Preparation method of hierarchical porous indium oxide nanotubes for lithium-ion battery anodes

Abstract

This invention discloses a method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, comprising the following steps: Step (1) Indium salt and terephthalic acid are placed in an organic solvent and stirred evenly under oil bath conditions to obtain a homogeneous dispersion; Step (2) The homogeneous dispersion is further heated and stirred continuously to carry out the reaction, and after the reaction is completed, it is naturally cooled to room temperature to obtain a mixed reaction system; Step (3) The mixed reaction system is filtered, and the solid product obtained by filtration is washed with anhydrous ethanol and dried to obtain the precursor MIL-68(In); Step (4) The precursor MIL-68(In) is placed in a tube furnace and pyrolyzed in an air atmosphere to obtain hierarchical porous indium oxide nanotubes. This invention can solve the problems of poor cycle performance and rate performance of existing In2O3-based anode materials.

Description

Technical Field

[0001] This invention relates to the field of battery anode materials technology. Specifically, it relates to a method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes. Background Technology

[0002] With the rapid development of electric vehicles and various electronic products, there is an urgent need for lithium-ion batteries to achieve higher energy and power densities. Currently, commercially available graphite anodes have reached their theoretical limits in terms of energy and power density. High-energy-density anode materials have become a key research focus for next-generation lithium-ion batteries. Among anode materials, transition metal compounds based on conversion reaction mechanisms have attracted widespread attention due to their high theoretical specific capacity and relatively low production cost. In particular, In2O3 has received increasing attention due to its mature preparation technology, environmental friendliness, low operating voltage, and high theoretical lithium storage specific capacity. However, these conversion-type anode materials undergo significant volume changes during lithium delithiation / intercalation, leading to electrode fragmentation. Furthermore, the poor conductivity of In2O3 itself results in poor rate performance. Therefore, In2O3 anode materials suffer from poor cycle performance and rate performance, failing to meet the needs of practical applications. It is necessary to modify its structure to improve the electrochemical performance of In2O3-based anode materials. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing multi-level porous indium oxide nanotubes for lithium-ion battery anodes, so as to solve the problems of poor cycle performance and rate performance of existing In2O3-based anode materials.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] The preparation method of multi-level porous indium oxide nanotubes for lithium-ion battery negative electrode, step (1): Indium salt and terephthalic acid are placed in an organic solvent and stirred evenly to obtain a homogeneous dispersion.

[0006] Step (2): Continue heating and stirring the homogeneous dispersion to carry out the hydrothermal synthesis reaction. After the reaction is completed, allow it to cool naturally to room temperature to obtain the mixed reaction system.

[0007] Step (3): Filter the mixed reaction system, wash the solid product obtained by filtration with anhydrous ethanol and dry it. After drying, the precursor MIL-68(In) is obtained.

[0008] Step (4): Place the precursor MIL-68(In) in a tube furnace and perform pyrolysis treatment in an air atmosphere. After the pyrolysis treatment, multi-level porous indium oxide nanotubes HPNT-In2O3 for lithium-ion battery anodes are obtained.

[0009] In the above-mentioned method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, in step (1), the indium salt is indium nitrate hydrate or indium chloride hydrate; the mass ratio of indium salt to terephthalic acid is 1:2 to 5, and the volume-mass ratio of organic solvent to terephthalic acid is 100 to 150 mL / g.

[0010] In the above-mentioned method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, in step (1), the indium salt is indium nitrate pentahydrate, the mass ratio of indium nitrate pentahydrate to terephthalic acid is 1:3, and the volume-mass ratio of organic solvent to terephthalic acid is 120 mL / g. If the mass ratio of indium nitrate pentahydrate to terephthalic acid is too small or too large, the nucleation rate of the reaction will be slow, resulting in the MIL-68(In) rods being too small or too large. Both small and large sizes are not conducive to preparing hierarchical porous indium oxide nanotubes HPNT-In2O3 with ideal electrochemical performance.

[0011] In the above-mentioned method for preparing multi-level porous indium oxide nanotubes for lithium-ion battery anodes, in step (2), the homogeneous dispersion is further heated to 115-125°C and stirred continuously for 45-75 minutes.

[0012] In the above-mentioned method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, in step (2), the homogeneous dispersion is further heated to 120°C and stirred continuously for 60 min. A low reaction temperature results in a low nucleation rate or even no nucleation, while a high temperature results in a high nucleation rate, leading to larger MIL-68(In) rod sizes. A short stirring reaction time results in smaller MIL-68(In) rod sizes, while a long reaction time leads to larger MIL-68(In) rod sizes. If the reaction is not stirred, inconsistent local reaction conditions result in different local nucleation rates, causing uneven MIL-68(In) rod sizes.

