Open type rechargeable all-seawater battery and preparation method thereof

Abstract

The application discloses an open rechargeable full-seawater battery and a preparation method thereof, and belongs to the field of electrochemistry and energy storage. The battery comprises a catalyst cathode, an electrolyte and a sodium storage anode. The catalyst cathode is a nitrogen-doped carbon nanotube array with embedded metal deposited on a flexible carbon fiber cloth. The sodium storage anode is a sodium titanium phosphate / carbon composite material coated on a flexible carbon fiber cloth. The electrolyte is natural seawater. The open rechargeable full-seawater battery is immersed in the natural seawater electrolyte in a container or directly immersed in an open ocean environment without a diaphragm. The battery is used for realizing charge storage in seawater. Through the design of double flexible positive and negative electrodes, the problems of long cycle voltage instability, sodium negative electrode leakage, inactivation or damage of traditional seawater battery systems can be solved, and the originally complex negative electrode structure is optimized, so that the whole battery is in a completely open system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrochemistry and energy storage, and relates to a full-seawater battery using natural seawater as an electrolyte and a preparation method thereof. BACKGROUND

[0002] Clean energy, such as solar energy, wind energy and water energy, has the advantages of no pollution, no emission and renewable, and is the main direction of future energy development. However, these energies also have the disadvantages of instability, discontinuity and uncontrollability, which makes it difficult to meet the actual energy demand. Therefore, how to effectively store and convert clean energy is one of the key technologies for realizing the utilization of clean energy. Seawater battery is an electrochemical device that uses seawater as an electrolyte, which can realize the storage and conversion of clean energy. Seawater battery has the advantages of abundant seawater resources, easy access, low cost and high safety, and is an energy technology with broad prospects. The biggest advantage of this battery technology is that it uses seawater, the most abundant resource on earth, as an electrolyte, which is both environmentally friendly and economical.

[0003] However, there are many challenges in directly using seawater battery for energy storage. The current seawater battery industry is just developing, and the research on each component structure is also not perfect. The traditional seawater battery is composed of a catalyst cathode, seawater, a sodium anode, a water circulation device and the like, and the sodium anode and the water circulation device also have a large volume. Among the factors affecting the performance of seawater battery, the cathode catalyst is the key. These catalysts can improve the efficiency of seawater redox reaction, but at the same time, they are also susceptible to corrosion by chloride ions in seawater, because most of the catalysts used at present are from the catalysts used in zinc-air batteries without anti-chlorine design. In addition, the bulky and complex structure of the sodium anode also restricts the further development of seawater battery. The complex sodium anode makes the corresponding conductive structure extremely cumbersome. Based on this, an open rechargeable full-seawater battery is designed. SUMMARY

[0004] The purpose of the present application is to solve the problems existing in the prior art and provide an open full-seawater rechargeable battery.

[0005] The purpose of the present application is achieved by providing an open rechargeable full-seawater battery with a simple structure, which comprises a catalyst cathode, an electrolyte and a sodium storage anode. The catalyst cathode is an array of metal-embedded nitrogen-doped carbon nanotubes deposited on a flexible carbon fiber cloth. The sodium storage anode is a sodium titanium phosphate / carbon composite material coated on a flexible carbon fiber cloth. The electrolyte is natural seawater. The open rechargeable full-seawater battery is immersed in the natural seawater electrolyte in the container without a separator between the catalyst cathode and the sodium storage anode, or directly immersed in the open ocean environment.

[0006] The application provides an open rechargeable full-seawater battery, which comprises a catalyst cathode, an electrolyte and a sodium storage anode; the catalyst cathode is an embedded metal nitrogen-doped carbon nanotube array deposited on a flexible carbon fiber cloth; the sodium storage anode is a sodium titanium phosphate / carbon composite material coated on the flexible carbon fiber cloth; and the open rechargeable full-seawater battery is obtained by immersing the catalyst cathode and the sodium storage anode in seawater electrolyte.

