Method for preparing nano tungsten trioxide by photoelectric synergistic oxidation and etching of micron tungsten trioxide and application of nano tungsten trioxide in ternary lithium battery

Abstract

The application provides a method for preparing nano tungsten trioxide through photoelectric synergistic oxidation and etching of micrometer tungsten trioxide and application of the nano tungsten trioxide in ternary lithium batteries, and belongs to the technical fields of nanometer material preparation and new energy batteries. Micrometer tungsten trioxide is loaded on a titanium net to prepare an anode, a graphite plate is used as a cathode, ultraviolet light is irradiated on the anode side, and the nano tungsten trioxide is prepared through photoelectric synergistic oxidation and etching reaction. Citrate is selectively adsorbed on high-energy crystal faces of tungsten trioxide through carboxyl groups, the growth of the high-energy crystal faces is strongly inhibited, low-energy crystal faces are dominated to expand, and a regular shape is formed. A pulse electric field breaks the anisotropic growth tendency of a direct current electric field by means of periodical relaxation and mass transfer reset, realizes uniform and mild deposition, and obtains isotropic crystals. The growth rates of different sites are coordinated through various paths such as charge compensation, in-situ oxidation and kinetic passivation, and the morphology is uniformly and regularly developed. The nano tungsten trioxide can improve the electrochemical performance of ternary lithium batteries as a positive electrode material additive.

Description

Technical Field

[0001] This invention belongs to the fields of nanomaterial preparation and new energy battery technology, specifically relating to a method for preparing nano-tungsten trioxide from micron-sized tungsten trioxide through photoelectric synergistic oxidation and etching, and its application in ternary lithium batteries. Background Technology

[0002] Tungsten oxide (WO3) is an important semiconductor material with excellent optoelectronic properties, and it typically appears as a yellow or pale yellow powder. Due to its unique microstructure and abundant surface active sites, WO3 is widely used in optics and new energy batteries, and has attracted considerable attention, particularly as a cathode material additive for ternary lithium batteries.

[0003] Changes in the size of WO3 powder significantly affect its surface reactivity. For example, nano-WO3 and micron-sized WO3 differ greatly in particle size and specific surface area, leading to changes in their physicochemical properties and application scenarios. Specifically, this manifests in the following ways:

[0004] 1. Particle size and specific surface area

[0005] Nano WO3: The particle size is usually between 30 and 300 nm, with a large specific surface area and high surface activity.

[0006] Micron-sized WO3: Particle size is in the micron range, with a small specific surface area, severe agglomeration, and more stable particles.

[0007] 2. Physicochemical properties

[0008] Solubility: Nano-sized WO3 is easier to disperse, while micro-sized WO3 will affect the solubility due to its strong aggregation.

[0009] Melting point and density: The melting point of micron-sized WO3 is approximately 1470 °C, while that of nano-sized WO3 may be slightly lower due to surface effects; their densities are similar (approximately 7.16 g / cm³). 3 ).

[0010] Optical and catalytic performance: Nanoscale WO3 exhibits superior performance in photocatalysis and gas sensors due to its quantum effect and high specific surface area.

[0011] 3. Application Areas

[0012] Nano WO3: Used in high-precision gas sensors, smart windows, solar cells and new energy storage.

[0013] Micron-sized WO3: It is mainly used in traditional industrial fields such as cemented carbide and tungsten powder production.

[0014] Currently, the main processes for preparing nanoscale WO3 are:

[0015] 1. Thermal decomposition method

[0016] Micron-sized WO3 is mixed with a reducing agent (such as carbon powder or hydrogen) to generate tungstate or tungstate acid. This is then decomposed by heating at 500–800°C, with particle agglomeration suppressed by precise control of temperature and atmosphere (such as inert gas). After cooling, the mixture is pulverized and sieved to obtain nano-WO3 with uniform particle size.

[0017] 2. Wet reduction method

[0018] Micron-sized WO3 is dissolved in a strong acid (such as hydrochloric acid) or alkaline solution to form a tungstate solution. A reducing agent (such as hydrogen or hydrazine hydrate) is added, and a hydrothermal reaction is carried out under high temperature and high pressure to generate nano-WO3 particles.

