A method for preparing molybdenum as a positive electrode of a lithium-carbon dioxide battery

Abstract

The present invention belongs to the field of new energy storage materials, and relates to a method for preparing a single molybdenum substance as a positive electrode of a lithium-carbon dioxide battery. The main purpose of the present invention is to use a single molybdenum substance as a transition metal with stable catalytic performance to have a relatively good catalytic effect on the reaction of a lithium-carbon dioxide battery, and proposes to use it to replace precious metals. The main scheme includes that the method first heats ammonium molybdate tetrahydrate in a nitric acid solution to obtain molybdenum trioxide, which is reduced at high temperature in an atmosphere of argon-hydrogen mixed gas to obtain a single molybdenum substance. When the single molybdenum substance in the present invention is used as a positive electrode catalyst, the charging voltage of the lithium-carbon dioxide battery is as low as 3.4V at a current density of 50mA / g.

Description

Technical Field

[0001] The invention belongs to the field of new energy storage materials and relates to a method for preparing molybdenum as a positive electrode of a lithium-carbon dioxide battery. Technical Background

[0002] Nowadays, lithium-ion batteries have been successfully commercialized and applied in various fields. However, the low energy density and safety of lithium-ion batteries limit its further development. Lithium-carbon dioxide batteries have higher energy density and have attracted people's attention in recent years.

[0003] There are still many problems to be solved in lithium-carbon dioxide, especially how to solve the decomposition problem of Li2CO3, the discharge product of Li and CO2. Li2CO3 is produced during the discharge process of the battery, but it is difficult to decompose during the charging process, and often requires a higher charging voltage, which affects the cycle stability of the battery.

[0004] Precious metals as catalysts generally have a good effect on reducing the charging voltage of lithium-carbon dioxide batteries. Although precious metals have excellent electrocatalytic properties, the price of precious metal materials is relatively high. It is necessary to find substitutes for precious metals while maintaining electrocatalytic properties. Molybdenum as a transition metal with stable catalytic properties has a relatively good catalytic effect on lithium-carbon dioxide battery reactions and can play a role in replacing precious metals.

[0005] The present invention provides a method for preparing single substance molybdenum as the positive electrode of a lithium-carbon dioxide battery. Single substance molybdenum is obtained by treating a molybdenum source compound and reducing a molybdenum source oxide precursor, thereby providing a new idea for using related transition metals as catalysts for energy storage batteries. Summary of the invention

[0006] The purpose of the present invention is to solve the above problems and to provide a method for preparing a single molybdenum substance as a positive electrode of a lithium-carbon dioxide battery. The present invention adopts the following technical solutions:

[0007] A method for preparing molybdenum as a positive electrode of a lithium-carbon dioxide battery comprises the following steps:

[0008] Step a. Mix concentrated acid and deionized water in a volume ratio of 1 to 5 to form an acid solution.

[0009] Step b. Add the molybdenum source compound into the prepared acid solution and perform ultrasonic treatment for five minutes to completely dissolve the molybdenum source compound in the acid solution.

[0010] Step c. The acid solution in which the molybdenum source compound is completely dissolved in step b is added into a reaction kettle and heated in an oven.

[0011] Step d. In step c, the reaction temperature of the oven is 200° C., the reaction time is 20 h, and a molybdenum source oxide precipitate is obtained, which is filtered and dried for later use.

[0012] Step e. The molybdenum source oxide obtained in step d is heated in a tubular furnace in an atmosphere of reducing gas and inert gas at a heating temperature of 850° C. for a reaction time of 12 h to obtain elemental molybdenum.

[0013] Step f. Take a molybdenum element and a binder in a mass ratio of 8:1 and mix them in a grinding mortar, grind them evenly for 20 minutes to fully mix the components, and evenly apply them on a carbon cloth as a positive electrode for a lithium-carbon dioxide battery.

[0014] Step g. Assemble the positive electrode in step f into a button battery, and the required materials are a negative electrode shell, a spring, a gasket, a lithium sheet, a diaphragm, a positive electrode material, a stainless steel mesh and a positive electrode shell. Stack the materials in the above order, and then compact them with a manual hydraulic button battery sealing machine to obtain a lithium-carbon dioxide button battery.

[0015] In the above technical solution, the concentrated acid in step a is concentrated nitric acid, concentrated hydrochloric acid or concentrated sulfuric acid.

[0016] In the above technical solution, the molybdenum source compound in step b is ammonium molybdate or sodium molybdate.

[0017] In the above technical solution, the molybdenum source oxide in step d is molybdenum trioxide.

