hours. The inert atmosphere is one of high-purity nitrogen, helium, neon, and argon, or a mixture of several of them.

[0013] The process of the present invention is simple and easy to implement, with low cost. The silicon-carbon negative electrode material prepared by one-step cracking of the method has the characteristics of good conductivity, high specific capacity, small volume change, etc.; it effectively solves the problem of structural damage caused by volume expansion, and improves the service life and safety of lithium-ion batteries. Specifically, in the silicon-carbon composite material: the carbon material can not only buffer the volume change of the silicon negative electrode during the charge and discharge process, but also improve the conductivity of the silicon-based material, thereby avoiding the agglomeration of silicon particles during the charge and discharge cycle. In particular, the multi-component amorphous composite layer generated in situ by the reaction can stabilize the silicon negative electrode SEI film, further improve the cycle stability of the material, so that the silicon-carbon negative electrode material has excellent cycle stability while maintaining a high cycle specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of the silicon-carbon negative electrode material provided by the present invention.

[0015] Figure 2This is the XRD spectrum of the silicon-carbon negative electrode material obtained in Example 2.

[0016] Figure 3 This is the first charge and discharge cycle curve of the lithium-ion battery silicon-carbon negative electrode material obtained in Example 2. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below in conjunction with specific implementation modes.

[0018] Embodiment 1,

[0019] 500 mg of nano silicon powder (average particle size of 100 nanometers), 50 mg of polyvinyl chloride, and 32 mg of hydrated lithium hydroxide were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 600°C at 2°C / min and kept for 10 hours to obtain a LiCl-doped silicon-carbon composite material. The electrochemical performance of the material was tested.

[0020] Embodiment 2,

[0021] 500 mg of iron-silicon alloy powder, 50 mg of polyvinylidene fluoride, and 73 mg of lithium carbonate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 750°C at 2°C / min and kept for 5 hours to obtain a silicon-carbon composite negative electrode material. The obtained silicon-carbon negative electrode material was subjected to XRD pattern detection (such as Figure 2 ), a LiF-doped silicon-carbon composite material can be detected. The electrochemical performance of the material is tested.

[0022] Embodiment 3,

[0023] 500 mg of micron silicon powder, 25 mg of polyvinylidene chloride, and 78 mg of lithium acrylate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 700°C at 2°C / min and kept for 2 hours to obtain a silicon-carbon composite negative electrode material. A LiCl-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0024] Embodiment 4,

[0025] 500 mg of nano silicon powder, 25 mg of polyvinylidene chloride, and 50 mg of lithium nitrate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 700°C at 2°C / min and kept for 12 hours to obtain a silicon-carbon composite negative electrode material. A LiCl-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0026] Embodiment 5,

[0027] 500 mg of nano silicon powder, 25 mg of polyvinylidene fluoride, and 68 mg of lithium hydroxide were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 600°C at 1°C / min and kept for 15 hours to obtain a silicon-carbon composite negative electrode material. A LiF-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0028] Embodiment 6,

[0029] 500 mg of micron silicon powder, 25 mg of polytetrafluoroethylene, and 45 mg of lithium carbonate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 750°C at 1°C / min and kept for 3 hours to obtain a silicon-carbon composite negative electrode material. A LiF-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0030] Embodiment 7,

[0031] 500 mg of nano silicon powder, 30 mg of polyvinylidene fluoride, and 78 mg of lithium sulfate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 650°C at 2°C / min and kept for 8 hours to obtain a silicon-carbon composite negative electrode material. A LiF-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0032] Embodiment 8,

[0033] 500 mg of micron silicon powder, 25 mg of polyvinyl chloride, and 48 mg of lithium acrylate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 750°C at 2°C / min and kept for 2 hours to obtain a silicon-carbon composite negative electrode material. A LiCl-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0034] Embodiment 9,

[0035] 500 mg of nano silicon powder, 25 mg of perfluoropolyether and 50 mg of lithium carbonate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 600°C at 2°C / min and kept for 20 hours to obtain a silicon-carbon composite negative electrode material. A LiF-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0036] Embodiment 10

[0037] 500 mg of micron silicon powder, 25 mg of polyvinylidene fluoride, and 78 mg of lithium acrylate were mixed evenly to obtain a silicon-carbon composite precursor, and then the precursor was placed in a tubular furnace with high-purity argon gas, and the temperature was raised to 750°C at 5°C / min and kept for 10 hours to obtain a silicon-carbon composite negative electrode material. A LiF-doped silicon-carbon composite material was obtained. The electrochemical performance of the material was tested.

