Open type rechargeable all-seawater battery and preparation method thereof

Abstract

The invention discloses an open type rechargeable all-seawater battery and a preparation method thereof, and belongs to the field of electrochemistry and energy storage. Comprising a catalyst cathode, an electrolyte and a sodium storage anode, the catalyst cathode is formed by depositing a metal-embedded nitrogen-doped carbon nanotube array on flexible carbon fiber cloth, the sodium storage anode is a sodium titanium phosphate / carbon composite material coated on the flexible carbon fiber cloth, the electrolyte is natural seawater, and the sodium storage anode is a sodium titanium phosphate / carbon composite material coated on the flexible carbon fiber cloth. According to the open type rechargeable all-seawater battery, a catalyst cathode and a sodium storage anode are immersed in a natural seawater electrolyte contained in a container without being separated by a diaphragm, or the catalyst cathode and the sodium storage anode are directly immersed in an open marine environment. The battery is used for realizing charge storage in seawater. Through the design of the double flexible positive and negative electrodes, the problems of instability of long-circulation voltage and leakage, inactivation or damage of a sodium negative electrode faced by a traditional seawater battery system can be solved; and the original complex negative electrode structure is optimized, so that the whole battery is in a completely open system.

Description

Technical Field

[0001] The invention belongs to the field of electrochemistry and energy storage, and relates to a full seawater battery using natural seawater as electrolyte and a preparation method thereof. Background Art

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

[0003] However, there are many challenges in directly using seawater batteries for energy storage. The current seawater battery industry has just developed, and the research on each component structure is not perfect. Traditional seawater batteries are composed of catalyst cathodes, seawater, sodium anodes, water circulation devices, etc., among which the sodium anodes and water circulation devices are also extremely large. Among the factors affecting the performance of seawater batteries, cathode catalysts are key. These catalysts can improve the efficiency of seawater redox reactions, but they are also susceptible to corrosion by chloride ions in seawater, because most of the catalysts currently used come from catalysts used in zinc-air batteries that are not designed to resist chlorine. In addition, the bulky and complex sodium anode structure also restricts the further development of seawater batteries. The complex sodium anode makes the corresponding conductive structure extremely cumbersome. Based on this, an open rechargeable all-seawater battery is designed. Summary of the invention

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

[0005] The objective of the present invention is achieved in this way: an open rechargeable all-seawater battery with a simple structure is provided, comprising a catalyst cathode, an electrolyte, and a sodium storage anode, wherein the catalyst cathode is a nitrogen-doped carbon nanotube array with embedded metals 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, and the open rechargeable all-seawater battery is a battery in which the catalyst cathode and the sodium storage anode are immersed in a natural seawater electrolyte contained in a container, without the need for a diaphragm to separate them, or are directly immersed in an open ocean environment.

[0006] The present invention provides an open rechargeable all-seawater battery, comprising a catalyst cathode, an electrolyte, and a sodium storage anode; the catalyst cathode is a nitrogen-doped carbon nanotube array with embedded metals 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; the open rechargeable all-seawater battery is a battery in which the catalyst cathode and the sodium storage anode are immersed in a seawater electrolyte.

[0007] Furthermore, the metal-embedded nitrogen-doped carbon nanotubes are hollow structures, the metal-embedded nitrogen-doped carbon nanotubes are 40 to 150 nm long and 20 to 50 nm in diameter; the metal-embedded nitrogen-doped carbon nanotube arrays are densely distributed; the embedded metal material is one or more of iron, cobalt, and nickel; the loading amount of the metal-embedded nitrogen-doped carbon nanotube arrays on the flexible carbon fiber cloth is 1 to 2 mg cm -2 The loading amount of sodium titanium phosphate / carbon composite material on the flexible carbon fiber cloth is 1-2 mg·cm -2 .