[0007] Further, the embedded metal nitrogen-doped carbon nanotube has a hollow structure, the length of the embedded metal nitrogen-doped carbon nanotube is 40-150 nm, and the diameter of the embedded metal nitrogen-doped carbon nanotube is 20-50 nm; the embedded metal nitrogen-doped carbon nanotube array is in high-density distribution; the embedded metal material is one or more of iron, cobalt and nickel; the loading amount of the embedded metal nitrogen-doped carbon nanotube array on the flexible carbon fiber cloth is 1-2 mg·cm -2 ; and the loading amount of the sodium titanium phosphate / carbon composite material on the flexible carbon fiber cloth is 1-2 mg·cm -2 .

[0008] The application further provides a preparation method of the open rechargeable full-seawater battery, which comprises the following steps:

[0009] Step 1: acid treatment is performed on the pretreated carbon fiber cloth; a mixed solution of nitrate and zinc nitrate is quickly poured into a 2-methylimidazole solution and continuously stirred, and the acid-treated carbon fiber cloth is immersed and vertically erected in the mixed aqueous solution, and is left to stand at room temperature, so as to synthesize a metal organic framework array precursor on the carbon cloth, and then the precursor is washed and dried;

[0010] Step 2: the catalyst cathode material obtained in step 1 is placed in a tube furnace under an argon atmosphere and is annealed under sublimation coating of dicyandiamide, and then is further annealed in an air atmosphere, so as to obtain an embedded metal nitrogen-doped carbon nanotube array catalyst cathode material deposited on a flexible carbon fiber cloth;

[0011] Step 3: tetrabutyl titanate is dissolved in a solvent and stirred to obtain a uniform transparent solution; sodium dihydrogen phosphate, phosphoric acid and glucose are dissolved in deionized water and stirred to obtain a uniform transparent solution; the two kinds of mixed solutions are mixed and further stirred uniformly, and then are transferred into an autoclave for hydrothermal reaction, centrifugation, washing and drying, so as to obtain a brown powder precursor; finally, the brown powder precursor is placed in a tube furnace under an argon atmosphere for annealing, so as to obtain a solid powder of sodium titanium phosphate / carbon composite material;

[0012] Step 4: the solid powder of sodium titanium phosphate / carbon composite material obtained in step 3, conductive carbon black and a binder are mixed to prepare a slurry, which is coated on a cleaned carbon fiber cloth to prepare a sodium titanium phosphate anode material;

[0013] Step 5: Assembling the catalyst cathode obtained in step 2 and step 4, the sodium titanate phosphate anode, and the seawater electrolyte into an open open rechargeable seawater battery.

[0014] Further, in step 1, the pretreatment of the carbon fiber cloth is ultrasonic cleaning in acetone, deionized water, and ethanol in sequence, and drying; the acid treatment adopts hydrothermal treatment of concentrated nitric acid solution in an oven.

[0015] Further, in step 1, the nitrate is cobalt nitrate, iron nitrate, or nickel nitrate; the molar ratio of the nitrate, zinc nitrate, and dimethyl imidazole is (0.5-2):1:(10-20).

[0016] Further, in step 1, the room temperature standing time is 2-4h; the drying is vacuum drying, the temperature is 40-80℃, and the time is 6-12h.

[0017] Further, in step 2, the two-step annealing is carried out in an argon atmosphere, the first step annealing temperature is 300-400℃, the time is 2-4h, the second annealing temperature is 700-800℃, the time is 2-4h, and the heating rate is 1-5℃ / min -1 ; the one-step annealing is carried out in an air atmosphere, the annealing temperature is 100-200℃, the time is 2-4h, and the heating rate is 1-5℃ / min -1 .

[0018] Further, in step 3, the molar ratio of tetrabutyl titanate, sodium dihydrogen phosphate, phosphoric acid, and glucose is (20-40):(10-20):(20-40):(10-20); the stirring time of the tetrabutyl titanate solution is 30-60min; the stirring time of the mixed solution of sodium dihydrogen phosphate, phosphoric acid, and glucose is 30-60min; the stirring time of the mixed solution of tetrabutyl titanate, sodium dihydrogen phosphate, phosphoric acid, and glucose is 60-120min.