[0019] However, all of the above preparation processes present several technical challenges. For example, the thermal decomposition method requires avoiding crystal form changes caused by high-temperature sintering; the wet reduction method requires strict control of pH value and reaction time, and is prone to introducing impurities during the reaction, placing a significant burden on subsequent separation steps and compromising purity. Therefore, how to rationally and effectively prepare nano-scale tungsten trioxide to improve the electrochemical performance of ternary lithium batteries is a pressing problem that needs to be solved by those skilled in the art. Summary of the Invention

[0020] To address the numerous problems existing in the preparation of nano-WO3 using current technologies, this invention proposes a method for preparing nano-tungsten trioxide from micron-sized tungsten trioxide via photoelectric synergistic oxidation and etching. This method enables rapid preparation of nano-tungsten trioxide with uniform particle morphology, high sphericity, and a high specific surface area. Furthermore, this nano-tungsten trioxide, as an additive in cathode materials, can enhance the electrochemical performance of ternary lithium batteries.

[0021] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0022] A method for preparing nano-sized tungsten trioxide from micron-sized tungsten trioxide via photoelectric synergistic oxidation and etching involves loading micron-sized tungsten trioxide onto a titanium mesh to form the anode, using a graphite plate as the cathode, and preparing an electrolyte solution using sodium tungstate, sodium citrate, hexadecyltrimethylammonium bromide, and water. The nano-sized tungsten trioxide is obtained by photoelectric synergistic oxidation and etching reactions under ultraviolet light irradiation on the anode side. The specific steps are as follows:

[0023] Step 1, Preparation of the anode:

[0024] Weigh out micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 50-100:10-20:0.5-1.5, mix them thoroughly with N-methylpyrrolidone, then uniformly coat the mixture onto a titanium mesh and repeatedly press and dry it to obtain the anode. Control the areal loading of the coating material to be 1-10 mg / cm². 2 ;

[0025] Step 2, preparation of electrolyte:

[0026] The molar ratio of sodium tungstate, sodium citrate, and hexadecyltrimethylammonium bromide in the electrolyte is 30~50:5~10:1~1.5, and the pH of the electrolyte is maintained at 4.5~5.5 by buffer solution.

[0027] Step 3, photoelectric synergistic oxidation and etching reaction:

[0028] An anode, cathode, and electrode solution are placed in an electrochemical reaction apparatus. Ultraviolet light is used to irradiate the anode side, and the following electrochemical reaction parameters are controlled to perform a photoelectric synergistic oxidation and etching reaction:

[0029] The reaction temperature is 20~30 ℃, and the reaction time is 20~50 min;

[0030] The electrode spacing is 1~3 cm, the pulse voltage is 20~40 V, the pulse frequency is 0.1~10 Hz, and the duty cycle is 10%~30%.

[0031] The ultraviolet wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 The illumination time is the same as the reaction time;

[0032] Step 4: Separate collection, washing, and drying:

[0033] After the reaction is complete, the reaction product is peeled off from the titanium mesh and dispersed at high speed along with the electrolyte, then filtered through a nanofiltration membrane; then it is washed by high-speed stirring and dispersion with deionized water, and filtered again through a nanofiltration membrane; finally, it is powdered by spray drying; during the washing process, large particles of conductive carbon black are filtered out, while the nano-tungsten trioxide particles that need to be retained flow out through the nanofiltration channels;

[0034] Step 5, low-temperature annealing and air jet milling:

[0035] Low-temperature annealing causes amorphous materials to crystallize, thereby stabilizing the structure. The spray-dried powder is heated to 300-400 °C in a clean air atmosphere and held for 0.5-1.5 h; after natural cooling to room temperature, it is pulverized by an air jet mill to eliminate agglomeration, finally obtaining nano-tungsten trioxide.

[0036] The reaction mechanism of photoelectric synergistic oxidation and etching is as follows:

[0037] 1. Pulsed current oxidation: relaxation effect and concentration field regulation, through intermittent energy supply, control nucleation and growth.

[0038] (1) The intermittent pulse current interrupts the growth rate of a specific crystal facet, resulting in balanced growth of the crystal facet and isotropic development.

[0039] (2) At the moment each current pulse begins, an extremely high instantaneous overpotential is generated on the electrode surface, inducing a large number of uniform nucleation points; the subsequent shutdown prevents the growth and fusion of these nuclei.

[0040] 2. Photoelectric synergistic oxidation: Driven by photogenerated carriers, the reaction efficiency is improved by photogenerated holes under low pressure, achieving tunability.

[0041] (1) Through photogenerated electron-hole pairs, W directly and simultaneously participates in the electrochemical oxidation and dissolution. 6+ This accelerates the dissolution rate of tungsten, achieving the same dissolution effect at a lower anode voltage.

