Hierarchical nano-porous Si quantum dot and C composite material, preparation thereof and application of hierarchical nano-porous Si quantum dot and C composite material in all-solid-state lithium ion battery

Abstract

The invention belongs to the field of lithium ion battery materials, and relates to a graded nano-porous Si quantum dot and C composite material, preparation thereof and application of the graded nano-porous Si quantum dot and C composite material in an all-solid-state lithium ion battery. According to the invention, the silicon-tin quantum dots are prepared through the cooperation of hydro-thermal synthesis and nanosecond pulse laser ablation; carrying out two-step treatment of'high-temperature oxidation-hydrogen reduction 'to prepare the graded nano-porous Si quantum dots; and then a hierarchical porous Si quantum dot core-carbon coating layer-three-dimensional interlaced conductive network composite structure is constructed with a conductive medium through sanding dispersion, ball milling compounding and high-temperature pyrolysis. The material relieves silicon lithiation volume expansion by virtue of a hierarchical porous structure, the electronic conductivity is improved by virtue of a three-dimensional conductive network, and the material is very suitable for constructing a battery negative pole piece and is used for an all-solid-state lithium ion battery. The first coulombic efficiency of the constructed all-solid-state lithium ion battery at the rate of 0.1 C is 85%-90%, and the capacity retention ratio of the constructed all-solid-state lithium ion battery after 100 cycles at the rate of 0.1 C is 95%-99%.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, and more specifically, relates to a hierarchical nanoporous Si quantum dots and C composite material, its preparation and its application in all-solid-state lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have become core energy storage devices in portable electronic devices, new energy electric vehicles, and large-scale energy storage systems due to their advantages such as high operating voltage, high energy density, long cycle life, and environmental friendliness. With the rapid development of these fields, higher requirements are being placed on the energy density, cycle stability, and safety of lithium-ion batteries.

[0003] Currently, commercially available lithium-ion battery anode materials are mainly graphite, with a theoretical lithium storage capacity of only 372 mAh / g, which is insufficient to meet the application requirements of high-energy-density batteries. In contrast, silicon (Si)-based anode materials have a theoretical lithium storage capacity as high as 4200 mAh / g, and also possess low lithium insertion / extraction potential. Furthermore, they are abundant in the Earth's crust, inexpensive, and environmentally compatible, making them one of the core potential materials for next-generation lithium-ion battery anodes.

[0004] However, silicon-based materials face two major technological bottlenecks in the lithiation / delithiation process: First, significant volume effect, the drastic volume change during charge and discharge can lead to material pulverization and active material shedding in the silicon-based anode, and cause repeated rupture and reconstruction of the SEI film, ultimately resulting in battery failure; Second, poor intrinsic conductivity, its low conductivity will hinder electron transport between the current collector and electrode materials, thereby degrading the electrochemical performance of lithium-ion batteries. These problems seriously restrict the cycle performance and service life of silicon-based materials, hindering their industrial application.

[0005] To address the core issues of significant volume expansion and poor conductivity during the lithiation / delithiation process of silicon-based anodes, existing technologies mainly focus on two major directions: structural design and silicon-carbon composite modification. At the structural design level, silicon nanostructuring (such as Si nanoparticles and Si quantum dots) can reduce the absolute volume change during alloying reactions, alleviate deformation stress, and shorten the solid-state lithium-ion transport distance. Simultaneously, constructing special microstructures such as hollow Si, 3D porous Si, and core-shell / yolk-shell / multi-level buffer structures provides expansion buffer space. Among these, the multi-level buffer structure relies on the expansion buffering effect of the internal porous carbon matrix and the electrolyte isolation effect of the outer dense carbon shell, resulting in superior electrochemical performance. However, pure nanoporous Si is prone to agglomeration, and the conductivity network lacks coherence, requiring improvement in cycle stability.

[0006] In terms of silicon-carbon composite modification, combining nano-silicon with carbon materials such as graphite, carbon nanotubes, and graphene can balance the high lithium storage capacity of silicon with the high conductivity of carbon materials (alleviating electron transport problems) and low volume expansion (<10%, buffering silicon expansion). A typical approach is to coat the silicon surface with a carbon layer to simultaneously improve structural integrity and conductivity.

[0007] Existing methods for preparing silicon-carbon composites (mechanical high-energy ball milling, sol-gel method, spray-thermal decomposition method, chemical vapor deposition method) generally suffer from uneven Si and carbon coating, loose conductive network, and difficulty in precisely controlling pore structure, resulting in large fluctuations in material properties and limited industrial applicability.

[0008] Related studies show that Su Liwei et al. obtained a Si / C initial charge capacity of 789.3 mAh / g by high-energy ball milling using glucose as a carbon source; Chen Yulong et al. obtained a Si-C discharge capacity of 1259 mAh / g (396 mAh / g after 100 cycles) prepared by plasma-assisted two-step ball milling; Liu N et al. obtained a Si / C 0.1C discharge specific capacity of 2800 mAh / g by sol-gel method combined with hydrofluoric acid etching; and Jun Lai et al. obtained a Si / C initial discharge capacity of 602.7 mAh / g (91.58% retention rate after 20 cycles) synthesized by spray drying-thermal decomposition. Although these studies have verified the feasibility of composite synthesis, they have not yet overcome the technical bottlenecks.