[0019] Further, in step 3, the hydrothermal reaction temperature is 100-200℃, and the time is 10-20h; the two-step annealing is carried out in an argon atmosphere, the first step annealing temperature is 300-400℃, the time is 2-4h, the second step annealing temperature is 700-800℃, the time is 2-4h, and the heating rate is 1-5℃ / min -1 .

[0020] Further, in step 4, the mass ratio of the sodium titanate phosphate anode material, conductive carbon black, and binder is (60-80):(10-20):(10-20).

[0021] Further, in step 4, the sodium titanate phosphate anode is a corresponding flexible carbon cloth loaded material, and the loading amount is 3-5 mg cm when used in a three-electrode test -2 .

[0022] Further, in step 5, the catalyst cathode and the sodium titanate phosphate anode used in the battery test are rectangular carbon cloth loaded materials with a length of 10-20 mm and a width of 10-20 mm.

[0023] The beneficial effects are:

[0024] The application provides a novel rechargeable seawater battery. The battery functions to realize charge storage in seawater. Through the design of double flexible positive and negative electrodes, the problems of long cycle voltage instability and sodium negative electrode leakage, deactivation or damage faced by traditional seawater battery systems can be solved; through the method of secondary annealing in air, the proportion of nitrogen element types in the positive electrode catalyst is adjusted, so that the stability of the catalyst in seawater is improved; and the originally complex negative electrode structure is optimized, so that the entire battery is in a completely open system, and only two pieces of flexible carbon fiber cloth loaded material are needed to assemble the simplest seawater battery, thereby reducing the cost and being very beneficial to large-scale energy storage.

[0025] The open rechargeable seawater battery prepared in the application provides a cycle life of more than 250 cycles at a large current of 5 mA cm -2 , and the capacity almost does not decay; the cycle life is more than 100 cycles at a large current of 1 mA cm -2 ; in addition, the rate performance of the battery is good, and the capacity remains almost unchanged in a large current span of 1 mA cm -2 to 10 mA cm -2 to 1 mA cm -2 . In addition, the open rechargeable seawater battery has the advantages of simple structure, environmental friendliness, low cost, high safety, simple process and easy production. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a structural, mechanism and material synthesis schematic diagram of the open rechargeable seawater battery of the application;

[0027] Figure 2 a is a scanning electron microscope picture of the metal-embedded nitrogen-doped carbon nanotube array catalyst cathode material of the comparative example 2, Figure 2 b is a transmission electron microscope picture thereof; Figure 2 c is a scanning electron microscope picture of the metal-embedded nitrogen-doped carbon nanotube array catalyst cathode material of the example 1 after air annealing, Figure 2 d is a transmission electron microscope picture thereof;

[0028] Figure 3 Image a is a scanning electron microscope (SEM) image of sodium titanium phosphate anode material. Figure 3 b is a transmission electron microscope image of sodium titanium phosphate anode material;

[0029] Figure 4 This refers to a conventional seawater battery assembled with the two catalysts mentioned above and a sodium metal anode, operating at a current density of 0.05 mA / cm². -2 Comparison chart of cycle performance;

[0030] Figure 5 The images show the flexible catalyst used as an electrode, the flexible sodium titanium phosphate anode, and the assembled open-type rechargeable seawater battery. The flexible catalyst used is a nitrogen-doped carbon nanotube array catalyst with embedded metal after air annealing, which has better stability.

[0031] Figure 6 The open-type rechargeable all-seawater battery provided in this embodiment has a scan rate of 1 mV / s in natural seawater. -1 Cyclic voltammetry curves;

[0032] Figure 7 The open-type rechargeable all-seawater battery provided in this embodiment operates at a current density of 1 mA cm⁻¹. -2 The first three charge-discharge cycles are shown below;

[0033] Figure 8 The open-type rechargeable all-seawater battery provided in this embodiment operates at a current density of 5 mA cm⁻¹. -2 The following is a graph showing the cyclic performance.

[0034] Figure 9 This is a rate performance diagram of the open-type rechargeable seawater battery provided in the embodiment. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] This invention provides an open-type rechargeable seawater battery. The overall concept of this embodiment is to optimize traditional seawater batteries and achieve charge storage in seawater through a dual flexible positive and negative electrode design. (See attached diagram) Figure 1 As shown, an open-type rechargeable seawater battery has a simple structure, consisting only of a catalyst cathode, seawater, sodium titanium phosphate anode, and a water container.

