Transition metal Fe doped vanadyl phosphate material and preparation method thereof

Abstract

The invention provides a transition metal Fe doped vanadyl phosphate material and a preparation method thereof. Fe partially replaces V metal cations in crystal lattices, a local coordination environment and an electronic structure are adjusted, a stable Fe-O-P-O-V delocalized electronic structure is formed, and Zn < 2 + > intercalation / deintercalation reversibility and crystal lattice stability are optimized. Compared with the traditional VOPO4, the Fe-doped vanadyl phosphate material has the advantages that the V-O bond strength is obviously enhanced, the interplanar spacing is reduced, the dissolution of PO4 < 3 > and the fracture of a lattice structure are inhibited, the symmetry of a VO6 octahedron is obviously improved, and excellent circulation (the capacity retention ratio reaches 80% after 2000 times of circulation) and rate capability are shown. The preparation process is simple, low in cost, mild in reaction condition, high in yield and low in equipment dependence; the obtained positive electrode material is improved in capacity, enhanced in structural stability and improved in rate capability, and an innovative solution is provided for developing a high-stability aqueous ion battery positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aqueous zinc-ion batteries, and particularly relates to a preparation method of a metal ion doped vanadium phosphate material. BACKGROUND

[0002] Aqueous zinc-ion batteries have become a promising new energy storage technology due to their inherent high safety, low cost, and environmental friendliness, as well as high theoretical capacity (820 mAh g -1 ) and low redox potential (-0.76 V vs. SHE). However, the commercialization process is still constrained by the performance of the positive electrode material. Among them, the structural stability and ion diffusion kinetics of the positive electrode material directly determine the cycle life and rate performance of the battery, which is a key problem that needs to be solved urgently.

[0003] Among the numerous candidate positive electrode materials (manganese-based, vanadium-based, and prussian blue and its analogues), vanadium-based polyanion compound vanadium phosphate (VOPO4) has a high theoretical capacity and a unique layered crystal structure, making it a promising positive electrode material for aqueous zinc-ion batteries. The strong P-O covalent bond in the VOPO4 structure effectively weakens the electron density of the V-O covalent bond through the "inductive effect", making it exhibit a relatively high discharge platform (≈1.1-1.8 V vs. Zn 2+ / Zn). However, VOPO4 still faces severe challenges in electrochemical cycling: First, during the discharge process, the high charge density of Zn 2+ has a strong electrostatic interaction with the lattice oxygen, resulting in a significant limitation of the diffusion kinetics of Zn 2+ between the layers; at the same time, the embedded Zn 2+ is prone to form a physical shielding layer, significantly reducing the effective zinc storage sites, resulting in low active material utilization and exhibiting a low specific capacity (170 mAh g -1 ). Second, with the insertion of Zn 2+ , the formation of Zn-O bonds will weaken the bond energy of V-O bonds and reduce the van der Waals force between the layered structures. This leads to a decrease in the structural thermodynamic stability of VOPO4 material, causing the polyanion PO4 3- group to dissolve and transform into VO x , resulting in a rapid decline in battery voltage and cycle stability.

[0004] To address the above problems, existing technologies mainly use pre-intercalation, introduction of oxygen vacancies, or optimization of electrolyte to improve the performance of VOPO4. However, these methods often only optimize the surface or local area of the material, and do not solve the problems of insufficient stability and limited ion diffusion from the intrinsic lattice structure. Therefore, developing a strategy to optimize VOPO4 material from the intrinsic level of the crystal structure is the key to breaking through the performance bottleneck of aqueous zinc-ion battery positive electrode materials. Summary of the Invention

[0005] The purpose of this application is to provide a method for improving the stability and rate performance of aqueous zinc-ion batteries by partially replacing the V lattice in VOPO4 with Fe.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, the present invention provides a method for doping Fe metal ions into vanadium oxyphosphate materials, comprising the following steps:

[0008] (1) Place V2O5, H3PO4 and iron metal salt in a solvent and stir to obtain a mixed solution;

[0009] (2) Reflux the above mixed solution. After the reaction is complete, allow it to cool to room temperature.

[0010] (3) After washing and vacuum drying, Fe metal ion-doped vanadium oxyphosphate material is obtained.