[0013] In the above-mentioned method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, step (4) includes the following two stages of pyrolysis treatment:

[0014] Step (4-1): Increase the temperature from room temperature to 120-130℃ at a rate of 4-6℃ / min, and hold for 2-2.5 hours;

[0015] Step (4-2): Continue heating to 400-410℃ at a heating rate of 4-6℃ / min, and hold for 2-2.5h. The heating rate, holding temperature, and holding time have a significant impact on the morphology and specific surface area of ​​the derivatives of MIL-68(In) as a self-sacrificing template. This invention controls the heating rate, holding temperature, and holding time at different stages of pyrolysis treatment, which can effectively accelerate the decomposition of organic components and avoid framework collapse, thus preparing hierarchical porous indium oxide nanotubes with large surface area and porosity.

[0016] In the above-mentioned method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, step (4) includes the following two stages of pyrolysis treatment:

[0017] Step (4-1): Increase the temperature from room temperature to 120℃ at a rate of 5℃ / min and hold for 2 hours;

[0018] Step (4-2): Continue heating to 400℃ at a heating rate of 5℃ / min and hold for 2 hours.

[0019] In the above-mentioned method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, in step (1), the organic solvent is N,N-dimethylformamide; the stirring time is 20 min. If the stirring time is too short, the indium salt will not be fully dispersed in the organic solvent, resulting in uneven local concentrations of the dispersion and affecting the inconsistent nucleation rate in the subsequent reaction process.

[0020] In the above-mentioned method for preparing multi-level porous indium oxide nanotubes for lithium-ion battery anodes, in step (3), during filtration, an organic filter membrane with a pore size of 0.22 μm is used to filter out the generated MIL-68(In); the washing with anhydrous ethanol is performed at least 3 times to remove unreacted impurities such as DMF, nitrate ions, indium ions, and terephthalate ions, thereby improving the purity of the target product; the drying temperature is 50-65℃ and the drying time is 4-5h.

[0021] In the above-mentioned method for preparing multi-level porous indium oxide nanotubes for lithium-ion battery anodes, in step (1), the mass ratio of indium nitrate pentahydrate to terephthalic acid is 1:3, the volume-to-mass ratio of organic solvent to terephthalic acid is 120 mL / g, the stirring time is 20 min, and the organic solvent is N,N-dimethylformamide.

[0022] In step (2), the homogeneous dispersion is heated to 120°C and stirred continuously for 60 minutes;

[0023] In step (3), during filtration, an organic filter membrane with a pore size of 0.22 μm is used for filtration; the number of times anhydrous ethanol is washed is 3; the drying temperature is 60℃ and the drying time is 4h.

[0024] In step (4), the pyrolysis treatment includes the following two stages:

[0025] Step (4-1): Increase the temperature from room temperature to 120℃ at a rate of 5℃ / min and hold for 2 hours;

[0026] Step (4-2): Continue heating to 400℃ at a heating rate of 5℃ / min and hold for 2 hours.

[0027] The technical solution of the present invention achieves the following beneficial technical effects:

[0028] 1. This invention utilizes the properties of MOFs to prepare a rod-shaped metal-organic framework (MIL-68(In)) through a simple hydrothermal synthesis method. Then, the organic framework MIL-68(In) is pyrolyzed in air to prepare a hierarchical porous nanotube, HPNT-In2O3, for use as a lithium-ion battery anode. This invention improves the electrochemical performance of In2O3-based anode materials by modifying the In2O3 structure.

[0029] 2. The homogeneous dispersion formed during the preparation process of this invention is In. 3+ Homogeneous solutions of organic ligands, In 3+ Organic ligands are periodically linked by intermolecular bonds to form a microrod precursor MIL-68(In) with an average diameter of about 1 μm. During the high-temperature pyrolysis of the precursor MIL-68(In) in an air atmosphere, its carbon components are oxidized into gaseous CO2 or CO and escape from the framework. The framework structure is gradually replaced by nano-indium oxide to form hollow tubular indium oxide HPNT-In2O3 with an average diameter of about 0.9 μm.

[0030] 3. The HPNT-In2O3 prepared in this invention is used as the negative electrode of a lithium-ion battery, at 0.1C (1C = 1000mAh g). -1 It can still maintain a stable 470mAh capacity after 180 cycles. -1 The reversible specific capacity is much higher than that of In2O3 material (140 mAh g). -1 This is because the hollow tubular indium oxide HPNT-In2O3 prepared by this invention can not only provide more contact surface between the electrolyte and the electrode, but also shorten the Li... + The diffusion distance can also act as a buffer, mitigating the volume effect of active materials, thus enabling HPNT-In2O3 to have higher specific capacity and better cycle performance and rate performance.

[0031] 4. The hollow tubular indium oxide (HPNT-In2O3) prepared using this invention is named hierarchical porous indium oxide nanotubes. This material can be used as a negative electrode material for lithium-ion batteries. Its continuous one-dimensional hierarchical porous nanotubes can shorten the diffusion distance of lithium ions, thereby improving the charge transfer rate. At the same time, the macropore (50nm-100nm) structure of the hierarchical porous indium oxide nanotubes can serve as an electrolyte storage pool, the mesopore (2-50nm) structure can serve as a mass transfer channel, and the micropore (less than 2nm) structure can provide electrochemical active sites, thus providing a more favorable way for effective electrolyte permeation, thereby improving the capacity, cycle performance, and rate performance of the battery negative electrode. Attached Figure Description

