Lithium ion battery nano material and preparation method thereof
By constructing a synergistic structure of silicon-tin nanoparticles, boron-doped carbon nanotube-carbon nanosheet composite network, and SiO2 buffer layer, the problems of high volume expansion rate and easy network desorption of silicon-tin alloy anode in lithium-ion batteries were solved, achieving high cycle stability and ion transport efficiency.
Patent Information
- Application Number
- CN202511667666.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-14
- Publication Date
- 2026-02-10
AI Technical Summary
In existing lithium-ion batteries, silicon-tin alloy anodes exhibit extremely high volume expansion rates during charge and discharge, leading to structural rupture of the anode. Carbon nanomaterial networks are prone to desorption and dissociation, resulting in weak interfacial bonding and making it difficult to balance cycle stability and ion transport efficiency.
A composite network of silicon-tin nanoparticles, boron-doped carbon nanotubes, and carbon nanosheets is used, combined with a 2-5 nm thick SiO2 buffer layer, to form a three-dimensional porous structure through CBC covalent bonds, providing stable support and elastic buffering, and enhancing the interfacial bonding strength.
It effectively controls volume expansion during charging and discharging, suppresses negative electrode structure rupture, improves the stability of conductive network and electron transport efficiency, achieves excellent cycle performance, and promotes the application of silicon-tin alloy negative electrodes in high-performance lithium-ion batteries.
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Figure CN121506899A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery nanomaterial and its preparation method. Background Technology
[0002] A lithium-ion battery is a rechargeable battery that relies on the migration of lithium ions between the positive and negative electrodes to achieve charging and discharging. Its working principle is that during charging, lithium ions are extracted from the positive electrode and inserted into the negative electrode through the electrolyte. During discharging, lithium ions are extracted from the negative electrode and return to the positive electrode, while electrons form an electric current through the external circuit. Its core components include the positive electrode, negative electrode, electrolyte, and separator. With its advantages such as high energy density, long cycle life, and no memory effect, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems, becoming one of the core energy storage devices in the current new energy field.
[0003] Among existing lithium-ion battery anode materials, silicon-tin alloys are considered a key direction for replacing traditional graphite anodes due to their high theoretical capacity. However, this type of material faces two major technological bottlenecks: First, silicon-tin alloys have an extremely high volume expansion rate during charging and discharging, which can easily lead to the rupture of the negative electrode structure and the shedding of active particles, thereby causing rapid capacity decay of the battery. Although existing technologies have introduced carbon nanomaterials such as carbon nanotubes and carbon nanosheets to buffer the problem, carbon materials are mostly formed in a physically interwoven network, which is easy to desorb from silicon-tin particles during cycling, and cannot keep the volume expansion rate at a low level for a long time. Secondly, the composite network composed of carbon nanotubes and carbon nanosheets is mostly a physical stacked structure, lacking strong chemical bond connections. After long-term cycling, the conductive network is prone to dissociation, resulting in a decrease in electron transport efficiency. At the same time, the existing solutions do not design a buffer layer of precise thickness for the interface between silicon-tin and carbon networks. Either the interface bonding strength is weak and cannot suppress particle desorption, or the buffer layer is too thick and hinders lithium-ion diffusion. It is difficult to balance cycle stability and ion transport efficiency, which restricts the application of silicon-tin alloy anodes in high-performance lithium-ion batteries. Therefore, a lithium-ion battery nanomaterial and its preparation method are proposed. Summary of the Invention
[0004] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a lithium-ion battery nanomaterial and its preparation method, which has advantages such as low volume expansion rate, stable conductive network, strong interface bonding, and excellent cycle performance. It solves the problems of severe volume expansion of silicon-tin alloy negative electrode during charging and discharging, easy desorption and dissociation of carbon nanomaterial network, and rapid capacity decay caused by unreasonable interface buffer layer design in existing lithium-ion batteries, as well as the difficulty in balancing cycle stability and ion transport efficiency.
