Preparation method of vanadium-based thin film electrode, vanadium-based thin film electrode and aqueous secondary battery

Abstract

The invention provides a preparation method of a vanadium-based thin film electrode, the vanadium-based thin film electrode and an aqueous secondary battery, and relates to the technical field of aqueous secondary batteries. The preparation of the vanadium-based thin film electrode is realized by modifying the H0. 39V2O5 vanadium-based thin film by adopting a mode of element doping or composite phase formation, and the crystal structure of the H0. 39V2O5 vanadium-based thin film can be changed in the modification process, so that the stability of the H0. 39V2O5 vanadium-based thin film serving as an electrode material is enhanced, and the electrode material is endowed with stronger corrosion resistance in water. Furthermore, when the vanadium-based thin film electrode is assembled into an aqueous secondary battery, a water-resisting layer is arranged between the working electrode and an aqueous electrolyte, and the water-resisting layer can be used for providing a physical isolation effect for the working electrode, so that corrosion of strong-polarity H2O in the electrolyte to a vanadium-based material crystal structure is inhibited, and the service life of the vanadium-based material crystal structure is prolonged. And the electrochemical cycle performance, the electrode structure stability and the water corrosion resistance are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of aqueous secondary batteries, and in particular to a method for preparing a vanadium-based thin film electrode, a vanadium-based thin film electrode and an aqueous secondary battery. Background Art

[0002] In the field of batteries, the water resistance of electrode materials is one of the key factors affecting battery performance and life, especially in aqueous secondary batteries. The application scenarios of modern aqueous batteries often require efficient, durable and stable battery materials. However, when facing highly polar water molecules in the electrolyte, traditional electrode materials are easily corroded and dissolved due to the high polarity and activity of water molecules, which poses a serious threat to the cycle life and energy density of the battery. The above situation is particularly obvious in the positive electrode of aqueous batteries. The high polarity of water molecules enables them to easily invade and destroy the crystal structure of the battery positive electrode material, especially under high potential conditions, this corrosion effect is particularly serious. Taking vanadium-based positive electrode materials as an example, their crystal structure is usually layered or porous. In aqueous electrolytes, water molecules will penetrate into the interior of the crystal, causing the material lattice to expand, interlayer ion migration to be hindered, and the loss of active substances. In addition, the chemical properties of vanadium-based materials are relatively active, and they are prone to side reactions with other components in the electrolyte (such as hydrogen ions and redox ions), causing irreversible damage to the crystal structure. For example, layered vanadium oxides (such as V 2 O 5 ) During the battery cycle, due to the instability of the crystal structure, it often exhibits poor capacity retention and limited cycle life. The destruction of this crystal structure not only reduces the energy storage capacity of the electrode material, but also accelerates the degradation of battery performance, becoming a bottleneck problem restricting the large-scale application of aqueous secondary batteries.

[0003] In order to solve this problem, the optimization of waterproof performance has become an important direction of electrode material research. In response to the problem that positive electrode materials of aqueous batteries are easily corroded by water, existing studies have proposed a variety of technical means to alleviate this challenge, mainly including the following categories: 1. Material modification: by introducing doping elements (such as rare earth metals, transition metals, etc.) to enhance the stability of electrode materials, change their crystal structure, and make them more resistant to corrosion in water; 2. Surface coating technology: coating a layer of inert oxide or carbon material on the surface of the electrode material to prevent direct contact with water molecules; 3. Electrolyte modification: optimizing the composition of the electrolyte, such as adding corrosion inhibitors or high-concentration salts, weakening the polarity of water molecules and reducing their erosion of electrode materials; 4. Battery structure optimization: designing more complex diaphragms or electrode structures to reduce the chance of water molecules contacting the positive electrode material. Although the above methods have alleviated the problem of water corrosion to a certain extent, these methods often have shortcomings such as complex preparation, high cost or limited waterproof effect.

[0004] In view of this, it is necessary to design an improved preparation method of a vanadium-based thin film electrode, a vanadium-based thin film electrode and an aqueous secondary battery to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a vanadium-based thin film electrode, a vanadium-based thin film electrode and an aqueous secondary battery.

[0006] To achieve the above invention purpose, on the one hand, the present invention provides a preparation method of a vanadium-based thin film electrode, including the following steps:

[0007] Add metal ion inorganic salts to a mixed solution of VOSO 4 and citric acid, and adjust the pH of the solution to 2.5 - 4.2 to obtain a precursor solution;

[0008] Immerse the substrate in the precursor solution, react for 30 - 60 h, and form a deposition film on the substrate; perform annealing treatment on the deposition film to obtain a vanadium-based thin film electrode.

[0009] Preferably, the metal ion inorganic salt is an inorganic salt containing metal ion M, and the metal ion M is one of Co, Ni, Cu, Ce, and Ca; the molar ratio of VOSO 4 to the metal ion M satisfies V:M = 4:1 - 8:1.

