Magnesium ion secondary battery epsilon-VOPO4 positive electrode material and preparation method thereof

Abstract

The invention relates to the field of new energy magnesium ion batteries, in particular to a magnesium ion secondary battery epsilon-VOPO4 positive electrode material and a preparation method thereof.The preparation method comprises the following steps that 1, a precursor solution is prepared, specifically, a phosphorus source and a vanadium source are added into deionized water, the pH value of the solution is adjusted to 2-3, and the solution is stirred for 1-2 h; 2, calculating according to the mass of V, adding 1-3wt.% of CTAB (Cetyltrimethyl Ammonium Bromide), and continuously stirring the solution for 1-2 hours; step 3, hydrothermal reaction: carrying out hydrothermal reaction on the solution in the step 2, after the reaction is finished, cleaning the solution until the pH value of the filtrate is neutral, and drying the product obtained by filtering to obtain a precursor; and 4, annealing treatment: uniformly grinding the precursor in the step 3, and sintering in an oxygen atmosphere to obtain the epsilon-VOPO4 material. By implementing the scheme, the battery capacity and the cycling stability are improved.

Description

Technical Field

[0001] This invention relates to the field of new energy magnesium-ion batteries, specifically to an ε-VOPO4 cathode material for magnesium-ion secondary batteries and its preparation method. Background Technology

[0002] The rapid development of renewable energy has placed demands on energy storage systems for higher energy density, better safety, and lower costs. Magnesium-ion batteries, due to their high volumetric capacity (3833 mAh / cm³), are particularly advantageous. 3 Magnesium rechargeable batteries, with their advantages of low dendrite risk and abundant reserves, exhibit good development potential in multivalent ion systems. Compared to lithium-ion batteries, magnesium rechargeable batteries have higher volumetric energy density and stronger intrinsic safety, but achieving reversible insertion / extraction of their cathode materials remains a challenge, mainly due to the fact that Mg... 2+ It diffuses slowly in the crystal lattice, has strong electrostatic interactions, and a high desolvation energy barrier.

[0003] In the research of magnesium secondary battery cathode materials, VOPO4 has attracted attention due to its diverse crystal forms, high voltage plateau, and excellent thermal stability. VOPO4 possesses α... I α II Seven crystal forms: α, β, ε, δ, ω, and γ; among which α... I α II It has a layered structure, which is suitable for intercalation modification; β and ε are three-dimensional cross-linked network structures, which are conducive to the construction of multidimensional diffusion channels; δ and ω phases are arranged in chains or in a disordered manner; V=O chains in the γ phase are arranged in a completely disordered manner.

[0004] Currently, commonly used intercalated materials such as VOPO4·2H2O (e.g., the preparation method of vanadium oxyphosphate dihydrate powder disclosed in CN117361460A) are suitable for lithium and zinc-ion batteries, but not for magnesium secondary battery systems, where the interlayer water in Mg... 2+ Intercalation can easily lead to structural collapse, electrode polarization, and even negative electrode passivation, resulting in severe capacity decay and poor performance. Compared to VOPO4·2H2O, ε-VOPO4 exhibits superior cycle stability due to its stable three-dimensional framework structure; however, existing ε-VOPO4 cathode materials only achieve a capacity of around 40 mAh / g and suffer from poor cycle life. Furthermore, most current research on VOPO4 is limited to half-cell testing and has not yet been applied to magnesium metal full cells; the technology remains in the validation stage and its maturity is relatively low. Summary of the Invention

[0005] The present invention aims to provide an ε-VOPO4 cathode material for magnesium-ion secondary batteries and a method for preparing the same, so as to improve battery capacity and cycle stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing ε-VOPO4 cathode material for magnesium-ion secondary batteries, comprising the following steps: Step 1, Preparation of precursor solution: Add phosphorus source and vanadium source to deionized water, adjust the pH of the solution to 2-3, and stir the solution for 1-2 hours; Step 2: Calculate by mass V, add 1 wt.% to 3 wt.% of surfactant, and continue stirring the solution for 1 to 2 hours; Step 3, hydrothermal reaction: The solution in step 2 is subjected to a hydrothermal reaction. After the reaction is completed, the solution is washed until the pH of the filtrate is neutral. The filtered product is dried to obtain the precursor. Step 4, Annealing: Grind the precursor from Step 3 evenly and sinter it in an oxygen atmosphere to obtain ε-VOPO4 material. Preferably, as an improvement, in step 1, the molar ratio of V:P in the phosphorus source and vanadium source is 1:1 to 1:2 to ensure that a pure-phase ε-VOPO4 cathode material is formed.