[0018] In the above technical solution, the reducing gas in step e is hydrogen, and the inert gas is nitrogen or argon.

[0019] Because the present invention adopts the above technical solution, it has the following beneficial effects:

[0020] The core of the present invention is to prepare a single molybdenum substance by hydrothermal and high-temperature calcination methods, and use it for the first time as a positive electrode material for a lithium-carbon dioxide battery. The material has a relatively low charging voltage, and the charging voltage is as low as 3.4V at a current density of 50mA / g (the carbon material is about 4.2V), and can be stably cycled for 20 cycles at a current density of 250mA / g when the charging voltage does not exceed 4.2V. The reduction in charging voltage can improve the rate and cycle performance of the battery, thereby achieving the effect of extending the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is a scanning electron microscope image of the molybdenum element in the embodiment.

[0022] Figure 2 : is the XRD spectrum of the molybdenum element in the embodiment.

[0023] Figure 3 This is the XRD pattern of molybdenum dioxide / molybdenum in Example 2.

[0024] Figure 4This is the XRD pattern of the molybdenum element in Example 3.

[0025] Figure 5 The charge and discharge rate curves of the lithium-carbon dioxide battery in Example 3 at current densities of 50, 100, 200, 300, 400, and 500 mAg-1.

[0026] Figure 6 This is the cyclic charge and discharge curve of the lithium-carbon dioxide battery in Example 3 at a current density of 250 mAg-1.

[0027] Figure 7 Schematic diagram of the internal structure of the lithium-carbon dioxide battery of the present invention.

[0028] Description of Reference Numerals

[0029] 1-lithium sheet, 2-diaphragm, 3-molybdenum element, 4-stainless steel mesh. DETAILED DESCRIPTION

[0030] The specific contents of the present invention are described in detail below in conjunction with specific embodiments:

[0031] Example 1

[0032] Dissolve 10 ml of concentrated nitric acid in 50 ml of deionized water, and sonicate for 2-5 min with an 800 W ultrasonic device to fully mix the components to obtain solution A.

[0033] Weigh 2 g of ammonium molybdate and add it to solution A. Ultrasonicate the solution for 2-5 min with an ultrasonicator at a power of 800 W to completely dissolve the ammonium molybdate, thereby obtaining a mixture B.

[0034] After the ultrasonic treatment, the mixture B was transferred into a polytetrafluoroethylene liner with a capacity of 100 ml, placed in a digestion tank, sealed, placed in a constant temperature drying oven, heated to 180°C at a heating rate of 10°C / min, and kept warm for 24 hours for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled to room temperature with the box. The digestion tank was opened, the mixed solution was filtered, rinsed repeatedly with deionized water for 3 times, and then dried in an oven at 70°C. After the water was completely removed, molybdenum trioxide powder was obtained.

[0035] 100 mg of dried molybdenum trioxide powder was placed in an ark, and the ark was placed in a tube furnace. A H2 / Ar mixed gas with a flow rate of 200 ml / min and a volume fraction of 5% was introduced. The air in the tube furnace was ventilated for 30 minutes, and the temperature was raised to 1000°C at a rate of 5°C / min and kept at this temperature for 3 hours to carry out a reduction reaction. After the reaction was completed, the H2 / Ar mixed gas was turned off and cooled to room temperature to obtain molybdenum dioxide. The XRD spectrum is shown as follows: Figure 2 shown.

[0036] Molybdenum dioxide and binder polyvinylidene fluoride were mixed in a grinding mortar at a mass ratio of 8 to 2, and the components were evenly ground for 20 minutes to fully mix. 0.2 mg of molybdenum was evenly applied on 1 square centimeter of carbon cloth as the positive electrode of the lithium-carbon dioxide battery. The materials were stacked in the order of negative electrode shell, shrapnel, gasket, lithium sheet, diaphragm, positive electrode material, stainless steel mesh and positive electrode shell, and then compacted with a manual hydraulic button battery sealing machine to obtain a lithium-carbon dioxide button battery.

[0037] The button cell was placed in a test bottle filled with carbon dioxide gas for rate and cycle tests. The current density in the rate test was 50, 100, 200, 300, 400 and 500 mA / g, and the end capacity was 500 mAh / g; the current density in the cycle test was 250 mA / g, and the end capacity was also 500 mAh / g. In the rate test, the charging voltage of the battery was above 4.5 V, and there was no obvious catalytic effect.