[0008] The present invention further provides a method for preparing an open rechargeable all-seawater battery, comprising the following steps:

[0009] Step 1: acid-treating the pretreated carbon fiber cloth; quickly pouring the mixed solution of nitrate and zinc nitrate into the 2-methylimidazole solution and continuously stirring, immersing the acid-treated carbon fiber cloth in the mixed aqueous solution and vertically standing it, standing it at room temperature, synthesizing the metal organic framework array precursor on the carbon cloth, washing it, and drying it;

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

[0011] Step 3: dissolving tetrabutyl titanate in a solvent and stirring to obtain a uniform and transparent solution; dissolving sodium dihydrogen phosphate, phosphoric acid and glucose in deionized water and stirring to obtain a uniform and transparent solution; mixing the two mixed solutions and further stirring them to obtain a uniform and transparent solution, transferring them to an autoclave, performing a hydrothermal reaction, centrifuging, washing and drying to obtain a brown powder precursor; finally, placing the brown powder precursor in a tubular furnace under an argon atmosphere for annealing to obtain a solid powder of sodium titanium phosphate / carbon composite material;

[0012] Step 4: mixing the solid powder of the sodium titanium phosphate / carbon composite material obtained in step 3, conductive carbon black and a binder to form a slurry, and coating the slurry on a cleaned carbon fiber cloth to obtain a sodium titanium phosphate anode material;

[0013] Step 5: Assemble the catalyst cathode, sodium titanium phosphate anode, and seawater electrolyte obtained in steps 2 and 4 into an open, open-type rechargeable all-seawater battery.

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

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

[0016] Furthermore, in step 1, the standing time at room temperature is 2 to 4 hours; and the drying is vacuum drying at a temperature of 40 to 80° C. for 6 to 12 hours.

[0017] Furthermore, in step 2, the two-step annealing is performed in an argon atmosphere, the first step annealing temperature is 300-400°C, the time is 2-4h, the second annealing temperature is 700-800°C, the time is 2-4h, and the heating rate is 1-5°C min -1 The one-step annealing in the air atmosphere, the annealing temperature is 100-200°C, the time is 2-4h, and the heating rate is 1-5°C min -1 .

[0018] Furthermore, 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 min; the stirring time of the mixed solution of sodium dihydrogen phosphate, phosphoric acid and glucose is 30-60 min; the stirring time of the mixed solution of tetrabutyl titanate, sodium dihydrogen phosphate, phosphoric acid and glucose is 60-120 min.

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

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

[0021] Furthermore, in step 4, the sodium titanium phosphate anode is a corresponding flexible carbon cloth support material for three-electrode testing with a loading capacity of 3 to 5 mg cm -2 .

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

[0023] The beneficial effects are:

[0024] The present invention provides a novel rechargeable all-seawater battery. The function of the battery is to realize charge storage in seawater. Through the design of dual flexible positive and negative electrodes, it can not only solve the instability of long-cycle voltage and leakage, deactivation or damage of sodium negative electrode faced by traditional seawater battery systems; through the method of secondary annealing in air, the ratio 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. Only two pieces of flexible carbon fiber cloth with load materials are needed to assemble into the simplest seawater battery, which reduces costs and is also very beneficial for large-scale energy storage.

[0025] The open rechargeable all-seawater battery prepared by the present invention can -2 The high current provides a cycle life of more than 250 cycles with almost no capacity decay; at 1mA cm -2 The battery has a cycle life of more than 100 cycles even at high currents. In addition, the battery has good rate performance. -2 to 10mA cm -2 Then to 1mA cm -2 The capacity is almost the same in such a large current span. In addition, the open rechargeable all-seawater battery of the present invention has a simple structure, is environmentally friendly, low cost, high safety, simple process and easy production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure, mechanism and material synthesis of the open rechargeable seawater battery of the present invention;

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

[0028] Figure 3 a is a scanning electron microscope 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 The conventional seawater battery assembled with the above two catalysts and sodium metal anode was operated at a current density of 0.05 mA cm -2 The following cycle performance comparison chart;

[0030] Figure 5 The flexible catalyst and flexible sodium titanium phosphate anode used as electrodes and the assembled open rechargeable all-seawater battery are shown in the figure. The flexible catalyst used is a nitrogen-doped carbon nanotube array catalyst embedded in metal after air annealing with better stability.

[0031] Figure 6 The scan rate of the open rechargeable all-seawater battery provided in the embodiment in natural seawater is 1 mV s -1 Cyclic voltammetry curves of

[0032] Figure 7 The open rechargeable all-seawater battery provided in the embodiment has a current density of 1 mA cm -2 The first three charge-discharge cycles below;

[0033] Figure 8 The open rechargeable all-seawater battery provided in the embodiment is -2 Cycle performance diagram below;

[0034] Fig. 9 1 is a rate performance diagram of an open rechargeable all-seawater battery provided in the embodiment. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0036] The present invention provides an open rechargeable all-seawater battery. The overall concept of this embodiment is to optimize the traditional seawater battery and realize charge storage in seawater through the design of dual flexible positive and negative electrodes. Figure 1 As shown, an open rechargeable all-seawater battery has a simple structure and only includes a catalyst cathode, seawater, a sodium titanium phosphate anode and a water container.