[0010] Preferably, when the metal ion M is Ce or Ca, the molar ratio of VOSO 4 to the metal ion M is V:M = 4:1 - 6:1.

[0011] Preferably, when the metal ion M is one of Co, Ni, and Cu, the molar ratio of VOSO 4 to the metal ion M is V:M = 4:1 - 8:1.

[0012] Preferably, the concentration of VOSO 4 in the mixed solution is 0.04 mol / L, and the concentration of citric acid is 0.013 mol / L.

[0013] Preferably, the conditions for the annealing treatment are: temperature 400 - 500 °C, time 2 h.

[0014] Preferably, the pH of the solution is adjusted using ammonia water; the substrate is ITO conductive glass.

[0015] Furthermore, the vanadium-based thin film electrode prepared by the preparation method proposed by the present invention includes ITO conductive glass and a vanadium-based thin film grown on the surface of the ITO conductive glass.

[0016] On the other hand, the present invention also provides an aqueous secondary battery, comprising:

[0017] a zinc counter electrode;

[0018] a working electrode, which is a vanadium-based thin film electrode;

[0019] a glass fiber membrane adsorbing an electrolyte, wherein the electrolyte is obtained by dispersing zinc trifluoromethanesulfonate and glycerol in deionized water.

[0020] Preferably, a water-repellent layer is fixed on the surface of the working electrode, and the water-repellent layer is one of weighing paper, coated white cardboard, and waxed paper.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. For the preparation method of the vanadium-based thin film electrode provided by the present invention, the H 0.39 V 2 O 5 vanadium-based thin film is modified by element doping or forming a composite phase to change the crystal structure of the H 0.39 V 2 O 5 vanadium-based thin film, thereby enhancing its stability as an electrode material and endowing the electrode material with stronger corrosion resistance in water.

[0023] 2. For the aqueous secondary battery provided by the present invention, by using the modified thin film electrode obtained by chemically modifying the H 0.39 V 2 O 5 vanadium-based thin film as the working electrode (vanadium-based thin film positive electrode material), and at the same time setting a water-repellent layer between the working electrode and the aqueous electrolyte, the water-repellent layer can provide a physical isolation effect for the working electrode, inhibit the corrosion of the strong polar H 2 O in the electrolyte on the crystal structure of the vanadium-based material, and improve the electrochemical cycling performance, the stability of the electrode structure and the waterproof corrosion performance. Description of the Drawings

[0024] Figure 1 is the XRD pattern of the vanadium-based thin film electrode prepared in Example 1 of the present invention;

[0025] Figure 2 is the optical photograph of the vanadium-based thin film electrode with weighing paper fixed on the surface in Example 5 of the present invention;

[0026] Figure 3 is a partial physical diagram of the battery disassembled after 200 cycles of charging in Example 5 of the present invention;

[0027] Figure 4 is the comparison of the cyclic discharge specific capacity of the battery with and without weighing paper in Example 5 of the present invention;

[0028] Figure 5 SEM images of the vanadium-based thin film before and after cycling with and without weighing paper in Example 5 of the present invention;

[0029] Figure 6 SEM images of the weighing paper before and after cyclic charging in Example 5 of the present invention;

[0030] Figure 7 Comparison of the cyclic discharge specific capacity of the battery with and without weighing paper in Example 6 of the present invention;

[0031] Figure 8 SEM images of the vanadium-based thin film before and after cycling in Example 6 of the present invention;

[0032] Figure 9 Cyclic discharge specific capacity of the battery in Example 7 of the present invention;

[0033] Figure 10 SEM images of the vanadium-based thin film before and after cycling in Example 7 of the present invention;

[0034] Figure 11 SEM images of the coated white cardboard before and after cycling in Example 7 of the present invention;

[0035] Figure 12 XRD patterns of the vanadium-based thin film before and after 100 cycles of the vanadium-based thin film electrode in Examples 5 to 8 of the present invention;

[0036] Figure 13 Comparison of the cyclic discharge specific capacity of the battery with and without a water barrier layer in Example 8 of the present invention;

[0037] Figure 14 SEM images of the vanadium-based thin film before and after cycling in Example 8 of the present invention;

[0038] Figure 15 In Comparative Example 1 of the present invention, H 0.39 V 2 O 5 XRD pattern of the vanadium-based thin film electrode;

[0039] Figure 16 Cyclic discharge specific capacity of the battery in Comparative Example 1 of the present invention;

[0040] Figure 17 SEM images of the vanadium-based thin film before and after cycling in Comparative Example 1 of the present invention;

[0041] Figure 18 SEM images of the glass fiber membrane before cycling and the weighing paper after cycling in Comparative Example 1 of the present invention. Detailed implementation manners

[0042] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less relevant to the present invention are omitted.