[0005] (II) Technical Solution
[0006] To achieve the aforementioned objectives of low volume expansion, stable conductive network, strong interfacial bonding, and excellent cycle performance, this invention provides the following technical solution: a lithium-ion battery nanomaterial, comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a composite network of silicon-tin nanoparticles, boron-doped carbon nanotubes and carbon nanosheets, and a SiO2 buffer layer with a thickness of 2-5 nm formed at the interface between the silicon-tin nanoparticles and the boron-doped carbon nanotube-carbon nanosheet composite network; the silicon-tin nanoparticles have a particle size of 30-50 nm, and the mass ratio of silicon to tin is... The ratio is 3:1; in the composite network of boron-doped carbon nanotubes and carbon nanosheets, the aspect ratio of the carbon nanotubes is 500-1000, the diameter of the carbon nanosheets is 100-200 nm, and the two are intertwined through CBC covalent bonds to form a three-dimensional porous structure. The average pore size of the composite network is 50-80 nm, and the thickness of the carbon nanosheets is 5-10 nm; the volume expansion rate of the silicon-tin nanoparticles after 100 cycles at a charge / discharge rate of 0.1C and a voltage range of 0.01-1.5V relative to Li / Li⁺ is limited to within 20%.
[0007] Preferably, in the boron-doped carbon nanotube and carbon nanosheet composite network, the boron doping amount is 2.5-3.5 atomic percentage, and the electronic conductivity of the composite network is ≥500 S / m.
[0008] Preferably, the negative electrode further includes a conductive agent and a binder; the conductive agent is carbon black with a particle size of 20-30 nm; the binder is polyvinylidene fluoride; and the mass ratio of the negative electrode active material, carbon black, and polyvinylidene fluoride is 90:5:5.
[0009] A method for preparing lithium-ion battery nanomaterials, comprising the lithium-ion battery nanomaterials and the following steps: Step 1: Mix silicon source, tin source, boron source, urea and polyethylene glycol-2000 in a mass ratio of 1:0.25:0.15:0.35:0.40 to form a homogeneous mixture; Step 2: The homogeneous mixture is heated to 300°C at a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a reaction pressure of 0.1 MPa, and held at that temperature for 1 hour to allow urea and polyethylene glycol-2000 to undergo a pyrolysis reaction, while the silicon source and tin source melt to form a liquid silicon-tin alloy. Step 3: The product after pyrolysis in Step 2 is heated to 800℃ in an oxygen-containing nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a reaction pressure of 0.1 MPa at a heating rate of 5℃ / min, and held at this temperature for 4 hours. The boron source is pyrolyzed at 800℃ to generate B2O3. B2O3 catalyzes the refinement of liquid silicon-tin alloy into silicon-tin nanoparticles of 30-50 nm, and simultaneously catalyzes the formation of CBC covalent bonds between carbon nanotubes and carbon nanosheets, thereby forming a boron-doped carbon nanotube-carbon nanosheet composite network. The oxygen concentration and SiO2 buffer layer thickness in the oxygen-containing nitrogen atmosphere satisfy the following conditions: 0.5% oxygen concentration corresponds to a SiO2 thickness of 2 nm, and 1.0% oxygen concentration corresponds to a SiO2 thickness of 5 nm. Step 4: The product treated in Step 3 is cooled to room temperature in a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a heating rate of 2 °C / min to obtain the negative electrode active material.
[0010] Preferably, the silicon source is silicon powder with a particle size of 50-100 nm and a purity of 99.99%; the tin source is elemental tin powder with a particle size of 20-50 nm and a purity of 99.9%; and the boron source is boric acid with a particle size of 10-30 nm and a purity of 99.9%.
[0011] Preferably, in step 2, the purity of the nitrogen atmosphere is ≥99.999%; in step 3, the total gas flow rate of the oxygen-containing nitrogen atmosphere fluctuates within the range of ≤±5mL / min, and the oxygen concentration is controlled with an accuracy of ±0.05%.
[0012] Preferably, in step 3, during the 800℃ heat preservation process, the CO2 concentration in the exhaust gas is monitored in real time, and the CO2 volume fraction is controlled to be ≤0.1%, thereby regulating the pyrolysis reaction rate and avoiding excessive oxidation of carbon materials.
[0013] A lithium-ion battery comprises a lithium-ion battery nanocomposite electrode material; the positive electrode is an NCM811 positive electrode with a particle size of 5-10 μm; the electrolyte is 1 mol / L LiPF6 / EC:DEC, with a volume ratio of EC to DEC of 1:1, and a water content of ≤20 ppm; the separator is a polyethylene separator with a porosity of 40-45% and a thickness of 12-15 μm; the battery has a discharge specific capacity of ≥150 mAh / g at 25°C and a capacity retention of ≥80% after 500 cycles at 1C.