[0037] The mechanism of the open rechargeable all-seawater battery is shown in the attached figure. Figure 1As shown, during the charging process, the hydroxyl ions generated by water ionization lose electrons on the catalyst surface to undergo an oxygen evolution reaction to generate oxygen and water, while the sodium ions in the seawater are embedded in the sodium titanium phosphate anode to complete the sodium storage, i.e. charging; during the discharging process, the oxygen dissolved in the seawater gains electrons and undergoes an oxygen reduction reaction with water molecules to generate hydroxyl ions, while the sodium titanium phosphate at the anode loses electrons to release sodium ions to complete the discharge. The cathode catalyst plays a role in lowering the potential barrier and improving the reaction kinetics of water oxidation and reduction, so that the electrochemical performance of the open rechargeable all-seawater battery in the present invention is greatly improved.

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

[0039] The invention discloses an open rechargeable all-seawater battery, comprising a catalyst cathode, an electrolyte, and a sodium storage anode. The catalyst cathode is a nitrogen-doped carbon nanotube array with embedded metals 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 electrolyte is natural seawater. The open rechargeable all-seawater battery is a battery in which the catalyst cathode and the sodium storage anode are immersed in the natural seawater electrolyte contained in a container without a diaphragm separating them, or are directly immersed in an open ocean environment.

[0040] The present invention further discloses a preparation method of an open rechargeable all-seawater battery, comprising the following steps:

[0041] Step 1: Ultrasonic clean the carbon fiber cloth in acetone, deionized water, and ethanol in turn, and then dry it in an oven. Subsequently, the cleaned carbon fiber cloth is hydrothermally treated with a concentrated nitric acid solution in an oven. Then, nitrate and zinc nitrate are dissolved in deionized water, and dimethylimidazole is dissolved in another portion of deionized water and stirred continuously. After stirring into a uniform solution at room temperature, the mixed solution of nitrate and zinc nitrate is quickly poured into the 2-methylimidazole solution and stirred continuously. Then, the above-mentioned acid-treated carbon cloth is immersed and vertically erected in the mixed aqueous solution, and allowed to stand at room temperature to synthesize the metal organic framework array precursor on the carbon cloth. Then, the carbon fiber cloth with the deposited metal organic framework is taken out and washed with water and ethanol in turn, and vacuum dried overnight.

[0042] Step 2: The catalyst cathode material obtained in step 1 is transferred to a tube furnace under an argon environment and annealed under the sublimation coating of dicyandiamide, and then further exposed to air for annealing to obtain a nitrogen-doped carbon nanotube array catalyst cathode material with embedded metal deposited on a flexible carbon fiber cloth.

[0043] Step 3: Dissolve tetrabutyl titanate in ethylene glycol and stir to obtain a uniform and transparent solution; dissolve sodium dihydrogen phosphate, phosphoric acid, and glucose in deionized water and stir to obtain a uniform and transparent solution. After mixing the above two mixed solutions and further stirring them evenly, transfer them to an autoclave for hydrothermal reaction. When the reaction is completed, centrifuge, wash and dry them with deionized water and ethanol to collect a brown powder precursor. Finally, transfer the brown powder precursor to a tubular furnace under an argon environment for annealing to obtain a solid powder of sodium titanium phosphate / carbon composite material.

[0044] Step 4: Mix the solid powder of the sodium titanium phosphate / carbon composite material obtained in step 3, conductive carbon black and a binder to form a slurry, and coat the slurry on a cleaned carbon fiber cloth to obtain a sodium titanium phosphate anode material.

[0045] Step 5: Assemble the catalyst cathode, sodium titanium phosphate anode, seawater electrolyte and water container obtained in steps 2 and 4 into an open rechargeable all-seawater battery.