[0011] Preferably, according to the mole ratio, n Fe / (n V +n Fe ) = 2%, where n Fe n is the amount of Fe. V Let V be the amount of substance.

[0012] Preferably, the reflux reaction temperature is 115°C and the time is 24 hours.

[0013] Preferably, drying is carried out in a vacuum oven at 60°C for 12 hours.

[0014] Preferably, the iron metal salt is a soluble iron metal salt, which can be any one of Fe(NO3)3, FeCl3 and Fe2(SO4)3.

[0015] Secondly, the present invention provides an Fe metal ion-doped vanadium oxyphosphate material prepared by the method described in the first aspect.

[0016] Thirdly, the present invention provides the use of the Fe metal ion-doped vanadium oxyphosphate material prepared by the method described in the first aspect as a positive electrode material for an aqueous zinc-ion battery.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. This invention proposes to partially substitute the V sites in the VOPO4 lattice with Fe ions, targeting Zn 2+ Strong electrostatic forces and an aqueous electrolyte environment optimize the local coordination environment and electronic structure, forming a Fe-OPOV delocalized structure, which significantly enhances the Zn content.2+ The reversibility of the intercalation / deintercalation and the lattice stability.

[0019] 2、The Fe-VOPO4 positive electrode material prepared in the application has obvious improvement in rate performance and cycle performance compared with undoped VOPO4 material. Fe V Fe The material obtained under the condition of n -1 The discharge capacity of the material obtained under the condition of n -1 The capacity retention rate of the material obtained under the condition of n -1 The capacity of the material obtained under the condition of n -1 The capacity of the material obtained under the condition of n -1

[0020] 3、The Fe doping enhances the V-O bond strength, reduces the interplanar spacing (from 0.747 nm to 0.736 nm), inhibits the dissolution of PO4 3- and structural rupture, and significantly improves the symmetry of VO6 octahedron and the mechanical stability of the material.

[0021] 4、The Fe-VOPO4 material prepared in the application has mild preparation conditions, only needs simple oil bath reflux, simple process, mild reaction conditions (115℃, 24 hours), no need for high pressure or complex equipment, low cost, high yield, and obvious industrialization advantage compared with the complex process of prior art (such as pre-intercalation or high temperature treatment). BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The SEM images of VOPO4 materials doped with different metal ions prepared in Example 1 of the application, wherein a: Fe-VOPO4; b: Co-VOPO4; c: Nb-VOPO4; d: Mo-VOPO4; e: Ta-VOPO4; f: W-VOPO4.

[0023] Figure 2 The XRD spectra of VOPO4 materials doped with different metal ions (Fe, Co, Nb, Mo, Ta and W) prepared in Example 1 of the application.

[0024] Figure 3 The SEM images of VOPO4 materials with different Fe doping contents prepared in Example 2 of the application, wherein a: VOPO4; b: 1% Fe-VOPO4; c: 2% Fe-VOPO4; d: 5% Fe-VOPO4. ​​​

[0025] Figure 4 XRD patterns of VOPO4, 1% Fe-VOPO4, 2% Fe-VOPO4 and 5% Fe-VOPO4 prepared in Example 2 of the present application, wherein a: full XRD pattern; b: XRD pattern of (001) crystal plane in enlargement.

[0026] Figure 5 Electron paramagnetic resonance (EPR) spectra of VOPO4, 1% Fe-VOPO4, 2% Fe-VOPO4 and 5% Fe-VOPO4 prepared in Example 2 of the present application.

[0027] Figure 6 Raman spectra of VOPO4 and 2% Fe-VOPO4 prepared in Example 2 of the present application.

[0028] Figure 7 High-angle annular dark field transmission scanning electron microscope (HAADF-STEM) images of VOPO4 and 2% Fe-VOPO4 prepared in Example 2 of the present application, wherein a: HAADF-STEM image of VOPO4; b: HAADF-STEM image of 2% Fe-VOPO4.

[0029] Figure 8 Cycle performance of VOPO4 and 2% Fe-VOPO4 cathode materials prepared in Example 2 as anode materials of aqueous zinc ion battery.