[0044] In addition, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0045] On the one hand, the present invention provides a method for preparing a vanadium-based thin film electrode, comprising the following steps:

[0046] Preparation of the thin film precursor solution: Add metal ion inorganic salts to a mixed solution of VOSO 4 and citric acid, and adjust the pH of the solution to 2.5 - 4.2 to obtain a precursor solution;

[0047] Preparation of the vanadium-based thin film electrode: Immerse the substrate in the above precursor solution and react for 30 - 60 h to form a deposited film on the substrate; perform annealing treatment on the deposited film to obtain a vanadium-based thin film electrode. Among them, the conditions for the annealing treatment are: temperature 400 - 500 °C, time 2 h, and the heating rate of the temperature rising from room temperature to the target temperature during the treatment process is 2 °C / min; the pH is adjusted using ammonia water.

[0048] In the above process, the film formation mechanism on the substrate is as follows: VOSO 4 is used as the vanadium source, citric acid is used as a complexing agent, and metal ion inorganic salts provide metal cations M. Under the action of the complexing agent, complexation reactions occur among metal cations M, VO 2+ and the complexing agent to form a stable complex; after adding ammonia water, under specific pH conditions, the complex stably releases metal cations M and VO 2+ , and the two combine with NH 4+ to form an insoluble compound. The insoluble compound gradually forms a precursor film of (NH 4 ) 2 V 10 O 25 ·H 2 O doped with metal ions M on the substrate surface through the processes of nucleation and growth. During the annealing treatment, water molecules between vanadium oxide layers in the precursor film and a part of NH 4 +is removed, finally forming H doped with metal ion M 0.39 V 2 O 5 or H composite with MVO in which M forms a phase 0.39 V 2 O 5 thin film.

[0049] In some embodiments, the concentration of VOSO 4 in the mixed solution is 0.04 mol / L, and the concentration of citric acid is 0.013 mol / L.

[0050] In some embodiments, the metal ion inorganic salt is an inorganic salt containing metal ion M, and metal ion M includes but is not limited to one of Co, Ni, Cu, Ce, and Ca. Its addition amount satisfies: molar amount of V:M = 4:1 - 8:1 (that is, the molar amount of VOSO 4 and the molar amount of metal ion M satisfy this condition). Specifically, when metal ion M is one of Co, Ni, and Cu, ion doping occurs, and the molar ratio of V:M = 4:1 - 8:1; when metal ion M is Ce or Ca, composite phase doping occurs, and the molar ratio of V:M = 4:1 - 6:1. The doping type of metal ions in vanadium oxide (H 0.39 V 2 O 5 ) is affected by the concentration and type of doping ions.

[0051] In the above technical solution, by controlling the molar amount of VOSO 4 and metal ion M within a specific range, overmodification of the crystal structure of H 0.39 V 2 O 5 can be avoided, which affects the stability of the crystal structure. If the addition amount of metal ion M is too much, due to the doping of metal ions between vanadium oxide layers, excessive doping may make the vanadium oxide layer spacing too small or too large, which is not conducive to ion insertion / extraction, and at the same time causes the reduction of the V 5+ proportion and reduces the theoretical capacity of the electrode; while when the metal ion doping is too little, the interlayer strut effect of doping ions is not strong enough, and the structure of the vanadium oxide layer is not stable enough.

[0052] In some embodiments, the substrate is ITO conductive glass. To ensure the smooth progress of the thin film growth process, the substrate needs to be pretreated before use. The pretreatment of ITO conductive glass is carried out as follows: The ITO conductive glass is ultrasonically washed 3 - 5 times with acetone, ethanol, and deionized water respectively to remove impurities on the surface of the ITO conductive glass. The washed ITO conductive glass is immersed in pure water, taken out when needed, and dried at room temperature for use.

[0053] Furthermore, the present invention also provides an aqueous secondary battery prepared by using the above vanadium-based thin film electrode, comprising:

[0054] A zinc counter electrode;

[0055] A working electrode, which is a vanadium-based thin film electrode;

[0056] A glass fiber membrane saturated with an adsorbed electrolyte, and the electrolyte is obtained by dispersing zinc trifluoromethanesulfonate and glycerol (C 3 H 8 O 3 , an antifreeze) in deionized water. The concentration of zinc trifluoromethanesulfonate in the electrolyte is 3 mol / L, the volume of deionized water is 10 mL, and the addition rule of glycerol is 3 g per 10 mL of deionized water.

[0057] Specifically, the above aqueous secondary battery is prepared as follows: Cut the zinc counter electrode, vanadium-based thin film electrode, water barrier layer, and glass fiber membrane into the required sizes, and use an insulating sealant to fix the water barrier layer on the surface of the vanadium-based thin film electrode; then, assemble the treated vanadium-based thin film electrode with the zinc counter electrode and the glass fiber membrane saturated with the adsorbed electrolyte (i.e., the glass fiber membrane is completely wetted by the solution), and seal and fix it with an insulating sealant, using deionized water as the electrolyte, thus obtaining the aqueous secondary battery.