[0009] Furthermore, all-solid-state lithium-ion batteries, due to the absence of leakage risk associated with liquid electrolytes and their high safety, have become an important development direction for next-generation batteries; however, existing Si-based anode materials have low compaction density (<1.0 g / cm³). 3 The poor compatibility with the solid electrolyte interface makes it difficult for the volumetric energy density of all-solid-state batteries to exceed 600 Wh / L, and the capacity decay rate after 100 cycles is often >15%, which limits their application. Summary of the Invention

[0010] This invention provides a hierarchical nanoporous Si quantum dot and C composite material, its preparation, and its application in all-solid-state lithium-ion batteries. Through the synergistic design of "hierarchical porous structure + three-dimensional conductive network" and the integrated process of "hydrothermal-laser ablation-redox-sand milling and ball milling", the prepared hierarchical nanoporous Si quantum dot and C composite material can effectively buffer the volume expansion during Si lithiation. The carbon coating layer can isolate the electrolyte to stabilize the SEI film, and the three-dimensional conductive network can effectively improve electron transport efficiency. This synergistically solves the technical problems of large volume expansion and poor conductivity of silicon-based anode materials.

[0011] According to a first aspect of the present invention, a method for preparing a composite material of hierarchical nanoporous Si quantum dots and C is provided, comprising the following steps: (1) Silane is passed into an acidic SnCl2 aqueous solution to obtain a reaction solution; the reaction solution is added to a hydrothermal reactor and hydrothermal reaction is carried out under a non-oxidizing protective atmosphere to obtain silicon-tin nanoparticles; the silicon-tin nanoparticles are added to water and then ultrasonically treated to obtain a dispersion; the dispersion is then ablated by a nanosecond pulsed laser, the supernatant is taken after centrifugation and dried to obtain silicon-tin quantum dots; (2) Place the silicon-tin quantum dots obtained in step (1) in a tube furnace, first introduce oxygen and heat for oxidation treatment, then introduce nitrogen for purging, then introduce hydrogen and heat for reduction treatment, cool, clean and dry to obtain hierarchical nanoporous Si quantum dots. (3) Add dispersant and solvent to the hierarchical nanoporous Si quantum dots obtained in step (2), then perform sand milling and drying to obtain hierarchical nanoporous Si quantum dot dispersion powder; mix the hierarchical nanoporous Si quantum dot dispersion powder, conductive medium and carbon source, add solvent and perform ball milling to obtain precursor slurry; pyrolyze the precursor slurry under a non-oxidizing protective atmosphere, during the pyrolysis process the carbon source carbonizes to form a carbon connecting layer, the conductive medium and the carbon connecting layer intertwine to form a three-dimensional conductive network, thus obtaining a composite material of hierarchical nanoporous Si quantum dots and C.

[0012] Preferably, in step (3), the carbon source is at least one of glucose, sucrose, artificial graphite, phenolic resin, chitosan, citric acid, polyethylene glycol, polyacrylonitrile, and asphalt.

[0013] Preferably, the conductive medium is at least one selected from single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon black, and conductive graphite.

[0014] Preferably, in step (3), the pyrolysis specifically involves heating to 800-1000℃ at a heating rate of 5-10℃ / min and holding at that temperature for 3-5 h.

[0015] Preferably, in step (2), oxygen is first introduced at a flow rate of 50-100 mL / min, and the temperature is increased to 400-600℃ at 5℃ / min and kept at the temperature for 1-3 h for oxidation treatment; after oxidation, nitrogen is introduced at a flow rate of 100-200 mL / min for 10-20 min, and hydrogen is introduced at a flow rate of 80-150 mL / min, and the temperature is increased to 500-700℃ at 5℃ / min and kept at the temperature for 2-4 h for reduction treatment.

[0016] Preferably, in step (3), the ball milling speed is 500-2500 r / min and the time is 2-5 h.

[0017] According to another aspect of the present invention, a composite material of hierarchical nanoporous Si quantum dots and C is provided.

[0018] According to another aspect of the present invention, the application of the aforementioned hierarchical nanoporous Si quantum dots and C composite material in the negative electrode sheet of a battery is provided.

[0019] According to another aspect of the present invention, a battery negative electrode sheet is provided, which is obtained by thoroughly mixing the composite material of hierarchical nanoporous Si quantum dots and C, a conductive material and a binder, adding a solvent, and then ultrasonically atomizing and spraying it onto the surface of a metal electrode sheet. After drying, the battery negative electrode sheet is obtained.

[0020] According to another aspect of the present invention, an all-solid-state lithium-ion battery is provided, including the aforementioned battery negative electrode sheet.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: (1) The present invention adopts a three-layer structure of “hierarchical nanoporous Si quantum dot core-carbon coating layer-three-dimensional interwoven conductive network”. The hierarchical porous core (pore size 0.1-1000 nm, 1-50 nm accounting for >50%) can fully buffer the volume expansion during Si lithiation. The carbon coating layer can isolate the electrolyte to stabilize the SEI film. The three-dimensional conductive network can effectively improve the electron transport efficiency, and synergistically solve the core problems of large volume expansion and poor conductivity of silicon-based anode.

[0022] (2) This invention meets the requirements of high-specification batteries: the tap density of the material reaches 0.3-0.8 g / cm³. 3 The compacted density reaches 1.0-1.5 g / cm³. 3 It balances processability and battery volumetric energy density; the initial coulombic efficiency at 0.1C rate is 85%-90%, and the capacity retention rate after 100 cycles at 0.1C rate is 95%-99%, with strong cycle stability, and can meet the performance requirements of high energy density and long life batteries.

