Calcium ion-doped vanadium oxide / carbon composite rich in oxygen defects and preparation method thereof

Abstract

The present invention discloses a calcium ion-doped vanadium oxide / carbon composite material rich in oxygen defects and a preparation method thereof, belonging to the technical field of battery materials. The above composite material is composed of a vanadium source, a carbon source and a soluble calcium salt, forming a composite structure composed of vanadium oxide rich in oxygen defects, calcium ion doping and carbon coating, and the microscopic morphology is a network structure composed of nanoparticles and nanosheets. The present invention applies the composite material to a zinc ion battery, obtaining good charge and discharge performance, and still maintaining an extremely high capacity during high-current charge and discharge. The main reason is that the in-situ electrochemical reaction changes the phase structure of the material, improves the conductivity of the material and expands the crystal plane spacing of the material by doping calcium ions, and stabilizes the material structure through carbon coating. The preparation method is a simple impregnation and calcination process, which is easy to operate, has strong universality, and uses raw materials with low cost, is easy to mass-produce, the prepared material has good performance, and has good practical application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly relates to a calcium ion-doped vanadium oxide / carbon composite material rich in oxygen defects and a preparation method thereof. Background Art

[0002] With the consumption of fossil fuels, the environment is deteriorating rapidly. It is crucial to develop clean and renewable energy. However, the instability in the production process of renewable energy has created a demand for energy storage devices of different scales. In the past 30 years, lithium-ion batteries have made great progress both commercially and academically due to their advantages such as high capacity and long cycle life. However, they also face the increasingly serious problems of lithium resource shortage and the safety of organic electrolytes. Compared with the safety problems such as the flammability of organic electrolytes, rechargeable aqueous zinc-ion batteries (AZIBs) are regarded as potential alternatives to lithium batteries due to their advantages such as sufficient supply, environmental friendliness, low cost, and fast ion transfer. With the development of zinc-ion batteries, a large amount of research has focused on finding high-performance and durable cathode materials. Polymorphic MnO2, Prussian blue analogues, organic polymers, and vanadium-based compounds have been widely studied as cathode materials for zinc-ion batteries. In particular, vanadium-based oxides have advantages such as high reversible capacity and variable structures when used as cathode materials for storing zinc.

[0003] V2O3 is a vanadium-based oxide material with a tunnel structure and has a theoretical capacity of up to 715 mAh g- 1 However, due to the large electrostatic repulsion between the low-valent vanadium-based oxide and Zn 2+ ions, structural damage is inevitably caused during the electrochemical process, resulting in capacity loss. Coupled with the fact that the tunnel structure of V2O3 itself is not conducive to zinc storage and its poor physicochemical properties, it is difficult to reach the theoretical capacity. Currently, there are two strategies for modifying its structure: (1) modifying the original lattice, such as inducing lattice distortion to form V vacancies and increasing zinc storage sites; (2) in-situ electrochemical conversion of the original structure to induce the formation of hydrated layered V2O5, and the layered structure is more suitable for zinc storage. Although these two strategies have been studied currently, they have not well solved the controllability of lattice spacing and defects, affecting the charge-discharge capacity and cycle performance of zinc-ion batteries. Summary of the Invention

[0004] Object of the Invention: To solve the existing technical problems, the present invention aims to provide a calcium ion-doped vanadium oxide / carbon composite material rich in oxygen defects with excellent electrochemical performance and applicable to zinc-ion batteries, and the present invention also provides a preparation method of the calcium ion-doped vanadium oxide / carbon composite material rich in oxygen defects.

[0005] Technical solution: The oxygen-deficient calcium-doped vanadium oxide / carbon composite material of the present invention is composed of a vanadium source, a carbon source, and a soluble calcium salt, forming a composite structure composed of oxygen-deficient vanadium oxide, calcium doping, and carbon coating, and the microscopic morphology is a network structure composed of nanoparticles and nanosheets.

[0006] Furthermore, the content of the soluble calcium salt in the composite material is 20-50%, and the content of the carbon source is 20-50%.

[0007] The preparation method of the oxygen-deficient calcium-doped vanadium oxide / carbon composite material of the present invention includes the following steps:

[0008] (1) Dissolve the vanadium source and hydrogen peroxide in a solvent to obtain a uniform solution A;

[0009] (2) Dissolve the carbon source and the soluble calcium salt in a solvent to obtain solution B;

[0010] (3) Drop solution B into solution A and stir vigorously to obtain a uniform solution C;

[0011] (4) After the solution C is evaporated to dryness, the obtained solid product is ground and calcined, and the obtained powder is washed and dried to obtain the oxygen-deficient calcium-doped vanadium oxide / carbon composite material.

