A nanoparticle monolayer self-assembled vanadium pentoxide nanosheet, a preparation method therefor and applications thereof

Abstract

The application discloses a kind of vanadium pentoxide nanoparticle monolayer self-assembly nanosheet and its preparation method and application, belong to lithium ion battery positive electrode material preparation technical field, its preparation method includes the following steps: vanadyl acetylacetonate is dissolved in the mixed solvent of isopropyl alcohol and nitric acid;The obtained solution is carried out in autoclave solvothermal reaction;The obtained product is separated by solid-liquid, washed by anhydrous ethanol and then dried;The product after drying is calcined, and the product is obtained.The nanosheet limits lithium ion de-embedding in single crystal grain, avoids particle irregular agglomeration, reduces concentration difference polarization;The pore volume between particles can reversibly absorb the volume expansion and shrinkage in charge and discharge process, and stabilize the cycle structure;Sheet morphology increases the contact area with electrolyte, and reduces ohmic resistance.As lithium ion battery positive electrode material, it can synergistically reduce polarization, stabilize structure and reduce impedance, thereby improving battery rate and cycle performance.In addition, the process is simple and easy to control, and the equipment requirement is low, suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material preparation technology, specifically relating to a vanadium pentoxide porous nanosheet composed of nanoparticles self-assembled in a single layer, its preparation method, and its application as a positive electrode material for lithium-ion batteries. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, developing lithium-ion batteries that combine high energy density, high power density, and long cycle life has become a key challenge. The cathode material, as a core component, directly determines the overall performance of the battery. Among numerous candidate materials, vanadium pentoxide (V₂O₅) stands out due to its unique layered structure and high theoretical specific capacity (approximately 294 mA h·g⁻¹ within a 2.0-4.0 V voltage window when two lithium ions are intercalated). -1 V₂O₅ has attracted much attention due to its low intrinsic electronic conductivity and low lithium-ion solid-phase diffusion coefficient (approximately 10⁻⁶). However, the practical application of V₂O₅ has long been hampered by its low intrinsic electronic conductivity and small lithium-ion solid-phase diffusion coefficient. - 12 cm 2 ·s -1 (scale) and volume changes caused by multi-step phase transitions during charging and discharging.

[0003] V₂O₅ nanostructuring is currently a hot research topic. Zero-dimensional nanoparticles can shorten the solid-phase diffusion distance of lithium ions to the nanoscale, but their extremely high specific surface energy makes them prone to random aggregation, forming dense secondary particles. This prevents the electrolyte from fully wetting the interior of the aggregates, forcing lithium ions to migrate slowly along tortuous paths within the aggregates. This results in highly uneven lithium intercalation / deintercalation processes, causing significant concentration polarization and severely limiting rate performance. Two-dimensional nanosheet particles, while possessing a high specific surface area and a short diffusion distance along the thickness direction, are prone to tight surface-to-face stacking during electrode fabrication, easily blocking ion transport channels. Furthermore, the anisotropic volume changes of two-dimensional nanosheet particles in the micrometer-scale direction can induce significant stress accumulation, and repeated volume expansion and contraction can easily lead to pulverization, resulting in poor cycle stability. Therefore, traditional V₂O₅ nanostructuring often only optimizes certain aspects of performance. Achieving short intercalation / deintercalation distances, high electrolyte wettability, and long-term structural self-buffering capabilities at the nanoscale is difficult to achieve simultaneously and may even be mutually restrictive.

[0004] By using elementary assembly, nanoparticles with short diffusion distances can be self-assembled into continuous porous nanosheets in a monolayer form, which holds promise for fundamentally resolving the contradiction of the aforementioned performance parameters being difficult to balance. However, how to induce primary nanocrystals to complete monolayer assembly into a stable whole in a two-dimensional plane through a simple and controllable liquid-phase self-assembly path is a key technical challenge in constructing such hierarchical structures, and there are currently few reports on this. Summary of the Invention