[0058] In some embodiments, the main component of the water barrier layer is cellulose, specifically weighing paper, coated whiteboard paper, waxed paper, etc., which are water-proof papers. The surface of the weighing paper has a wax layer, and the surface of the coated whiteboard paper is coated with a waterproof pigment (such as kaolin) as a water-resistant layer. By fixing the water barrier layer composed of the above components on the surface of the vanadium-based thin film electrode, its waterproof property can be used to protect the vanadium-based thin film electrode, so as to inhibit the corrosion of the strong polar H 2 O molecules in the aqueous electrolyte to the vanadium-based material, and improve the cycle stability and cycle life of the battery.

[0059] The following further illustrates the preparation method of the vanadium-based thin film electrode, the vanadium-based thin film electrode, and the aqueous secondary battery provided by the present invention with specific embodiments. The weighing paper used in the embodiments is purchased from Biosharp, model BS-WP-100; the coated whiteboard paper is purchased from Beijing Lanjieke Technology Co., Ltd.; the model of the glass fiber membrane is Whatman GF / D, CATNO.1823:

[0060] Example 1

[0061] In this example, a vanadium-based thin film electrode was prepared, and its preparation method included the following steps:

[0062] Weigh analytical pure raw materials VOSO 4Mix with citric acid to form a mixed solution, stir well to make them complex; then, add cobalt sulfate heptahydrate to the above solution, mix evenly, and add ammonia water to adjust the pH of the solution to 4.12 to obtain a precursor solution; wherein, the concentration of VOSO 4 in the mixed solution is 0.04 mol / L, and the molar ratio of VOSO 4 to cobalt sulfate heptahydrate satisfies: molar ratio V:Co = 4:1;

[0063] Add the pretreated ITO conductive glass to the above precursor solution, completely immerse the ITO conductive glass in the solution, react at 70 °C for 36 h to form a deposition film on the ITO conductive glass; heat from 25 °C to 400 °C at a heating rate of 2 °C / min, then calcine for 2 h to anneal the deposition film, and naturally cool to room temperature after the calcination ends to obtain the N / Co-H 0.39 V 2 O 5 vanadium-based thin film electrode. The XRD pattern of the vanadium-based thin film electrode prepared in this example is as shown in Figure 1 the figure. The small figure on the right is the enlarged view of the characteristic peak. It can be seen that compared with N-400, the characteristic diffraction peak position of NC-400 shifts to the left after doping, indicating that the interplanar spacing of this crystal plane becomes larger after doping.

[0064] Among them, the pretreatment of the ITO conductive glass is carried out as follows: Ultrasonically wash the ITO conductive glass with a length × width of 2 cm × 2 cm with acetone, ethanol, and deionized water for 3 - 5 times, and dry the washed ITO conductive glass at room temperature for use. It should be noted that the reagents and raw materials used in the examples can be obtained by market purchase without special instructions, and will not be elaborated here.

[0065] Example 2

[0066] This example prepared a vanadium-based thin film electrode, and its preparation method includes the following steps:

[0067] Weigh analytical pure raw materials VOSO 4 and citric acid according to the molar ratio of 3:1 to form a mixed solution, stir well to make them complex; then, add cerium nitrate hexahydrate to the above solution, mix evenly, and add ammonia water to adjust the pH of the solution to 2.58 to obtain a precursor solution; wherein, the concentration of VOSO 4 in the mixed solution is 0.04 mol / L, and the molar ratio of VOSO 4 to cerium nitrate hexahydrate satisfies: molar ratio V:Ce = 6:1;

[0068] Add the pretreated ITO conductive glass to the above precursor solution, completely immerse the ITO conductive glass in the solution, and react at 70 °C for 36 h to form a 0.04 mol / L deposition film on the ITO conductive glass; heat from 25 °C to 500 °C at a heating rate of 2 °C / min, then calcine for 2 h to anneal the deposition film. After the calcination is completed, cool down to room temperature to obtain CeVO 4 Composite modified H 0.39 V 2 O 5 vanadium-based thin film electrode. Among them, the pretreatment of the ITO conductive glass is carried out as follows: ultrasonically wash the ITO conductive glass with length × width = 2 cm × 2 cm with acetone, ethanol, and deionized water for 3 - 5 times respectively. After washing, dry the ITO conductive glass at room temperature and it can be used.

