Silicon-carbon negative electrode material

Abstract

This invention belongs to the field of secondary battery technology, specifically relating to a silicon-carbon anode material. The silicon-carbon anode material provided by this invention comprises a Si-O-C microsphere core and a silicon-oxygen material outer layer coating the surface of the Si-O-C microspheres. The silicon-carbon anode material provided by this invention has a core-shell structure, with silicon-oxygen as the coating layer and silicon-oxygen-carbon microspheres as the core structure. The carbon atoms in the Si-O-C microspheres can significantly improve the conductivity of the anode material. Simultaneously, using the porous silicon-oxygen material as the outer layer of the core-shell structure can effectively alleviate the volume expansion of the anode material. This allows the silicon-carbon anode material to achieve both good electrochemical performance and low volume expansion, resulting in a lithium-ion battery with a conductivity of 100 mA g / g. ‑1 At a current density of 761 mAh g, the initial charge specific capacity reaches 761 mAh g. ‑1 The charge / discharge efficiency is 71.8%.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a silicon-carbon anode material. Background Technology

[0002] High-capacity electrode materials are essential for the fabrication of high-energy-density power lithium-ion batteries. Currently, graphite-based anode materials for power lithium-ion batteries have reached their specific capacity limit, making it impossible to further increase the energy density of power lithium-ion batteries. Silicon anode materials, however, possess an ultra-high theoretical specific capacity (4200 mAh g⁻¹). -1 And a relatively low electrochemical lithium intercalation potential (~0.4 V vs. Li / Li) + Silicon anode materials have become ideal anode materials for lithium-ion batteries. However, the commercialization of silicon anode materials still faces multiple challenges: First, the volume expansion after lithium intercalation is as high as 320% (graphite is only 12%), which can easily lead to material pulverization and anode failure; second, the initial cycle coulombic efficiency is low; and third, the poor conductivity limits its high-current charge and discharge performance.

[0003] To address the challenges of silicon anode materials, researchers have widely adopted silicon-carbon composite technology to improve the electrochemical performance of silicon-based anodes. Among these, core-shell silicon-carbon composite materials with an outer carbon layer and an inner silicon layer have achieved a breakthrough in the market and have been initially applied in power lithium-ion batteries with good results. However, core-shell silicon-carbon anode materials often require complex processes to prepare successfully, which undoubtedly reduces the preparation efficiency and increases time costs. Summary of the Invention

[0004] This invention provides a silicon-carbon anode material that solves the problem that existing silicon-carbon composite materials cannot simultaneously achieve low volume expansion and high conductivity.

[0005] To solve the above-mentioned technical problems, the technical solution of the silicon-carbon anode material of the present invention is as follows: A silicon-carbon anode material includes a Si-OC microsphere core and a silicon-oxygen material outer layer coated on the surface of the Si-OC microspheres.

[0006] This invention provides a pioneering silicon-carbon anode material with a core-shell structure. The material uses silicon-oxygen as a coating layer and silicon-oxygen-carbon microspheres as the core structure. This unique coating structure effectively mitigates the volume expansion of the silicon-oxygen-carbon anode during lithium intercalation, significantly improving its electrochemical performance. By using densely structured Si-OC microspheres as the core of the silicon-carbon anode material, the carbon atoms in the Si-OC microspheres significantly improve the conductivity of the anode material. Simultaneously, the loosely structured silicon-oxygen material serves as the outer layer of the core-shell structure, effectively mitigating the volume expansion of the anode material. This allows the silicon-carbon anode material to achieve both good electrochemical performance and low volume expansion. The silicon-carbon anode material provided by this invention exhibits good electrochemical performance and excellent charge-discharge performance under high current. The resulting lithium-ion battery achieves a charge-discharge performance of 100 mA g / L. -1 At a current density of 761 mAh g, the initial charge specific capacity reaches 761 mAh g. -1 The charge / discharge efficiency is 71.8%.

[0007] To further improve the conductivity of the silicon-carbon anode and alleviate volume expansion, preferably, the diameter of the Si-OC microspheres is 50 nm to 1 μm, and the thickness of the silicon-oxygen material outer layer is 20 to 100 nm. More preferably, the diameter of the Si-OC microspheres is 0.2 to 0.5 μm, and the thickness of the silicon-oxygen material outer layer is 30 to 100 nm.

[0008] To further improve the conductivity of the silicon-carbon anode and control volume expansion, preferably, based on a mass fraction of 100%, the mass fractions of silicon, carbon, and oxygen in the silicon-carbon anode material are 50-75%, 15-40%, and 5-20%, respectively. More preferably, the mass fractions of silicon, carbon, and oxygen in the silicon-carbon anode material are 50-75%, 15-30%, and 10-20%, respectively.