[0005] The purpose of this invention is to provide a monolayer self-assembled vanadium pentoxide nanosheet, its preparation method, and its applications, to solve the problems of existing V2O5 nanomaterials being unable to simultaneously possess short-range insertion / extraction distance, efficient electrolyte wetting, and a self-buffering structure, resulting in high polarization, high impedance, and poor cycle stability. This nanosheet is composed of a monolayer of V2O5 nanoparticles arranged in the same plane, with the layer thickness corresponding to the particle size of a single nanoparticle; there are pores between adjacent nanoparticles; and the overall structure exhibits a micron-scale, laterally extended two-dimensional sheet morphology. This unique monolayer self-assembled porous nanosheet architecture synergistically resolves the conflict between lithium-ion transport and structural stability at the nanoscale: the single-layer, single-particle thickness ensures that all grains can be directly exposed to the electrolyte, eliminating the tortuous diffusion path in traditional aggregates and suppressing concentration polarization; the pores between particles can reversibly absorb the expansion and contraction of grain volume during charge-discharge cycles, ensuring structural stability; and the two-dimensional sheet morphology ensures that it forms an extended conductive surface contact in the electrode, reducing the ohmic impedance at the electrode / electrolyte interface. Therefore, the monolayer self-assembled vanadium pentoxide nanosheets of the present invention, as a cathode material for lithium-ion batteries, can achieve synergistic optimization among reducing polarization, stabilizing structure, and reducing impedance, thereby improving the rate capability and cycle performance of the battery. Furthermore, the preparation method of the present invention is simple, easy to control, and requires minimal equipment, making it suitable for industrial production.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a single-layer self-assembled vanadium pentoxide nanosheet, comprising the following steps:

[0008] (1) Measure out isopropanol and nitric acid, mix them to obtain a mixed solvent;

[0009] (2) Add acetylacetone vanadium oxide to the mixed solvent obtained in step (1) and stir thoroughly;

[0010] (3) Transfer the solution obtained in step (2) into the reaction vessel for solvothermal reaction. After the reaction, remove the reaction vessel and allow it to cool naturally to room temperature.

[0011] (4) The solvothermal product obtained in step (3) is subjected to solid-liquid separation, washed with anhydrous ethanol, and dried in an oven to obtain a black product;

[0012] (5) The black product obtained in step (4) is placed in a tube furnace for calcination to obtain a single-layer self-assembled vanadium pentoxide nanosheet with a thickness of about 100 nm. The nanosheet is composed of a single layer of vanadium pentoxide nanoparticles assembled in the same plane, with pores between adjacent particles.

[0013] Preferably, in step (1), the volume ratio of isopropanol to nitric acid is 3:1 to 7:1; in step (2), the proportion of acetylacetone vanadium oxide in the mixed solvent is 0.001 to 0.1 g / mL.

[0014] In step (3), the solvothermal temperature is 120-220℃ and the holding time is 1-24h.

[0015] In step (5), the calcination temperature is 300-600℃, the calcination time is 1-12h, and the heating rate is 0.5-5℃ / min.

[0016] The aforementioned application of vanadium pentoxide nanosheets with monolayer self-assembled nanoparticles is used to prepare lithium-ion battery electrodes.

[0017] The vanadium pentoxide nanosheets, which are self-assembled monolayers of nanoparticles, are prepared by the method of any one of claims 1-4. Compared with the prior art, the advantages of this invention are: the nanosheets are composed of a monolayer of V₂O₅ nanoparticles, each of which is an independent electrochemical reaction unit and is fully surrounded by the electrolyte. The solid-phase diffusion of lithium ions is confined to the interior of individual particles rather than within the particle group of traditional aggregates. This structure reliably avoids the random aggregation between nanoparticles and solves the problem of "deactivation" of the active sites at the center of aggregates due to the inability of the electrolyte to wet and the excessively long ion pathway. This allows the electrode to reduce the concentration difference caused by the lithium insertion / extraction concentration gradient during cycling. Polarization ensures high-rate capacity release; the interconnected pores between monolayer particles effectively act as nanoscale "stress buffer chambers," synergistically accommodating the anisotropic volume expansion and contraction of each grain during charging / discharging, preventing particle compression, peeling, and current collector detachment, thus enhancing structural integrity and electrochemical reaction reversibility; the micron-scale laterally extended sheet-like morphology provides a large active solid-liquid contact area and abundant electrolyte storage space, forming a "surface contact" conductive network. This network can respond promptly to charge transfer demands at high current densities, providing unobstructed rapid lithium-ion replenishment channels and significantly reducing ohmic impedance caused by electrolyte transport lag and insufficient contact. Therefore, using it as a cathode material for lithium-ion batteries can reduce polarization, stabilize the structure, lower impedance, and improve the rate performance and cycle stability of lithium-ion batteries. Furthermore, the synthesis process of this invention is simple, the reaction conditions are easy to control, and the equipment requirements are low, making it suitable for industrial production. Attached Figure Description