[0069] Example 3

[0070] In this example, a vanadium-based thin film electrode was prepared, and its preparation method includes the following steps:

[0071] Weigh analytical pure raw materials VOSO 4 and citric acid according to a molar ratio of 3:1 to prepare a mixed solution, stir well to make them complex; then, add cerium nitrate hexahydrate to the above solution, mix evenly, and add ammonia water to adjust the pH of the solution to 2.58 to obtain a precursor solution; among them, the concentration of VOSO 4 in the mixed solution is 0.04 mol / L, and the molar ratio between VOSO 4 and cerium nitrate hexahydrate satisfies: molar ratio V:Ce = 6:1;

[0072] Add the pretreated ITO conductive glass to the above precursor solution, completely immerse the ITO conductive glass in the solution, and react at 70 °C for 36 h to form a deposition film on the ITO conductive glass; heat from 25 °C to 450 °C at a heating rate of 2 °C / min, then calcine for 2 h to anneal the deposition film. After the calcination is completed, cool down to room temperature to obtain CeVO 4 Composite modified H 0.39 V 2 O 5 vanadium-based thin film electrode. Among them, the pretreatment of the ITO conductive glass is carried out as follows: ultrasonically wash the ITO conductive glass with length × width = 2 cm × 2 cm with acetone, ethanol, and deionized water for 3 - 5 times respectively. After washing, dry the ITO conductive glass at room temperature and it can be used.

[0073] Example 4

[0074] In this example, a vanadium-based thin film electrode was prepared, and its preparation method includes the following steps:

[0075] Weigh analytically pure raw material VOSO according to the molar ratio of 3:1 4 and citric acid to prepare a mixed solution, and stir it thoroughly to make it complex; then, add calcium nitrate tetrahydrate to the above solution, mix it evenly, and then add ammonia water to adjust the solution pH to 4.0 to obtain a precursor solution; wherein, VOSO in the mixed solution 4 The concentration of VOSO is 0.04 mol / L. 4 The molar ratio between calcium nitrate tetrahydrate and V:Ca is 4:1;

[0076] The pretreated ITO conductive glass was added to the above-mentioned precursor solution, so that the ITO conductive glass was completely immersed in the solution, and reacted at 70°C for 36 hours to form a deposited film on the ITO conductive glass; the temperature was increased from 25°C to 400°C at a heating rate of 2°C / min, and then calcined for 2 hours to anneal the deposited film. After the calcination, the temperature was lowered to room temperature to obtain Ca 0.17 V 2 O 5 Composite modified H 0.39 V 2 O 5 Vanadium-based thin film electrode. The pretreatment of the ITO conductive glass is carried out as follows: the ITO conductive glass with a length × width = 2 cm × 2 cm is ultrasonically washed 3-5 times with acetone, ethanol, and deionized water respectively, and the washed ITO conductive glass is dried at room temperature and can be used.

[0077] Example 5

[0078] In this embodiment, the vanadium-based thin film electrode prepared in Example 1 is used to further prepare an aqueous secondary battery, and the preparation method is as follows:

[0079] The zinc counter electrode with a length × width = 2.3 cm × 2 cm was polished with sandpaper until the surface was smooth. After the vanadium-based thin film electrode was polished with sandpaper until the surface was smooth, a weighing paper with a length × width = 1.5 cm × 2 cm was fixed on the surface of the vanadium-based thin film electrode (the area of ​​the active material on the electrode surface is 1.5 cm × 2 cm) using insulating sealant. The optical photograph of the vanadium-based thin film electrode with the weighing paper fixed on the surface is shown in the figure. Figure 2 As shown;

[0080] The treated zinc counter electrode, vanadium-based thin film electrode and glass fiber membrane adsorbing a certain amount of electrolyte are sealed and fixed with insulating glue to obtain an aqueous secondary battery; wherein the electrolyte is zinc trifluoromethanesulfonate and glycerol dispersed in deionized water, the concentration of zinc trifluoromethanesulfonate in the electrolyte is 3 mol / L, the volume of deionized water is 10 mL, and the addition rule of glycerol is 3 g.