[0042] (2) Under the action of the anodic electric field, photogenerated electrons are driven into the material and transferred through the external circuit, while holes are driven to the surface to participate in the reaction. The effective separation of charges fully suppresses electron-hole recombination to the ground, thus maximizing its utilization rate.

[0043] (3) Oxidation and dissolution are mainly completed by photogenerated holes, which reduces the dependence on electric field, allowing sufficient time and a mild environment for chemical reactions at the interface, inhibiting the severe disorder corrosion caused by electric field, and making it easy to form near-spherical shapes.

[0044] As a preferred embodiment of the present invention, in step 1, micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride are weighed according to a mass ratio of 80:15:1, mixed evenly with N-methylpyrrolidone, coated onto a titanium mesh, dried, and the area loading of the coating material is controlled to be 5 mg / cm². 2 .

[0045] As a preferred embodiment of the present invention, in step 2, the molar ratio of sodium tungstate, sodium citrate and hexadecyltrimethylammonium bromide in the electrolyte is 40:5:1, and the pH value of the electrolyte is stably maintained at 4.8~5.0 by using 0.1 M HAc-NaAc buffer solution.

[0046] As a preferred embodiment of the present invention, in step 3, the following electrochemical reaction parameters are controlled to carry out the photoelectric synergistic oxidation and etching reaction:

[0047] The reaction temperature was 25 ℃, and the reaction time was 30 min.

[0048] The electrode spacing is 3 cm, the pulse voltage is 35 V, the pulse frequency is 1 Hz, and the duty cycle is 20%.

[0049] The ultraviolet wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 The illumination time is the same as the reaction time.

[0050] As a preferred technical solution of the present invention, in step 5, the heating process is as follows: first, the temperature is increased to 100°C at 1°C / min, then increased to 350°C at 2°C / min, and then maintained for 1 hour before natural cooling.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] 1. Adding sodium citrate to the electrolyte allows its carboxyl functional groups (-COOH) to selectively and strongly adsorb onto the high-energy crystal faces of tungsten oxide. This exerts a strong kinetic inhibition on the growth of these crystal faces, significantly altering the relative growth rates of the crystals in different directions. This makes the previously slow-growing low-energy planes the dominant growth direction, ultimately leading to the large-area exposure of high-energy crystal faces and thus shaping a more regular tungsten oxide crystal shape. Adding hexadecyltrimethylammonium bromide forms a protective layer on the particle surface, preventing excessive crystal growth and agglomeration.

[0053] 2. The pulsed electric field, through periodic relaxation and mass transfer reset, kinetically breaks the anisotropic growth problem caused by the DC electric field, thereby directing the growth process towards a globally uniform and gentler reaction path, effectively avoiding local severe corrosion or excessively rapid deposition, and finally obtaining isotropic WO3 nanocrystals.

[0054] 3. By using 365 nm ultraviolet light to convert light energy into a localized, real-time responsive surface control capability, the growth rate of different surface sites can be selectively controlled through three parallel pathways: electrostatic neutralization or charge compensation, chemical in-situ oxidation of interfaces with faster growth, and kinetic passivation of active sites and activation of inert sites. This inhibits excessively fast growth and promotes excessively slow growth, thereby promoting the reaction towards a uniform, mild, and regular morphology.

[0055] 4. This invention enables the rapid preparation of nano-tungsten trioxide, with uniform particle morphology distribution (5~50 nm), high sphericity, and a high specific surface area (50~80 nm). 2 / g). At the same time, this nano-tungsten trioxide can be used as a cathode material additive, which can significantly improve the electrochemical performance of ternary lithium batteries. Attached Figure Description

[0056] Figure 1 This is a SEM image of micron-sized tungsten trioxide.

[0057] Figures 2-4 The images shown are SEM images of the products prepared in Experiment Examples 1-3, respectively.

[0058] Figures 5-7 The images shown are SEM images of the products prepared in Experiments 7-9.

[0059] Figures 8-10 The images shown are SEM images of the products prepared in Experimental Examples 10-12.

[0060] Figures 11-13 The images shown are SEM images of the products prepared in Examples 1-3, respectively.

[0061] Figure 14 The particle size distribution diagrams are for the products prepared in Examples 1-3 (corresponding to A, B, and C, respectively).

[0062] Figures 15-17 The particle size distribution curves are for the products prepared in Examples 1-3, respectively.