[0032] Figure 1a TG curve of In(NO3)3·5H2O in the embodiments of the present invention;

[0033] Figure 1b TG diagram of precursor MIL-68(In) in an embodiment of the present invention;

[0034] Figure 2a SEM image (1 μm) of In2O3 in an embodiment of the present invention;

[0035] Figure 2b SEM image (200nm) of In2O3 in this embodiment of the invention;

[0036] Figure 2c SEM image (100nm) of In2O3 in an embodiment of the present invention;

[0037] Figure 2d SEM image (10 μm) of the precursor MIL-68(In) in an embodiment of the present invention;

[0038] Figure 2e SEM image (500nm) of the precursor MIL-68(In) in an embodiment of the present invention;

[0039] Figure 2f Another SEM image (500 nm) of the precursor MIL-68(In) in this embodiment of the invention;

[0040] Figure 2g SEM image (10 μm) of HPNT-In2O3 in an embodiment of the present invention;

[0041] Figure 2h SEM image (500 nm) of HPNT-In2O3 in an embodiment of the present invention;

[0042] Figure 2i Another SEM image (500 nm) of HPNT-In2O3 in this embodiment of the invention;

[0043] Figure 3a TEM image of HPNT-In2O3 in an embodiment of the present invention;

[0044] Figure 3b HRTEM image of HPNT-In2O3 in the embodiments of the present invention;

[0045] Figure 3c Lattice spacing diagram of HPNT-In2O3 in the embodiments of the present invention;

[0046] Figure 4a XRD patterns of In2O3 and HPNT-In2O3 in the embodiments of the present invention;

[0047] Figure 4b XPS total spectra of In2O3 and HPNT-In2O3 in the embodiments of the present invention;

[0048] Figure 4c Fine spectra of element In in In2O3 and HPNT-In2O3 in the embodiments of the present invention;

[0049] Figure 4d Fine spectra of element O in In2O3 and HPNT-In2O3 in the embodiments of the present invention;

[0050] Figure 5a Nitrogen adsorption-desorption curves of In2O3 and HPNT-In2O3 in the embodiments of the present invention;

[0051] Figure 5b Pore ​​size distribution curves of In2O3 and HPNT-In2O3 in embodiments of the present invention;

[0052] Figure 6a CV curve of In2O3 in the embodiments of the present invention;

[0053] Figure 6b CV curve of HPNT-In2O3 in the embodiments of the present invention;

[0054] Figure 6c Charge-discharge curves of In2O3 in embodiments of the present invention;

[0055] Figure 6d Charge-discharge curves of HPNT-In2O3 in embodiments of the present invention;

[0056] Figure 7a Cyclic performance diagrams of In2O3 and HPNT-In2O3 in embodiments of the present invention;

[0057] Figure 7b Rate performance diagrams of In2O3 and HPNT-In2O3 in embodiments of the present invention;

[0058] Figure 7c EIS diagram of In2O3 in the embodiments of the present invention;

[0059] Figure 7d EIS diagram of HPNT-In2O3 in the embodiments of the present invention;

[0060] Figure 8 Morphology of the In2O3 negative electrode sheet before cycling in an embodiment of the present invention;

[0061] Figure 9 Morphology of the HPNT-In2O3 negative electrode sheet before cycling in an embodiment of the present invention;

[0062] Figure 10 Morphology of the In2O3 negative electrode sheet after 250 cycles in an embodiment of the present invention;

[0063] Figure 11 Morphology of the HPNT-In2O3 negative electrode sheet after 250 cycles in an embodiment of the present invention. Detailed Implementation

[0064] 1. Preparation of hierarchical porous nanotubes HPNT-In2O3 for lithium-ion battery anodes

[0065] (1) Take 1g of In(NO3)3·5H2O and 3g of PTA (terephthalic acid) into a 500mL round-bottom flask, add 360mL of N,N-dimethylformamide (DMF), transfer to an oil bath and stir rapidly for 20min to form a homogeneous solution; after forming a homogeneous solution, heat to 120℃ and continue heating and stirring for 1h; after the reaction is completed, cool naturally to room temperature, filter by a 0.22μm organic filter membrane, and wash 3 times with anhydrous ethanol; after washing, dry in a forced-air drying oven at 60℃ for 4 hours to obtain the precursor MIL-68(In).

[0066] (2) The precursor MIL-68(In) was placed in a tube furnace and heated from room temperature to 120°C for 2 hours in an air atmosphere at a heating rate of 5°C / min. This process mainly removes water and unreacted DMF. The temperature was then increased to 400°C at a heating rate of 5°C / min and held for 2 hours to decompose the organic framework and prepare porous In2O3 rods (HPNT-In2O3).

[0067] (3) For comparison, 1g of In(NO3)3·5H2O was placed in a tube furnace and heated from room temperature to 120℃ for 2h under air atmosphere at a heating rate of 5℃ / min. This process mainly removes the water of crystallization. The temperature was then increased to 400℃ at a heating rate of 5℃ / min and held for 2h to decompose In(NO3)3 and prepare In2O3 particles (In2O3).