[0009] To further simplify the preparation process of silicon-carbon anode, preferably, the preparation method of silicon-carbon anode material includes the following steps: mixing organosilicon and carbon source and then performing three-stage calcination treatment in sequence, wherein the holding temperature during the first stage of calcination treatment is 400~450℃, the holding temperature during the second stage of calcination treatment is 700~900℃, and the holding temperature during the third stage of calcination treatment is 1000~1200℃.

[0010] Through a three-stage calcination process, the first stage of calcination involves the pyrolysis of the carbon source to produce gaseous CN. x / CO x As the insulation process continues, CN x / CO xThe first stage involves the dissociation of silicon into carbon atoms (C). During the second stage of calcination, the organosilicon pyrolysis leads to the breakage of Si-C bonds, generating a siloxane intermediate containing Si-O bonds. As the temperature is maintained, the siloxane intermediate reacts with the carbon atoms (C) generated from the pyrolysis of the carbon source to form solid silicon-oxygen-carbon Si-OC microspheres. The carbon atoms (C) generated from the pyrolysis of the carbon source are fully involved in the reaction during the temperature maintenance stage until they are completely consumed and no longer participate in subsequent reactions. During the third stage of calcination, as the temperature increases, the siloxane intermediate continues to decompose at high temperatures, depositing silicon-oxygen materials on the surface of the silicon-oxygen-carbon Si-OC microspheres, thus preparing a core-shell structured composite material of silicon-oxygen-coated silicon-oxygen-carbon Si-OC microspheres.

[0011] In the preparation method provided by this invention, organosilicon serves as both the core silicon source and the shell silicon source. No other raw materials are added during the subsequent preparation process. The carbon source can not only provide carbon atoms for the preparation of silicon-oxygen-carbon composite materials, but also adjust the ratio of silicon, oxygen, and carbon elements. Moreover, the preparation process is a one-step sintering method, which includes three heat preservation processes. This method is simple and easy to implement, and is suitable for large-scale production applications.

[0012] To ensure complete reaction during each stage of calcination, the holding time during the first, second, and third stages of calcination is preferably 1-3 hours.

[0013] To further improve the efficiency of calcination at each stage, preferably, the heating rate during the first, second, and third stages of calcination is 5~8℃ / min. -1 .

[0014] To further improve the reaction efficiency during each stage of calcination, preferably, the organosilicon is selected from one or more of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methylphenyl silicone oil, and chlorophenyl silicone oil; the carbon source is selected from one or more of aminocyanide, dicyandiamide, melamine, and urea.

[0015] To further regulate the silicon-carbon ratio in the silicon-carbon anode material and improve electrochemical performance, preferably, the mass ratio of organosilicon to carbon source is (10~50):1. More preferably, the mass ratio of organosilicon to carbon source is (20~50):1. Attached Figure Description

[0016] Figure 1 This is a TEM image of the silicon-carbon anode material of Example 1 of the present invention; Figure 2 This is an elemental distribution diagram of the silicon-carbon anode material of Example 1 of the present invention; Figure 3 The graphs show the charge-discharge curves and cycle performance test results of the lithium-ion battery made from the silicon-carbon anode material of Example 1 of this invention. Detailed Implementation

[0017] The technical concept of the silicon-carbon anode material of the present invention is as follows: To address the issues of low theoretical specific capacity of graphite materials and volume expansion and low conductivity of silicon materials, current approaches generally employ silicon nano-sizing or porous structures to reduce the absolute volume expansion rate of silicon, effectively mitigating electrode structure collapse and reducing lithium-ion diffusion distance, thereby increasing electrochemical reaction rates. Additionally, silicon-carbon composite materials are used to improve conductivity.

[0018] However, silicon-carbon anode materials prepared by silicon / carbon composite using nano-silicon particles are mostly simple combinations of nano-silicon and porous carbon. No in-situ buffer groups are generated during the first lithium insertion / extraction process, and no vacancies are reserved to accommodate the volume changes during lithium insertion / extraction. Therefore, they cannot fundamentally suppress the volume effect during the charge and discharge process. Porous silicon-carbon anode materials prepared by methods such as etching nano-silicon alloys, porous framework deposition, and silicon oxide reduction are prone to producing byproducts that are detrimental to battery performance or are themselves complex in process.