[0012] Furthermore, in step (1), the vanadium source is one or more of vanadium pentoxide, vanadium trioxide, or vanadium dioxide, and the molar amount of the vanadium source to the volume of hydrogen peroxide is 4 mmol: 5-20 ml; the volume ratio of hydrogen peroxide to the solvent is 1-4: 10-20, preferably 1:15; the solvent is deionized water.

[0013] Furthermore, in step (2), the carbon source is glucose, and the soluble calcium salt is one or more of calcium chloride, calcium nitrate, calcium acetate, calcium gluconate, calcium dihydrogen phosphate, calcium bicarbonate, or calcium bisulfate; the molar ratio of the carbon source to the soluble calcium salt is 1: 2-2: 1; the molar amount of the carbon source to the volume of the solvent is 4 mmol: 50-100 ml.

[0014] Furthermore, in step (3), the molar ratio of the vanadium source in solution A to the carbon source in solution B is 1: 2-2: 1; the stirring conditions are: the stirring time is 12-24 h.

[0015] Furthermore, in step (4), the conditions for the evaporation to dryness treatment are: the temperature is 60-150 °C; the conditions for the calcination treatment are: under an inert atmosphere, the heating rate is 2-10 °C / min, the calcination temperature is 600-900 °C, and the calcination time is 1-6 h.

[0016] Principle of the invention: The present invention changes its phase structure through an in-situ electrochemical method, and adjusts its conductivity and the interlayer spacing of the crystal layer through calcium ion doping. In addition to introducing Ca 2+ as a guest ion, oxygen defects are also injected into the precursor. The oxygen defects can increase the 2+ Gibbs free energy of Zn ion adsorption, enhance the adsorption and desorption ability, reduce the diffusion barrier, and are beneficial to fast ion kinetics, thus effectively improving the capacity and rate performance.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0018] (1) For the composite material prepared by the present invention, the first key improvement lies in creating oxygen defects during the high-temperature calcination process under an inert atmosphere, changing the local electronic structure of the material, and improving the charge and discharge ability of the material;

[0019] (2) For the composite material prepared by the present invention, the second key improvement lies in using the liquid-phase stirring and calcination processes to dope calcium ions into the composite material, improving the conductivity and the interlayer spacing of the crystal plane of the material. At the same time, a carbon layer is formed by high-temperature carbonization of the carbon source glucose to coat the material, playing a role in stabilizing and protecting the material structure, thereby improving the charge and discharge capacity and the rate cycling performance of the material;

[0020] (3) The composite material prepared by the present invention has excellent zinc ion battery performance. Compared with the existing battery materials, its performance is more excellent, and the cost is low. The synthesis method is simple and easy to operate, and it has a very high practical application prospect. Description of the drawings

[0021] Figure 1 XRD patterns of the composite materials prepared in Examples 1-4 and Comparative Example 1 of the present invention;

[0022] Figure 2 SEM images of the composite materials prepared in Examples 1-4 and Comparative Example 1 of the present invention. In the figures: (a) is Comparative Example 1, (b) is Example 1, (c) is Example 2, (d) is Example 3, and (e) is Example 4;

[0023] Figure 3 XRD patterns of the composite materials prepared in Examples 5-7 and Comparative Example 2 of the present invention;

[0024] Figure 4 SEM images of the composite materials prepared in Examples 5-7 and Comparative Example 2 of the present invention. In the figures: (a) is Comparative Example 2, (b) is Example 5, (c) is Example 6, and (d) is Example 7;

[0025] Figure 5 Rate performance graphs of the composite materials prepared in Examples 1-4 and Comparative Example 1 of the present invention;

[0026] Figure 6 It is the rate performance diagram of the composite material prepared in Examples 5-7 of the present invention. Comparative Example 2 has no capacity contribution;

[0027] Figure 7 It is the long cycle performance diagram of the composite materials prepared in Example 2 and Examples 5-7 of the present invention at the corresponding 10Ag- 1 ;

[0028] Figure 8 It is the long cycle performance diagram of the composite material prepared in Example 2 of the present invention at the corresponding 20Ag- 1 ; Specific Embodiments

[0029] Next, the present invention will be further described in conjunction with specific embodiments and drawings.