[0081] The above aqueous secondary battery was subjected to charge-discharge cycling on a Neware battery tester, stopped at the end of 200 charging cycles, and the battery was disassembled. The vanadium-based thin film and weighing paper were characterized for their structural morphology. The partial physical pictures of the battery after 200 cycles until the end of charging and disassembly are as follows Figure 3 shown, where Figure 3 a is provided with a water isolation layer (weighing paper), Figure 3 b is not provided with a water isolation layer. It can be seen from the figure that without the water isolation layer ( Figure 3 b), the vanadium-based thin film is severely dissolved, while Figure 3 after setting the water isolation layer in a, the vanadium-based thin film shows no obvious dissolution, indicating that the setting of the water isolation layer can effectively delay the dissolution on the electrode surface. The cyclic discharge specific capacities of the battery with and without the weighing paper are as follows Figure 4 shown. When there is a weighing paper ( Figure 4 a), at a current density of 117 mA / m 2 , the initial discharge specific capacity of the N / Co-H 0.39 V 2 O 5 vanadium-based thin film electrode is 72.4 mAh / m 2 , and reaches 145.8 mAh / m 2 after 200 cycles, with a capacity retention rate of 201.4%; while without the weighing paper ( Figure 4 b), the discharge specific capacity has declined to less than 50.0 mAh / m 2 after the first 25 cycles, and is only 13.8 mAh / m 2 after 100 cycles. The results show that during the cyclic charge-discharge process, the water isolation layer can inhibit the damage of water to the electrode structure and effectively extend the battery cycle life. After the cyclic charging ends, the SEM images of the vanadium-based thin film before and after cyclic charging are as follows Figure 5 shown, where Figure 5 a is the SEM of the vanadium-based thin film before cycling, Figure 5 b is the SEM of the vanadium-based thin film after setting the weighing paper and cycling, Figure 5 c is the SEM image of the vanadium-based thin film after cycling without setting the weighing paper. Comparing Figure 5 a with Figure 17 , it can be seen that after doping with ions, the morphology of the vanadium oxide particles transforms into flower-like nanosheets with uniform distribution, good dispersion, increased specific surface area and favorable for ion insertion / extraction; comparing Figure 5 b and Figure 5 c, it can be seen that in the case of setting the weighing paper, due to the protection of the weighing paper, the crystal structure of the vanadium-based thin film is well maintained, while without setting the weighing paper, during the cyclic charging process, the three-dimensional flower-like structure of the vanadium-based thin film shows obvious collapse. This result can further illustrate that the setting of the weighing paper can physically inhibit the strong polar H in the electrolyte 2O corrosion of the crystal structure of vanadium-based materials. SEM images of weighing paper before and after cyclic charging are shown in Figure 2. Figure 6 As shown, compared with the pre-cycle ( Figure 6 a), discharge end ( Figure 6 b) When the 250 cycles are not fully charged ( Figure 6 c), when charging is finished ( Figure 6 d) shows that at the end of full discharge, the fiber is attached with nanosheets, and at the end of full charge, the nanosheets disappear and the fiber surface is smooth. This shows that in the initial cycle, the discharge process of Zn 2+ The new phase was generated by embedding, and reversible transformation occurred during charging, which may be due to the three-dimensional network structure of cellulose and the zinc-philic oxygen-containing groups in its structure that can adsorb Zn 2+ This result also more intuitively confirms that the vanadium oxide interlayer structure of the electrode is more stable and has better waterproof performance after the water-proof layer is set; secondly, Figure 6 a and Figure 6 c, we can see that Figure 6 There are some agglomerated nanosheets attached to the fibers in c, which are incompletely converted ZnVO.

[0082] Example 6

[0083] In this embodiment, the vanadium-based thin film electrode prepared in Example 2 is used to further prepare an aqueous secondary battery. The preparation method is the same as that in Example 5, except that the thin film electrode in Example 5 is replaced by the vanadium-based thin film electrode prepared in Example 2.

[0084] The above aqueous secondary battery was charged and discharged on a Xinwei battery tester. The battery was stopped when the charge was not fully charged to 1.45V after 250 cycles. The battery was disassembled and the structure and morphology of the vanadium-based film and weighing paper were characterized. The battery's cyclic discharge specific capacity is shown in Figure 2. Figure 7 As shown, when weighing paper is provided ( Figure 7 a) At 100mA / m 2 At a current density of 4 Composite modified H 0.39 V 2 O 5 The initial discharge capacity is 153.5 mAh / m 2 , after 250 cycles, it reaches 108.5mAh / m 2 , with a capacity retention rate of 70.7%; while without weighing paper ( Figure 7 b) After 50 cycles, the discharge capacity has declined to 24.0 mAh / m 2 The capacity retention rate is only 13.7%. The results show that the water barrier can effectively prolong the battery cycle life. The discharge capacity is compared with the pure H 0.39V 2 O 5 The battery prepared from the vanadium-based thin film electrode is compared with ( Figure 16 ), and this example is significantly better than Comparative Example 1, which may be because: CeVO 4 and H 0.39 V 2 O 5 have a synergistic effect, and the combination of the two can play the function of structural support or capacity contribution. The SEM images of the vanadium-based thin film before and after cycling are as shown in Figure 8 . Figure 8 a is before cycling, Figure 8 b is the SEM image of the vanadium-based thin film when charging is incomplete to 1.45 V after 250 cycles. Before cycling ( Figure 8 a), the thin film is a nanostructure formed by the aggregation of several regularly shaped block structures. After cycling ( Figure 8 b), the nanostructure is not significantly dissolved.

[0085] Example 7

[0086] In this example, the aqueous secondary battery is further prepared by using the vanadium-based thin film electrode prepared in Example 3. The preparation method is the same as that in Example 5, except that the weighing paper in Example 5 is replaced with a coated whiteboard paper, and the thin film electrode in Example 5 is replaced with the vanadium-based thin film electrode prepared in Example 3.