[0023] (3) The preparation process of this invention is suitable for industrialization and has high production feasibility: the process adopts mature technologies such as hydrothermal synthesis, nanosecond pulsed laser ablation, sand milling, ball milling and spray drying, without complex special equipment; the raw materials (silane, SnCl2, carbon source, etc.) are widely available, the parameters of each step (such as temperature, rotation speed and solid-liquid ratio) are highly controllable, and the particle size is ensured by 200-300 mesh sieve grading after pyrolysis, which is suitable for large-scale continuous production.

[0024] (4) The composite electrode of this invention is precisely prepared and has good interfacial compatibility: the electrode is prepared by ultrasonic atomization spraying (pressure 0.3-0.5MPa, rate 5-10mL / min), and the surface density of the active material is 1-5mg / cm³. 2The coating thickness (5-20μm) is controllable, and the coating uniformity is high. The purification step (acid soaking + water washing to neutral) removes residual impurities, improves material purity, and ensures the interfacial compatibility between the electrode and the electrolyte (liquid / solid).

[0025] (5) The composite material of the present invention has a wide range of applications and is compatible with the development direction of all-solid-state batteries: the material can be used in liquid electrolytes and all-solid-state batteries. When adapted to all-solid-state structures, it can meet the diverse needs of new energy electric vehicles (power batteries), large-scale energy storage systems, and portable electronic devices, and conform to the technological development trend of all-solid-state batteries. Attached Figure Description

[0026] Figure 1 The charge / discharge voltage-specific capacity curves of Embodiment 1 of the present invention under different cycles (1 cycle, 50 cycles, 100 cycles) at a 0.1C rate.

[0027] Figure 2 The charge / discharge voltage-specific capacity curves of Embodiment 2 of the present invention under different number of cycles (1 cycle, 50 cycles, 100 cycles) at a 0.1C rate.

[0028] Figure 3 The charge / discharge voltage-specific capacity curves of Embodiment 3 of the present invention under different number of cycles (1 cycle, 50 cycles, 100 cycles) at a 0.1C rate.

[0029] Figure 4 The charge / discharge voltage-specific capacity curves of Comparative Example 1 of this invention are shown at a 0.1C rate for different number of cycles (1 cycle, 50 cycles, 100 cycles). Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] This invention discloses a method for preparing a hierarchical nanoporous Si quantum dot and C composite material, comprising the following steps: step: S1: Fabrication of silicon-tin quantum dots Silane (SiH4) was introduced into a 0.1-0.5 mol / L acidic SnCl2 solution (containing a small amount of hydrochloric acid to inhibit hydrolysis) at a flow rate of 10-50 mL / min, and reacted at a constant temperature of 25-35℃ for 30 min. Then, the reaction solution was mixed with anhydrous ethanol at a volume ratio of 1:3, transferred to a polytetrafluoroethylene-lined hydrothermal reactor, and hydrothermally reacted at 80-200℃ for 2-6 h under nitrogen protection to obtain silicon-tin nanoparticles. Silicon-tin nanoparticles were dispersed in deionized water at a solid-liquid ratio of 1:(20-50) and ultrasonically treated for 10-30 min until homogeneous; a nanosecond pulsed laser (wavelength 532nm, pulse width 1-100ns, energy density 1-5 J / cm³) was then used. 2 The dispersion was ablated for 10-60 min, followed by centrifugation (8000-12000 rpm, 10-15 min) to collect the supernatant. The supernatant was then heated and dried at 60 °C until all the water was evaporated, and the silicon-tin quantum dots were collected. S2: Preparation of hierarchical nanoporous Si quantum dots Silicon-tin quantum dots were placed in a tube furnace and oxidized by first introducing oxygen (flow rate 50-100 mL / min) and heating to 400-600℃ at 5℃ / min for 1-3 h. After oxidation, nitrogen gas (flow rate 100-200 mL / min) was used to purge for 10-20 min, followed by introducing hydrogen gas (flow rate 80-150 mL / min) and heating to 500-700℃ at 5℃ / min for 2-4 h. After natural cooling to room temperature, the dots were washed with 0.1-1 mol / L hydrochloric acid multiple times and then dried at 50-200℃ to obtain hierarchical nanoporous Si quantum dots with a pore size distribution of 0.1-1000 nm (where 0.1-1 nm accounts for <10%, 1-50 nm accounts for >50%, and 50-1000 nm accounts for >30%). S3: Construction of a three-dimensional interwoven conductive network and preparation of composite anode materials a. Sand milling dispersion: Graded nanoporous Si quantum dots and dispersant are mixed at a mass ratio of (80-95):(5-20), deionized water or ethanol is added (solid-liquid ratio 1:(10-20)), and the mixture is sand milled in a sand mill at 1000-2000 r / min for 1-3 h. After spray drying (inlet temperature 120-150℃, outlet temperature 50-80℃), graded nanoporous Si quantum dot dispersion powder is obtained. b. Ball milling composite: Take the above graded nanoporous Si quantum dot dispersion powder, conductive medium and carbon source in a mass ratio of (50-90):(5-30):(5-20), add solvent (solid-liquid ratio 1:(5-10)), and ball mill in a planetary ball mill at a ball-to-material ratio of (10-15):1 and a speed of 500-2500 r / min for 2-5 h to obtain precursor slurry; c. High-temperature pyrolysis: The precursor slurry is spray-dried at 50-150℃ to obtain composite powder, which is then placed in a tube furnace and heated to 800-1000℃ at 5-10℃ / min under argon protection and held for 3-5 hours for pyrolysis. After natural cooling, it is ground and passed through a 200-300 mesh sieve to obtain a composite material of graded nanoporous Si quantum dots and C.