[0030] Figure 9 Rate performance of VOPO4 and 2% Fe-VOPO4 cathode materials prepared in Example 2 as anode materials of aqueous zinc ion battery. DETAILED DESCRIPTION

[0031] The present application will be further described below in conjunction with specific embodiments.

[0032] It should be noted that the terms such as “upper”, “lower”, “left”, “right”, “intermediate” and the like cited in the present specification are merely for the convenience of clear description, and are not intended to limit the scope of implementation, and the change or adjustment of the relative relationship is also regarded as the scope of implementation of the present application without substantial change of technical content.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the term “and / or” used herein includes any and all combinations of one or more related listed items.

[0034] Unless otherwise indicated, conventional methods or those modifications thereof known to those of ordinary skill in the art were employed in the examples. Unless otherwise indicated, all reagents or instruments were commercially available and were used according to the manufacturer's instructions.

[0035] As used herein, the term "about" is used to provide flexibility to a numerical range endpoint by providing support for a somewhat greater or lesser inclusion of the values used in the endpoint range. The extent to which concreteness is provided is readily determined by one of ordinary skill in the art in the context of the relevant art, the associated discussion, and the examples.

[0036] Since aqueous lithium-ion, sodium-ion, potassium-ion and zinc-ion batteries have the same working principle, i.e., the reversible intercalation and deintercalation of metal ions (e.g., Li + , Na + , K + , Zn 2+ ) between the positive and negative electrodes during the charging and discharging process, we deduce that the stable lattice structure and efficient ion migration channel constructed by Fe-doped VOPO4 materials can also significantly improve the cycle stability and rate performance of the materials in aqueous lithium-ion, sodium-ion and potassium-ion batteries. Therefore, the following examples only take aqueous zinc-ion batteries as representatives.

[0037] Example 1:

[0038] The preparation method of the VOPO4 material doped with different metal ions comprises the following steps:

[0039] I. At room temperature, 4.8 g of V2O5, 26.6 mL of H3PO4, and a soluble M metal salt (M = Fe, Co, Nb, Mo, Ta, and W) with a molar ratio of n M / (n V +n M ) = 2% and 115.4 mL of deionized water were added into a three-necked flask, a rotor was added, and magnetic stirring was performed for 30 min to obtain a mixed solution;

[0040] II. The mixed solution was heated to reflux at 115°C in an oil bath for 24 h. After the reaction was completed, the product was allowed to cool to room temperature to obtain a flocculent product;

[0041] III. The flocculent product was washed with acetone three times and dried in a vacuum oven at 60°C for 12 hours to obtain six VOPO4 materials doped with different metals (M-VOPO4);

[0042] Figure 1 Figures b-f in the drawings show SEM images of the VOPO4 materials doped with different metals of Example 1. As can be seen from the figures, the Fe-VOPO4 material prepared in Example 1 has a more uniform particle size and better crystallinity than the VOPO4 material. Figure 1 Figure 3 ​a) are similar, all showing rectangular platelet morphology, but the Fe-VOPO4 material morphology remains relatively intact. This is because the ionic radius of Fe is 0.63, and the ionic radius of V is 0.59, which is larger than the metal ion radius of Co 0.69. Fe can better replace the position of V to maintain the complete structure. From Figure 1 It can be seen that the Nb, Mo, Ta, and W prepared in Example 1 have strong electronegativity, but because the local d-orbital electrons are strongly localized, the effective conduction of a / b-axis electrons is limited, the morphology remains rectangular platelets, but the material is relatively fragile and easy to break during the cycle.

[0043] Figure 2 The X-ray diffraction (XRD) pattern of the material prepared in Example 1 is shown by Figure 2 It can be seen that the material prepared in Example 1 corresponds well to the standard card of VOPO4. Among them, the (001) diffraction peak of Fe-doped VOPO4 is right-shifted, and the interplanar spacing is reduced from 0.747 nm to 0.736 nm. This is because the large ionic radius of Fe leads to the strengthening of the electrostatic interaction between the c-axis lattice oxygen and the interlayer water molecules, reducing the interplanar spacing and causing the (001) diffraction peak to right-shift. In contrast, the larger ionic radius of Co leads to stronger interlayer forces, causing the c-axis lattice to shrink, resulting in the (001) diffraction peak to right-shift. However, the more serious shrinkage causes the material to break. The large ionic radius of Nb, Mo, Ta, and W (Nb 0.69, Mo 0.62, Ta 0.68, W 0.62) and strong electron localization increase the M-O bond, leading to an increase in interlayer forces, causing the c-axis lattice to shrink, resulting in the (001) diffraction peak to right-shift. However, strong electron localization easily leads to the material to break during the cycle.