[0068] 2. Differential thermal and thermogravimetric analysis of materials

[0069] Thermogravimetric analysis (TG or TGA) was performed using a STA449F3 Jupiter thermogravimetric analyzer manufactured by Netzsch GmbH, Germany. The test temperature ranges were 20–400℃ and 20–700℃, with a heating rate of 10℃ / min. The samples were tested in oxygen and nitrogen atmospheres.

[0070] In this embodiment, differential thermal and thermogravimetric analyses were performed on In(NO3)3·5H2O in an oxygen atmosphere. Figure 1a As shown, under an oxygen atmosphere, the temperature was increased to 400℃ at a heating rate of 5℃ / min. Thermogravimetric analysis (TG) indicated that the decomposition of In(NO3)3·5H2O into indium oxide particles mainly occurs in three stages. Between 20 and 110℃, the water of crystallization evaporates to form anhydrous In(NO3)3 salt. Between 110 and 190℃, a reaction may occur where In(NO3)3 decomposes into InO(NO3), NO2, and O2, with a weight loss of 35%. Between 190 and 250℃, the anhydrous salt begins to decompose into In2O3, NO2, and O2, with a weight loss of 18%. Therefore, during material preparation, heating to 120℃ and holding for 2 hours to remove the water of crystallization, followed by further heating to 400℃ at a rate of 5℃ / min and holding for 2 hours, allows for the complete decomposition of the anhydrous salt into In2O3. Differential thermal and thermogravimetric tests were performed on MIL-68(In) in this embodiment. Figure 1b As shown, under an O2 atmosphere, the temperature was increased to 400℃ at a heating rate of 5℃ / min. Thermogravimetric analysis (TG) indicated that the synthesis of hierarchical porous indium oxide from MIL-68(In) mainly occurred in one stage. Between 200 and 360℃, MIL-68(In) decomposed into HPNT-In2O3, CO2, and H2O, with a weight loss of 68%. Therefore, heating to 400℃ at a heating rate of 5℃ / min and holding for 2 hours during material preparation can ensure the complete decomposition of MIL-68(In) into HPNT-In2O3.

[0071] 3. Structural morphology characterization of materials

[0072] X-ray diffraction (XRD) was performed using a Rigaku Ultima IV X-ray diffractometer manufactured in Japan. The test range was 5–90°, with a scan rate of 5° / min, using continuous scanning. A Cu target and a high-sensitivity D / teX Ultra250 detection system were employed. The crystal structure of the material was analyzed using XRD. X-ray photoelectron spectroscopy (XPS) was performed using a Thermo ESCALAB 250XI X-ray photoelectron spectroscopy instrument manufactured by Thermo-Fisher, USA, calibrated using the characteristic peak of C1s at 248.5 eV. XPS results were used to analyze the content and valence states of carbon, oxygen, indium, and titanium in the material. Scanning electron microscopy (SEM) was performed using a TESCAN MIRA LMS microscope manufactured in the Czech Republic. The microstructure and structure of the material were analyzed by SEM; the transmission electron microscope (TEM) used was a JEOL JEM-2100F from Japan; the nitrogen adsorption-desorption analyzer, which utilizes the adsorption and desorption characteristics of N2 on the sample surface to obtain the specific surface area, pore volume and pore size distribution of the material, was a Micron ASAP2460.

[0073] Figures 2a to 2c SEM image of indium oxide particles In2O3 generated by the pyrolysis of In(NO3)3·5H2O; As can be seen from the figure, In2O3 has a large particle size, compact structure, low porosity and small specific surface area. As a negative electrode material, it has a small contact surface with the electrolyte. The huge volume expansion that accompanies it during cycling will lead to the continuous decomposition of the solid electrolyte layer (SEI) and limit its cycle life as an electrode. Figures 2d to 2f SEM image of MIL-68(In), the precursor for the synthesis of hierarchical porous indium oxide tubes HPNT-In2O3; Figures 2g to 2i This is a SEM image of hierarchical porous indium oxide tubes (HPNT-In2O3). The image shows that the MIL-68(In) microrods have a compact structure and smooth surface, while the HPNT-In2O3 tubes have thinner walls and a smooth surface, exhibiting a well-developed porous structure. This structure reflects the preparation process of HPNT-In2O3. First, In(NO3)3·5H2O and PTA dissolve in DMF to form In... 3+ Homogeneous solutions of organic ligands, In 3+Organic ligands are periodically linked by intermolecular bonds to form microrods MIL-68(In) with an average diameter of approximately 1 μm. During subsequent calcination, the carbon components in MIL-68(In) are oxidized to gaseous CO2 or CO and escape from the framework. The framework structure is gradually replaced by nano-indium oxide, forming hollow tubular indium oxide HPNT-In2O3 with an average diameter of approximately 0.9 μm. Compared to In2O3, HPNT-In2O3 not only provides more contact surface between the electrolyte and electrode, but also shortens the Li... + The diffusion distance also acts as a buffer, mitigating the volume effect of the active material. Therefore, HPNT-In2O3 exhibits higher specific capacity and better cycling and rate performance.