[0032] The obtained hierarchical nanoporous Si quantum dot and C composite material was purified and electrode prepared. Specifically, S4: The hierarchical nanoporous Si quantum dot and C composite material was soaked in 0.1-1 mol / L acid solution for 0.5-24 h, washed with deionized water until neutral, and dried at 80-120℃ for 4-8 h; the purified product, conductive material, and binder were mixed in a mass ratio of (70-85):(5-15):(5-20), and the corresponding solvent (N-methylpyrrolidone (NMP) for polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC) for water) was added to adjust the solid content to 30%-50%, and stirred for 12-24 h until the slurry was homogeneous. The slurry was then sprayed using an ultrasonic atomizing sprayer (spraying pressure 0.3-0.5 MPa, spraying rate 5-10). The slurry was sprayed onto the surface of copper foil at a rate of mL / min, and then vacuum dried at 80-100℃ for 12-24h to obtain a negative electrode sheet of a composite material of hierarchical nanoporous Si quantum dots and C.

[0033] In step S1, the silicon-tin nanoparticles have a particle size of 50-200 nm. The anhydrous ethanol in step S1 serves three main purposes: first, it reduces the polarity of the system, slows particle growth, and helps form quantum dots of uniform size; second, it adsorbs onto the particle surface, preventing aggregation and improving dispersibility; and third, it assists in dissolving reaction intermediates, making the reaction more uniform. In step S2, high-temperature oxidation forms initial SiO pores on the surface of the silicon-tin quantum dots, and hydrogen reduction removes SnO impurities and expands the pores. The final hierarchical nanoporous Si quantum dots have a specific surface area of ​​100-800 m². 2 / g, with a porosity of 0.6-0.9.

[0034] In step S3a, the dispersant can be selected from one or more of the following: polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), Tween 80, nonylphenol polyoxyethylene ether (TX-10), polyethylene glycol (PEG), hexadecyltrimethylammonium bromide (CTAB), polyacrylamide (PAM), sodium dodecylbenzene sulfonate (LAS). In step S3b, the carbon source can be selected from any one or more of glucose, sucrose, artificial graphite, phenolic resin, chitosan, citric acid, polyethylene glycol, polyacrylonitrile (PAN), asphalt, etc. In step S3b, the conductive medium can be selected from any one or more of carbon nanotubes (CNTs), graphene, carbon black, and conductive graphite; the aspect ratio of the carbon nanotubes is 100-1000, the graphene is a single layer or few layers (number of layers ≤5), the carbon black is 20-50 nm in particle size, and the conductive graphite is 0.5-2 μm in particle size.

[0035] In step S3b, the solvent may be selected from any one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), methanol, ethanol, etc. The acid solution in step S4 can be selected from any one or more of hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid, etc.; the soaking temperature is 25-60℃. The adhesive used in step S4 can be selected from one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and polyvinyl alcohol (PVA); the molecular weight of the adhesive is: 500,000-1,000,000 for polyvinylidene fluoride (PVDF) and 100,000-500,000 for sodium carboxymethyl cellulose (CMC); the thickness of the copper foil is 8-12 μm, and the areal density of the active material on the copper foil after spraying is 1-5 mg / cm³. 2 The coating thickness is 5-20μm.

[0036] In steps S1 and S3c, the flow rate of the inert protective gas is 50-100 mL / min; in step S3c, after pyrolysis, the composite material is ground and sieved through a 200-300 mesh sieve to ensure that the particle size is controlled to be 1-10 μm.

[0037] The material has a three-layer structure of "hierarchical nanoporous Si quantum dot core - carbon coating layer - three-dimensional interwoven conductive network"; wherein the carbon coating layer includes an amorphous carbon layer on the surface of Si quantum dots and a carbon connecting layer between particles, and the three-dimensional conductive network is formed by the interweaving of carbon source carbonization products and conductive medium, with a network conductivity >90%.

[0038] The tap density of the material is 0.3-0.8 g / cm³. 3 The compacted density is 1.0-1.5 g / cm³. 3 The material has an initial coulombic efficiency of 85%-90% at a 0.1C rate and a capacity retention of 95%-99% after 100 cycles at a 0.1C rate.

[0039] In addition, the present invention provides the application of the composite material of hierarchical nanoporous Si quantum dots and C in all-solid-state lithium-ion batteries.

[0040] Application of the hierarchical nanoporous Si quantum dots and C composite material in lithium-ion battery anode sheets.

[0041] The lithium-ion battery negative electrode sheet is characterized in that the composite material of hierarchical nanoporous Si quantum dots and C, conductive material and binder are thoroughly mixed, a solvent is added, and then ultrasonically atomized and sprayed onto the surface of the metal electrode sheet. After drying, the lithium-ion battery negative electrode sheet is obtained.

[0042] The all-solid-state lithium-ion battery is characterized by comprising the lithium-ion battery negative electrode sheet.

[0043] The following are specific embodiments. Example 1 This embodiment uses silane (SiH4)-stannous chloride (SnCl2) as raw materials to prepare Si via hydrothermal synthesis-nanosecond pulsed laser ablation. 0.7 Sn 0.3 Quantum dots are prepared into graded nanoporous Si quantum dots through oxidation-reduction, and then a three-dimensional conductive network is constructed using single-walled carbon nanotubes as the conductive medium and glucose as the carbon source. Finally, a composite negative electrode is prepared by ultrasonic atomization spraying and assembled into an all-solid-state battery.

