Composite silicon-based negative electrode material, preparation method and solid-state battery

Abstract

The present invention belongs to the technical field of composite silicon-based negative electrode materials and discloses a composite silicon-based negative electrode material, a preparation method, and a solid-state battery. The composite silicon-based negative electrode material comprises a graphite substrate and silicon carbide nanowires and nanosilicon particles attached to the surface of the graphite substrate. The silicon carbide nanowires are interwoven to form a network structure, and the nanosilicon particles are dispersed in the network structure. The nanosilicon particles are dispersed in the network of interwoven silicon carbide nanowires, presenting a porous structure similar to that of reinforced concrete. The porous structure provides space for volume expansion, mitigating damage to the electrode structure caused by volume expansion during lithium insertion and extraction of the silicon-based negative electrode. At the same time, the one-dimensional silicon carbide therein, due to its high mechanical strength, can mitigate damage to the electrode structure caused by long-term cycling of the silicon negative electrode, thereby improving the mechanical properties of the silicon negative electrode and thus improving the cycling performance of the silicon electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite silicon-based negative electrode materials, and specifically relates to a composite silicon-based negative electrode material, a preparation method and a solid-state battery. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The rapid development of electric vehicles, distributed energy systems, and smart grids is placing increasing demands on battery energy density, lifespan, and safety. Compared to flammable organic liquid electrolytes, solid-state electrolytes offer advantages such as higher thermal stability, non-flammability, no leakage, and no volatility. They also have a higher thermal runaway onset temperature, which helps improve battery safety and stability. While improving safety, the use of solid-state electrolytes also enables the use of high-voltage cathode materials, thereby increasing battery energy density.

[0004] To achieve high-energy-density all-solid-state batteries, the market has focused on metallic lithium and its alloys or silicon-based anodes. However, when applied to sulfide solid-state batteries, which offer ultra-high ionic conductivity and good plasticity, metallic lithium anodes still suffer from poor cycling stability and low safety. The root causes lie in the solid-solid contact between the lithium metal and the sulfide solid electrolyte, the large volume change of the lithium metal during cycling, the growth of lithium dendrites, and side reactions at the lithium metal / electrolyte interface.

[0005] Compared with graphite (0.1V) and lithium metal negative electrodes, which are unstable at the interface with sulfides, the lithium insertion potential of silicon is 0.4V, which can alleviate the side reactions at the interface to a certain extent while achieving a higher open circuit voltage. Combined with the high specific capacity of the silicon-based negative electrode, it is conducive to the realization of high-energy density and high-safety solid-state batteries; at the same time, the combination of silicon-based negative electrode and sulfide solid electrolyte can avoid the problem of repeated generation of solid electrolyte interface layer (SEI) of silicon-based negative electrode in liquid battery, give full play to the high capacity of silicon-based negative electrode, and use the better mechanical properties of sulfide to buffer the huge volume expansion of silicon negative electrode, improve solid-solid contact, promote ion diffusion, and is expected to achieve long-term circulation of high-energy density batteries.

[0006] To improve the cycling performance of silicon anode materials, nanosizing silicon is one approach to enhance their stability. Nanomaterials have the characteristics of large specific surface area, short ion diffusion paths, strong creeping properties, and high plasticity. They can alleviate the volume effect of silicon anode materials to a certain extent and improve their electrochemical performance. However, nanomaterials tend to agglomerate during cycling, which is insufficient to improve battery performance to a practical level.

[0007] Another effective approach is to create silicon-containing composite materials, leveraging the synergistic effects between the composite's components to achieve complementary advantages. For example, Jian et al. (Journal of Power Sources, 2017, 342:529-536) prepared a core-shell Si@C@void@C nanocomposite. This structure not only reduces interfacial resistance but also effectively maintains the structural stability of the silicon material. However, its preparation method is complex and unsuitable for industrial production.

[0008] Others use etching to prepare silicon nanowires, then use CVD to coat the surface of the silicon nanowires with a layer of silicon carbon to produce silicon-carbon-silicon nanowires. Finally, a layer of highly conductive graphene is grown on the silicon-carbon-silicon surface to produce a sandwich-structured Gr-silicon-carbon-silicon nanowire. This material has a large initial discharge capacity and good cycling performance, but the preparation process is complex and costly, making it unsuitable for industrial production. Furthermore, both the core-shell structured silicon@carbon@void@carbon nanocomposites and Gr-silicon-carbon-silicon nanowires feature carbon coated on the surface of silicon particles, preventing contact between silicon and the solid electrolyte, resulting in low ionic conductivity of the silicon-based electrode. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a composite silicon-based negative electrode material, a preparation method and a solid-state battery.