[0063] Figure 18 XRD patterns (A), W 4f XPS pattern (B), and O 1s XPS pattern (C) of micron-sized tungsten trioxide and nano-sized tungsten trioxide (prepared in Example 3).

[0064] Figure 19 The N2 isothermal adsorption curves of micron-sized tungsten trioxide (corresponding to A) and nano-sized tungsten trioxide prepared in Examples 1-3 (corresponding to B, C, and D, respectively). Detailed Implementation

[0065] The present invention will be further described in detail below with reference to embodiments, test examples and accompanying drawings.

[0066] Experimental Examples 1-6: Effects of Different Electrolyte Component Concentrations on the Prepared Products

[0067] The preparation steps are as follows:

[0068] Step 1, Preparation of the anode:

[0069] Micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride were weighed according to a mass ratio of 80:15:1, mixed evenly with N-methylpyrrolidone, and then uniformly coated onto a titanium mesh. The mixture was repeatedly pressed and dried to obtain the anode, with the areal loading of the coating material controlled at 5 mg / cm². 2 .

[0070] Step 2, preparation of electrolyte:

[0071] The concentrations of sodium tungstate, sodium citrate, and cetyltrimethylammonium bromide in the electrolytes of the six test cases were as follows: 40 mM, 5 mM, 0.1 mM (Test Case 1), 40 mM, 5 mM, 1 mM (Test Case 2), 40 mM, 5 mM, 2 mM (Test Case 3), 40 mM, 1 mM, 1.5 mM (Test Case 4), 40 mM, 5 mM, 1.5 mM (Test Case 5), and 40 mM, 15 mM, 1.5 mM (Test Case 6).

[0072] The electrolyte pH was maintained at 4.8–5.0 during the reaction using 0.1 M HAc-NaAc buffer.

[0073] Step 3, photoelectric synergistic oxidation and etching reaction:

[0074] An anode, cathode (graphite plate), and electrode solution are placed in a reaction tank. Ultraviolet light is used to irradiate the anode side, and the following electrochemical reaction parameters are controlled to carry out a photoelectric synergistic oxidation and etching reaction:

[0075] Circulating water was introduced into the jacket of the reaction tank to control the reaction temperature at 25 ℃ and the reaction time at 30 min;

[0076] The electrode spacing is 3 cm, the pulse voltage is 30 V, the pulse frequency is 1 Hz, and the duty cycle is 20%.

[0077] Turn on the 365 nm UV-LED lamp above the reaction tank (illuminance of 100 mW / cm²). 2 The illumination time was 30 minutes.

[0078] Step 4: Separate collection, washing, and drying:

[0079] After the reaction is complete, the reaction product is peeled off from the titanium mesh and dispersed at high speed along with the electrolyte, then filtered through a nanofiltration membrane; then it is washed by high-speed stirring and dispersion with deionized water, and filtered again through a nanofiltration membrane; finally, it is powdered by spray drying; the washing process removes large conductive carbon black particles, while the nano-tungsten trioxide particles that need to be retained flow out through the nanofiltration channels.

[0080] Step 5, low-temperature annealing and air jet milling:

[0081] After spray drying, the powder is first heated to 100°C at 1°C / min in a clean air atmosphere, then heated to 350°C at 2°C / min, maintained for 1 hour and then naturally cooled to room temperature. The powder is then pulverized by an air jet mill to eliminate agglomeration, and finally nano-tungsten trioxide is obtained.

[0082] Figure 1 This is a SEM image of micron-sized tungsten trioxide. Figures 2-4The images show SEM images of the products prepared in Examples 1-3, respectively. As can be seen from the images, when the concentration of hexadecyltrimethylammonium bromide is too low (0.1-0.5 mM), the nano-tungsten trioxide particles are found to be irregular. Figure 2 When the concentration is 0.5~1 mM, the nano-tungsten trioxide particles gradually become more uniform. Figure 3 The product was also relatively uniform at a concentration of 1-2 mM. Figure 4 However, the reaction rate decreases. Therefore, the optimal concentration range for hexadecyltrimethylammonium bromide is 1–1.5 mM.

[0083] When the sodium citrate concentration is too low (0.1~1 mM), nano-tungsten trioxide flakes are easily formed and are not uniform. When the concentration is 1~5 mM, the nano-flakes transform into particles and gradually become more uniform. When the concentration is 5~10 mM, the prepared nano-tungsten trioxide crystals are well-crystallized and nearly spherical. When the concentration is 10~20 mM, the nano-tungsten trioxide particles gradually decrease in size and the crystallinity decreases. Therefore, the optimal sodium citrate concentration range is 5~10 mM.