[0044] Step S1: Preparation of silicon-tin quantum dots Preparation of acidic SnCl2 solution: Add 5.6 g SnCl2•2H2O (analytical grade) to 100 mL of deionized water, and stir magnetically (500 r / min) until completely dissolved; add concentrated hydrochloric acid (37% by mass) dropwise to adjust the pH of the solution to 1.5 to inhibit Sn. 2+ Hydrolysis yields a 0.3 mol / L acidic SnCl2 solution; Silane reaction: The SnCl2 solution was transferred into a 250mL three-necked flask and placed in a constant temperature water bath (30℃); silane (SiH4) gas was introduced and the flow rate was controlled at 30mL / min by a gas mass flow meter. The reaction was continued for 30min. During the reaction, the solution gradually changed from colorless to light gray, indicating the formation of silicon-tin nanoparticles. Hydrothermal synthesis: After the reaction is completed, the reaction solution is mixed with anhydrous ethanol at a volume ratio of 1:3 (total volume 120mL), and transferred to a 50mL polytetrafluoroethylene-lined hydrothermal reactor; nitrogen gas (flow rate 80mL / min) is introduced to replace the air in the reactor 3 times (10min each time), and after sealing, it is placed in an oven and kept at 150℃ for 4h to carry out the hydrothermal reaction. Purification: After hydrothermal reaction, the mixture was allowed to cool naturally to room temperature, centrifuged (8000 rpm, 10 min) to collect the precipitate, washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 2 h to obtain Si. 0.7 Sn 0.3Nanoparticles (particle size measured by laser particle size analyzer: 80-150nm); Take 0.5g of the nanoparticles, add 15mL of deionized water at a solid-liquid ratio of 1:30, and sonicate for 20min (power 300W) to form a uniform suspension; Laser ablation and quantum dot collection: The suspension was transferred into a nanosecond pulsed laser reaction cell (model: XL-532), and the laser parameters were set as follows: wavelength 532nm, pulse width 50ns, energy density 3J / cm³. 2 The scanning speed was 10 mm / s, and the ablation was continued for 30 min. After ablation, the supernatant was collected by centrifugation (10000 rpm, 12 min) and then rotary evaporated at 60℃ until all water was evaporated to obtain Si. 0.7 Sn 0.3 Quantum dots.

[0045] Step S2: Preparation of hierarchical nanoporous Si quantum dots Oxidation treatment: Take 0.3g Si 0.7 Sn 0.3 Quantum dots are uniformly spread in a quartz boat (50mm×10mm×5mm) and placed in the constant temperature zone of a tube furnace; oxygen is introduced (flow rate 80mL / min), and the temperature is increased from room temperature to 500℃ at a rate of 5℃ / min and held for 2h. In this step, SiO initial pores are generated on the surface of silicon-tin quantum dots, and Sn element is oxidized to SnO. Reduction treatment: After oxidation, oxygen was turned off and nitrogen (flow rate 150 mL / min) was used to purge for 15 min to remove residual oxygen in the furnace; then hydrogen (flow rate 120 mL / min) was introduced and the temperature was raised to 600℃ at a rate of 5℃ / min, and held for 3 h. SiO was reduced to Si and SnO was reduced to Sn and volatilized. The furnace was then allowed to cool naturally to room temperature, washed multiple times with 0.2 mol / L hydrochloric acid, and then dried at 100℃. Performance characterization: The product, collected after natural cooling to room temperature, was identified as hierarchical nanoporous Si quantum dots; its specific surface area was determined to be 550 m² / g by liquid nitrogen adsorption-desorption (BET) method. 2 / g, the porosity measured by mercury intrusion porosimetry is 0.75; pore size analyzer test shows that 0.1-1nm accounts for 5%, 1-50nm accounts for 65%, and 50-1000nm accounts for 30%, which fully meets the requirements of hierarchical nanoporous structures.

[0046] Step S3: Construction of a three-dimensional interwoven conductive network and preparation of composite anode materials a. Sand milling dispersion: Take 2.7g of hierarchical nanoporous Si quantum dots, add 0.3g of polyvinylpyrrolidone (PVP, dispersant, K30 type), add 45mL of ethanol at a solid-liquid ratio of 1:15, transfer to a sand mill (grinding media is 0.1mm zirconia beads), set the speed to 1500r / min, and sand mill for 2h; after sand milling, send the slurry to a spray dryer (inlet temperature 135℃, outlet temperature 65℃) to obtain hierarchical nanoporous Si quantum dot dispersion powder (particle size 10-20μm). b. Ball milling and compounding: Weigh 1.4g of graded nanoporous Si quantum dot dispersion powder, 0.3g of single-walled carbon nanotubes, and 0.3g of glucose (carbon source) at a mass ratio of 70:15:15. Add 16mL of N-methylpyrrolidone (NMP) at a solid-liquid ratio of 1:8 and transfer to a planetary ball mill (grinding media: 5mm agate balls). Set the ball-to-material ratio to 12:1 and the rotation speed to 1000r / min, and ball mill for 3 hours to obtain a uniform precursor slurry. c. High-temperature pyrolysis: The precursor slurry is fed into a spray dryer (inlet temperature 100℃, outlet temperature 50℃) to obtain composite powder; the composite powder is transferred into a quartz boat, placed in a tube furnace, and argon gas (protective gas, flow rate 80mL / min) is introduced to raise the temperature to 900℃ at a rate of 8℃ / min and hold for 4 hours to pyrolyze glucose to form a carbon linking layer. CNTs and the carbon linking layer intertwine to form a three-dimensional conductive network; after pyrolysis, the mixture is naturally cooled, ground, and passed through a 250-mesh sieve to obtain a graded nanoporous Si quantum dot and C composite material (particle size 3-8μm).