[0010] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0011] In a first aspect, the present invention provides a composite silicon-based negative electrode material, comprising a graphite substrate and silicon carbide nanowires and nano-silicon particles attached to the surface of the graphite substrate, wherein the silicon carbide nanowires are interwoven to form a network structure, and the nano-silicon particles are dispersed in the network structure.

[0012] In some embodiments, the mass percentage of graphite in the composite silicon-based negative electrode material is 9.9%-25%.

[0013] In some embodiments, the mass percentage of nano-silicon particles in the composite silicon-based negative electrode material is 20%-90%.

[0014] Preferably, the particle size of the nano-silicon particles is 30-150 nm.

[0015] In some embodiments, the mass percentage of silicon carbide nanowires in the composite silicon-based negative electrode material is 0.1%-5%.

[0016] Preferably, the diameter of the silicon carbide nanowires is 10-100 nm.

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

[0018] Nano-silicon dioxide, graphite and carbon powder are mixed in proportion and pressed into shape to obtain a precursor; the precursor is compounded with a current collector as a cathode, and molten salt is used as an electrolyte. Under an inert atmosphere, electrolysis is carried out at a temperature greater than 500°C for a set time to obtain a composite silicon-based negative electrode material.

[0019] Carbon powder is the carbon source for silicon carbide; graphite is conductive and can also serve as a carrier for nano-silicon. Molten salt melts at high temperatures and acts as an electrolyte, a medium for conducting ions.

[0020] In some embodiments, the mass ratio of nano-silica, graphite, and carbon powder is 40-200:8-90:0.1-1.

[0021] Preferably, the mass ratio of nano-silicon dioxide, graphite and carbon powder is 40-90:50-80:0.5-1.

[0022] More preferably, the mass ratio of nano-silicon dioxide, graphite and carbon powder is 40-90:50-80:0.8-1.

[0023] Preferably, the average particle size of the nano-silicon dioxide is less than 100 nm.

[0024] More preferably, the shape of the nano-silica is spherical or quasi-spherical.

[0025] In some embodiments, the electrolyte is molten CaCl2, sodium chloride, potassium chloride, or lithium chloride.

[0026] In some embodiments, the electrolysis temperature is 500-1000° C., and the electrolysis time is 6-10 h.

[0027] In some embodiments, the electrolysis voltage is lower than 3.0 V. When the voltage is greater than 3 V, the molten salt may be electrolyzed or other impurities may be generated.

[0028] Preferably, the voltage of electrolysis is 1-3V, preferably 2-3V.

[0029] In some embodiments, the process further includes cleaning the electrolytically prepared composite silicon-based negative electrode material. The cleaning method comprises sequentially soaking the electrolytically prepared composite silicon-based negative electrode material in dilute hydrochloric acid, rinsing with water, and then rinsing with anhydrous ethanol, followed by drying. The sequential soaking in dilute hydrochloric acid, rinsing with water, and then rinsing with anhydrous ethanol is performed to remove molten salts.

[0030] In a third aspect, the present invention provides a solid silicon-based negative electrode, comprising a supporting conductive substrate and an active coating, wherein the active coating is coated on the supporting conductive substrate, and the active coating is a mixture of the composite silicon-based negative electrode material, an electrolyte, and a conductive agent.

[0031] In a fourth aspect, the present invention provides a solid-state battery comprising the solid-state silicon-based negative electrode.

[0032] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0033] The composite silicon-based negative electrode material of the present invention includes graphite and silicon carbide nanowires and nano-silicon particles generated on the graphite surface, wherein the nano-silicon particles are dispersed in a network interwoven by the silicon carbide nanowires, presenting a porous structure similar to the structure of reinforced concrete. The porous structure can provide space for volume expansion, thereby slowing down the damage to the electrode structure caused by volume expansion during the lithium insertion and extraction process of the silicon-based negative electrode. At the same time, the one-dimensional silicon carbide therein has high mechanical strength, which can alleviate the damage to the electrode structure caused by the long cycle of the silicon negative electrode, improve the mechanical properties of the silicon negative electrode, and thus improve the cycle performance of the silicon electrode.

[0034] In addition, in the composite silicon-based negative electrode material of the present invention, since nano-silicon carbide grows on the graphite surface, the nano-silicon particles are dispersed in the network formed by the nano-silicon carbide wires, which can effectively prevent the agglomeration of nano-silicon particles and ensure good contact between nano-silicon and the conductive material (graphite) during the lithium insertion and extraction process of the electrode.

[0035] The composite silicon-based negative electrode material of the present invention has readily available raw materials, inexpensive equipment, a simple preparation method, easy operation and industrial production, and no pollution is generated during the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0037] Figure 1 This is a microscopic morphology of the composite silicon-based negative electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0039] The present invention will be described below in conjunction with the accompanying drawings and embodiments. These descriptions are only intended to further illustrate the present invention, rather than to limit the present invention.