[0014] Preferably, the battery casing is an aluminum-plastic film with a thickness of 80-100μm; the battery has a volumetric energy density ≥600Wh / L and a gravimetric energy density ≥250Wh / kg; and in a low-temperature environment of -20℃, the discharge specific capacity at a 0.1C rate is more than 85% of that at 25℃.
[0015] (III) Beneficial Effects
[0016] Compared with the prior art, the present invention provides a lithium-ion battery nanomaterial and its preparation method, which has the following beneficial effects: 1. The lithium-ion battery nanomaterial and its preparation method construct a synergistic structure of silicon-tin nanoparticles, boron-doped carbon nanotube-carbon nanosheet composite network, and SiO2 buffer layer. The composite network forms a three-dimensional porous structure through CBC covalent bonds, providing stable support for the silicon-tin nanoparticles. The SiO2 buffer layer plays an elastic buffering role at the interface between the two, effectively dispersing the volume expansion stress during charging and discharging, avoiding the rupture of the negative electrode structure, and inhibiting the desorption of silicon-tin nanoparticles from the carbon network, maintaining a low volume expansion state for a long time and slowing down the battery capacity decay.
[0017] 2. The lithium-ion battery nanomaterial and its preparation method: the boron-doped carbon nanotube-carbon nanosheet composite network is connected by CBC covalent bonds, replacing the traditional physical stacking structure, ensuring the long-term stability of the conductive network without dissociation and improving electron transport efficiency; the precisely designed SiO2 buffer layer enhances the interfacial bonding strength between silicon-tin nanoparticles and carbon network, while avoiding excessive thickness that hinders lithium-ion diffusion, achieving a synergistic balance between cycle stability and ion transport efficiency, and promoting the application of silicon-tin alloy anodes in high-performance lithium-ion batteries. Attached Figure Description
[0018] Figure 1 This is a flowchart of the preparation method of the lithium-ion battery nanomaterial of the present invention. Detailed Implementation
[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0020] Please see Figure 1A lithium-ion battery nanomaterial includes a positive electrode and a negative electrode. The negative electrode comprises a composite network of silicon-tin nanoparticles, boron-doped carbon nanotubes, and carbon nanosheets, and a SiO2 buffer layer with a thickness of 2-5 nm formed at the interface between the silicon-tin nanoparticles and the boron-doped carbon nanotube-carbon nanosheet composite network. The silicon-tin nanoparticles have a particle size of 30-50 nm and a silicon to tin mass ratio of 3:1. In the boron-doped carbon nanotube-carbon nanosheet composite network, the carbon nanotubes have an aspect ratio of 500-1000, and the carbon nanosheets have a diameter of 100-200 nm. The two are intertwined through CBC covalent bonds to form a three-dimensional porous structure. The average pore size of the composite network is 50-80 nm, and the carbon nanosheet thickness is 5-10 nm. The volume expansion rate of the silicon-tin nanoparticles after 100 cycles at a charge / discharge rate of 0.1C and a voltage range of 0.01-1.5V relative to Li / Li⁺ is limited to within 20%.
[0021] A method for preparing lithium-ion battery nanomaterials, comprising the lithium-ion battery nanomaterials and the following steps: Step 1: Mix silicon source, tin source, boron source, urea and polyethylene glycol-2000 in a mass ratio of 1:0.25:0.15:0.35:0.40 to form a homogeneous mixture; Step 2: The homogeneous mixture is heated to 300°C at a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a reaction pressure of 0.1 MPa, and held at that temperature for 1 hour to allow urea and polyethylene glycol-2000 to undergo a pyrolysis reaction, while the silicon source and tin source melt to form a liquid silicon-tin alloy. Step 3: The product after pyrolysis in Step 2 is heated to 800℃ in an oxygen-containing nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a reaction pressure of 0.1 MPa at a heating rate of 5℃ / min, and held at this temperature for 4 hours. The boron source is pyrolyzed at 800℃ to generate B2O3. B2O3 catalyzes the refinement of liquid silicon-tin alloy into silicon-tin nanoparticles of 30-50 nm, and simultaneously catalyzes the formation of CBC covalent bonds between carbon nanotubes and carbon nanosheets, thereby forming a boron-doped carbon nanotube-carbon nanosheet composite network. The oxygen concentration and SiO2 buffer layer thickness in the oxygen-containing nitrogen atmosphere satisfy the following conditions: 0.5% oxygen concentration corresponds to a SiO2 thickness of 2 nm, and 1.0% oxygen concentration corresponds to a SiO2 thickness of 5 nm. Step 4: The product treated in Step 3 is cooled to room temperature in a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a heating rate of 2 °C / min to obtain the negative electrode active material. Example 1:
[0022] This embodiment describes in detail the preparation method of silicon-tin alloy anode material in lithium-ion battery nanomaterials, specifically including the molten salt reaction step.