[0018] Figure 1 The XRD pattern shows that the prepared product is an orthorhombic V2O5 pure phase;

[0019] Figure 2 The image is a low-magnification SEM image, showing that the product has a micron-sized, laterally extended sheet-like morphology.

[0020] Figure 3 The high-magnification SEM image shows that the nanosheets are assembled from a single layer of nanoparticles with uniform thickness, approximately 100 nm.

[0021] Figure 4 The TEM image shows a contrast between light and dark areas, revealing pores between adjacent particles within the nanosheet, confirming its porous structure.

[0022] Figure 5 Rate performance diagrams at different current densities (from 0.2C to 5C and then back to 0.2C);

[0023] Figure 6 For 1C (294mA g) -1 Cyclic performance diagram at current density. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the 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.

[0025] Example 1

[0026] (1) Measure 30 mL of isopropanol and 10 mL of nitric acid (65-68 wt%), stir for 10 min to mix them evenly, and obtain a mixed solvent;

[0027] (2) Add 0.663g of acetylacetone vanadium to the mixed solvent obtained in step (1) and stir thoroughly for 20min;

[0028] (3) The solution obtained in step (2) is transferred into a stainless steel high-pressure reactor lined with polytetrafluoroethylene and sealed. The reactor is then subjected to a solvothermal reaction at 200°C for 10 hours. After the reaction, the reactor is removed and allowed to cool naturally to room temperature.

[0029] (4) The solvothermal product obtained in step (3) is separated into solid and liquid by centrifugation, washed with anhydrous ethanol 3 to 5 times, and then dried in an oven at 60°C to obtain a black product.

[0030] (5) The black product obtained in step (4) is placed in a tube furnace and heated to 350°C at a heating rate of 1.5°C / min in an air atmosphere. The product is then kept warm and calcined for 2 hours to obtain a yellowish-brown product, namely a monolayer self-assembled vanadium pentoxide nanosheet with a thickness of about 100 nm. The nanosheet is composed of a monolayer assembly of nanoparticles in the same plane, with pores between adjacent particles.

[0031] The monolayer self-assembled vanadium pentoxide nanosheets prepared in this embodiment were tested using X-ray diffraction. The test results are as follows: Figure 1 As shown. (Through) Figure 1 It can be seen that all diffraction peaks can be identified as orthorhombic V2O5 (JCPDS card number: 41-1426), and no impurity phase peaks appear.

[0032] The self-assembled vanadium pentoxide nanosheets prepared in this embodiment were observed using a scanning electron microscope. Figure 2 , Figure 3 These are low-magnification and high-magnification SEM images, respectively. (Through...) Figure 2 As can be seen, vanadium pentoxide nanosheets were prepared; through Figure 3 It can be seen that the nanosheet is assembled from a single layer of nanocrystals in the same plane. The nanosheet is about 100 nm thick, which is comparable to the particle size of a single nanoparticle.

[0033] The self-assembled vanadium pentoxide nanosheets prepared in this embodiment were observed using transmission electron microscopy, such as... Figure 4 The TEM image shown. (Through...) Figure 4 It can be seen that the darker contrast areas correspond to particles, while the brighter contrast areas correspond to the pores between particles, further confirming its porous structure.