[0040] Example 1

[0041] (1) Nano-silica, graphite, and cracked carbon were weighed in a mass ratio of 192.8:9.9:0.1, with the average particle size of the nano-silica being less than 100 nm, mixed uniformly, and pressed into a shape to obtain a precursor;

[0042] The precursor was compounded with a conductive cathode current collector and used as the cathode, a graphite rod was used as the anode, and molten CaCl2 was used as the electrolyte. In an argon environment, the temperature was 850°C, and constant voltage electrolysis was performed with a voltage regulator controlling the voltage. The cell voltage was 2.5V and the electrolysis time was 6h.

[0043] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and washed with deionized water, filtered and washed with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0044] (2) Using a homogenizer, the composite silicon-based negative electrode material, sulfide electrolyte, and conductive agent were mixed in a mass ratio of 60:40:3 for 30 minutes. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into thin sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested. The micromorphology of the composite silicon-based negative electrode material, such as Figure 1 shown.

[0045] Example 2

[0046] (1) Nano-silica, graphite, and cracked carbon were weighed in a mass ratio of 171.4:19.5:0.5, with the average particle size of the nano-silica being less than 100 nm, mixed uniformly, and pressed into a shape to obtain a precursor;

[0047] The precursor and the conductive cathode current collector were composited as the cathode, the graphite rod was used as the anode, and the molten CaCl2 was used as the electrolyte. In an argon environment, the temperature was 850°C, and the voltage was controlled by a potentiostat for constant voltage electrolysis. The cell voltage was 2.5V and the electrolysis time was 7h.

[0048] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and washed with deionized water, filtered and washed with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0049] (2) The composite silicon-based negative electrode material, sulfide electrolyte, and conductive agent were uniformly mixed in a mass ratio of 60:40:3 using a homogenizer for 30 minutes. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0050] Example 3

[0051] (1) Nano-silica, graphite and cracked carbon are weighed in a mass ratio of 150:29:1, wherein the average particle size of the nano-silica is less than 100 nm, mixed uniformly, and pressed into a shape to obtain a precursor;

[0052] The precursor and the conductive cathode current collector are composited as the cathode, the graphite rod is used as the anode, and the molten CaCl2 is used as the electrolyte. In an argon environment, the temperature is 850℃, and the voltage is controlled by a potentiostat for constant voltage electrolysis. The cell voltage is 2.5V and the electrolysis time is 8h.

[0053] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and cleaned with deionized water, filtered and cleaned with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0054] (2) The composite silicon-based negative electrode material, sulfide electrolyte and conductive agent were uniformly mixed in a mass ratio of 60:40:3 for 30 minutes using a homogenizer. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0055] Example 4

[0056] (1) Nano-silica, graphite and cracked carbon were weighed in a mass ratio of 128.6:39:1, with the average particle size of the nano-silica being less than 100 nm, mixed uniformly, and pressed into a shape to obtain a precursor;

[0057] The precursor and the conductive cathode current collector are composited as the cathode, the graphite rod is used as the anode, and the molten CaCl2 is used as the electrolyte. In an argon environment, the temperature is 850℃, and the voltage is controlled by a potentiostat for constant voltage electrolysis. The cell voltage is 2.5V and the electrolysis time is 9h.

[0058] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and washed with deionized water, filtered and washed with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0059] (2) The composite silicon-based negative electrode material, sulfide electrolyte and conductive agent were uniformly mixed in a mass ratio of 60:40:3 for 30 minutes using a homogenizer. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0060] Example 5

[0061] (1) Nano-silica, graphite and cracked carbon were weighed in a mass ratio of 107.1:49:1, with the average particle size of the nano-silica being less than 100 nm, mixed uniformly, and pressed into a shape to obtain a precursor;

[0062] The precursor and the conductive cathode current collector are composited as the cathode, the graphite rod is used as the anode, and the molten CaCl2 is used as the electrolyte. In an argon environment, the temperature is 850°C, and the voltage is controlled by a potentiostat for constant voltage electrolysis. The cell voltage is 2.5V and the electrolysis time is 10h.

[0063] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and washed with deionized water, filtered and washed with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0064] (2) The composite silicon-based negative electrode material, sulfide electrolyte and conductive agent were uniformly mixed in a mass ratio of 60:40:3 for 30 minutes using a homogenizer. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0065] Example 6

[0066] (1) Nano-silica, graphite and cracked carbon were weighed in a mass ratio of 85.7:59:1, with the average particle size of the nano-silica being less than 100 nm, mixed uniformly, and pressed into a shape to obtain a precursor;

[0067] The precursor and the conductive cathode current collector are composited as the cathode, the graphite rod is used as the anode, and the molten CaCl2 is used as the electrolyte. In an argon environment, the temperature is 850°C, and the voltage is controlled by a potentiostat for constant voltage electrolysis. The cell voltage is 2.5V and the electrolysis time is 10h.