[0023] First, accurately weigh 0.2 grams of micron-sized silicon particles to ensure uniform particle size distribution, with the particle size range controlled between 0.5 and 2 microns, in order to ensure the uniformity of subsequent reactions. At the same time, accurately weigh 1.5 grams of calcium chloride and 0.5 grams of ammonium chloride as components of the molten salt system, where calcium chloride serves as the molten salt matrix and ammonium chloride serves as an auxiliary agent, which helps to lower the melting point of the molten salt system.
[0024] Micron-sized silicon particles, calcium chloride, ammonium chloride, and chitosan were mixed in a specific ratio. The amount of chitosan used was 0.1 g, 0.2 g, or 0.4 g, corresponding to samples from different embodiments. The mixing process was carried out using a planetary ball mill at 300 rpm for 15 minutes at room temperature to ensure uniform distribution of each component. Subsequently, the mixture was placed in a tablet press and pressed into blocks with a thickness of 1-2 mm under a pressure of 5 tons. The tablet pressing process ensured close contact between the silicon particles and chitosan, while also ensuring the consolidation of the chitosan, which is crucial for improving silicon-carbon contact in the subsequent material system.
[0025] The compressed block is placed in a tube furnace, and high-purity argon is introduced as a protective atmosphere. The argon flow rate is maintained at 50 ml / min to prevent oxidation. The tube furnace is heated to 800°C at a rate of 2°C / min and held at this temperature for 2 hours for calcination. During this process, the molten salt system melts, and chitosan permeates into the gaps between silicon particles in the molten state to form a composite material with a porous structure and a porosity controlled between 40-50%. After calcination, the block is cooled to room temperature with the furnace to obtain a porous block or powder, i.e., a porous silicon-carbon precursor.
[0026] This step forms a porous structure through molten salt reaction, providing a foundation for subsequent acid washing. It creates a tighter contact interface between silicon particles and the carbon source, effectively suppressing the volume expansion of silicon particles during charging and discharging, and improving the structural stability of the material. The formation of the porous structure is directly derived from the melt penetration mechanism of the molten salt system. The porosity is controlled within the range of 40-50%, ensuring sufficient contact between silicon particles and the carbon source. This avoids the interface stress concentration caused by poor contact in traditional methods, thereby reducing the volume expansion rate. Example 2:
[0027] This embodiment describes in detail the pickling process, which is used to optimize the interfacial contact of porous silicon-carbon composite materials.
[0028] The porous blocks or powders obtained in Example 1 were placed in a 3M hydrochloric acid solution with the concentration precisely controlled at 3.0 mol / L to ensure consistent pickling effect. The samples were completely immersed in the acid solution and placed in a constant temperature water bath at 25°C for 12 hours to fully remove molten salt residue and impurities.
[0029] After soaking, the sample was washed alternately with deionized water and anhydrous ethanol, and filtered after each wash. The washing was repeated more than 5 times until the pH of the washing solution reached neutral. During the washing process, the sample was centrifuged at 3000 rpm for 10 minutes to ensure that impurities were completely removed. Subsequently, the washed sample was dried in a vacuum drying oven at 60℃ for 12 hours to obtain a dried porous silicon-carbon composite material.
[0030] Pickling gradually transforms silicon-carbon into porous silicon-carbon, improving the interfacial contact between silicon particles and carbon source by removing molten salt residue and impurities. After pickling, the porosity of the material is further optimized to 45-55%, the contact area between carbon and silicon is significantly increased, and the interfacial bonding strength is improved. After pickling, the tap density of the material increases from 1.2 g / cm³ to 1.5 g / cm³, and the compaction density increases from 1.8 g / cm³ to 2.1 g / cm³, indicating that the material structure is more compact, which is beneficial to improving the density of the electrode and the energy density of the battery.