[0019] Chinese patent application CN113851627A, published on December 28, 2021, discloses a porous silicon-carbon anode material and its preparation method. The method involves heat-treating nano-silicon raw materials and a first carbon source to obtain a first precursor, then heat-treating the first precursor and a second carbon source to obtain a second precursor, and finally heat-treating the second precursor and a third carbon source to obtain the porous silicon-carbon anode material. This porous silicon-carbon anode material has a core-shell structure. The core is a silicon-carbon anode material with porous pores distributed within it. The outer shell consists of two layers: an inner conductive material layer and an outer carbon coating layer. The porous structure acts as a buffer during the contraction and expansion of the silicon material. The conductive material formed by the second carbon source, a carbon allotrope with a specific structure, effectively improves the conductivity of the battery material, and the gap between the second carbon source and the first precursor minimizes the impact of expansion after lithium insertion.

[0020] The aforementioned porous silicon-carbon anode material with a core-shell structure has a complex structure, consisting of a porous core, a conductive inner layer, and a carbon-coated outer layer. It requires an additional conductive material layer to improve conductivity while forming a gap with the core to slow down the volume expansion of the silicon material. Furthermore, the preparation method is complex and cumbersome, requiring three different carbon sources to undergo multiple heat treatments to form the corresponding core-shell structure.

[0021] The silicon-carbon anode material provided by the present invention comprises a two-layer structure: a Si-OC microsphere core and a silicon-oxygen material outer layer coated on the surface of the Si-OC microsphere. The carbon atoms in the Si-OC microsphere core can significantly improve the conductivity of the anode material, and the silicon-oxygen material outer layer has a fluffy structure that can alleviate the volume expansion of the anode material, thereby improving the conductivity and electrochemical performance of the silicon-carbon anode material.

[0022] To more clearly describe the technical features and effects achieved by the present invention, specific embodiments are described below. The specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] I. Specific Embodiments of the Silicon-Carbon Anode Material of the Present Invention Example 1 The silicon-carbon anode material in this embodiment consists of a Si-OC microsphere core and a silicon-oxygen material outer layer covering the surface of the Si-OC microsphere. The diameter of the Si-OC microsphere is 0.3-0.4 μm, the thickness of the silicon-oxygen material outer layer is 30-50 nm, and the mass fractions of silicon, carbon, and oxygen in the silicon-carbon anode material are 75%, 15%, and 10%, respectively.

[0024] The preparation method of silicon-carbon anode material is as follows: (1) Weigh out dimethyl silicone oil (C6H) 18 OSi2 and melamine (mass ratio 40:1) were placed in a tube furnace and protected with argon gas at a flow rate of 120 mL / min. -1 .

[0025] (2) Set the heating program and perform three stages of calcination treatment in sequence. The heating rate during the first stage of calcination treatment is 5 °C / min. -1 The heat treatment temperature was 500℃ and the heat treatment time was 2h, and melamine was pyrolyzed to obtain carbon atoms.

[0026] (3) The heating rate during the second stage of calcination is 5 °C / min. -1 The heat preservation temperature is 900℃ and the heat preservation time is 1h. Dimethyl silicone oil is pyrolyzed to obtain siloxane intermediate. As the heat preservation proceeds, the carbon atoms in step (2) react with the siloxane intermediate to generate silicon-oxygen carbon Si-OC microspheres.

[0027] (4) The heating rate during the third stage calcination treatment is 5 °C / min. -1 The heat preservation temperature was 1100℃, and the heat preservation time was 1h. The siloxane intermediate in step (3) continued to decompose at high temperature to generate silicon-oxygen materials and deposited on the surface of silicon-oxygen carbon microspheres, thus preparing a core-shell structured composite material of silicon-oxygen coated silicon-oxygen carbon microspheres. Its morphology and elemental distribution are as follows: Figure 1-2 As shown, from Figure 1-2 It can be seen that the fabricated silicon-carbon anode material microspheres have a dense core and a fluffy outer layer, especially... Figure 2 It can be seen that silicon is densely distributed in the core of the microsphere and sparsely distributed in the outer layer, which further confirms that the silicon-carbon anode material of the present invention has the structural characteristics of a dense core and a loose outer layer. Its carbon element is only distributed in the dense core. The elemental composition of the silicon-carbon anode material is silicon: 75%, oxygen: 10%, and carbon: 15%.

[0028] Example 2 The silicon-carbon anode material of this embodiment consists of a Si-OC microsphere core and a silicon-oxygen material outer layer covering the surface of the Si-OC microsphere. The diameter of the Si-OC microsphere is 0.4-0.5 μm, the thickness of the silicon-oxygen material outer layer is 30-60 nm, and the mass fractions of silicon, carbon and oxygen in the silicon-carbon anode material are 60%, 25% and 15%, respectively.