[0030] Example 1: The preparation method of the calcium ion-doped vanadium oxide / carbon composite material rich in oxygen defects of the present invention is as follows:

[0031] Dissolve 4 mmol of V2O5 and 5 mL of H2O2 in 75 mL of distilled water, and stir at room temperature for 30 min to form solution A; dissolve 4 mmol of glucose and 2 mmol of CaCl2 in 75 mL of distilled water to form solution B; slowly drop solution B into solution A and stir for 24 h to obtain solution C. Transfer solution C to a blast drying oven and evaporate the solvent at 80 °C; collect the solid product after evaporation, grind it evenly and then put it into a tubular furnace for calcination. Under an inert atmosphere, heat it to 700 °C at a heating rate of 4 °C / min and keep it at this temperature for 1 hour. Wash the calcined product 3 times with distilled water and ethanol respectively, and dry it in vacuum at 60 °C for 24 h to obtain the calcium ion-doped vanadium oxide / carbon composite material rich in oxygen defects.

[0032] Example 2: The difference from Example 1 is that the dosage of CaCl2 is 4 mmol (calcium content is 30%, carbon content is 30%).

[0033] Example 3: The difference from Example 1 is that the dosage of CaCl2 is 6 mmol.

[0034] Example 4: The difference from Example 1 is that the dosage of CaCl2 is 8 mmol.

[0035] Example 5: The difference from Example 2 is that the dosage of glucose is 2 mmol.

[0036] Example 6: The difference from Example 2 is that the dosage of glucose is 6 mmol.

[0037] Example 7: The difference from Example 2 is that the dosage of glucose is 8 mmol.

[0038] Comparative Example 1: The difference from Example 2 is that CaCl2 is not added.

[0039] Comparative Example 2: The difference from Example 2 is that glucose is not added.

[0040] The composite materials prepared in Examples 1 - 7 and Comparative Examples 1 - 2 were subjected to XRD testing, microscopic characterization, and electrochemical performance testing.

[0041] The method for electrochemical performance testing is as follows: The materials prepared in Examples 1 - 7 and Comparative Examples 1 - 2 were respectively and uniformly mixed with acetylene black conductive agent and polyvinylidene fluoride (PVDF) binder in a ratio of 7:2:1 in N - methylpyrrol (thiophene) alkane ketone (NMP) to make electrodes, and placed in a small beaker and stirred for 24 h. Then the mixed slurry was uniformly coated on a titanium foil, placed in a vacuum drying oven at a temperature of 60 °C for 12 h. After taking it out, the titanium foil was cut into electrode discs with a diameter of 12 mm. The battery was assembled under air. A 14 - mm metal zinc sheet was used as the counter electrode and reference electrode, and the electrolyte was Zn(CF3SO3)2 with a concentration of 3 M. A CR2032 type button battery was assembled. After the battery assembly was completed, a Neware battery test system was used to conduct constant current charge / discharge testing at a voltage of 0.2 - 1.8 V.

[0042] The test results are shown in Figures 1 to 8 。

[0043] As Figure 1 shown, the positions and intensities of the XRD diffraction peaks are exactly the same as the standard pattern (PDF#34 - 0187). The shift of the XRD diffraction peak positions indicates that the obtained product is Ca x V2O 3-x materials with different calcium contents.

[0044] As Figure 2 shown, it can be found from the SEM pictures that the sample without calcium ion doping is composed of large - block substances piled up ( Figure 2 a), as the concentration of Ca 2+ increases, the material generates more fine particles, and the gradually decreasing volume indicates that with the doping of Ca 2+ , the morphology of the material has changed significantly, which is beneficial to the full contact of the electrolyte and improves the capacity and rate performance.

[0045] As Figure 3As shown, the XRD pattern shows that C plays a key role. The structure of Comparative Example 2 corresponds to the substance of the standard pattern (PDF#34-0187), and there is no capacity retention in the subsequent capacity test. The characteristic peaks of the substances in other examples show no obvious changes, which are Ca with different C contents 0.17 V2O 3-x materials.