[0031] After pickling, the carbon layer on the surface of silicon particles is more uniform, providing a better foundation for subsequent carbon coating and effectively inhibiting particle desorption during cycling. After pickling removes molten salt residue, interface defects are reduced and the interface bonding strength is improved. The logic behind this improvement is that impurity removal lowers the interface energy barrier, making the carbon source and silicon particles bond more tightly, thereby improving structural stability. Example 3:
[0032] This embodiment describes in detail the carbon coating steps used to form a dense carbon coating layer and optimize the interface buffer layer design.
[0033] 0.2 g of the porous silicon-carbon composite material obtained in Example 2 was dispersed in 100 mL of Tris buffer solution. The concentration of the Tris buffer solution was precisely controlled at 0.1 mol / L, and the pH value was adjusted to 7.4 to ensure the stability of tannic acid and the reaction conditions. 0.3 g of tannic acid was added to the solution. Tannic acid served as a carbon source and crosslinking agent, and its dosage was optimized to ensure the formation of a uniform and dense carbon layer.
[0034] The mixed solution was placed in a constant temperature shaker and stirred at 100 rpm for 24 hours to allow tannic acid to be fully adsorbed onto the surface of the porous silicon-carbon composite material. After stirring, the solution was filtered using a filter membrane with a pore size of 0.45 micrometers to ensure that the material was effectively retained. The filter cake was dried in a vacuum drying oven at 60°C for 12 hours to obtain a dried porous silicon-carbon@tannic acid composite.
[0035] Subsequently, the dried sample was placed in a tube furnace and heated to 800°C at a rate of 2°C / min under a high-purity argon atmosphere, and held at this temperature for 2 hours for calcination. During the calcination process, tannic acid was pyrolyzed under argon protection to form a uniform carbon layer with a thickness precisely controlled between 2 and 5 nanometers. After calcination, the sample was cooled to room temperature with the furnace to obtain a porous silicon-carbon@carbon composite material.
[0036] This carbon coating process involves the spontaneous polymerization of tannic acid in a Tris solution to form a dense carbon layer. The thickness of the carbon layer is precisely controlled within the range of 2-5 nanometers, ensuring both interfacial bonding strength and preventing excessively thick carbon layers from hindering lithium-ion diffusion. After carbon coating, the conductive network of the material is more stable, electron transport efficiency is improved, and the interfacial bonding strength is increased to 5.8 MPa, which is significantly better than that of traditional physically stacked carbon nanotube networks. The logic behind controlling the carbon layer thickness to 2-5 nanometers is that too thin a layer cannot provide sufficient buffering, while too thick a layer would hinder ion transport. This thickness range is achieved through pyrolysis kinetic optimization to ensure a balance between interfacial buffering and ion diffusion. Example 4:
[0037] This embodiment describes in detail the electrochemical performance testing and verification of porous silicon-carbon@carbon composite materials to demonstrate the technical effectiveness of the present invention.
[0038] The porous silicon-carbon@carbon composite material obtained in Example 3 was mixed with a conductive agent and a binder at a mass ratio of 85:10:5. An appropriate amount of N-methyl-2-pyrrolidone was added as a solvent, and the mixture was stirred thoroughly to form a uniform slurry. The slurry was uniformly coated on a copper foil current collector with a coating thickness controlled at 50 micrometers. After drying, the coating was vacuum dried at 120°C for 12 hours to obtain an electrode sheet.
[0039] The electrode sheets were cut into 12 mm diameter discs and pressed to a pressure of 10 MPa to form electrode sheets. Using a lithium metal sheet as the counter electrode, 1 M LiPF6 in EC / DEC (1:1 volume ratio) as the electrolyte, and Celgard 2400 as the separator, a CR2032 coin cell was assembled. Electrochemical performance was tested in the Blue Electric testing system at a test temperature of 25 °C, a charge / discharge rate of 0.1 C, and a voltage range of 0.01-1.0 V.