[0037] The mechanism of an open-source rechargeable all-seawater battery is as follows: Figure 1As shown, during the charging process, the hydroxyl ion ionized from water loses electrons on the surface of the catalyst to generate oxygen and water through the oxygen evolution reaction, and the sodium ion in seawater is embedded into the sodium titanophosphate anode to complete the storage of sodium, i.e. charging; during the discharging process, the dissolved oxygen in seawater gains electrons and water molecules to generate hydroxyl through the oxygen reduction reaction, and the sodium titanophosphate at the anode loses electrons to release sodium ions, i.e. discharging. The cathode catalyst plays a role in reducing the potential barrier and improving the reaction kinetics of water oxidation and reduction, so that the electrochemical performance of the open rechargeable full-seawater battery in the application is greatly improved.

[0038] The technical solutions claimed in the application will be further described below by means of some embodiments and drawings. However, the embodiments are used to explain the embodiments of the application and do not exceed the scope of the subject matter of the application, and the protection scope of the application is not limited by the described embodiments. Unless otherwise specified, the materials and reagents used in the application can be obtained from commercial products in the art.

[0039] The application discloses an open rechargeable full-seawater battery, which comprises a catalyst cathode, an electrolyte and a sodium storage anode. The catalyst cathode is an embedded metal nitrogen-doped carbon nanotube array deposited on a flexible carbon fiber cloth. The sodium storage anode is a sodium titanophosphate / carbon composite material coated on a flexible carbon fiber cloth. The electrolyte is natural seawater. The open rechargeable full-seawater battery is immersed in the natural seawater electrolyte in a container without a separator between the catalyst cathode and the sodium storage anode, or directly immersed in an open ocean environment.

[0040] The application further discloses a preparation method of the open rechargeable full-seawater battery, which comprises the following steps.

[0041] Step one: The carbon fiber cloth is sequentially ultrasonically cleaned in acetone, deionized water and ethanol, and then dried in an oven. Subsequently, the cleaned carbon fiber cloth is hydrothermally treated with a concentrated nitric acid solution in an oven. Then, the nitrate and zinc nitrate are dissolved in deionized water, and dimethyl imidazole is dissolved in another portion of deionized water and continuously stirred. After stirring at room temperature to form a uniform solution, the mixed solution of nitrate and zinc nitrate is quickly poured into the 2-methyl imidazole solution and continuously stirred. Then, the above-mentioned acid-treated carbon cloth is immersed and vertically erected in the mixed aqueous solution, and is left to stand at room temperature, so that a metal organic framework array precursor is synthesized on the carbon cloth. Subsequently, the carbon fiber cloth with the deposited metal organic framework is taken out and sequentially washed with water and ethanol, and vacuum dried overnight.

[0042] Step two: The catalyst cathode material obtained in step one is transferred to a tube furnace under an argon environment and annealed under the sublimation coating of dicyandiamide, and then further annealed in air to obtain a nitrogen-doped carbon nanotube array catalyst cathode material with embedded metal deposited on a flexible carbon fiber cloth.

[0043] Step three: Dissolve tetrabutyl titanate in ethylene glycol and stir to obtain a uniform transparent solution; dissolve sodium dihydrogen phosphate, phosphoric acid, and glucose in deionized water and stir to obtain a uniform transparent solution. Mix the above two mixed solutions and further stir uniformly, then transfer to an autoclave for hydrothermal reaction. When the reaction is completed, centrifuge, wash and dry with deionized water and ethanol, and collect the brown powder precursor. Finally, transfer the brown powder precursor to a tube furnace under argon environment for annealing to obtain a solid powder of sodium titanium phosphate / carbon composite material.

[0044] Step four: Mix the solid powder of sodium titanium phosphate / carbon composite material obtained in step three, conductive carbon black and binder to make a slurry, and coat it on a cleaned carbon fiber cloth to obtain a sodium titanium phosphate anode material.

[0045] Step five: Assemble the catalyst cathode, sodium titanium phosphate anode, seawater electrolyte and water container obtained in steps two and four into an open open rechargeable seawater battery.