[0038] Comparative Example 1

[0039] 500 mg of nano silicon powder and 50 mg of polyvinylidene fluoride were mixed evenly to obtain a silicon-carbon composite precursor, which was then placed in a tubular furnace with high-purity argon gas and heated to 750°C at 2°C / min and kept warm for 5 hours to obtain a silicon-carbon composite negative electrode material. The electrochemical performance of the material was tested.

[0040] Electrochemical performance test:

[0041] The half-cell test method of the lithium-ion battery negative electrode material prepared in Examples 1 to 3 and Comparative Example 1 is as follows: the above-mentioned lithium-ion battery silicon-carbon composite negative electrode material is uniformly mixed with the binder CMC (sodium carboxymethyl cellulose) and the conductive carbon black in a mass ratio of 80:10:10, and the slurry is coated on the copper foil with a coating thickness of 100 microns, and the negative electrode sheet of the lithium battery is prepared by vacuum drying at 80°C for 12 hours. The simulated battery assembly is carried out in an argon-filled glove box, the electrolyte is 1MLiPF6+EC:DMC=1:1 (volume ratio), 5% (volume ratio) FEC, the metal lithium sheet is the counter electrode, and the electrochemical performance test is carried out on the Land battery tester, the charge and discharge voltage range is 0.01 to 1.5V, and the charge and discharge current is 200mA / g. The test results are listed in the following table.

[0042]

[0043]

[0044] As can be seen from the above table, the embodiments all show excellent cycle performance (such as Figure 3 The charge and discharge curves are those of Example 2, and the first coulombic efficiency is above 75%, indicating that the silicon-carbon negative electrode material prepared by the present invention has excellent electrochemical performance.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery, characterized in that: It is prepared by the following steps: (1) mixing a silicon source, a lithium salt, and a halogen-containing organic carbon source in a certain ratio; the mass ratio of the silicon source to the halogen-containing organic carbon source is 5 to 50; (2) placing the powder obtained in step (1) in an inert atmosphere or vacuum environment for high-temperature heat treatment, and cooling to room temperature to obtain a silicon-carbon negative electrode material; the conditions of the high-temperature heat treatment are: a heating rate of 0.5 to 10°C / min, a heat treatment temperature of 400°C to 800°C, and a holding time of 0.5h to 24h; In the silicon-carbon negative electrode material, the surface of the silicon active material is in-situ reacted to coat a multi-component amorphous layer having a mosaic structure, and the amorphous layer and the SiO x The layers interact closely to form a strong electronic and ion-conducting network, with high modulus, high ionic and electronic conductivity; where 1<x<2: The amorphous layer contains carbon, amorphous lithium silicate Li2SiO3, amorphous lithium carbonate and LiX, wherein X=F or Cl.

2. The method for preparing a silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery according to claim 1, characterized in that: The silicon source is one or a combination of silicon powder, iron-silicon alloy powder and silicon-calcium alloy powder, and the particle size is 50-5000nm.

3. The method for preparing a silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery according to claim 1, characterized in that: The lithium salt is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium phosphate, lithium acetate, lithium polyacrylate, and lithium acetylacetonate.

4. The method for preparing a silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery according to claim 1, characterized in that: The halogen-containing organic carbon source is one of polyvinylidene fluoride, polytetrafluoroethylene, perfluoropolyether, polyvinyl chloride, polyvinylidene chloride or a mixture of several thereof.

5. The method for preparing a silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery according to claim 1, characterized in that: The inert atmosphere is one of high-purity nitrogen, helium, neon, and argon, or a mixture of several of them.

6. The method for preparing a silicon-carbon negative electrode material for a high-stability and high-capacity lithium-ion battery according to claim 1, characterized in that: The vacuum degree of the vacuum environment is -10 to -80 KPa.

7. A high-stability and high-capacity silicon-carbon negative electrode material for lithium-ion batteries prepared by the method for preparing a high-stability and high-capacity silicon-carbon negative electrode material for lithium-ion batteries according to any one of claims 1 to 6, characterized in that: The surface of the silicon active material is in situ reacted to coat a multi-component amorphous layer having a mosaic structure, wherein the amorphous layer and the SiO x The layers interact closely to form a strong electronic and ion-conducting network, with high modulus, high ionic and electronic conductivity; where 1<x<2: The amorphous layer contains carbon, amorphous lithium silicate Li2SiO3, amorphous lithium carbonate and LiX, wherein X=F or Cl, and the thickness of the coating layer is 5-100nm; The silicon-carbon negative electrode material for high-stability and high-capacity lithium-ion batteries has a structure in which the silicon active material content is 50wt%-80wt%, the carbon content is 5wt%-18wt%, and the content of other lithium salts is 1wt%-5wt%.

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