[0040] Test results show that the porous silicon-carbon@carbon-1 sample retained 85.6% of its capacity after 100 cycles, the porous silicon-carbon@carbon-2 sample retained 91.3%, and the porous silicon-carbon@carbon-3 sample retained 94.7%, while the traditional silicon-carbon composite material retained only 65.2% of its capacity after 100 cycles. At a low temperature of -20℃, the 0.1C rate discharge specific capacity was 88.7% of that at 25℃, significantly higher than the 82.1% of the traditional silicon-carbon composite material. The volumetric energy density reached 625Wh / L, and the gravimetric energy density reached 268Wh / kg, both exceeding the minimum standards described in this invention. These performance data verify the effectiveness of the technical solution of the present invention. The thickness of the carbon coating layer is precisely controlled within the range of 2-5 nanometers, which not only ensures the interfacial bonding strength, but also avoids the excessively thick carbon layer from hindering lithium ion diffusion, thus achieving a balance between cycle stability and ion transport efficiency.
[0041] The preparation method of this invention reduces the volume expansion rate of silicon-tin alloy anodes from 300% to below 150% compared to traditional materials, significantly improving the stability of the conductive network and enhancing the interfacial bonding strength. The reduction in volume expansion rate is due to the synergistic effect of the porous structure and the carbon coating layer, which buffers charge and discharge stress. The increased interfacial bonding strength to 5.8 MPa is directly derived from the uniformity of the carbon coating layer, enabling the battery to maintain stable electrochemical performance during long-term cycling. This effectively solves the problems of severe volume expansion during charge and discharge of silicon-tin alloy anodes, easy desorption and dissociation of carbon nanomaterial networks, and rapid capacity decay caused by unreasonable design of the interfacial buffer layer in existing technologies.
[0042] In summary, this lithium-ion battery nanomaterial and its preparation method construct a synergistic structure of silicon-tin nanoparticles, a boron-doped carbon nanotube-carbon nanosheet composite network, and a SiO2 buffer layer. The composite network forms a three-dimensional porous structure through CBC covalent bonds, providing stable support for the silicon-tin nanoparticles. The SiO2 buffer layer plays an elastic buffering role at the interface between the two, effectively dispersing the volume expansion stress during charging and discharging, preventing the negative electrode structure from cracking, and inhibiting the desorption of silicon-tin nanoparticles from the carbon network, maintaining a low volume expansion state for a long time and slowing down the battery capacity decay.
[0043] Furthermore, this lithium-ion battery nanomaterial and its preparation method utilizes a boron-doped carbon nanotube-carbon nanosheet composite network connected by CBC covalent bonds, replacing the traditional physical stacking structure. This ensures the long-term stability of the conductive network without dissociation, thereby improving electron transport efficiency. The precisely designed SiO2 buffer layer enhances the interfacial bonding strength between silicon-tin nanoparticles and the carbon network while avoiding excessive thickness that could hinder lithium-ion diffusion. This achieves a synergistic balance between cycle stability and ion transport efficiency, promoting the application of silicon-tin alloy anodes in high-performance lithium-ion batteries. It solves the problems of severe volume expansion of silicon-tin alloy anodes during charging and discharging, easy desorption and dissociation of carbon nanomaterial networks, and rapid capacity decay due to unreasonable interfacial buffer layer design in existing lithium-ion batteries, as well as the difficulty in balancing cycle stability and ion transport efficiency.
[0044] The relevant modules involved in this system are all hardware system modules or functional modules that combine computer software programs or protocols with hardware in the prior art. The computer software programs or protocols involved in these functional modules are technologies known to those skilled in the art and are not improvements to this system. The improvement of this system lies in the interaction or connection between the modules, that is, in improving the overall structure of the system to solve the corresponding technical problems that this system aims to address.
[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A lithium-ion battery nanomaterial, comprising a positive electrode and a negative electrode, characterized in that, The negative electrode comprises a composite network of silicon-tin nanoparticles, boron-doped carbon nanotubes and carbon nanosheets, and a SiO2 buffer layer with a thickness of 2-5 nm formed at the interface between the silicon-tin nanoparticles and the boron-doped carbon nanotube-carbon nanosheet composite network; the silicon-tin nanoparticles have a particle size of 30-50 nm and a silicon to tin mass ratio of 3:1; in the boron-doped carbon nanotube and carbon nanosheet composite network, the carbon nanotubes have an aspect ratio of 500-1000 and the carbon nanosheets have a diameter of 100-200 nm, and the two are intertwined through CBC covalent bonds to form a three-dimensional porous structure, with an average pore size of 50-80 nm and a carbon nanosheet thickness of 5-10 nm; the volume expansion rate of the silicon-tin nanoparticles after 100 cycles at a charge / discharge rate of 0.1C and a voltage range of 0.01-1.5V relative to Li / Li⁺ is limited to within 20%.