[0046] Example 1

[0047] Preparation of nitrogen-doped carbon nanotube array cathode material with embedded metal deposited on carbon cloth:

[0048] (1) Ultrasonically clean the carbon fiber cloth (CC) in acetone, deionized water (DI), and ethanol, respectively, and then dry in an oven. Subsequently, the cleaned CC is hydrothermally treated with concentrated nitric acid (HNO3) solution in an oven at 80°C for 1 h. Then, 2 mmol of cobalt nitrate (Co(NO3)2) and 1 mmol of zinc nitrate (Zn(NO3)2) are dissolved in 50 mL of deionized water to obtain a solution, which is referred to as solution A. 20 mmol of 2-methylimidazole (2-mim) is dissolved in another 50 mL of deionized water with continuous stirring to obtain a solution, which is referred to as solution B. After stirring to obtain a uniform solution at room temperature, solution A is quickly poured into solution B and continuously stirred. Then, the above acid-treated CC (3×4 cm 2 ) is immersed and vertically erected in the mixed aqueous solution, and left to stand at room temperature for 3 h to synthesize a cobalt-zinc zeolitic imidazolate framework (CoZn-ZIF) array on the CC. Finally, the CoZn-ZIF / CC is taken out and washed with water and ethanol, respectively, and dried in a vacuum oven at 40°C overnight.

[0049] (2) A piece of prepared CoZn-ZIF / CC (1×4 cm 2 ) and 0.6 g of dicyandiamide (DCDA) are placed in two separate ceramic boat furnaces, respectively, with DCDA located upstream of the argon atmosphere. First, the sample and DCDA are heated at 400°C under argon at a rate of 5°C min -1at a rate of 2°C / min, and then annealed at 700°C for 2h. Then the temperature was further increased to 700°C at a rate of 2°C / min, and then annealed at 700°C for 2h. Then it was further annealed at 700°C for 2h in the exposed 200°C air environment at a rate of 5°C / min -1 at a rate of 2°C / min, and then annealed at 700°C for 2h. The obtained air-annealed embedded metal nitrogen-doped carbon nanotube array catalyst cathode material of this step is denoted as H-Co catalyst; the scanning electron microscope image and the transmission electron microscope image of the H-Co catalyst are shown in FIGS. 6A and 6B, respectively. Figure 2 a-b.

[0050] Preparation of sodium titanium phosphate / carbon composite material:

[0051] (1) 2 mmol of tetrabutyl titanate was dissolved in 20 mL of ethylene glycol and stirred to obtain a uniform transparent solution A; 1 mmol of sodium dihydrogen phosphate (NaH2PO4), 2 mmol of phosphoric acid (H3PO4), and 1 mmol of glucose were dissolved in 20 mL of water and stirred to obtain a uniform transparent solution B.

[0052] (2) After the above solution B was added to solution A and further stirred uniformly, it was transferred to an autoclave for hydrothermal reaction at 180°C for 12 hours. When the reaction was completed, the system was naturally cooled to room temperature, and the mixed solution was washed and dried by centrifugation with ethanol to obtain a brown powder precursor.

[0053] (3) Finally, the above precursor powder was annealed at 350°C for 2h and then at 700°C for 4h under an argon atmosphere at a rate of 2°C / min -1 , to obtain a sodium titanium phosphate / carbon composite material (NTP / C).

[0054] Preparation of sodium titanium phosphate / carbon composite material anode:

[0055] The sodium titanium phosphate / carbon composite material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 70:20:10 in a manual stirring manner in an agate mortar to obtain a mixed slurry; then the obtained mixed slurry was coated on a cleaned carbon fiber cloth, and then the carbon fiber cloth coated with the mixed slurry was dried in a vacuum oven for 12h to obtain a sodium titanium phosphate / carbon composite material anode.

[0056] Example 2

[0057] An open rechargeable full-seawater battery was assembled, as shown in FIG. 2. Figure 5

[0058] (1) The carbon cloth used for the sodium titanium phosphate / carbon composite material anode and the H-Co catalyst cathode material was cut into square pieces with a side length of 1 cm 2 .