[0046] Example 1

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

[0048] (1) Carbon fiber cloth (CC) was ultrasonically cleaned in acetone, deionized water (DI), and ethanol in sequence, and then dried in an oven. Subsequently, the cleaned CC was quenched with concentrated nitric acid (HNO 3 ) solution was hydrothermally treated in an oven at 80 °C for 1 h. Then 2 mmol of cobalt nitrate (Co(NO 3 ) 2 ) and 1mmol zinc nitrate (Zn(NO 3 ) 2 ) was dissolved in 50 mL of deionized water, and the resulting solution was called solution A. 20 mmol of 2-methylimidazole (2-mim) was dissolved in another 50 mL of deionized water and stirred continuously, and the resulting solution was called solution B. After stirring at room temperature to form a uniform solution, solution A was quickly poured into solution B and stirred continuously. Then, the above acid-treated CC (3×4 cm 2 ) was immersed and vertically erected in the mixed aqueous solution and allowed to stand at room temperature for 3 hours to synthesize the cobalt zinc zeolite imidazolate framework (CoZn-ZIF) array on CC. Finally, the CoZn-ZIF / CC was taken out, washed with water and ethanol in turn, and dried in a vacuum oven at 40°C overnight.

[0049] (2) Place 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-shaped furnaces, with DCDA located upstream of the argon atmosphere. First, the sample and DCDA were heated at 400 °C under argon at 5 °C min -1 The samples were annealed at a heating rate of 200 °C for 2 h. The temperature was then further increased to 700 °C and maintained for 2 h. The samples were then exposed to air at 200 °C for 5 °C min -1 The nitrogen-doped carbon nanotube array catalyst cathode material embedded with metal after air annealing is denoted as H-Co catalyst. The scanning electron microscope image and transmission electron microscope image of H-Co catalyst are shown in Figure 2 As shown in ab.

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

[0051] (1) Dissolve 2 mmol of tetrabutyl titanate in 20 mL of ethylene glycol and stir to obtain a uniform and transparent solution A; add 1 mmol of sodium dihydrogen phosphate (NaH 2 PO 4 ), 2mmol phosphoric acid (H 3 PO 4 ), 1 mmol of glucose was dissolved in 20 mL of water and stirred to obtain a uniform and transparent solution B.

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

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

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

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

[0056] Example 2

[0057] Assemble an open rechargeable all-seawater battery, such as Figure 5 As shown:

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

[0059] (2) Use two platinum electrode clamps to clamp the carbon cloth at both electrodes;

[0060] (3) Add an appropriate amount of seawater to a beaker or other water container;

[0061] (4) Immerse the two electrodes in seawater and fix the electrode clamps to obtain an open rechargeable all-seawater battery.

[0062] Comparative Example 1

[0063] Assembling a traditional seawater battery:

[0064] (1) The carbon cloth used for the H-Co catalyst cathode prepared in Example 1 was cut into pieces with a side length of 2 cm. 2 Small square pieces;

[0065] (2) Clamp the cathode carbon cloth with a platinum electrode clamp;

[0066] (3) Assembling and pressing the battery bottom shell, spring, gasket, metal sodium sheet, electrolyte, and battery top cover containing solid electrolyte in order from bottom to top into a conventional seawater battery anode;

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

[0068] (5) Immerse the two electrodes in seawater and fix the electrode clamps to obtain a traditional seawater battery.

[0069] Comparative Example 2

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

[0071] (1) Carbon fiber cloth (CC) was ultrasonically cleaned in acetone, deionized water (DI), and ethanol in sequence, and then dried in an oven. Subsequently, the cleaned CC was quenched with concentrated nitric acid (HNO 3 ) solution was hydrothermally treated in an oven at 80 °C for 1 h. Then 2 mmol of cobalt nitrate (Co(NO 3 ) 2 ) and 1mmol zinc nitrate (Zn(NO 3 ) 2 ) was dissolved in 50 mL of deionized water, and the resulting solution was called solution A. 20 mmol of 2-methylimidazole (2-mim) was dissolved in another 50 mL of deionized water and stirred continuously, and the resulting solution was called solution B. After stirring at room temperature to form a uniform solution, solution A was quickly poured into solution B and stirred continuously. Then, the above acid-treated CC (3×4 cm2 ) was immersed and vertically erected in the mixed aqueous solution and allowed to stand at room temperature for 3 hours to synthesize the cobalt zinc zeolite imidazolate framework (CoZn-ZIF) array on CC. Finally, the CoZn-ZIF / CC was taken out, washed with water and ethanol in turn, and dried in a vacuum oven at 40°C overnight.