[0084] Experimental Examples 7-9: Effects of Different Pulse Voltages on the Prepared Products

[0085] The preparation steps are as follows:

[0086] Step 1, Preparation of the anode:

[0087] Micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride were weighed according to a mass ratio of 80:15:1, mixed evenly with N-methylpyrrolidone, and then uniformly coated onto a titanium mesh. The mixture was repeatedly pressed and dried to obtain the anode, with the areal loading of the coating material controlled at 5 mg / cm². 2 .

[0088] Step 2, preparation of electrolyte:

[0089] The concentrations of sodium tungstate, sodium citrate, and hexadecyltrimethylammonium bromide in the electrolyte were 40 mM, 10 mM, and 1 mM, respectively. The pH of the electrolyte was maintained at 4.8–5.0 during the reaction using 0.1 M HAc-NaAc buffer.

[0090] Step 3, photoelectric synergistic oxidation and etching reaction:

[0091] An anode, cathode (graphite plate), and electrode solution are placed in a reaction tank. Ultraviolet light is used to irradiate the anode side, and the following electrochemical reaction parameters are controlled to carry out a photoelectric synergistic oxidation and etching reaction:

[0092] Circulating water was introduced into the jacket of the reaction tank to control the reaction temperature at 25 ℃ and the reaction time at 30 min;

[0093] The electrode spacing was 3 cm, and the pulse voltages were 20 V (Experiment 7), 35 V (Experiment 8), and 50 V (Experiment 9), respectively. The pulse frequency was 1 Hz, and the duty cycle was 20%.

[0094] Turn on the 365 nm UV-LED lamp above the reaction tank (illuminance of 100 mW / cm²). 2 The illumination time was 30 minutes.

[0095] Step 4: Separate collection, washing, and drying:

[0096] After the reaction is complete, the reaction product is peeled off from the titanium mesh and dispersed at high speed along with the electrolyte, then filtered through a nanofiltration membrane; then it is washed by high-speed stirring and dispersion with deionized water, and filtered again through a nanofiltration membrane; finally, it is powdered by spray drying; the washing process removes large conductive carbon black particles, while the nano-tungsten trioxide particles that need to be retained flow out through the nanofiltration channels.

[0097] Step 5, low-temperature annealing and air jet milling:

[0098] After spray drying, the powder is first heated to 100°C at 1°C / min in a clean air atmosphere, then heated to 350°C at 2°C / min, maintained for 1 hour and then naturally cooled to room temperature. The powder is then pulverized by an air jet mill to eliminate agglomeration, and finally nano-tungsten trioxide is obtained.

[0099] Figures 5-7 The images show SEM images of the products prepared in Examples 7-9. As can be seen from the images, under low voltage (15-20 V), the nano-tungsten trioxide particles are relatively large and irregular in size. Figure 5 At medium voltage (20~40 V), irregular particles gradually tend to become nearly spherical. Figure 6 High-voltage (40~60 V) high-voltage particles tend to be two-dimensional nanosheets and are irregular ( Figure 7 Therefore, the optimal pulse voltage is 35 V.

[0100] Experimental Examples 10-12: Effect of Different Reaction Times on the Preparation of Products

[0101] The preparation steps are as follows:

[0102] Step 1, Preparation of the anode:

[0103] Micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride were weighed according to a mass ratio of 80:15:1, mixed evenly with N-methylpyrrolidone, and then uniformly coated onto a titanium mesh. The mixture was repeatedly pressed and dried to obtain the anode, with the areal loading of the coating material controlled at 5 mg / cm². 2 .

[0104] Step 2, preparation of electrolyte:

[0105] The concentrations of sodium tungstate, sodium citrate, and hexadecyltrimethylammonium bromide in the electrolyte were 40 mM, 10 mM, and 1 mM, respectively. The pH of the electrolyte was maintained at 4.8–5.0 during the reaction using 0.1 M HAc-NaAc buffer.

[0106] Step 3, photoelectric synergistic oxidation and etching reaction:

[0107] An anode, cathode (graphite plate), and electrode solution are placed in a reaction tank. Ultraviolet light is used to irradiate the anode side, and the following electrochemical reaction parameters are controlled to carry out a photoelectric synergistic oxidation and etching reaction:

[0108] Circulating water was introduced into the jacket of the reaction tank to control the reaction temperature at 25 ℃, and the reaction times were 20 min (Experiment 10), 30 min (Experiment 11), and 50 min (Experiment 12).