[0034] A single-layer self-assembled vanadium pentoxide nanosheet was used as the positive electrode material for lithium-ion batteries. A slurry was formed by uniformly mixing the prepared material (70 wt.%), acetylene black (20 wt.%), and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) solvent. This slurry was coated onto an aluminum foil current collector, dried at 60°C for 12 hours, and then rolled and punched into circular electrode sheets with a diameter of 15.5 mm. After vacuum drying at 120°C for 10 hours, the electrode sheets were assembled into CR2032 coin cells using lithium metal as the counter electrode, 1 M LiPF6 dissolved in a 1:1 EC / DMC solution as the electrolyte, and Celgard 2400 polypropylene as the separator. The battery was tested at different rates (1C = 294 mA g) within a voltage range of 2.0-4.0 V. -1 A constant current charge-discharge test was performed.

[0035] Ratio testing, such as Figure 5 As shown, at current densities of 0.2, 0.5, 1, 2, and 5C, the discharge specific capacities were 263, 247, 223, 197, and 155 mA hg, respectively. -1 When the current density switches from 5C back to 0.2C, the discharge specific capacity can recover to approximately 245 mA hg. -1 Rate testing showed that the prepared vanadium pentoxide nanosheets exhibited excellent structural stability and good rate performance.

[0036] Loop testing, such as Figure 6 As shown. At a current density of 1C, the discharge specific capacity after 100 cycles is 176 mA hg. -1 The specific capacity retention rate was 79%. Cyclic tests showed that the prepared vanadium pentoxide nanosheets had stable cycling performance.

Claims

1. A method for preparing a single-layer self-assembled vanadium pentoxide nanosheet, characterized in that, A solvothermal-calcination process was employed to induce the monolayer assembly of vanadium pentoxide primary nanocrystals into nanosheets by controlling the self-assembly conditions of vanadium salts and the liquid phase. The process included the following steps: (1) Measure out isopropanol and nitric acid, stir and mix them evenly to obtain a mixed solvent; (2) Add acetylacetone vanadium oxide to the mixed solvent obtained in step (1) and stir thoroughly; (3) Transfer the solution obtained in step (2) into the reaction vessel, seal it and carry out a solvothermal reaction. After the reaction is completed, let it cool naturally to room temperature. (4) The solvothermal product obtained in step (3) is centrifuged, washed with anhydrous ethanol, and dried in an oven to obtain a black product; (5) The black product obtained in step (4) is placed in a tube furnace and calcined in an oxygen atmosphere to obtain a single-layer self-assembled vanadium pentoxide nanosheet. The nanosheet is composed of a single layer of nanoparticles assembled in the same plane, with pores between adjacent nanoparticles. (6) In the monolayer self-assembled vanadium pentoxide nanosheets, the thickness of the nanosheets corresponds to the average particle size of a single vanadium pentoxide nanoparticle, and the lateral dimension of the nanosheets is in the micrometer range.

2. The method for preparing monolayer self-assembled vanadium pentoxide nanosheets according to claim 1, characterized in that: In step (1), the volume ratio of isopropanol to nitric acid is 3:1 to 7:1; in step (2), the ratio of acetylacetone vanadium oxide in the mixed solvent is 0.001 to 0.1 g / mL.

3. The method for preparing monolayer self-assembled vanadium pentoxide nanosheets according to claim 1, characterized in that... In step (3), the solvothermal temperature is 120–220°C and the holding time is 1–24 h.

4. The method for preparing monolayer self-assembled vanadium pentoxide nanosheets according to claim 1, characterized in that... In step (5), the calcination temperature is 300-600℃ in an oxygen-containing atmosphere, the calcination time is 1-12h, and the heating rate is 0.5-5℃ / min.

5. A single-layer self-assembled vanadium pentoxide nanosheet, characterized in that, The nanosheet is composed of vanadium pentoxide nanoparticles assembled in a single layer in the same plane. The thickness of the nanosheet corresponds to the particle size of a single nanoparticle. There are pores between adjacent nanoparticles. The lateral dimension of the nanosheet is on the micrometer scale. Preferably, the nanosheet is prepared by the method described in any one of claims 1-4.

6. The application of the monolayer self-assembled vanadium pentoxide nanosheets according to claim 5 as a positive electrode active material for lithium-ion batteries.

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