[0046] As Figure 4 shown, the SEM images show that with the increase of C content, all morphological changes occur. Figure 4 (a) in [reference] is the SEM image of the carbon-free material. It can be observed that the prepared product is composed of particles about 10 μm in size and is stacked, and the surface is smooth without holes. As the carbon content gradually increases, in contrast, the particles gradually become larger, and a foamy covering appears on the surface. It may be due to the formation of a carbon-coated structure, and microscopic holes appear, which is beneficial for the electrolyte to fully contact, providing space for Zn 2+ storage, and the capacity and rate performance are improved. The surface carbon-coated structure can prevent the material from deforming during long-term cycling, which is beneficial to the stability of cycling. As the carbon content continues to increase, the particles continue to agglomerate to form larger-sized particles, and the surface holes become larger.

[0047] As Figure 5 shown, the different discharge rate performance diagrams of Examples 1-4 and Comparative Example 1. The composite material (Ca 2+ with a concentration of 30%) prepared in Example 2 has relatively prominent performance. The rate performance in the voltage window of 0.2-1.8V is excellent. It can be seen from the figure that the rate performance is excellent, and there is still a capacity retention of 220 mAh g -1 at 40 Ag -1 .

[0048] As Figure 6 shown, the rate performance diagrams of the products obtained in Examples 5-7. The figure shows that the sample (Example 6) with a doped carbon content of 40% in the original material has the best charge-discharge capacity and rate performance, but there is still a slight gap compared with the performance of Example 2. Since Comparative Example 2 has no capacity contribution, it is not listed in this figure.

[0049] As Figure 7 shown, the cycle performance diagrams of samples with different carbon contents. It can be seen from the figure that the sample (Example 2) with a carbon content of 30% has relatively excellent performance in long-term cycling at 10 Ag -1 , and still maintains a discharge capacity of 300 mAh g -1 after 2000 cycles.

[0050] As Figure 8 shown, Example 2 shows good cycle performance at 20 Ag -1After 10,000 cycles of high current cycling, the discharge specific capacity still remains at 221 mAh g -1 , and the capacity retention rate is 91.3%, showing good long cycle performance, which is better than the cycle performance of aqueous zinc-ion batteries reported in current literature.

Claims

1. A calcium-ion-doped vanadium oxide / carbon composite rich in oxygen vacancies, characterized in that, The composite material is composed of a vanadium source, a carbon source, and a soluble calcium salt, forming a composite structure consisting of oxygen-deficient vanadium oxide, calcium ion doping, and carbon coating, and the micro-morphology is a network structure composed of nanoparticles and nanosheets; the vanadium source is vanadium pentoxide. The above-mentioned oxygen-deficient calcium ion-doped vanadium oxide / carbon composite material is applied to a zinc ion battery, and the preparation method includes the following steps: (1) Dissolve the vanadium source and hydrogen peroxide in a solvent to obtain a uniform solution A; (2) Dissolve the carbon source and the soluble calcium salt in a solvent to obtain solution B; the molar ratio of the carbon source to the soluble calcium salt is 1:2 - 2:1; (3) Drop solution B into solution A and stir vigorously to obtain a uniform solution C; the molar ratio of the vanadium source in solution A to the carbon source in solution B is 1:2 - 2:1; (4) After solution C is subjected to evaporation to dryness, the obtained solid product is then subjected to grinding treatment and calcination treatment, and the obtained powder is washed and dried to obtain the oxygen-deficient calcium ion-doped vanadium oxide / carbon composite material.

2. The oxygen-defect-rich calcium-ion-doped vanadium oxide / carbon composite material according to claim 1, characterized in that, In step (1), the volume ratio of hydrogen peroxide to the solvent is 1 - 4:10 - 20.

3. The oxygen-defect-rich calcium ion-doped vanadium oxide / carbon composite material according to claim 1, characterized in that, In step (2), the carbon source is glucose, and the soluble calcium salt is one or more of calcium chloride, calcium nitrate, calcium acetate, calcium gluconate, calcium dihydrogen phosphate, calcium bicarbonate, or calcium bisulfate.

4. The oxygen-defect-rich calcium-ion-doped vanadium oxide / carbon composite material according to claim 1, wherein In step (4), the conditions for the evaporation to dryness treatment are: the temperature is 60 - 150 °C.

5. The oxygen-defect-rich calcium-ion-doped vanadium oxide / carbon composite material according to claim 1, characterized in that, In step (4), the conditions for the calcination treatment are: under an inert atmosphere, the heating rate is 2 - 10 °C / min, the calcination temperature is 600 - 900 °C, and the calcination time is 1 - 6 h.

6. Application of the oxygen-deficient calcium ion-doped vanadium oxide / carbon composite material as described in claim 1 as a cathode material for a zinc ion battery.

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