[0059] (2) Two platinum electrodes were used to clamp the two carbon cloth poles, respectively. ​

[0060] (3) Add an appropriate amount of seawater into a water container such as a beaker;

[0061] (4) Submerge both electrodes into seawater and fix the electrode holder, and then an open type rechargeable seawater battery is obtained.

[0062] Comparative Example 1

[0063] Assemble a traditional seawater battery:

[0064] (1) Cut the carbon cloth used for the cathode of the H-Co catalyst prepared in Example 1 into a square piece with a side length of 2 cm 2 ;

[0065] (2) Hold the cathode carbon cloth with a platinum electrode holder;

[0066] (3) Assemble and press the battery bottom shell, spring, gasket, metal sodium sheet, electrolyte, and battery top cover containing a solid electrolyte in the order from bottom to top to form the anode of a traditional seawater battery;

[0067] (4) Add an appropriate amount of seawater into a water container such as a beaker;

[0068] (5) Submerge both electrodes into seawater and fix the electrode holder, and then a traditional seawater battery is obtained.

[0069] Comparative Example 2

[0070] Prepare a cathode material of nitrogen-doped carbon nanotube array with embedded metal deposited on carbon cloth:

[0071] (1) Ultrasonically clean carbon fiber cloth (CC) in acetone, deionized water (DI), and ethanol in sequence, and then dry it in an oven. Subsequently, hydrothermally treat the cleaned CC with concentrated nitric acid (HNO3) solution in an oven at 80°C for 1 h. Then, dissolve 2 mmol of cobalt nitrate (Co(NO3)2) and 1 mmol of zinc nitrate (Zn(NO3)2) in 50 mL of deionized water to obtain a solution A. Dissolve 20 mmol of 2-methylimidazole (2-mim) in another 50 mL of deionized water and continuously stir to obtain a solution B. After stirring to form a uniform solution at room temperature, quickly pour solution A into solution B and continuously stir. Then immerse and vertically stand the above acid-treated CC (3×4 cm 2 ) in the mixed aqueous solution, and let it stand at room temperature for 3 h to synthesize a cobalt-zinc zeolitic imidazolate framework (CoZn-ZIF) array on the CC. Finally, take out the CoZn-ZIF / CC, wash it with water and ethanol in sequence, and dry it in a vacuum oven at 40°C overnight.

[0072] (2) Hold a piece of prepared CoZn-ZIF / CC (1×4 cm 2) and 0.6 g of dicyandiamide (DCDA) were placed in two separate ceramic boat furnaces, with the DCDA upstream of the argon atmosphere. The sample and DCDA were first heat annealed at 400 °C under argon at a ramping rate of 5 °C min -1 for 2 h. The temperature was then further increased to 700 °C and held for 2 h. After carbonization, the CoZn-ZIF array was converted into a metal-embedded nitrogen-doped carbon nanotube array. The metal-embedded nitrogen-doped carbon nanotube array obtained in this step is denoted as Co catalyst; scanning electron microscope images and transmission electron microscope images of the Co catalyst are shown in Figures 1c-d, and the structure of the Co catalyst is more compact than that of the H-Co catalyst structure, which is caused by the oxidation of the Co catalyst in air at 200 °C to obtain the H-Co catalyst. Figure 2

[0073] Comparative Example 3

[0074] Assembling a conventional seawater battery:

[0075] (1) The Co catalyst cathode carbon cloth prepared in Comparative Example 2 above was cut into small square pieces with a side length of 2 cm 2 ;

[0076] (2) The cathode carbon cloth was clamped with a platinum electrode clamp;

[0077] (3) The battery bottom shell, spring, gasket, metal sodium sheet, electrolyte, and battery top cover containing the solid electrolyte were assembled and pressed into a conventional seawater battery anode in the order from bottom to top;

[0078] (4) An appropriate amount of seawater was added to the water container;

[0079] (5) The two electrodes were immersed in seawater, and the electrode clamp was fixed, obtaining a conventional seawater battery.