[0087] The above-mentioned aqueous secondary battery is subjected to charge-discharge cycling on a Neware battery tester, stopped at the end of 100 cycles of charging, and the battery is disassembled to characterize the structural morphology of the vanadium-based thin film and the coated whiteboard paper. The cyclic discharge specific capacity of the battery is as shown in Figure 9 . At a current density of 100 mA / m 2 , the initial discharge specific capacity of CeVO 4 -composite modified H 0.39 V 2 O 5 is 36.7 mAh / m 2 . In the first about 30 cycles, it is the process of the electrolyte gradually penetrating the coated whiteboard paper. After 35 cycles, the discharge specific capacity stabilizes to 244.0 mAh / m 2 , and remains at 221.4 mAh / m 2 at 100 cycles. The SEM images of the vanadium-based thin film before and after cycling are as shown in Figure 10 . Figure 10 a is the morphology of the vanadium-based film before cycling. The branched part in the figure is the H 0.39 V 2 O 5 phase, and the irregularly dispersed hazelnut-shaped part at the upper end of the branched nanosheets is the composite phase CeVO 4 . After cycling with the coated whiteboard paper,Figure 10 At the end of charging, it can be seen that the dendritic nanosheet morphology still exists, while the paste-like part on the surface may be the newly formed phase. The SEM images of the coated whiteboard paper before and after cycling are as Figure 11 shown, Figure 11 a is the surface morphology of the coated whiteboard paper. After cycling, the morphology is as Figure 11 shown in b. It can be seen that the surface waterproof layer has peeled off.

[0088] Example 8

[0089] In this example, the vanadium-based thin film electrode prepared in Example 4 was further used to prepare an aqueous secondary battery. The preparation method was the same as that in Example 5, except that the thin film electrode in Example 5 was replaced with the vanadium-based thin film electrode prepared in Example 4.

[0090] The above-mentioned aqueous secondary battery was subjected to charge-discharge cycling on a Neware battery tester. The cycling was stopped at the end of 100 cycles of charging, and the battery was disassembled. The structural morphology of the vanadium-based thin film and the weighing paper was characterized. The XRD patterns of the vanadium-based thin films of the vanadium-based thin film electrodes in Examples 5 to 8 before and after 100 cycles are respectively as Figure 12 shown in a-d, Figure 12 a is the XRD results of Co ion-doped modified H 0.39 V 2 O 5 before cycling and at the end of 200 cycles of discharging and charging, Figure 12 b is the XRD results of CeVO 4 composite modified H 0.39 V 2 O 5 before cycling and at the end of 250 cycles of incomplete charging, Figure 12 c-d are respectively the XRD results of CeVO 4 composite modified H 0.39 V 2 O 5 and Ca 0.17 V 2 O 5 composite modified H 0.39 V 2 O 5 before cycling and at the end of 100 cycles of charging. It can be seen from the figure that some diffraction peaks at the end of cycling charging correspond to the new phase Zn 3 (OH) 2 V 2 O 7 ·2H 2 O, while Figure 12The remaining diffraction peaks in c-d are attributed to glycerol in the electrolyte because when the battery is disassembled after cycling, some electrolyte remains on the surface of the membrane electrode. The cyclic discharge specific capacities of the battery with and without the water isolation layer are as Figure 13 shown. When there is weighing paper ([[]] Figure 13 a), at a current density of 100 mA / m 2 2 0.17 V 2 O 5 -composite modified H 0.39 V 2 O 5 has a discharge specific capacity of 87.5 mAh / m 2 after 100 cycles. Without weighing paper ([[]] Figure 13 b), the discharge specific capacity has declined to less than 10.0 mAh / m 2 after only 25 cycles; the SEM images of the vanadium-based thin film before and after cycling are as Figure 14 shown. Figure 14 In Figure 14 a, the original morphology of the vanadium-based film is flower-like nanosheets, while in

[0091] Comparative Example 1

[0092] The difference between Comparative Example 1 and Example 5 is only that: in the process of preparing the vanadium-based thin film electrode, metal ion inorganic salts are not added. The specific preparation steps are as follows:

[0093] Weigh analytical pure raw materials VOSO 4 and citric acid according to a molar ratio of 3:1 to prepare a mixed solution, stir well to make them complex; then, add ammonia water to adjust the pH of the solution to 4.12 to obtain a precursor solution; among them, the concentration of VOSO 4 in the mixed solution is 0.04 mol / L;

[0094] Add the pretreated ITO conductive glass to the above precursor solution, immerse the ITO conductive glass completely in the solution, react at 70 °C for 30 h to form a deposition film on the ITO conductive glass; heat from 25 °C to 400 °C at a heating rate of 2 °C / min, then calcine for 2 h to anneal the deposition film, and cool to room temperature after calcination to obtain the H 0.39 V 2 O 5 vanadium-based thin film electrode. Among them, the pretreatment of the ITO conductive glass is carried out as follows: Ultrasonically wash the ITO conductive glass with a length × width of 2 cm × 2 cm with acetone, ethanol, and deionized water for 3-5 times, and dry the washed ITO conductive glass at room temperature for use. H 0.39 V2 O 5 The XRD pattern of the vanadium-based thin film electrode is as Figure 15 shown, and the results show that the H 0.39 V 2 O 5 vanadium-based thin film electrode was successfully prepared.