[0007] Preferably, as an improvement, the phosphorus source is one of H3PO4 and P2O5; the vanadium source is one of NH4VO3, V2O5, and VCl3; and the surfactant is one of CTAB, SDS, and Span80.

[0008] Preferably, as an improvement, in step 4, the sintering temperature is 500℃~700℃, and the sintering time is 3.5-4h. This temperature range can optimize the crystallinity and particle dispersion of the material, promote the formation of a porous three-dimensional interconnected framework, and enhance the Mg... 2+ This improves the diffusion channels, thereby enhancing battery capacity and cycle stability. If the sintering temperature is too low (below 500℃), crystal nuclei will not form completely, resulting in poor crystallinity and affecting the ability to store Mg2+, leading to poor battery performance. Conversely, if the temperature is too high (above 700℃), excessive grain growth and severe material agglomeration will occur, which is detrimental to Mg2+ storage. 2+ The insertion and extraction of ions reduces ion diffusion kinetics, thus affecting battery performance.

[0009] Preferably, as an improvement, in step 3, the cleaning is performed by alternating between water and ethanol.

[0010] Preferably, as an improvement, in step 3, the filtered product is dried at 80℃-90℃ for 10-15 hours.

[0011] Preferably, as an improvement, in step 3, the temperature of the hydrothermal reaction is 170℃-190℃, and the reaction time is 48h~72h.

[0012] Preferably, as an improvement, in step 2, the amount of CTAB added is 2 wt.%.

[0013] Preferably, as an improvement, the sintering temperature in step 4 is 600°C.

[0014] An ε-VOPO4 cathode material for a magnesium-ion secondary battery, which is prepared according to the preparation method described in any one of claims 1-8.

[0015] The principle and advantages of this scheme are: The applicant conducted extensive analysis and research on various stages of the synthesis process to address the low capacity and poor cycle life exhibited by ε-VOPO4 cathode materials. The analysis revealed grain agglomeration and uneven crystallinity during material synthesis, which could potentially limit the development of Mg... 2+ The diffusion of [something] leads to problems such as low capacity and poor cycle life in the cathode material.

[0016] For the reasons mentioned above, the applicant explored various combinations of raw materials, adjustments to proportions, and doping techniques, ultimately developing the low-cost, high-efficiency, and time-efficient technical route described in this invention. Specifically, this invention is the first to propose using the cationic surfactant CTAB as a structure-directing agent, effectively optimizing the crystal growth process of the ε-VOPO4 cathode material. The quaternary ammonium head group of CTAB can interact with H2VO4 via electrostatic attraction. - Once vanadate ions form stable micelles, the interfacial energy during crystal nucleation is reduced, allowing for synchronous and uniform nucleus formation within the system. Simultaneously, the long-chain alkyl tails of CTAB form an organic passivation layer on the surface of the newly formed nuclei, promoting rapid and uniform crystal nucleation and effectively inhibiting disordered grain growth and agglomeration, ultimately yielding nanoscale, well-dispersed ε-VOPO4 crystals. Finally, after annealing at 500℃-700℃, the precursor undergoes pyrolysis to construct a porous three-dimensional interconnected framework, significantly increasing the specific surface area and providing a suitable environment for Mg... 2+ The intercalation and deintercalation provided an efficient diffusion channel. The resulting product exhibited significantly reduced particle aggregation, and both its dispersibility and crystallinity were markedly improved.

[0017] In addition, the CTAB-assisted hydrothermal synthesis process used in this scheme has mild conditions and does not require the use of a large amount of VCl3 precursor, which reduces raw material costs and environmental burden. At the same time, the synthesis reaction time of the precursor is only 48 hours, which is significantly shorter than the traditional method that requires at least 72 hours, shortening the time by nearly 40%.

[0018] In terms of performance, the discharge specific capacity of a magnesium metal full cell assembled using unmodified ε-VOPO4 cathode material is only 46.7 mAh / g. However, after using the cathode material prepared by this method, the discharge specific capacity of the full cell is increased to 64.7 mAh / g, an increase of more than 38%, and the cycle stability is also enhanced.

[0019] Most importantly, unlike traditional VOPO4 materials which are only evaluated in half-cell systems, this invention is the first to realize the construction and application of ε-VOPO4 in a full-cell system of metallic magnesium, filling the gap in the research of this type of material in full-cell systems and providing a new technical path for the development of high-performance multivalent ion batteries. Attached Figure Description

[0020] Figure 1 The image shows the SEM image of the cathode material obtained in Comparative Example 1.