[0109] The electrode spacing is 3 cm, the pulse voltage is 35 V, the pulse frequency is 1 Hz, and the duty cycle is 20%.

[0110] Turn on the 365 nm UV-LED lamp above the reaction tank (illuminance of 100 mW / cm²). 2 The illumination time was 30 min (the lights were kept on for 30 min in all experimental cases 10-12).

[0111] Step 4: Separate collection, washing, and drying:

[0112] After the reaction is complete, the reaction product is peeled off from the titanium mesh and dispersed at high speed along with the electrolyte, then filtered through a nanofiltration membrane; then it is washed by high-speed stirring and dispersion with deionized water, and filtered again through a nanofiltration membrane; finally, it is powdered by spray drying; the washing process removes large conductive carbon black particles, while the nano-tungsten trioxide particles that need to be retained flow out through the nanofiltration channels.

[0113] Step 5, low-temperature annealing and air jet milling:

[0114] After spray drying, the powder is first heated to 100°C at 1°C / min in a clean air atmosphere, then heated to 350°C at 2°C / min, maintained for 1 hour and then naturally cooled to room temperature. The powder is then pulverized by an air jet mill to eliminate agglomeration, and finally nano-tungsten trioxide is obtained.

[0115] Figures 8-10 The images show SEM images of the products prepared in Examples 10-12. As can be seen from the images, with increasing time, the nano-tungsten trioxide particles gradually grow into uniform spheres. Figure 8 , 9 Furthermore, the longer the reaction time, the more severe the particle aggregation becomes. Figure 10 Therefore, the optimal reaction time range is 30 min.

[0116] Examples 1-3: Preparation of nano-sized tungsten trioxide from micron-sized tungsten trioxide via photoelectric synergistic oxidation and etching

[0117] The preparation steps are as follows:

[0118] Step 1, Preparation of the anode:

[0119] Micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride were weighed according to a mass ratio of 80:15:1, mixed evenly with N-methylpyrrolidone, and then uniformly coated onto a titanium mesh. The mixture was repeatedly pressed and dried to obtain the anode, with the areal loading of the coating material controlled at 5 mg / cm². 2 .

[0120] Step 2, preparation of electrolyte:

[0121] The concentrations of sodium tungstate, sodium citrate, and hexadecyltrimethylammonium bromide in the electrolytes of the three examples were 40 mM, 10 mM, and 1 mM (Example 1), 40 mM, 5 mM, and 1.5 mM (Example 2), and 40 mM, 5 mM, and 1 mM (Example 3), respectively.

[0122] The electrolyte pH was maintained at 4.8–5.0 during the reaction using 0.1 M HAc-NaAc buffer.

[0123] Step 3, photoelectric synergistic oxidation and etching reaction:

[0124] An anode, cathode (graphite plate), and electrode solution are placed in a reaction tank. Ultraviolet light is used to irradiate the anode side, and the following electrochemical reaction parameters are controlled to carry out a photoelectric synergistic oxidation and etching reaction:

[0125] Circulating water was introduced into the jacket of the reaction tank to control the reaction temperature at 25 ℃ and the reaction time at 30 min;

[0126] The electrode spacing is 3 cm, the pulse voltage is 35 V, the pulse frequency is 1 Hz, and the duty cycle is 20%.

[0127] Turn on the 365 nm UV-LED lamp above the reaction tank (illuminance of 100 mW / cm²). 2 The illumination time was 30 minutes.

[0128] Step 4: Separate collection, washing, and drying:

[0129] After the reaction is complete, the reaction product is peeled off from the titanium mesh and dispersed at high speed along with the electrolyte, then filtered through a nanofiltration membrane; then it is washed by high-speed stirring and dispersion with deionized water, and filtered again through a nanofiltration membrane; finally, it is powdered by spray drying; the washing process removes large conductive carbon black particles, while the nano-tungsten trioxide particles that need to be retained flow out through the nanofiltration channels.

[0130] Step 5, low-temperature annealing and air jet milling:

[0131] After spray drying, the powder is first heated to 100°C at 1°C / min in a clean air atmosphere, then heated to 350°C at 2°C / min, maintained for 1 hour and then naturally cooled to room temperature. The powder is then pulverized by an air jet mill to eliminate agglomeration, and finally nano-tungsten trioxide is obtained.