[0068] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and washed with deionized water, filtered and washed with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0069] (2) The composite silicon-based negative electrode material, sulfide electrolyte and conductive agent were uniformly mixed in a mass ratio of 60:40:3 for 30 minutes using a homogenizer. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0070] Example 7

[0071] (1) Nano-silica, graphite, and cracked carbon were weighed and mixed uniformly in a mass ratio of 42.8:79:1, wherein the average particle size of the nano-silica was less than 100 nm, and pressed into a shape to obtain a precursor;

[0072] The precursor and the conductive cathode current collector are composited as the cathode, the graphite rod is used as the anode, and the molten CaCl2 is used as the electrolyte. In an argon environment, the temperature is 850℃, and the voltage is controlled by a potentiostat for constant voltage electrolysis. The cell voltage is 2.5V and the electrolysis time is 8h.

[0073] After the electrolysis is completed, the electrolysis product is sequentially soaked with dilute hydrochloric acid, filtered and washed with deionized water, filtered and washed with anhydrous ethanol, and vacuum dried to obtain a composite silicon-based negative electrode material.

[0074] (2) The composite silicon-based negative electrode material, sulfide electrolyte and conductive agent were uniformly mixed in a mass ratio of 60:40:3 for 30 minutes using a homogenizer. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0075] Comparative Example 1

[0076] (1) Nano-silicon particles and graphite are weighed in a silicon-carbon mass ratio of 70:30, placed in a solvent and mixed evenly, and then blow-dried to obtain a composite silicon-based negative electrode material.

[0077] (2) The composite silicon-based negative electrode material, sulfide electrolyte and conductive agent were uniformly mixed in a mass ratio of 60:40:3 for 30 minutes using a homogenizer. The mixed slurry was then coated on copper foil, dried at 100 °C for 3 hours, and punched into sheets with a diameter of 9 mm. Finally, the solid-state battery was assembled and its electrochemical performance was tested.

[0078] Comparative Example 2

[0079] The difference from Example 6 is that the voltage of electrolysis is 3.1V, and the rest is the same as Example 6.

[0080] Comparative Example 3

[0081] The difference from Example 6 is that the cracked carbon in Example 6 is omitted, and the rest is the same as Example 6.

[0082] Table 1 Comparison of initial charge and discharge capacity of composite silicon-based solid-state anodes with different silicon contents

[0083]

[0084] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A solid-state battery, characterized in that: The invention comprises a solid silicon-based negative electrode, which comprises a supporting conductive substrate and an active coating, wherein the active coating is coated on the supporting conductive substrate, and the active coating is a mixture of a composite silicon-based negative electrode material, an electrolyte and a conductive agent; The method for preparing the composite silicon-based negative electrode material comprises the following steps: Nano-silicon dioxide, graphite and carbon powder are mixed in proportion and pressed into shape to obtain a precursor; the precursor is composited with a current collector to serve as a cathode, and molten salt is used as an electrolyte. Under an inert atmosphere, electrolysis is carried out at 500-1000°C for 6-10 hours, and the electrolysis voltage is lower than 3.0V to obtain a composite silicon-based negative electrode material; The mass ratio of nano-silicon dioxide, graphite and carbon powder is 40-200:8-90:0.1-1; The composite silicon-based negative electrode material includes a graphite matrix and silicon carbide nanowires and nano-silicon particles attached to the surface of the graphite matrix, wherein the silicon carbide nanowires are interwoven to form a network structure, and the nano-silicon particles are dispersed in the network structure.

2. The solid-state battery according to claim 1, characterized in that: The mass ratio of nano silicon dioxide, graphite and carbon powder is 40-90:50-80:0.5-1.

3. The solid-state battery according to claim 1, wherein: The electrolyte is molten CaCl2, sodium chloride, potassium chloride or lithium chloride.

4. The solid-state battery according to any one of claims 1 to 3, characterized in that: The composite silicon-based negative electrode material includes a graphite matrix and silicon carbide nanowires and nano-silicon particles attached to the surface of the graphite matrix, wherein the silicon carbide nanowires are interwoven to form a network structure, and the nano-silicon particles are dispersed in the network structure.

5. The solid-state battery according to claim 4, characterized in that: In the composite silicon-based negative electrode material, the mass percentage of graphite is 9.9%-25%.

6. The solid-state battery according to claim 3, characterized in that: In the composite silicon-based negative electrode material, the mass percentage of nano-silicon particles is 20%-90%.

7. The solid-state battery according to claim 6, characterized in that: In the composite silicon-based negative electrode material, the mass percentage of silicon carbide nanowires is 0.1%-5%.

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