[0047] Step S4: Purification and Electrode Preparation Purification: Take 1g of hierarchical nanoporous Si quantum dots and C composite material, add 50mL of 0.5mol / L hydrochloric acid solution, and soak in a constant temperature water bath (40℃) for 12h to remove residual zirconium oxide impurities and unreduced SiO; after soaking, centrifuge (8000rpm, 10min) to collect the precipitate, wash repeatedly with deionized water until the pH of the filtrate is 7 (neutral), and vacuum dry at 100℃ for 6h to obtain the purified product; Slurry preparation: Weigh 0.8g of purified product, 0.1g of CNT (conductive dielectric), and 0.1g of polyvinylidene fluoride (PVDF, binder, molecular weight 800,000) at a mass ratio of 80:10:10. Add NMP to adjust the solid content to 40%. Transfer to a magnetic stirrer (500r / min) and stir for 18h to obtain a uniform, particle-free electrode slurry. Ultrasonic atomization spraying: The slurry was transferred into an ultrasonic atomization spraying machine (model: UM-300), and the parameters were set as follows: spraying pressure 0.4MPa, spraying rate 8mL / min, and nozzle distance from copper foil 15cm; a 10μm thick copper foil (size 10cm×10cm) was fixed on a heating platform (60℃) for spraying; after spraying, the copper foil was transferred into a vacuum drying oven and vacuum dried at 80℃ for 18h to obtain a negative electrode sheet of a composite material of hierarchical nanoporous Si quantum dots and C. Electrode parameter testing: The surface density of the active material was measured to be 3 mg / cm³ using an electronic balance and vernier calipers. 2 The coating thickness is 12μm; the tape peel test showed that the coating did not peel off and had excellent adhesion.

[0048] Performance test results Material properties: Tap density 0.55 g / cm³ 3 Compacted density 1.30 g / cm³ 3 Specific surface area 550 m² 2 / g, porosity 0.75; All-solid-state battery assembly was carried out in an inert glove box (Ar atmosphere, water and oxygen content <0.1ppm): For positive electrode preparation, lithium indium alloy with an In content of 50%-70% is cut into circular pieces (e.g., 10-12 mm in diameter and 0.2-0.3 mm in thickness) that fit the positive electrode chamber of the PEEK mold. After wiping with anhydrous ethanol, it is lightly pressed at 2-3 MPa for 10-20 seconds at the positive electrode station.

[0049] For electrolyte treatment, take Li6PS5Cl powder with a particle size <1μm, calculate the amount based on the volume of the electrolyte layer in the mold (e.g., approximately 0.02-0.03g is needed for a 50μm thick, 10mm diameter cavity), pour it into the electrolyte station, and press it at 4-6MPa for 30-60s to form a density ≥2.2g / cm³. 3 The dense layer.

[0050] For battery assembly, first clean the PEEK mold assembly with anhydrous ethanol and then dry it at 60℃ for 30 minutes. Then, precisely stack the components in the following order: "lower cover → negative electrode plate → Li6PS5Cl electrolyte layer → lithium indium alloy positive electrode → upper cover" (deviation ≤ 0.1 mm). Tighten the bolts with a torque of 5-8 N•m to ensure that the interlayer interface pressure is 1-2 MPa. After sealing, measure the open circuit voltage (OCV ≥ 2.5V is normal).

[0051] Performance testing was performed using the AC impedance method (frequency 10). -2 -10 6 Electrolyte conductivity was measured at Hz, 25℃ (≥1×10⁻⁶ Hz). -3The S / cm value was tested by charging and discharging at 0-2.0V and 0.1C current using the Blue Electric system, and the test temperature did not exceed the long-term tolerance temperature of the PEEK mold (≤250℃).

[0052] Figure 1 This is the charge / discharge voltage-specific capacity curve of Embodiment 1 of the present invention under different cycle numbers (1 cycle, 50 cycles, 100 cycles) at a 0.1C rate. Figure 1 It can be seen that the initial discharge specific capacity at 0.1C rate is 1857.38mAh / g, and the initial coulombic efficiency is 88%; after 100 cycles at 0.1C rate, the discharge capacity is 1833.23mAh / g, and the capacity retention rate is 98.7%.

[0053] Example 2 In this embodiment, except that the carbon source in the ball milling composite step S3 is replaced by phenolic resin (analytical grade, softening point 80℃) instead of glucose, and the conductive medium is replaced by multi-walled carbon nanotubes and conductive graphite instead of single-walled carbon nanotubes, the remaining steps (S1, S2, S3(a)(c), S4) and parameters are completely consistent with those in Example 1, with the specific adjustments as follows: Step S3 ball milling composite: Weigh 1.4g of graded nanoporous Si quantum dot dispersion powder, 0.3g of multi-walled carbon nanotubes, 0.1g of conductive graphite, and 0.3g of phenolic resin in a mass ratio of 70:15:15, add 16mL of NMP, keep the ball milling parameters unchanged, and obtain the precursor slurry.

[0054] Performance test results Material properties: Tap density 0.52 g / cm³ 3 Compacted density 1.25 g / cm³ 3 Specific surface area 520 m² 2 / g, porosity 0.72; Figure 2 This is the charge / discharge voltage-specific capacity curve of Embodiment 2 of the present invention under different cycle numbers (1 cycle, 50 cycles, 100 cycles) at a 0.1C rate. (From...) Figure 2 It can be seen that the initial discharge specific capacity at 0.1C rate is 1804.54mAh / g, and the initial coulombic efficiency is 86%; after 100 cycles at 0.1C rate, the discharge capacity is 1761.23mAh / g, and the capacity retention rate is 97.6%.