[0074] Figures 3a to 3c The images show the TEM, HRTEM, and lattice spacing diagrams of HPNT-In2O3, respectively. Figure 3a As can be seen, HPNT-In2O3 exhibits a nanotube structure overall. This can be further analyzed through analysis of HPNT-In2O3. Figure 3b Interplanar spacing was measured at the location. Figure 3c The interplanar spacing of the nanoparticles is clearly shown to be 0.178 nm, consistent with the (4 4 0) plane of In2O3 (JCPDS: No. 06-0416). These results indicate that HPNT-In2O3 is composed of In2O3 nanoparticles.

[0075] Figure 4a The XRD patterns of In₂O₃ and HPNT-In₂O₃ are shown. As can be seen from the figures, the diffraction peak positions and intensities of HPNT-In₂O₃ are consistent with those of In₂O₃. The diffraction peaks at approximately 21.5°, 30.6°, 35.5°, 45.7°, and 51.3° are all In₂O₃ diffraction peaks, indicating that both are In₂O₃ crystals, differing only in structure. This suggests that MIL-68(In) itself acts as a sacrificial template, and the derived indium oxide largely inherits the original morphology and key structural features of the parent MIL-68(In). Moreover, the derived material HPNT-In₂O₃ generally exhibits higher conductivity and stability than the parent MIL-68(In). Compared to In₂O₃, these derived materials HPNT-In₂O₃ have a larger surface area and higher porosity. These properties make HPNT-In₂O₃, a derivative of MIL-68(In), superior to In₂O₃ as a negative electrode material. The elemental composition of In2O3 and HPNT-In2O3 was determined using XPS. Figure 4b The image shows the total XPS spectrum, indicating the presence of oxygen and indium in the In2O3 and HPNT-In2O3 composite materials. Figure 4c and Figure 4dThe images show the fine spectra of elements In and O, respectively. The In 3d spectrum has two prominent peaks at 444.9 eV and 452.4 eV, corresponding to In 3d... 3 / 2 and In 3 d5 / 2 Peak, corresponding to In in In2O3 3+ The O1s spectrum indicates the presence of three types of oxygen. O2 is located at 530.2 eV. L The peak corresponds to lattice oxygen in the In₂O₃ phase, located at 530.9 eV. V Peak corresponds to O -2 The adsorbed oxygen, while O at 532.5 eV C Peaks are associated with functional groups O - OH - and O 2- related.

[0076] Specific surface area and pore size distribution have a significant impact on electrochemical behavior. Figure 5a and Figure 5b The isothermal nitrogen adsorption-desorption curves and pore size distribution curves are shown in Table 1. Table 1 shows the specific surface area and pore volume of the two indium oxide structures. The specific surface area of ​​sample In₂O₃ is 5.7780 m² / s. 2 / g, the nitrogen adsorption-desorption curves exhibit typical Type III isotherms for non-porous or macroporous solid materials; the total pore volume of In₂O₃ is 0.036809 cm⁻². 3 The pore size distribution curves show that In₂O₃ has almost no porous structure; these data are consistent with the morphology characterized by SEM. The specific surface area of ​​the MIL-68(In) derived HPNT-In₂O₃ material is 46.7261 m² / g. 2 The nitrogen adsorption isotherm of this sample exhibits a type IV isotherm, with an H3-type hysteresis loop at P / P0 of 0.9–1.0, indicating the presence of a disordered mesoporous structure (2–50 nm). Rapid N2 absorption in the low-pressure region (P / P0–0) suggests the presence of a small number of micropores (less than 2 nm). The total pore volume of HPNT-In2O3 is 0.204241 cm³. 3 The pore size distribution, assessed by Barrett-Joyner-Halenda (BJH), shows that the pores exist in the range of 2 nm to 100 nm. This pore size range facilitates charge carrier insertion and electrolyte permeation, and buffers electrode volume expansion. The gas generated during the decomposition of MIL-68(In) escapes from its interior, contributing to the formation of porous properties. The larger BET surface area and hierarchical pore size distribution provide more active reaction sites, thereby improving the battery's specific capacity and cycle stability. Therefore, the prepared composite material holds promise for improving the energy storage capacity and electrochemical stability of the anode material.

[0077] Table 1. Specific surface area and pore volume of In2O3 and HPNT-In2O3

[0078]

[0079] 4. Electrochemical performance testing of materials

[0080] Electrochemical testing methods include: electrode preparation, battery assembly, constant current charge-discharge testing, cyclic voltammetry (CV) testing, and electrochemical impedance spectroscopy (EIS).

[0081] Electrode preparation: Active material, Super P, SBR, and CMC were added to a weighing bottle in a ratio of 8:1:0.5:0.5, followed by the addition of a certain amount of ultrapure water. The mixture was magnetically stirred for 8 hours to obtain a uniformly mixed slurry. This slurry was then evenly coated onto copper foil, with a thickness controlled between 0.01 and 0.03 mm. The foil was then vacuum-dried at 80°C for 12 hours. After stamping, the resulting negative electrode sheet was weighed and ready for use. Super P was used as a conductive agent, and SBR and CMC were used as binders.