[0021] Figure 2 This is a SEM image of the ε-VOPO4 cathode material obtained in Example 1 of the present invention.

[0022] Figure 3 The image shows the XRD pattern of the cathode material obtained in Comparative Example 1.

[0023] Figure 4 The image shows the XRD pattern of the ε-VOPO4 cathode material obtained in Example 1.

[0024] Figure 5 The charge-discharge curves of the cathode material obtained in Comparative Example 1 at 0.2 C are shown.

[0025] Figure 6 The charge-discharge curves of the ε-VOPO4 cathode material obtained in Example 1 at 0.2 C are shown.

[0026] Figure 7 The image shows the long-cycle curve of the cathode material obtained in Comparative Example 1 at 0.2 C.

[0027] Figure 8 The image shows the long-cycle curve of the ε-VOPO4 cathode material obtained in Example 1 at 0.2 C.

[0028] Figure 9 The diagram shows the rate performance of the cathode material obtained in Comparative Example 1.

[0029] Figure 10 The rate performance diagram is shown for the ε-VOPO4 cathode material obtained in Example 1. Detailed Implementation

[0030] The following detailed description illustrates the specific implementation method: The basic implementation examples are as follows: Figure 1As shown: A method for preparing ε-VOPO4 cathode material for magnesium-ion secondary batteries includes the following steps: S1. Preparation of precursor solution: Add 0.892 g of V₂O₅ and 1.358 g of H₃PO₄ (85 wt.%) to a beaker at a V:P molar ratio of 1:1.2. Add 30 mL of deionized water, adjust the pH of the solution to 2.5 with triethylamine, and stir for 1 h.

[0031] S2. Addition of surfactant: Calculate by mass V, add 2 wt.% CTAB (0.01 g), and continue stirring the solution for 1 h.

[0032] S3. Hydrothermal reaction: The well-stirred solution was transferred to a 100 mL PTFE-lined reactor and hydrothermally reacted at 180 °C for 48 h. After the reaction, the solution was washed alternately with water and ethanol until the pH of the filtrate was neutral. The filtered product was dried at 80 °C for 12 h to obtain the precursor.

[0033] S4. Annealing treatment: The dried precursor was ground into a homogeneous form and placed in a tube furnace. It was sintered at 550 °C for 4 h in an oxygen atmosphere to obtain the final ε-VOPO4 product.

[0034] Example 2 Unlike Example 1, the amount of CTAB added was 1 wt.%, and the sintering temperature was 500°C.

[0035] Example 3 Unlike Example 1, the amount of CTAB added was 3 wt.%, and the sintering temperature was 600°C.

[0036] Example 4 Unlike Example 1, the surfactant used in this example is SDS, and the amount added is 2 wt.%.

[0037] Example 5 Unlike Example 1, the surfactant used in this example is Span80, and its addition amount is 2 wt.%.

[0038] Comparative Example 1 Unlike Example 1, CTAB was not added, i.e., step 2 was not performed.

[0039] The ε-VOPO4 product obtained in this comparative example had uneven particle size and severe agglomeration, with a discharge specific capacity of 46.7 mAh / g.

[0040] Comparative Example 2 Unlike Example 1, the amount of CTAB added was 4 wt.%.

[0041] The ε-VOPO4 product obtained in this comparative example exhibited excessive particle refinement and further agglomeration, resulting in a discharge specific capacity far lower than that of Example 1, at 42.5 mAh / g.

[0042] Comparative Example 3 Unlike Example 1, in step 1, the pH of the solution was adjusted to 4.0 using triethylamine.

[0043] The ε-VOPO4 product obtained in the comparative example exhibited agglomeration, decreased crystallinity, and a significantly reduced specific capacity, with a discharge specific capacity of 49.8 mAh / g. Agglomeration resulted in insufficient wetting of the electrolyte between the grains, inhibiting the growth of Mg. 2+ The ineffective diffusion of [something] affects the battery's charge and discharge performance, leading to a decrease in capacity.