[0044] Therefore, here we finally choose the metal Fe to prove the effectiveness of the doping on the microstructure regulation of VOPO4.

[0045] Example 2:

[0046] The difference between Example 2 and Example 1 is that in step one, different molar ratios of iron chloride are used, i.e. n Fe / (n V +n Fe ) = 0%, 1%, 2%, 5%, wherein 0% is pure VOPO4 material, and other steps and parameters are the same as Example 1.

[0047] Figure 3 The SEM images of the four materials prepared in Example 2 are shown by Figure 3It can be seen that the materials prepared in Example 2 have similar rectangular plate morphology to VOPO4, which proves that Fe successfully replaces V in the lattice of VOPO4. With the increase of Fe doping amount, the in-plane anisotropy of VOPO4 gradually increases, and the rectangular plate gradually appears to be broken, which is due to the excessive Fe doping content.

[0048] Figure 4 The XRD patterns of the materials prepared in Example 2 are shown, which correspond well to the standard card of VOPO4. Figure 4 It can be seen that the materials prepared in Example 2 correspond well to the standard card of VOPO4. With the increase of Fe doping gradient, the (001) c-axis diffraction peak of VOPO4 gradually shifts to the right (JCPDS: 36-1472), which is due to the gradual increase of Fe doping content with large ionic radius, which gradually increases the electrostatic interaction between the c-axis lattice oxygen and the interlayer water molecules, gradually reduces the interlayer spacing, and gradually shifts the diffraction peak to the right from 0.747 nm to 0.730 nm.

[0049] Figure 5 The EPR spectrum of the materials prepared in Example 2 shows a g factor of 2.005, which presents an oxygen vacancy response signal, but with the increase of Fe doping amount, the defect vacancies gradually decrease, which is due to the replacement of V atoms by more Fe and the occupation of part of the defect vacancies.

[0050] Figure 6 The electronic Raman spectra of the VOPO4 and 2% Fe-VOPO4 materials prepared in Example 2 are shown. As shown in Figure 6 , the peaks at 202, 281, 381, 641 cm -1 are related to FeO x groups, and the peaks at 542, 954, 989 and 1038 cm -1 are related to VO6 and PO4 groups. The appearance of FeO x group Raman spectrum indicates that Fe ions are successfully doped into VOPO4 material, which is consistent with the SEM results. Compared with the Raman spectrum of VOPO4 nanosheet, the V=O at 1038 cm -1 in 2% Fe-VOPO4 is shifted to the right, which makes the shorter c-axis V=O in VO6 lattice appear tensile strain, improves the symmetry of VO6 octahedron, and enhances the stability of the material.

[0051] Figure 7 The HAADF-STEM images of the VOPO4 and 2% Fe-VOPO4 materials prepared in Example 2 are shown, and the elements in the materials are uniformly distributed, which indicates that Fe ions are successfully doped into VOPO4 material, which is consistent with the Raman results.

[0052] Therefore, we ultimately chose 2% Fe-VOPO4 as the target material to compare with VOPO4 in our energy storage study, in order to demonstrate the effectiveness of doping in regulating the microstructure of VOPO4 in aqueous zinc-ion battery storage.

[0053] Testing process:

[0054] The preparation method of aqueous zinc-ion batteries is as follows:

[0055] A paste was prepared by mixing 2% Fe-VOPO4 or VOPO4 as the positive electrode material, acetylene black as the conductive agent, and PVDF as the binder in a mass ratio of 7:2:1, and then grinding with an appropriate amount of N-methylpyrrolidone for 20 min. The electrode paste was then uniformly coated onto graphene foil and dried in a vacuum oven at 60℃ for 12 hours to obtain an electrode sheet. The prepared electrode sheet was used as the positive electrode (the mass loading of the active material was maintained at 1-2 mg / cm²). -2 Within a certain range (diameter 1.2cm), a zinc sheet (thickness 0.05mm, diameter 1.2cm) was used as the negative electrode, glass fiber as the separator (diameter 1.9cm), and 3M Zn(CF3SO3)2 solution as the electrolyte, to assemble a CR-2032 type button cell. The voltage of the aqueous zinc-ion battery was tested in the range of 0.5-1.8V, and the capacitance was measured at 1.0Ag. -1 Cyclic performance was tested at current density, and the cycling performance was as follows: Figure 8 As shown, the rate performance is as follows Figure 9 As shown.