[0055] Conclusion: After replacing the carbon source with phenolic resin, the initial discharge specific capacity of the material decreased from 1857.38 mAh / g to 1804.54 mAh / g, the initial coulombic efficiency decreased from 88% to 86%, and the capacity retention rate after 100 cycles decreased from 98.7% to 97.6%. The performance decreased slightly but remained excellent. The performance decline stemmed from the lower density of the carbonized carbon layer in phenolic resin compared to glucose, leading to a slight decrease in electron transport efficiency. Compared with the core requirements of high-energy-density battery anode materials (specific capacity ≥1500 mAh / g, initial coulombic efficiency ≥85%, capacity retention rate after 100 cycles ≥95%), Example 2 met all performance standards, demonstrating that the process of this invention has strong adaptability to carbon sources, and the resulting material can meet the application requirements of high-energy-density batteries.

[0056] Example 3 In this embodiment, except that the conductive medium in step S3, ball milling and compounding, is replaced by graphene (1-5 μm in diameter) and carbon black instead of carbon nanotubes, the remaining steps and parameters are the same as in Example 1. The specific adjustments are as follows: Step S3 Ball milling composite step: Weigh 1.4g of Si quantum dot dispersion powder, 0.3g of graphene, 0.1g of carbon black, and 0.3g of glucose at a mass ratio of 70:15:15, add 16mL of NMP solvent, keep the ball milling parameters unchanged, and obtain the precursor slurry.

[0057] Performance test results Material properties: Tap density 0.50 g / cm³ 3 Compacted density 1.20 g / cm³ 3 Specific surface area 530 m² 2 / g, porosity 0.73; Figure 3 This is the charge / discharge voltage-specific capacity curve of Embodiment 3 of the present invention under different cycle numbers (1 cycle, 50 cycles, 100 cycles) at a 0.1C rate. Figure 3 It can be seen that the initial discharge specific capacity at 0.1C rate is 1827.83mAh / g, and the initial coulombic efficiency is 87%; after 100 cycles at 0.1C rate, the discharge capacity is 1793.10mAh / g, and the capacity retention rate is 98.1%.

[0058] Conclusion: After replacing the conductive medium with graphene and carbon black, the initial discharge specific capacity of the material decreased from 1857.38 mAh / g to 1827.83 mAh / g, the initial coulombic efficiency decreased from 88% to 87%, and the capacity retention after 100 cycles decreased from 98.7% to 98.1%. However, the conductivity and cycle stability remained at a high level. The sheet-like structure of graphene can form a uniform conductive network, but due to its lower aspect ratio compared to carbon nanotubes (CNTs), the continuity of the electron transport path is slightly worse. Overall, the performance is close to that of the carbon nanotube approach, demonstrating the flexibility of this invention in selecting the conductive medium.

[0059] Comparative Example 1 To highlight the technical advantages of this invention, a comparative sample was prepared by referring to the method described by Su Liwei et al., which uses glucose as a carbon source to prepare Si / C materials via high-energy ball milling. The specific steps are as follows: Take 1g of commercial Si powder (particle size 1-5μm, purity 99.9%) and 0.5g of glucose, add 10mL of ethanol, transfer to a high-energy ball mill (ball-to-material ratio 20:1, speed 3000r / min), and ball mill for 5h; After ball milling, the powder was dried at 60°C and then placed in a tube furnace for carbonization at 800°C for 3 hours under nitrogen protection to obtain Si / C material. The electrode was prepared and the all-solid-state battery was assembled according to step S4 of Example 1, and the test parameters were the same as those in Example 1.

[0060] Performance test results Material properties: Tap density 0.25 g / cm³ 3 Compacted density 0.80 g / cm³ 3 Specific surface area 180 m² 2 / g, porosity 0.45; Figure 4 This is the charge-discharge voltage-specific capacity curve of Comparative Example 1 of the present invention at a 0.1C rate for different number of cycles (1 cycle, 50 cycles, 100 cycles). Figure 4 It can be seen that the initial discharge specific capacity at 0.1C rate is 1175.72mAh / g, and the initial coulombic efficiency is 78%; after 100 cycles at 0.1C rate, the discharge capacity is 999.83mAh / g, and the capacity retention rate is 85.04%.

[0061]

[0062] Performance comparison analysis of Examples 1, 2, and 3 with Comparative Example 1: (1) Significant differences in basic material properties: Comparative Example 1 tap density (0.25 g / cm³) 3 Compacted density (0.80 g / cm³) 3 (Example 1 only, 0.55g / cm) 3 1.30g / cm 3 45%-61% of the total surface area (180m²) 2 / g) Insufficient Example 1 (550m) 2The porosity (0.45) of the sample was 1 / 3 of that of Examples 1-3 (0.72-0.75). The root cause lies in the "hydrothermal synthesis-nanosecond pulsed laser ablation + three-dimensional conductive network construction" process of this invention, which can achieve hierarchical nanoporous structures and optimized stacking morphology, preventing silicon lithiation expansion; while the "high-energy ball milling + simple carbonization" process of Comparative Example 1 cannot form this structure, resulting in inferior basic performance.