[0082] Battery Assembly: The entire battery assembly process is carried out in a glove box filled with a high-purity argon inert atmosphere. The oxygen and moisture content within the glove box are controlled to be O2 < 1 ppm and H2O < 1 ppm, respectively. During assembly, the (CR2032) battery is assembled in the following order: negative electrode shell, spring contact, gasket, 1 drop of electrolyte, negative electrode sheet, 1 drop of electrolyte, separator, 2 drops of electrolyte, lithium sheet, and positive electrode shell. To ensure the assembled battery does not short-circuit and to adequately protect the separator, a porous polypropylene film is punched into a 19 mm diameter disc as the separator, and both the lithium sheet and the gasket have smooth, rounded corners facing the separator. During assembly, the centers of all the components must be aligned in a straight line. The assembled battery needs to stand for at least 24 hours to ensure the electrolyte fully wets the electrode materials. A 1 mol / L LiPF6 in EC:DMC = 1:1 (vol% with 5% FEC) solution is used as the electrolyte.

[0083] Constant current charge / discharge test: A Land CT2001A battery charge / discharge tester (Wuhan Land Electronics Co., Ltd.) was used. At room temperature, the constant current charge / discharge voltage range was 0.01–3V.

[0084] Cyclic voltammetry (CV) was performed using a Princeton PMC1000A electrochemical workstation with a voltage range of 0.01–3 V and a scan rate of 0.01 mV / s.

[0085] AC impedance testing (EIS): A Princeton PMC1000A electrochemical workstation was used, with a test frequency of 0.1–100 kHz and an amplitude of 5 mV.

[0086] The CV and charge-discharge curves of In2O3 and HPNT-In2O3 are as follows: Figures 6a to 6d As shown. Figure 6a The CV curve for In₂O₃ shows a distinct reduction peak (0.57 V) in the first cycle, which disappears in subsequent cycles. Very sharp irreversible reduction peaks appear near 0.57 V and 0.8 V. This is because In₂O₃ forms a large amount of a solid electrolyte interphase (SEI) film composed of lithium carbonate and alkyl lithium components in contact with the electrolyte. Simultaneously, In₂O₃ reacts with Li in a multi-step electrochemical reduction reaction following reactions (1) and (2) to form a Li-ln alloy. Correspondingly, in... Figure 6c The charge-discharge curves show a significant ultra-long discharge plateau between 0.5V and 0.8V during the first discharge, indicating a substantial decrease in specific capacity after the first charge-discharge cycle. This is attributed to the formation of a large SEI film during the first charge-discharge process, resulting in a relatively high irreversible specific capacity. The CV curves for the second and third cycles are essentially identical, indicating that the electrode-electrolyte reaction approaches stability after these irreversible reactions. The three oxidation peaks (0.43V, 0.70V, 1.74V) and three reduction peaks (0.39V, 0.51V, 0.82V) observed in the second cycle indicate multi-step electrochemical reactions related to the lithium delithiation / intercalation process, corresponding to... Figure 6b The charge-discharge curves show distinct charging plateaus near 0.43V, 0.70V, and 1.74V, and distinct discharging plateaus near 0.39V, 0.51V, and 0.82V. In subsequent cycles, the reduction peak at 0.82V shifted to 1.0V in the third cycle, which may be attributed to the largely irreversible reduction of In2O3 to metallic In. The charge-discharge curves show a significant decrease in specific capacity after each cycle. This is because during reaction (2), the large volume change of the active material during alloying and dealloying continuously breaks down the old SEI layer and forms a new SEI layer, leading to a decrease in specific capacity. Figure 6b The CV curves for HPNT-In2O3 show a sharp irreversible reduction peak (0.62V) and a distinct reduction peak (0.75V) in the first cycle, which disappear in subsequent cycles. This is attributed to the decomposition of the organic framework, which gives HPNT-In2O3 a hierarchical porous structure and a high specific surface area, resulting in the formation of a large amount of solid electrolyte interphase (SEI) film composed of lithium carbonate and alkyl lithium components. Simultaneously, In2O3 reacts with Li in a multi-step electrochemical reduction reaction following reactions (1) and (2) to form a Liln alloy. Correspondingly, in... Figure 6dThe charge-discharge curves show a significant ultra-long discharge plateau between 0.5V and 0.8V during the first discharge, indicating a substantial decrease in specific capacity after the first charge-discharge cycle. This is attributed to the formation of a large SEI film during the first charge-discharge process, resulting in a relatively high irreversible specific capacity. The CV curves for the second and third cycles are essentially identical, indicating that the electrode-electrolyte reaction approaches stability after these irreversible reactions. The three oxidation peaks (0.44V, 0.69V, 1.74V) and three reduction peaks (0.43V, 0.5V, 0.64V) observed in the second cycle indicate multi-step electrochemical reactions related to the lithium delithiation / intercalation process, corresponding to... Figure 6d The charge-discharge curves show distinct charging plateaus near 0.44V, 0.69V, and 1.74V, and distinct discharge plateaus near 0.43V, 0.5V, and 0.64V. In the third cycle, the reduction peak at 0.64V in the second cycle shifted to 1.13V, which may be attributed to the largely irreversible reduction of In2O3 to metallic In. Simultaneously, during reaction (2), the large volume change of the active material during alloying and dealloying continuously breaks down the old SEI layer and forms a new SEI layer, leading to a decrease in specific capacity. Based on these CV curves, it can be concluded that alloying and dealloying are the main lithium storage mechanisms for In2O3 and HPNT-In2O3 during charge-discharge processes, and their storage mechanisms can be described by the following equations (1) and (2):