[0095] An aqueous secondary battery was prepared according to the method of Example 5. The above aqueous secondary battery was subjected to charge and discharge cycling on a Neware battery tester, stopped at the end of 60 charge cycles, and the battery was disassembled. The structural morphology of the vanadium-based thin film and weighing paper was characterized. The cyclic discharge specific capacity of the battery is as Figure 16 shown. It can be seen from the figure that after the first cycle activation at a small current density of 33 mA / m 2 , the initial discharge specific capacity of H 0.39 V 2 O 5 is 150.7 mAh / m 2 . After 20 cycles, the discharge specific capacity remains at 105.9 mAh / m 2 , while after 60 cycles, it decays to less than 50.0 mAh / m 2 , indicating that the thin film electrode must be activated at a very small current before allowing ion insertion / extraction. The SEM images of the vanadium-based thin film before and after cycling are as Figure 17 shown. Before cycling ( Figure 17 a), the vanadium-based thin film consists of many nanoscale structures in the form of irregularly shaped blocks aggregated together. After cycling ( Figure 17 b), the nanoscale structures are not significantly dissolved. The SEM images of the glass fiber membrane before cycling and the weighing paper after cycling are as Figure 18 shown. Figure 18 b is the SEM image of the glass fiber membrane before cycling. It can be seen from the figure that the glass fiber membrane has a porous morphology. Figure 18 a is the SEM image of the weighing paper after 60 cycles. It can be seen from the figure that the fibers inside the weighing paper are connected together. This may be because the current is too small, and the fibers of the glass fiber membrane used to store the electrolyte have pierced into the weighing paper acting as a water barrier, resulting in overly sufficient ion insertion / extraction and causing the water barrier to fail. Thus, although the setting of the water barrier can effectively prevent water from corroding the crystal structure of the vanadium-based thin film, the electrochemical cycling performance of the pure H 0.39 V 2 O 5 vanadium-based thin film electrode itself is poor.

[0096] Comparing the electrochemical cycling performance, electrode structure stability, and waterproof corrosion performance of the vanadium-based electrodes in Examples 5 to 8 and Comparative Example 1, it can be seen that the performance of the vanadium-based electrodes in Examples 5 to 8 is significantly better than that of Comparative Example 1. This is because the vanadium-based thin film electrode obtained by element doping / composite phase modification can change the pure H0.39 V 2 O 5 The crystal structure of the vanadium-based thin film is improved, thereby enhancing its stability as an electrode material and endowing the electrode material with stronger corrosion resistance in water.

[0097] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a vanadium-based thin film electrode, characterized in that: The steps include: Adding metal ion inorganic salt to the mixed solution of VOSO4 and citric acid, and adjusting the pH of the solution to 2.5-4.2 to obtain a precursor solution; Immersing the substrate in the precursor solution and reacting for 30-60 hours to form a deposited film on the substrate; The deposited film is annealed to obtain a vanadium-based thin film electrode.

2. The preparation method according to claim 1, characterized in that: The metal ion inorganic salt is an inorganic salt containing a metal ion M, and the metal ion M is one of Co, Ni, Cu, Ce, and Ca; the molar ratio of the VOSO4 to the metal ion M satisfies V:M=4:1-8:

1.

3. The preparation method according to claim 2, characterized in that: When the metal ion M is Ce or Ca, the molar ratio of the VOSO4 to the metal ion M is V:M=4:1-6:

1.

4. The preparation method according to claim 2, characterized in that: When the metal ion M is one of Co, Ni, and Cu, the molar ratio of the VOSO4 to the metal ion M is V:M=4:1-8:

1.

5. The preparation method according to claim 1, characterized in that: The concentration of VOSO4 in the mixed solution is 0.04 mol / L, and the concentration of citric acid is 0.013 mol / L.

6. The preparation method according to claim 1, characterized in that: The annealing treatment conditions are: temperature 400-500° C., time 2 h.

7. The preparation method according to claim 1, characterized in that: The pH value of the solution is adjusted by ammonia water; the substrate is ITO conductive glass.

8. A vanadium-based thin film electrode, characterized in that: The vanadium-based thin film electrode is prepared by the preparation method described in any one of claims 1 to 7, and comprises ITO conductive glass and a vanadium-based thin film grown on the surface of the ITO conductive glass.

9. An aqueous secondary battery, characterized in that: include: Zinc counter electrode; A working electrode, which is the vanadium-based thin film electrode according to claim 8; A glass fiber membrane for adsorbing electrolyte, wherein the electrolyte is obtained by dispersing zinc trifluoromethanesulfonate and glycerol in deionized water.

10. The aqueous secondary battery according to claim 9, characterized in that: A water-proof layer is fixed on the surface of the working electrode, and the water-proof layer is one of weighing paper, coated white paper, and wax paper.

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