[0063] (2) The advantages of electrochemical performance are prominent: the first coulombic efficiency: the comparative example 1 (78%) is 8-10 percentage points lower than that of examples 1-3 (86%-88%). This is because the hierarchical porous structure of the present invention can buffer the volume expansion of Si and reduce the side reactions of the electrolyte, while the Si powder of comparative example 1 has a large particle size and no porous buffer, and the side reactions are more intense. (3) Cyclic stability: The capacity retention rate (85.04%) of Comparative Example 1 after 100 cycles at 0.1C was 12.56-13.66 percentage points lower than that of Examples 1-3 (97.6%-98.7%). This is because the three-dimensional conductive network of the present invention can maintain the continuity of electron transport and prevent silicon lithiation expansion. Comparative Example 1 has no stable conductive network, and Si particles are prone to agglomeration and detachment, resulting in capacity decay.

[0064] (4) Difference in process flexibility and application value: Comparative Example 1 relies on a single carbon source and a fixed process, with no flexibility to adjust; after the carbon source (glucose → phenolic resin) and conductive medium (CNT → graphene) are replaced, the present invention still maintains excellent performance (specific capacity ≥1804mAh / g, initial coulombic efficiency ≥86%, 100-cycle retention rate ≥97.6%), and meets the core requirements of high energy density battery anode (specific capacity ≥1500mAh / g, initial coulombic efficiency ≥85%, 100-cycle retention rate ≥95%). The process flexibility and material performance are far superior to the existing technology (Comparative Example 1), and are more suitable for the large-scale application of high energy density all-solid-state batteries.

[0065] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical nanoporous Si quantum dot and C composite material, characterized in that, The method comprises the following steps: (1) passing silane into an acidic SnCl2 aqueous solution to obtain a reaction solution; adding the reaction solution into a hydrothermal reactor, and performing hydrothermal reaction under a non-oxidizing protective atmosphere to obtain silicon-tin nanoparticles; adding the silicon-tin nanoparticles into water, and then performing ultrasonic treatment to obtain a dispersion liquid; performing ablation on the dispersion liquid by using a nanosecond pulse laser; taking supernatant after centrifugation; and drying to obtain silicon-tin quantum dots; (2) placing the silicon-tin quantum dots obtained in step (1) into a tube furnace; first passing oxygen and heating to perform oxidation treatment; then passing nitrogen to perform purging; then passing hydrogen and heating to perform reduction treatment; cooling; washing; and drying to obtain hierarchical nano-porous Si quantum dots; (3) adding a dispersant and a solvent into the hierarchical nano-porous Si quantum dots obtained in step (2), and then performing sand milling; drying to obtain hierarchical nano-porous Si quantum dot dispersion powder; mixing the hierarchical nano-porous Si quantum dot dispersion powder, a conductive medium and a carbon source; adding a solvent and performing ball milling to obtain a precursor slurry; and performing pyrolysis on the precursor slurry under a non-oxidizing protective atmosphere; in the pyrolysis process, the carbon source is carbonized to form a carbon connecting layer, and the conductive medium and the carbon connecting layer are intertwined to form a three-dimensional conductive network, thereby obtaining a hierarchical nano-porous Si quantum dot and C composite material.

2. The method for preparing the hierarchical nanoporous Si quantum dots and C composite material as described in claim 1, characterized in that, In step (3), the carbon source is at least one of glucose, sucrose, artificial graphite, phenolic resin, chitosan, citric acid, polyethylene glycol, polyacrylonitrile and pitch.

3. The method for preparing a hierarchical nanoporous Si quantum dot and C composite material according to claim 1 or 2, characterized in that, The conductive medium is at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon black and conductive graphite.

4. The method of claim 1, wherein the preparation of the hierarchical nanoporous Si quantum dot and C composite material is characterized by, In step (3), the pyrolysis is specifically performed by increasing the temperature to 800-1000 ℃ at a temperature increasing rate of 5-10 ℃ / min, and maintaining the temperature for 3-5 h.

5. The method of claim 1, wherein the preparation of the hierarchical nanoporous Si quantum dot and C composite material is characterized by, In step (2), first, oxygen is passed at a flow rate of 50-100 mL / min, and the temperature is increased to 400-600 ℃ at a rate of 5 ℃ / min, and the oxidation treatment is performed by maintaining the temperature for 1-3 h; after the oxidation is completed, nitrogen is passed at a flow rate of 100-200 mL / min for purging for 10-20 min, hydrogen is then passed at a flow rate of 80-150 mL / min, the temperature is increased to 500-700 ℃ at a rate of 5 ℃ / min, and the reduction treatment is performed by maintaining the temperature for 2-4 h.

6. The method of claim 1, wherein the preparation of the hierarchical nanoporous Si quantum dot and C composite material is characterized by, In step (3), the ball milling is performed at a rotation speed of 500-2500 r / min for 2-5 h.

7. A hierarchical nano-porous Si quantum dot and C composite material prepared by the method of any one of claims 1-6.

8. Application of the hierarchical nano-porous Si quantum dot and C composite material of claim 7 to a battery negative electrode sheet.

9. A battery negative electrode sheet characterized by comprising: The hierarchical nano-porous Si quantum dot and C composite material, a conductive material and a binder are mixed uniformly, a solvent is then added, and the mixture is ultrasonic atomized and sprayed onto the surface of a metal electrode sheet, and after drying, a battery negative electrode sheet is obtained.

10. An all-solid-state lithium-ion battery, characterized by comprising: A battery negative electrode sheet comprising the hierarchical nano-porous Si quantum dot and C composite material of claim 7.

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