[0087] In₂O₃ + 6Li → 2In + 3Li₂O Equation (1)

[0088]

[0089] By assembling indium oxide with different structures as anode materials and lithium foil as the symmetrical electrode in a 2032 half-cell, the electrochemical performance of the two half-cells was tested. Figures 7a to 7d The excellent performance of HPNT-In2O3 indium oxide tube was verified, demonstrating that the battery specific capacity and stability were improved by changing the indium oxide structure. Figure 7a For In2O3 and HPNT-In2O3 at 0.1C (1C = 1000mAh g) -1 The cycling performance diagram under the given conditions shows that the significant capacity loss in the first cycle is likely due to electrolyte decomposition. The initial discharge specific capacity of HPNT-In2O3 is 1127.3 mAh g. -1 The specific capacity is higher than that of In2O3, which is 1026.7 mAh g. -1 Furthermore, in the second cycle, the discharge capacity of the HPNT-In2O3 anode was 852.5 mAh g. -1 Higher than In2O3's 845.6 mAh g-1 The increased capacity of HPNT-In2O3 may be attributed to its hierarchical porous structure and one-dimensional nanotube structure, which provides a large specific surface area and more active sites for the anode. This facilitates the anode's ability to capture more Li during cycling. + The specific capacity of the In2O3 anode rapidly decayed in the first few cycles, but remained at 140 mAh g⁻¹ until the 40th cycle. -1 After 50 cycles, the discharge specific capacity of the HPNT-In2O3 negative electrode rapidly decreased to 326.4 mAh g. -1 Subsequently, the discharge specific capacity gradually increased until, after 180 cycles, the discharge capacity remained at 470 mAh g. -1 This is due to the gradient activation of the active material. The low specific capacity of the In2O3 anode may be due to the low utilization rate of the metal oxide, while the rapid capacity decay may be due to the large volume change of the indium oxide material during repeated lithium extraction / intercalation processes, resulting in the continuous fragmentation and irreversible formation of the SEI layer and the continuous consumption of electrolyte. The coulombic efficiency of the HPNT-In2O3 anode increased from 67.22% in the first cycle to 98.22% in the 30th cycle, and remained above 98% in subsequent cycles, further confirming the good reversibility of HPNT-In2O3. Figure 7b The rate performance graphs for In2O3 and HPNT-In2O3 are shown. Rate performance testing further confirms the advantages of the HPNT-In2O3 indium oxide diode. At rates of 0.1C, 0.5C, 1C, 2.5C, and 5C, the average discharge specific capacity of In2O3 is 594.1 mAh g⁻¹. -1 178.6mAh g -1 95.7mAh g -1 22.5mAh g -1 and 7.8mAh g -1 When restored to 0.1C, the reversible specific capacity still reaches 308.7 mAh g. -1 At the same rate, the average discharge specific capacity of HPNT-In2O3 is 594.1 mAh g. -1 239.1mAhg -1 186.5mAh g -1 100.5mAh g -1 and 23.5mAh g -1 When restored to 0.1C, the reversible specific capacity still reaches 376.4 mAh g. -1This indicates that HPNT-In2O3 exhibits superior rate performance compared to In2O3, fully demonstrating the outstanding characteristics of HPNT-In2O3 indium oxide tubes. Compared to In2O3 particles, this hollow and porous structure provides sufficient additional free space to accommodate volume changes. However, from a rate performance perspective... Figure 7b It can be seen that HPNT-In2O3 no longer exhibits capacity increase after high-rate charge-discharge, which may be because the harsh conditions of high current density destroy the structure of HPNT-In2O3. Furthermore, the kinetic properties of In2O3 and HPNT-In2O3 were further investigated using electrochemical impedance spectroscopy (EIS). Figure 7c and Figure 7d The images show the EIS spectra of In2O3 and HPNT-In2O3, respectively. Both spectra show a concave semicircle in the mid-to-high frequency range and a diagonal line in the low frequency range. The semicircle is related to the charge transfer resistance at the electrode-electrolyte interface, while the diagonal line is related to the lithium-ion diffusion resistance within the active material block. The figures show that the radius of the In2O3 anode material increases sharply in the mid-to-high frequency range after 10 cycles, indicating that the In2O3 anode material undergoes significant volume changes during cycling, leading to pulverization and delamination, while simultaneously forming a new SEI film. The increasingly thick SEI film and the shedding of active material increase the charge transfer resistance. The sharp decrease in the semicircle of the HPNT-In2O3 anode material in the mid-to-high frequency range indicates that the charge transfer resistance gradually decreases during continuous lithium-ion insertion / extraction cycling, thereby improving electrode conductivity and achieving excellent rate performance.