[0132] Figures 11-13 SEM images of the products prepared in Examples 1-3 are shown below. Figure 14 The following are particle size distribution diagrams of the products prepared in Examples 1-3 (corresponding to A, B, and C, respectively). Figures 15-17 The figures show the particle size distribution curves of the products prepared in Examples 1-3, respectively. As can be seen from the figures, the microscopic size of the prepared tungsten trioxide is 5-50 nm, with uniform size distribution, regular morphology, and high particle sphericity.

[0133] Figure 18 The XRD patterns (A), W 4f XPS pattern (B), and O 1s XPS pattern (C) of micron-sized and nano-sized tungsten trioxide (prepared in Example 3) are shown. As can be seen from the figures, the X-ray diffraction patterns of micron-sized tungsten trioxide before and after photoelectric synergistic oxidation and etching are obtained by XRD peak intensities. After photoelectric synergistic oxidation and annealing at 350℃, the micron-sized tungsten trioxide shows a significant reduction in peak intensity (e.g., (002), (200), (022), and (220) crystal planes). Analysis of the W 4f and O 1s XPS patterns shows that W... 5+ / W 6+ The area ratio increases, O v The significant increase indicates the formation of a large number of oxygen vacancies, directly proving that photoelectric synergistic oxidation and etching lead to lattice oxygen loss and defects. Through the above-mentioned tungsten valence state reduction and oxygen vacancy formation, it is further confirmed that micron-sized tungsten trioxide was obtained from nano-sized tungsten trioxide through photoelectric synergistic oxidation and etching.

[0134] Figure 19 The N2 isotherm adsorption curves are shown for micron-sized tungsten trioxide and nano-sized tungsten trioxide prepared in Examples 1-3. As can be seen from the figure, the specific surface area of ​​micron-sized tungsten trioxide is 8.425 m². 2 / g, the specific surface area of ​​nano-tungsten trioxide after photoelectric synergistic oxidation and etching is 19.026 m² / g, respectively. 2 / g, 37.117 m 2 / g, 53.034 m2 The result shows that the tungsten trioxide particles after photoelectro-coordinated oxidation and etching have smaller particle sizes and higher specific surface areas, providing more reactive sites for catalytic reactions. This further confirms that micron-sized tungsten trioxide can be converted into nano-sized tungsten trioxide through photoelectro-coordinated oxidation and etching.

[0135] Example 4: Application of nano-tungsten trioxide in ternary lithium batteries

[0136] Nano-tungsten trioxide (WO3) can be used as an additive in cathode materials in ternary lithium batteries (such as NCM and NCA systems). It functions through doping or surface coating, and its performance improvement is mainly reflected in:

[0137] 1. Increase energy density

[0138] Nano-WO3 possesses a high theoretical capacity (693 mAh / g) and can be used as an additive to improve the specific capacity of cathode materials, indirectly enhancing battery energy density. For example, introducing WO3 nanoparticles into ternary materials can optimize lithium-ion diffusion channels and enhance the utilization rate of active materials.

[0139] 2. Improve cycle stability

[0140] The nanoscale particle size (typically 5~50nm) of nano-WO3 can suppress the volume expansion of the cathode material during charge and discharge, reducing structural collapse. At the same time, the high stability of WO3 helps to suppress the dissolution of transition metal ions and extend the battery cycle life.

[0141] 3. Enhanced rate performance

[0142] Nano WO3 has a high specific surface area (50-80 m²). 2 With its high conductivity ( / g) and excellent conductivity, it can accelerate the transport rate of lithium ions and electrons, enabling the battery to maintain a high capacity even during high-rate charging and discharging.

[0143] Analysis of the role mechanism of nano-tungsten trioxide in cathode materials:

[0144] 1. Structural regulation

[0145] WO3 can act as a "structural stabilizer" by doping into the lattice of ternary materials, inhibiting the transformation of layered structures into spinel phases and maintaining the integrity of the crystal structure.

[0146] 2. Interface optimization

[0147] The WO3 coating on the surface of the positive electrode particles can form a stable solid electrolyte interface (SEI film), reducing side reactions between the electrolyte and the active material and lowering impedance.

[0148] 3. Synergistic effect

[0149] It forms a composite system with ternary materials (such as LiNiCoMnO2), taking advantage of WO3's high energy density and low cost (compared to precious metals such as cobalt and nickel), thus balancing battery performance and cost.