[0080] Test Example

[0081] Performance test: The conventional seawater batteries assembled with the above two catalysts were tested for cycle performance; the open-type rechargeable seawater batteries assembled above were tested for cyclic voltammetry curves and charge-discharge curves, cycle performance and rate performance. Among them, the test results are shown in Figures 2a-b. Figure 4 , Figures 6-9

[0082] Figure 4 is the conventional seawater battery assembled with Co and H-Co two catalysts and sodium metal anode at a current density of 0.05 mA cm -2 ​​The comparison chart of the cycle performance of the above-mentioned open rechargeable seawater battery device obtained according to the technical solution of Example 2 of the present application. It is shown that the H-Co catalyst of Example 1 (0.57 V) has a lower overpotential than the Co catalyst of Comparative Example 2 (0.75 V) in the fifth charge-discharge cycle. And the H-Co catalyst shows better cycle stability in the subsequent cycles.

[0083] The Figure 6 The cyclic voltammogram of the open rechargeable seawater battery device obtained according to the technical solution of Example 2 of the present application. It is shown that the open rechargeable seawater battery device obtained according to the technical solution of the present application has obvious redox peaks, corresponding to the redox peaks of sodium titanium phosphate and the oxygen reduction peaks of oxygen.

[0084] The Figure 7 The first three charge-discharge cycle charts of the open rechargeable seawater battery device obtained according to the technical solution of Example 2 of the present application at a current density of 1 mA cm -2 . It is shown that the battery works between 0-2.2 V, and there is a sodium insertion platform at about 2 V in the charging process. In addition, due to the hydrogen evolution side reaction of the sodium titanium phosphate / carbon anode material in the charging process, the discharge capacity of the battery is slightly lower than the charging capacity.

[0085] The Figure 8 The cycle performance chart of the open rechargeable seawater battery device obtained according to the technical solution of Example 2 of the present application at a current density of 5 mA cm -2 . It is shown that the battery has a very high capacity retention rate at a current density of 5 mA cm -2 . After removing the first lower discharge capacity, the second discharge capacity is 79.3 mAh g -1 , the 250th is 76.5 mAh g -1 , and the capacity retention rate is 96.5%.

[0086] The Figure 9 The rate performance chart of the open rechargeable seawater battery device obtained according to the technical solution of Example 2 of the present application. The discharge capacity of the device at different current densities remains almost unchanged. This is mainly due to the existence of the above-mentioned hydrogen evolution reaction, which can be inhibited to some extent by increasing the current density, and offset the capacity reduction caused by the increase of the current density. This shows that the open rechargeable seawater battery obtained according to the technical solution of the present application has good rate performance.

[0087] The above-mentioned is the preferred embodiment of the present application. It should be noted that for ordinary skilled persons in the technical field, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing an open-type rechargeable all-seawater battery, characterized by, The open rechargeable full-seawater battery comprises a catalyst cathode, an electrolyte and a sodium storage anode; the catalyst cathode is an array of metal-embedded nitrogen-doped carbon nanotubes deposited on a flexible carbon fiber cloth; the sodium storage anode is a sodium titanium phosphate / carbon composite material coated on a flexible carbon fiber cloth; the open rechargeable full-seawater battery is obtained by immersing the catalyst cathode and the sodium storage anode in seawater electrolyte. The preparation method of the open rechargeable full-seawater battery comprises the following steps: Step 1: pretreated carbon fiber cloth is subjected to acid treatment; a mixed solution of nitrate and zinc nitrate is quickly poured into a 2-methyl imidazole solution and continuously stirred, and the acid-treated carbon fiber cloth is immersed and vertically erected in the mixed aqueous solution, and is left to stand at room temperature, and a metal organic framework array precursor is synthesized on the carbon cloth, and then the precursor is washed and dried; Step 2: the catalyst cathode material obtained in step 1 is placed in a tube furnace under an argon atmosphere and subjected to annealing under the sublimation coating of dicyandiamide, and then is further annealed in an air atmosphere to obtain an array catalyst cathode material of metal-embedded nitrogen-doped carbon nanotubes deposited on a flexible carbon fiber cloth; the annealing in the air atmosphere is performed at a temperature of 100-200 DEG C for 2-4 hours; Step 3: tetrabutyl titanate is dissolved in a solvent and stirred to obtain a uniform transparent solution; sodium dihydrogen phosphate, phosphoric acid and glucose are dissolved in deionized water and stirred to obtain a uniform transparent solution; the two mixed solutions are mixed and further stirred uniformly, and then are transferred into an autoclave for hydrothermal reaction, centrifugation, washing and drying to obtain a brown powder precursor; finally, the brown powder precursor is placed in a tube furnace under an argon atmosphere for annealing to obtain a solid powder of sodium titanium phosphate / carbon composite material; Step 4: the solid powder of sodium titanium phosphate / carbon composite material obtained in step 3, conductive carbon black and a binder are mixed to form a slurry, which is coated on a cleaned carbon fiber cloth to obtain a sodium titanium phosphate anode material; Step 5: the catalyst cathode, the sodium titanium phosphate anode and seawater electrolyte obtained in steps 2 and 4 are assembled into an open rechargeable full-seawater battery.