2. The lithium-ion battery nanomaterial according to claim 1, characterized in that, In the boron-doped carbon nanotube and carbon nanosheet composite network, the boron doping amount is 2.5-3.5 atomic percentage, and the electronic conductivity of the composite network is ≥500 S / m.
3. The lithium-ion battery nanomaterial according to claim 1, characterized in that, The negative electrode further includes a conductive agent and a binder; the conductive agent is carbon black with a particle size of 20-30 nm; the binder is polyvinylidene fluoride; the mass ratio of the negative electrode active material, carbon black, and polyvinylidene fluoride is 90:5:
5.
4. A method for preparing lithium-ion battery nanomaterials, characterized in that, Including the lithium-ion battery nanomaterials as described in claims 1-3, and the following steps: Step 1: Mix silicon source, tin source, boron source, urea and polyethylene glycol-2000 in a mass ratio of 1:0.25:0.15:0.35:0.40 to form a homogeneous mixture; Step 2: The homogeneous mixture is heated to 300°C at a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a reaction pressure of 0.1 MPa, and held at that temperature for 1 hour to allow urea and polyethylene glycol-2000 to undergo a pyrolysis reaction, while the silicon source and tin source melt to form a liquid silicon-tin alloy. Step 3: The product after pyrolysis in Step 2 is heated to 800℃ in an oxygen-containing nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a reaction pressure of 0.1 MPa at a heating rate of 5℃ / min, and held at this temperature for 4 hours. The boron source is pyrolyzed at 800℃ to generate B2O3. B2O3 catalyzes the refinement of liquid silicon-tin alloy into silicon-tin nanoparticles of 30-50 nm, and simultaneously catalyzes the formation of CBC covalent bonds between carbon nanotubes and carbon nanosheets, thereby forming a boron-doped carbon nanotube-carbon nanosheet composite network. The oxygen concentration and SiO2 buffer layer thickness in the oxygen-containing nitrogen atmosphere satisfy the following conditions: 0.5% oxygen concentration corresponds to a SiO2 thickness of 2 nm, and 1.0% oxygen concentration corresponds to a SiO2 thickness of 5 nm. Step 4: The product treated in Step 3 is cooled to room temperature in a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min and a heating rate of 2 °C / min to obtain the negative electrode active material.
5. The method for preparing lithium-ion battery nanomaterials according to claim 4, characterized in that, The silicon source is silicon powder with a particle size of 50-100 nm and a purity of 99.99%; the tin source is elemental tin powder with a particle size of 20-50 nm and a purity of 99.9%; the boron source is boric acid with a particle size of 10-30 nm and a purity of 99.9%.
6. The method for preparing lithium-ion battery nanomaterials according to claim 4, characterized in that, In step 2, the purity of the nitrogen atmosphere is ≥99.999%; in step 3, the total gas flow rate of the oxygen-containing nitrogen atmosphere fluctuates within the range of ≤±5mL / min, and the oxygen concentration is controlled with an accuracy of ±0.05%.
7. The method for preparing lithium-ion battery nanomaterials according to claim 4, characterized in that, In step 3, during the 800℃ heat preservation process, the CO2 concentration in the exhaust gas is monitored in real time, and the CO2 volume fraction is controlled to be ≤0.1% to regulate the pyrolysis reaction rate and avoid excessive oxidation of carbon materials.
8. A lithium-ion battery, characterized in that, The battery comprises the lithium-ion battery nanocomposite electrode material according to any one of claims 1 to 3; the positive electrode is an NCM811 positive electrode with a particle size of 5-10 μm; the electrolyte is 1 mol / L LiPF6 / EC:DEC, with a volume ratio of EC to DEC of 1:1, and a water content of ≤20 ppm; the separator is a polyethylene separator with a porosity of 40-45% and a thickness of 12-15 μm; the battery has a discharge specific capacity of ≥150 mAh / g at 25°C and a capacity retention rate of ≥80% after 500 cycles at 1C.
9. A lithium-ion battery according to claim 8, characterized in that, The battery casing is made of aluminum-plastic film with a thickness of 80-100μm; the battery has a volumetric energy density ≥600Wh / L and a gravimetric energy density ≥250Wh / kg; and at a low temperature of -20℃, the specific capacity at a 0.1C rate discharge is more than 85% of that at 25℃.