[0090] To more clearly illustrate the charge-discharge mechanism of the two types of electrodes, we disassembled a coin cell after it had undergone 250 cycles at a current density of 2C. The negative electrode was washed in DEC solvent and then dried. Figures 8 to 11 The images show the morphology of In2O3 and HPNT-In2O3 electrodes before and after cycling, respectively. Figure 8 This is a SEM image of the In2O3 negative electrode before cycling. Figure 10 The image shows the SEM image of the In2O3 anode after cycling. It can be seen from the image that the surface of the In2O3 anode becomes rough after cycling, which is caused by the huge volume change of the In2O3 anode during the cycling process. Figure 9 This is a SEM image of the In2O3 negative electrode before cycling. Figure 11 The image shows a SEM image of the HPNT-In2O3 anode after cycling. The nanotube structure is not visible, indicating that the HPNT-In2O3 electrode collapsed under high-current charging and discharging conditions. However, the surface of the HPNT-In2O3 anode is relatively smoother than that of the In2O3 anode. This is because the tubular and hierarchical porous structure of HPNT-In2O3 provides space for volume expansion during cycling.

[0091] This embodiment employs a metal-organic framework approach, using In(NO3)3·5H2O as the indium source and PTA as the organic ligand, to prepare hierarchical porous In2O3 nanotubes via hydrothermal synthesis and subsequent high-temperature pyrolysis. In2O3 particles were also prepared by directly pyrolyzing In(NO3)3·5H2O at high temperature. The influence of different structures on the electrochemical performance of In2O3 was investigated. The following main conclusions were drawn:

[0092] (1) In2O3 is used as a negative electrode. Its particle structure has low porosity and small specific surface area, resulting in low utilization of active materials and low lithium storage capacity.

[0093] (2) HPNT-In2O3 is used as the negative electrode. The continuous one-dimensional multi-level porous nanotubes can shorten the diffusion distance of lithium ions and improve the charge transfer rate. At the same time, the macropores (50nm-100nm) can serve as electrolyte storage pools, the mesopores (2-50nm) can serve as mass transfer channels, and the micropores (less than 2nm) can provide electrochemical active sites, providing a more favorable way for effective electrolyte penetration, thereby improving the capacity, cycle performance and rate performance of the battery negative electrode.

Claims

1. A method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes, characterized in that, Includes the following steps: Step (1): Indium salt and terephthalic acid are placed in an organic solvent and stirred until homogeneous dispersion is obtained; Step (2): Continue heating and stirring the homogeneous dispersion to carry out the hydrothermal synthesis reaction. After the reaction is completed, allow it to cool naturally to room temperature to obtain the mixed reaction system. Step (3): Filter the mixed reaction system, wash the solid product obtained by filtration with anhydrous ethanol and dry it. After drying, the precursor MIL-68(In) is obtained. Step (4): Place the precursor MIL-68(In) in a tube furnace and perform pyrolysis treatment in an air atmosphere. After the pyrolysis treatment, multi-level porous indium oxide nanotubes HPNT-In2O3 for lithium-ion battery anodes are obtained. In step (1), the indium salt is indium nitrate hydrate or indium chloride hydrate; the mass ratio of indium salt to terephthalic acid is 1:2 to 5, and the volume-mass ratio of organic solvent to terephthalic acid is 100 to 150 mL / g. In step (2), the homogeneous dispersion is heated to 115-125°C and stirred continuously for 45-75 minutes. In step (4), the pyrolysis treatment includes the following two stages: Step (4-1): Increase the temperature from room temperature to 120-130℃ at a rate of 4-6℃ / min, and hold for 2-2.5 hours; Step (4-2): Continue heating at a rate of 4-6℃ / min to 400-410℃, and hold for 2-2.5 hours; In step (1), the organic solvent is N,N-dimethylformamide; the stirring time is 20 min; The hierarchical porous indium oxide nanotubes have macroporous structures of 50nm-100nm, mesoporous structures of 2-50nm, and microporous structures of less than 2nm.

2. The method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes according to claim 1, characterized in that, In step (1), the indium salt is indium nitrate pentahydrate, the mass ratio of indium nitrate pentahydrate to terephthalic acid is 1:3, and the volume-mass ratio of organic solvent to terephthalic acid is 120 mL / g.

3. The method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes according to claim 1, characterized in that, In step (2), the homogeneous dispersion is heated to 120°C and stirred continuously for 60 minutes.

4. The method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes according to claim 1, characterized in that, In step (4), the pyrolysis treatment includes the following two stages: Step (4-1): Increase the temperature from room temperature to 120℃ at a rate of 5℃ / min and hold for 2 hours; Step (4-2): Continue heating to 400℃ at a heating rate of 5℃ / min and hold for 2 hours.

5. The method for preparing hierarchical porous indium oxide nanotubes for lithium-ion battery anodes according to claim 1, characterized in that, In step (3), during filtration, an organic filter membrane with a pore size of 0.22 μm is used for filtration; the number of times anhydrous ethanol is washed is at least 3; the drying temperature is 50-65℃ and the drying time is 4-5 h.

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