[0029] The preparation method of silicon-carbon anode material is as follows: (1) Weigh out phenyl silicone oil (C 15 H 32 O3Si4 and urea (mass ratio 50:1) were placed in a tube furnace and protected with argon gas at a flow rate of 120 mL / min. -1 .

[0030] (2) Set the heating program and perform three stages of calcination treatment in sequence. The heating rate during the first stage of calcination treatment is 5 °C / min. -1 The urea was pyrolyzed to obtain carbon atoms by holding it at 550℃ for 2 hours.

[0031] (3) The heating rate during the second stage of calcination is 5 °C / min. -1 The heat preservation temperature is 850℃ and the heat preservation time is 1h. Phenyl silicone oil is pyrolyzed to obtain siloxane intermediate. As the heat preservation proceeds, the carbon atoms in step (2) react with the siloxane intermediate to generate silicon-oxygen carbon Si-OC microspheres.

[0032] (4) The heating rate during the third stage calcination treatment is 5 °C / min. -1 The heat preservation temperature is 1000℃ and the heat preservation time is 1h. The siloxane intermediate in step (3) continues to decompose at high temperature to generate silicon oxide material and deposit on the surface of silicon oxide carbon microspheres, thus preparing a core-shell structure composite material of silicon oxide coated silicon oxide carbon microspheres.

[0033] Example 3 The silicon-carbon anode material in this embodiment consists of a Si-OC microsphere core and a silicon-oxygen material outer layer covering the surface of the Si-OC microsphere. The diameter of the Si-OC microsphere is 0.3-0.5 μm, the thickness of the silicon-oxygen material outer layer is 50-100 nm, and the mass fractions of silicon, carbon, and oxygen in the silicon-carbon anode material are 50%, 30%, and 20%, respectively.

[0034] The preparation method of silicon-carbon anode material is as follows: (1) Weigh out methylphenyl silicone oil (C4H) 12OSi and dicyandiamide (mass ratio 30:1) were placed in a tube furnace and protected with argon gas at a flow rate of 120 mL / min. -1 .

[0035] (2) Set the heating program and perform three stages of calcination treatment in sequence. The heating rate during the first stage of calcination treatment is 5 °C / min. -1 The heat treatment temperature was 450℃ and the heat treatment time was 2h, and carbon atoms were obtained by pyrolysis of dicyandiamide.

[0036] (3) The heating rate during the second stage of calcination is 5 °C / min. -1 The heat preservation temperature is 900℃ and the heat preservation time is 1h. Methylphenyl silicone oil is pyrolyzed to obtain siloxane intermediate. As the heat preservation proceeds, the carbon atoms in step (2) react with the siloxane intermediate to generate silicon-oxygen carbon Si-OC microspheres.

[0037] (4) The heating rate during the third stage calcination treatment is 5 °C / min. -1 The heat preservation temperature is 1000℃ and the heat preservation time is 1h. The siloxane intermediate in step (3) continues to decompose at high temperature to generate silicon oxide material and deposit on the surface of silicon oxide carbon microspheres, thus preparing a core-shell structure composite material of silicon oxide coated silicon oxide carbon microspheres.

[0038] Example 4 The silicon-carbon anode material of this embodiment consists of a Si-OC microsphere core and a silicon-oxygen material outer layer covering the surface of the Si-OC microsphere. The diameter of the Si-OC microsphere is 0.2-0.3 μm, the thickness of the silicon-oxygen material outer layer is 30-50 nm, and the mass fractions of silicon, carbon and oxygen in the silicon-carbon anode material are 50%, 30% and 20%, respectively.

[0039] The preparation method of silicon-carbon anode material is as follows: (1) Weigh out methylphenyl silicone oil (C4H) 12 OSi and urea (mass ratio 20:1) were placed in a tube furnace and protected with argon gas at a flow rate of 120 mL / min. -1 .

[0040] (2) Set the heating program and perform three stages of calcination treatment in sequence. The heating rate during the first stage of calcination treatment is 5 °C / min. -1 The urea was pyrolyzed to obtain carbon atoms by holding it at 500℃ for 2 hours.

[0041] (3) The heating rate during the second stage of calcination is 5 °C / min. -1The heat preservation temperature is 900℃ and the heat preservation time is 1h. Methylphenyl silicone oil is pyrolyzed to obtain siloxane intermediate. As the heat preservation proceeds, the carbon atoms in step (2) react with the siloxane intermediate to generate silicon-oxygen carbon Si-OC microspheres.