[0044] Experimental Test The cathode materials of Example 1 and Comparative Example 1 were subjected to SEM and XRD tests, and the test results are as follows: Figures 1-4 As shown, SEM results indicate that the particle size of the sample without CTAB addition is between 300 and 600 nm, and it exhibits obvious agglomeration. In contrast, the particle size of the sample synthesized after adding CTAB is significantly reduced, and the particles are more uniform and thinner, showing better dispersibility. XRD results show that both the sample before and after adding CTAB are single-phase, and all diffraction peaks can be attributed to ε-VOPO4, with no impurities generated.

[0045] The cathode materials prepared in each embodiment and the comparative example were assembled into full cells, and performance tests were conducted. Specific test results are shown in Table 1 and... Figures 5-10 .

[0046]

[0047] Table 1 Table 1 shows that the discharge specific capacity of cathode materials prepared with different surfactants varies, with CTAB exhibiting the best performance. Furthermore, when using the same surfactant CTAB, different addition amounts significantly affect the battery's discharge specific capacity, with the highest discharge specific capacity (64.7 mAh / g) observed at an addition amount of 2 wt.%. Therefore, the ε-VOPO4 cathode material exhibits optimal performance when 2 wt.% CTAB is added and the solution pH is 2.5.

[0048] Charge and discharge test The charge-discharge performance of the cathode materials of Example 1 and Comparative Example 1 at 0.2 C was tested, and the test results are as follows: Figure 5 , Figure 6The discharge specific capacity of the original sample was 46.7 mAh / g, while the discharge specific capacity of the sample synthesized with CTAB assistance increased to 64.7 mAh / g.

[0049] Cyclic performance test The cathode materials of Example 1 and Comparative Example 1 were subjected to long-cycle performance tests at 0.2 C. The test results are as follows: Figure 7 , Figure 8 The original sample had a discharge specific capacity of 34.5 mAh / g and a capacity retention of 74% after 50 cycles; the sample synthesized with CTAB assistance had a discharge specific capacity of 51.8 mAh / g and a capacity retention of 80% after 50 cycles.

[0050] Ratio Performance Test The positive electrode materials of Example 1 and Comparative Example 1 were subjected to rate performance testing, and the test results are as follows: Figure 9 , Figure 10 At discharge rates of 0.2C, 0.5C, 1C, 2C, and 5C, the discharge specific capacities of the original sample and the modified sample were 46.8, 40.3, 35.1, 30.46, and 23.5 mAh / g and 62.4, 53.3, 44.1, 37.9, and 28.5 mAh / g, respectively.

[0051] In summary, compared with the material without CTAB, the ε-VOPO4 cathode material prepared by this method has an increased discharge specific capacity of 46.7 mAh / g to 64.7 mAh / g in magnesium metal full cells, and its cycle stability is also significantly improved.

[0052] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing ε-VOPO4 cathode material for magnesium-ion secondary batteries, characterized in that: Includes the following steps: Step 1, Preparation of precursor solution: Add phosphorus source and vanadium source to deionized water, adjust the pH of the solution to 2-3, and stir the solution for 1-2 hours; Step 2: Calculate by mass V, add 1 wt.% ~ 3 wt.% surfactant, and continue stirring the solution for 1~2 hours; Step 3, hydrothermal reaction: The solution in step 2 is subjected to a hydrothermal reaction. After the reaction is completed, the solution is washed until the pH of the filtrate is neutral. The filtered product is dried to obtain the precursor. Step 4, Annealing: Grind the precursor from Step 3 evenly and sinter it in an oxygen atmosphere to obtain ε-VOPO4 material.

2. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 1, the molar ratio of V:P in the phosphorus source and vanadium source is 1:1 to 1:

2.

3. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 2, characterized in that: The phosphorus source is one of H3PO4 or P2O5; the vanadium source is one of NH4VO3, V2O5, or VCl3; and the surfactant is one of CTAB, SDS, or Span80.

4. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 4, the sintering temperature is 500℃~700℃ and the sintering time is 3.5-4h.

5. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 3, the cleaning process involves alternating between water and ethanol.

6. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 3, the filtered product is dried at 80℃-90℃ for 10-15 hours.

7. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 3, the hydrothermal reaction temperature is 170℃-190℃, and the reaction time is 48h~72h.

8. A method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 2, the surfactant is CTAB, and its addition amount is 2 wt.%.

9. The method for preparing an ε-VOPO4 cathode material for a magnesium-ion secondary battery according to claim 1, characterized in that: In step 4, the sintering temperature is 600℃.

10. A magnesium-ion secondary battery ε-VOPO4 cathode material, characterized in that: The magnesium-ion secondary battery ε-VOPO4 cathode material prepared according to any one of claims 1-9.

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