[0056] Depend on Figure 8 It can be seen that the 2% Fe-VOPO4 cathode material prepared in Example 2 exhibits excellent cycle performance at 1.0 Ag. -1 The discharge capacity at the given current density is 104 mAh g. -1 Furthermore, after 2000 cycles, 80% of the capacity was retained, demonstrating excellent rate performance. This is attributed to the formation of a stable Fe-OPOV electronic delocalization structure by appropriate Fe doping, which enhances the VO bond strength and reduces PO4 content. 3- The dissolution of the material ensures structural stability. In contrast, the VOPO4 cathode material at 1Ag... -1 The discharge capacity at the current density is 76 mAh g. -1 After 2000 cycles, 42% of the capacity was retained, which is somewhat different from that of the 2% Fe-VOPO4 material.

[0057] Depend on Figure 9 It can be seen that the 2% Fe-VOPO4 cathode material prepared in Example 2 exhibits higher rate performance. At a low current density of 0.1 Ag... -1 Below, the maximum specific capacity of 150mAh g is shown. -1Even at 5 Ag -1 At high rate, the capacity can still maintain 82 mAh g -1 -1. At the same time, the specific capacity can recover to 149 mAh g -1 -1 when the rate decreases to 0.1 Ag -1 , which is equivalent to the initial specific capacity. This is because Fe as active sites increases the storage of zinc ions. At the same time, the appropriate amount of Fe doping enhances the complete lattice, increases the percolation channel of Zn 2+ , and expands the interlayer spacing, which promotes the storage of more zinc ions, improves the specific capacity and rate performance. In contrast, the VOPO4 positive electrode material exhibits poor rate performance and has a certain gap with the 2% Fe-VOPO4 material.

[0058] In summary, the comparative example 1 material has a large gap in cycle performance and rate performance with example 1 and example 2, which shows that 2% Fe doping in the VOPO4 material has obvious improvement in the cycle and rate performance of the material in the aqueous zinc ion battery.

[0059] The above embodiments are only the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments. For example, various forms of combinations of the schemes in the embodiments, any changes, modifications, substitutions, combinations made without departing from the spirit and principles of the present application should be equivalent replacement methods, which are within the protection scope of the present application.

Claims

1. A method for producing Fe metal ion-doped vanadium oxyphosphate material, characterized in that, Includes the following steps: (1) Place V2O5, H3PO4 and iron metal salt in a solvent and stir to obtain a mixed solution; (2) Reflux the above mixed solution. After the reaction is complete, allow it to cool to room temperature. (3) After washing and vacuum drying, Fe metal ion doped vanadium oxyphosphate material is obtained.

2. The method as described in claim 1, characterized in that, Molepi, n Fe / (n V +n Fe ) = 2%, where n Fe n is the amount of Fe. V Let V be the amount of substance.

3. The method as described in claim 1, characterized in that, The reflux reaction was carried out at a temperature of 115°C for 24 hours.

4. The method as described in claim 1, characterized in that, Dry in a vacuum oven at 60°C for 12 hours.

5. The method as described in claim 1, characterized in that, The iron metal salt is a soluble iron metal salt, preferably any one of Fe(NO3)3, FeCl3 and Fe2(SO4)3.

6. An Fe metal ion-doped vanadium oxyphosphate material prepared by the method according to any one of claims 1-5.

7. The use of Fe metal ion-doped vanadium oxyphosphate material prepared by the method according to any one of claims 1-5 as a positive electrode material for an aqueous ion battery.

8. The use as described in claim 7, characterized in that, Aqueous ion batteries include aqueous zinc-ion batteries, aqueous lithium-ion batteries, aqueous sodium-ion batteries, and aqueous potassium-ion batteries.

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