[0042] (4) The heating rate during the third stage calcination treatment is 5 °C / min. -1 The heat preservation temperature is 1200℃ and the heat preservation time is 1h. The siloxane intermediate in step (3) continues to decompose at high temperature to generate silicon oxide material and deposit on the surface of silicon oxide carbon microspheres, thus preparing a core-shell structure composite material of silicon oxide coated silicon oxide carbon microspheres.

[0043] II. Experimental Examples This experimental example uses the silicon-carbon anode material from the previous example as the anode active material to form the anode sheet, assembles it into a lithium-ion battery, and tests its initial charge specific capacity and charge-discharge efficiency. Specifically, the silicon-carbon anode material, conductive carbon black, and PVDF from the previous example are mixed in an 8:1:1 ratio to form a slurry, which is then uniformly coated onto copper foil as the anode sheet. Pure lithium foil is used as the positive electrode sheet. A Celgard 2400 separator is selected, and the battery is assembled into a lithium-ion battery. The battery is tested at 100 mA g / L. -1 Charge-discharge tests were performed at a current density of 1 A g; and at 1 A g -1 Cyclic performance tests were conducted at a current density of [value missing]. The charge-discharge curves and cycle performance test results of the lithium-ion battery made from the silicon-carbon anode material in Example 1 are shown below. Figure 3 As shown, where Figure 3 Figure A in the graph is a charge-discharge curve. Figure 3 Figure B in the graph shows the changes in specific capacity and number of cycles. Figure 3 It can be seen that at 100 mA g -1 At a current density of 761 mAh g, the initial charge specific capacity reaches 761 mAh g. -1 The charge / discharge efficiency was 71.8%. The electrochemical performance test results of lithium-ion batteries made of different silicon-carbon anode materials are shown in Table 1.

[0044] The material used in Comparative Example 1 is silicon-carbon anode material produced by Sibao New Energy Materials Co., Ltd., product model: Sibao SGP-450; the material used in Comparative Example 2 is silicon-carbon anode material produced by Sibao New Energy Materials Co., Ltd., product model: Sibao SGP-420; the material used in Comparative Example 3 is nano-silicon-carbon anode material produced by Yinsi Technology Co., Ltd., product model: YSN-1.

[0045] Table 1 Electrochemical performance test results of different silicon-carbon anode materials Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, It includes the Si-OC microsphere core and the outer layer of silicon-oxygen material coating the surface of the Si-OC microsphere.

2. The silicon-carbon anode material as described in claim 1, characterized in that, The diameter of the Si-OC microspheres is 50 nm to 1 μm, and the thickness of the outer layer of silicon-oxygen material is 20 to 100 nm.

3. The silicon-carbon anode material as described in claim 1, characterized in that, Based on a mass fraction of 100%, the mass fractions of silicon, carbon, and oxygen in silicon-carbon anode materials are 50-75%, 15-40%, and 5-20%, respectively.

4. The silicon-carbon anode material as described in claim 3, characterized in that, The mass fractions of silicon, carbon, and oxygen in silicon-carbon anode materials are 50-75%, 15-30%, and 10-20%, respectively.

5. The silicon-carbon anode material according to any one of claims 1-4, characterized in that, The preparation method of the silicon-carbon anode material includes the following steps: mixing organosilicon and carbon source and then performing three-stage calcination treatment in sequence. The holding temperature during the first stage of calcination treatment is 400~450℃, the holding temperature during the second stage of calcination treatment is 700~900℃, and the holding temperature during the third stage of calcination treatment is 1000~1200℃.

6. The silicon-carbon anode material as described in claim 5, characterized in that, The holding time during the first, second, and third stages of calcination is 1 to 3 hours.

7. The silicon-carbon anode material as described in claim 5, characterized in that, The heating rate during the first, second, and third stages of calcination is 5-8℃ / min. -1 .

8. The silicon-carbon anode material as described in claim 5, characterized in that, The organosilicon is selected from one or more of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methylphenyl silicone oil, and chlorophenyl silicone oil; the carbon source is selected from one or more of aminocyanide, dicyandiamide, melamine, and urea.

9. The silicon-carbon anode material as described in claim 5, characterized in that, The mass ratio of organosilicon to carbon source is (10~50):

1.

10. The silicon-carbon anode material as described in claim 9, characterized in that, The mass ratio of organosilicon to carbon source is (20~50):1.

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