[0072] (2) Place 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-shaped furnaces, with DCDA located upstream of the argon atmosphere. First, the sample and DCDA were heated at 400 °C under argon at 5 °C min -1 The temperature was then further increased to 700°C and maintained for 2 hours. After carbonization, the CoZn-ZIF array was transformed into a metal-embedded nitrogen-doped carbon nanotube array. The metal-embedded nitrogen-doped carbon nanotube array catalyst cathode material obtained in this step is recorded as Co catalyst; the scanning electron microscope image and transmission electron microscope image of the Co catalyst are shown in Figure 2 As shown in cd, the structure of the Co catalyst is denser than that of the H-Co catalyst, which is caused by the oxidation of the Co catalyst at 200°C in air to obtain the H-Co catalyst.

[0073] Comparative Example 3

[0074] Assembling a traditional seawater battery:

[0075] (1) The Co catalyst cathode carbon cloth prepared in the above comparative example 2 was cut into pieces with a side length of 2 cm. 2 Small square pieces;

[0076] (2) Clamp the cathode carbon cloth with a platinum electrode clamp;

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

[0078] (4) Add an appropriate amount of seawater into a water container;

[0079] (5) Immerse the two electrodes in seawater and fix the electrode clamps to obtain a traditional seawater battery.

[0080] Test Case

[0081] Performance test: Cyclic performance test was conducted on the conventional seawater battery assembled with the above two catalysts; cyclic voltammetry curve, charge-discharge curve, cycle performance and rate performance test were conducted on the open rechargeable all-seawater battery assembled above. The test results are shown in the attached Figure 4 , Figure 6-9 shown.

[0082] Figure 4 The conventional seawater battery assembled with two catalysts, Co and H-Co, and a sodium metal anode was used to generate a high current density of 0.05 mA cm -2 The cycle performance comparison chart under . It shows that in the fifth charge and discharge cycle, the H-Co catalyst of Example 1 (0.57V) has a lower overpotential than the Co catalyst of Comparative Example 2 (0.75V). And in the subsequent cycle process, the H-Co catalyst shows better cycle stability.

[0083] Attached Figure 6 The cyclic voltammetry curve of the open rechargeable all-seawater battery device obtained according to the technical solution of Example 2 of the present application shows that the open rechargeable all-seawater battery device obtained according to the technical solution of the embodiment of the present application has obvious redox peaks, corresponding to the redox peak of sodium titanium phosphate and the oxygen reduction peak of oxygen.

[0084] Attached Figure 7 The open rechargeable all-seawater battery device obtained according to the technical solution of Example 2 of the present application has a current density of 1 mA cm -2 The first three charge and discharge cycle diagrams below show that the battery operates between 0 and 2.2 V, and there is a sodium embedding platform at around 2 V during the charging process. In addition, due to the hydrogen evolution side reaction of the sodium titanium phosphate / carbon anode material during the charging process, the discharge capacity of the battery is slightly lower than the charging capacity.

[0085] Attached Figure 8 The open rechargeable all-seawater battery device obtained according to the technical solution of Example 2 of the present application has a current density of 5 mA cm -2 The cycling performance diagram under the condition of 5 mA cm -2 After removing the low discharge capacity of the first time, the second discharge capacity during the cycle is 79.3 mAh g -1 , the 250th time is 76.5mAh g -1 , the capacity retention rate is 96.5%.

[0086] Attached Fig. 9 The figure is a rate performance diagram of an open rechargeable all-seawater battery device obtained by 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 presence of the above-mentioned hydrogen evolution reaction, which can be suppressed to a certain extent by increasing the current density, and offsets part of the capacity reduction caused by the increase in current density. This shows that the open rechargeable all-seawater battery obtained by the technical solution of the embodiment of the present application has good rate performance.

[0087] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An open rechargeable all-seawater battery, characterized in that: It includes a catalyst cathode, an electrolyte, and a sodium storage anode; the catalyst cathode is a nitrogen-doped carbon nanotube array with embedded metals 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 all-seawater battery is a catalyst cathode and a sodium storage anode immersed in a seawater electrolyte.