Claims

1. A method for preparing nano-sized tungsten trioxide from micron-sized tungsten trioxide via photoelectric synergistic oxidation and etching, characterized in that, Micron-sized tungsten trioxide was loaded onto a titanium mesh to form the anode, and a graphite plate was used as the cathode. An electrolyte was prepared using sodium tungstate, sodium citrate, hexadecyltrimethylammonium bromide, and water. The anode side was irradiated with ultraviolet light, and nano-tungsten trioxide was prepared through photoelectric synergistic oxidation and etching reactions. The reaction parameters for the photoelectric synergistic oxidation and etching reaction are as follows: The reaction temperature is 20~30 ℃, and the reaction time is 20~50 min; The electrode spacing is 1~3 cm, the pulse voltage is 20~40 V, the pulse frequency is 0.1~10 Hz, and the duty cycle is 10%~30%. The ultraviolet wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 The illumination time is the same as the reaction time.

2. The method as described in claim 1, characterized in that, The specific steps are as follows: Step 1, Preparation of the anode: Weigh out micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 50-100:10-20:0.5-1.5, mix them thoroughly with N-methylpyrrolidone, then coat the mixture evenly onto a titanium mesh and repeatedly press and dry it to obtain the anode. Control the areal loading of the coating material to be 1-10 mg / cm². 2 ; Step 2, preparation of electrolyte: The molar ratio of sodium tungstate, sodium citrate, and hexadecyltrimethylammonium bromide in the electrolyte is 30~50:5~10:1~1.5, and the pH of the electrolyte is maintained at 4.5~5.5 by buffer solution. Step 3, photoelectric synergistic oxidation and etching reaction: An anode, cathode, and electrode solution are placed in an electrochemical reaction device. Ultraviolet light is used to irradiate the anode side to carry out a photoelectric synergistic oxidation and etching reaction. Step 4: Separate collection, washing, and drying: After the reaction is complete, the reaction product is peeled off from the titanium mesh and dispersed at high speed along with the electrolyte, then filtered through a nanofiltration membrane; then it is washed by high-speed stirring and dispersion with deionized water, and filtered again through a nanofiltration membrane; finally, it is powdered by spray drying; during the washing process, large particles of conductive carbon black are filtered out, while the nano-tungsten trioxide particles that need to be retained flow out through the nanofiltration channels; Step 5, low-temperature annealing and air jet milling: The spray-dried powder was heated to 300-400 °C in a clean air atmosphere and held for 0.5-1.5 h. After naturally cooling to room temperature, it was pulverized by an air jet mill to eliminate agglomeration, and finally nano-tungsten trioxide was obtained.

3. The method as described in claim 2, characterized in that, In step 1, micron-sized tungsten trioxide, conductive carbon black, and polyvinylidene fluoride are weighed out at a mass ratio of 80:15:1 and mixed evenly with N-methylpyrrolidone. The mixture is then coated onto a titanium mesh and dried, with the area loading of the coating material controlled at 5 mg / cm². 2 .

4. The method as described in claim 2, characterized in that, In step 2, the pH of the electrolyte is stabilized at 4.8-5.0 using 0.1 M HAc-NaAc buffer.

5. The method as described in claim 2, characterized in that, In step 2, the molar ratio of sodium tungstate, sodium citrate, and hexadecyltrimethylammonium bromide in the electrolyte is 40:5:

1.

6. The method as described in claim 2, characterized in that, In step 3, the following electrochemical reaction parameters are controlled to carry out the photoelectric synergistic oxidation and etching reaction: The reaction temperature was 25 ℃, and the reaction time was 30 min. The electrode spacing is 3 cm, the pulse voltage is 35 V, the pulse frequency is 1 Hz, and the duty cycle is 20%. The ultraviolet wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 The illumination time is the same as the reaction time.

7. The method as described in claim 2, characterized in that, In step 5, the heating process is as follows: first, the temperature is increased to 100℃ at 1℃ / min, then increased to 350℃ at 2℃ / min, and then maintained for 1 hour before natural cooling.

8. The nano-tungsten trioxide prepared by the method according to any one of claims 1 to 7, characterized in that, Its microscopic size is 5~50 nm, and its specific surface area is 50~80 m². 2 / g.

9. The application of nano-tungsten trioxide prepared by the method according to any one of claims 1 to 7 as an additive for the cathode material of ternary lithium batteries.

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