2. The preparation method of the open-type rechargeable all-seawater battery according to claim 1, characterized in that, The embedded metal nitrogen-doped carbon nanotube is a hollow structure, the length of the embedded metal nitrogen-doped carbon nanotube is 40-150 nm, and the diameter of the embedded metal nitrogen-doped carbon nanotube is 20-50 nm; the embedded metal nitrogen-doped carbon nanotube array is distributed at a high density; the embedded metal material is one or more of iron, cobalt and nickel; the loading amount of the embedded metal nitrogen-doped carbon nanotube array on the flexible carbon fiber cloth is 1-2 mg·cm -2 ; the loading amount of the titanium sodium phosphate / carbon composite material on the flexible carbon fiber cloth is 1-2 mg·cm -2 .

3. The preparation method of the open type rechargeable all-seawater battery according to claim 1, characterized in that, In step 1, the pretreatment of the carbon fiber cloth comprises ultrasonic cleaning in acetone, deionized water and ethanol in sequence, and drying; the acid treatment is hydrothermal treatment of concentrated nitric acid solution in an oven.

4. The method of claim 1, wherein the openable rechargeable all-seawater battery is prepared by the steps of: In step 1, the nitrate is one or more of cobalt nitrate, iron nitrate and nickel nitrate; the molar ratio of the nitrate, zinc nitrate and dimethyl imidazole is (0.5-2):1:(10-20).

5. The method of claim 1, wherein the openable rechargeable all-seawater battery is prepared by the steps of: In step 1, the standing time at room temperature is 2-4 hours; the drying is vacuum drying at a temperature of 40-80 DEG C for 6-12 hours.

6. The method of claim 1, wherein the openable rechargeable all-seawater battery is prepared by the steps of: In step 2, the two-step annealing is performed in an argon atmosphere, the first step is annealing at 300-400℃ for 2-4 h, and the second step is annealing at 700-800℃ for 2-4 h, and the heating rate is 1-5℃ min -1 .

7. The method for preparing an open-type rechargeable all-seawater battery according to claim 1, characterized in that, In step 3, the molar ratio of tetrabutyl titanate, sodium dihydrogen phosphate, phosphoric acid and glucose is (20-40):(10-20):(20-40):(10-20); the stirring time of the tetrabutyl titanate solution is 30-60 minutes; the stirring time of the mixed solution of sodium dihydrogen phosphate, phosphoric acid and glucose is 30-60 minutes; the stirring time of the mixed solution of tetrabutyl titanate, sodium dihydrogen phosphate, phosphoric acid and glucose is 60-120 minutes.

8. The method of claim 1, wherein the openable rechargeable all-seawater battery is prepared by the steps of: In step 3, the hydrothermal reaction temperature is 100-200℃, and the time is 10-20 h; the two-step annealing is performed in an argon atmosphere, the first step annealing temperature is 300-400℃, the time is 2-4 h, the second step annealing temperature is 700-800℃, the time is 2-4 h, and the heating rate is 1-5℃ min -1 .

9. The method for preparing an open-type rechargeable all-seawater battery according to claim 1, characterized in that, In step 4, the mass ratio of the sodium titanium phosphate anode material, conductive carbon black and binder is (60-80):(10-20):(10-20).

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