2. The open rechargeable all-seawater battery according to claim 1, characterized in that: The metal-embedded nitrogen-doped carbon nanotubes are hollow structures, the metal-embedded nitrogen-doped carbon nanotubes are 40 to 150 nm long and 20 to 50 nm in diameter; the metal-embedded nitrogen-doped carbon nanotube arrays are densely distributed; the embedded metal material is one or more of iron, cobalt, and nickel; the loading amount of the metal-embedded nitrogen-doped carbon nanotube arrays on the flexible carbon fiber cloth is 1 to 2 mg cm -2 The loading amount of sodium titanium phosphate / carbon composite material on the flexible carbon fiber cloth is 1-2 mg·cm -2 .

3. A method for preparing an open rechargeable all-seawater battery as claimed in claim 1, characterized in that: The following steps are involved: Step 1: acid-treating the pretreated carbon fiber cloth; quickly pouring the mixed solution of nitrate and zinc nitrate into the 2-methylimidazole solution and continuously stirring, immersing the acid-treated carbon fiber cloth in the mixed aqueous solution and vertically standing it, standing it at room temperature, synthesizing the metal organic framework array precursor on the carbon cloth, washing it, and drying it; Step 2: placing the catalyst cathode material obtained in step 1 in a tube furnace under an argon atmosphere and annealing it under the sublimation coating of dicyandiamide, and further annealing it in an air atmosphere to obtain a nitrogen-doped carbon nanotube array catalyst cathode material with embedded metal deposited on a flexible carbon fiber cloth; Step 3: dissolving tetrabutyl titanate in a solvent and stirring to obtain a uniform and transparent solution; dissolving sodium dihydrogen phosphate, phosphoric acid and glucose in deionized water and stirring to obtain a uniform and transparent solution; mixing the two mixed solutions and further stirring them to obtain a uniform and transparent solution, transferring them to an autoclave, performing a hydrothermal reaction, centrifuging, washing and drying to obtain a brown powder precursor; finally, placing the brown powder precursor in a tubular furnace under an argon atmosphere for annealing to obtain a solid powder of sodium titanium phosphate / carbon composite material; Step 4: mixing the solid powder of the sodium titanium phosphate / carbon composite material obtained in step 3, conductive carbon black and a binder to form a slurry, and coating the slurry on a cleaned carbon fiber cloth to obtain a sodium titanium phosphate anode material; Step 5: Assemble the catalyst cathode, sodium titanium phosphate anode, and seawater electrolyte obtained in steps 2 and 4 into an open, open-type rechargeable all-seawater battery.

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

5. The method for preparing an open rechargeable all-seawater battery according to claim 3, characterized in that: In step 1, the nitrate is cobalt nitrate, iron nitrate, or nickel nitrate; and the molar ratio of the nitrate, zinc nitrate, and dimethylimidazole is (0.5-2):1:(10-20).

6. The method for preparing an open rechargeable all-seawater battery according to claim 3, characterized in that: In step 1, the standing time at room temperature is 2 to 4 hours; the drying is vacuum drying at a temperature of 40 to 80° C. for 6 to 12 hours.

7. The method for preparing an open rechargeable all-seawater battery according to claim 3, characterized in that: In step 2, two-step annealing is performed in an argon atmosphere, the first step annealing temperature is 300-400°C, the time is 2-4h, the second annealing temperature is 700-800°C, the time is 2-4h, and the heating rate is 1-5°C min -1 ; One-step annealing in the air atmosphere, the annealing temperature is 100-200°C, and the time is 2-4h.

8. The method for preparing an open rechargeable all-seawater battery according to claim 3, 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 min; the stirring time of the mixed solution of sodium dihydrogen phosphate, phosphoric acid and glucose is 30-60 min; the stirring time of the mixed solution of tetrabutyl titanate, sodium dihydrogen phosphate, phosphoric acid and glucose is 60-120 min.

9. The method for preparing an open rechargeable all-seawater battery according to claim 3, characterized in that: In step 3, the hydrothermal reaction temperature is 100-200°C, and the time is 10-20h; the two-step annealing is performed in an argon atmosphere, the first step annealing temperature is 300-400°C, the time is 2-4h, the second step annealing temperature is 700-800°C, the time is 2-4h, and the heating rate is 1-5°C min -1 .

10. The method for preparing an open rechargeable all-seawater battery according to claim 3, characterized in that: In step 4, the mass ratio of the sodium titanium phosphate anode material, the conductive carbon black and the binder is (60-80):(10-20):(10-20).

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