[0038] Example 2

[0039] Dissolve 10 ml of concentrated nitric acid in 50 ml of deionized water, and sonicate for 2-5 min with an 800 W ultrasonic device to fully mix the components to obtain solution A.

[0040] Weigh 2 g of ammonium molybdate and add it to solution A. Ultrasonicate the solution for 2-5 min with an ultrasonicator at a power of 800 W to completely dissolve the ammonium molybdate, thereby obtaining a mixture B.

[0041] After the ultrasonic treatment, the mixture B was transferred into a polytetrafluoroethylene liner with a capacity of 100 ml, placed in a digestion tank, sealed, placed in a constant temperature drying oven, heated to 180°C at a heating rate of 10°C / min, and kept warm for 24 hours for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled to room temperature with the box. The digestion tank was opened, the mixed solution was filtered, rinsed repeatedly with deionized water for 3 times, and then dried in an oven at 70°C. After the water was completely removed, molybdenum trioxide powder was obtained.

[0042] 100 mg of dried molybdenum trioxide powder was placed in an ark, and the ark was placed in a tube furnace. A H2 / Ar mixed gas with a flow rate of 200 ml / min and a volume fraction of 5% was introduced. The air in the tube furnace was ventilated for 30 minutes, and the temperature was raised to 1000°C at a rate of 5°C / min and kept at this temperature for 6 hours to carry out a reduction reaction. After the reaction was completed, the H2 / Ar mixed gas was turned off and cooled to room temperature to obtain molybdenum dioxide / molybdenum. The XRD spectrum is shown as follows: Figure 3 shown.

[0043] Molybdenum dioxide / molybdenum and binder polyvinylidene fluoride were mixed in a grinding mortar at a mass ratio of 8 to 2, and the components were evenly ground for 20 minutes to fully mix, and 0.2 mg of molybdenum was evenly applied on 1 square centimeter of carbon cloth as the positive electrode of the lithium-carbon dioxide battery. The materials were stacked in the order of negative electrode shell, shrapnel, gasket, lithium sheet, diaphragm, positive electrode material, stainless steel mesh and positive electrode shell, and then compacted with a manual hydraulic button battery sealing machine to obtain a lithium-carbon dioxide button battery.

[0044] The button cell was placed in a test bottle filled with carbon dioxide gas for rate and cycle tests. The current density in the rate test was 50, 100, 200, 300, 400 and 500 mA / g, and the end capacity was 500 mAh / g; the current density in the cycle test was 250 mA / g, and the end capacity was also 500 mAh / g. In the rate test, the battery charging voltage was between 3.7V and 4.5V.

[0045] Example 3

[0046] Dissolve 10 ml of concentrated nitric acid in 50 ml of deionized water, and sonicate for 2-5 min with an 800 W ultrasonic device to fully mix the components to obtain solution A.

[0047] Weigh 2 g of ammonium molybdate and add it to solution A. Ultrasonicate the solution for 2-5 min with an ultrasonicator at a power of 800 W to completely dissolve the ammonium molybdate, thereby obtaining a mixture B.

[0048] After the ultrasonic treatment, the mixture B was transferred into a polytetrafluoroethylene liner with a capacity of 100 ml, placed in a digestion tank, sealed, placed in a constant temperature drying oven, heated to 180°C at a heating rate of 10°C / min, and kept warm for 24 hours for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled to room temperature with the box. The digestion tank was opened, the mixed solution was filtered, rinsed repeatedly with deionized water for 3 times, and then dried in an oven at 70°C. After the water was completely removed, molybdenum trioxide powder was obtained.

[0049] Place 100 mg of dried molybdenum trioxide powder in an ark, place the ark in a tube furnace, introduce H2 / Ar mixed gas with a flow rate of 200 ml / min and a volume fraction of 5%, ventilate for 30 minutes to exhaust the air in the tube furnace, and heat to 1000°C at a rate of 5°C / min, keep warm for 12 hours, and perform reduction reaction. After the reaction is completed, turn off the H2 / Ar mixed gas and cool to room temperature to obtain molybdenum. The XRD spectrum is as follows Figure 4As shown. Molybdenum and binder polyvinylidene fluoride are mixed in a grinding mortar at a mass ratio of 8 to 2, and the components are evenly ground for 20 minutes to fully mix. 0.2 mg of molybdenum is evenly applied on 1 square centimeter of carbon cloth as the positive electrode of the lithium-carbon dioxide battery. The materials are stacked in the order of negative electrode shell, shrapnel, gasket, lithium sheet, diaphragm, positive electrode material, stainless steel mesh and positive electrode shell, and then compacted with a manual hydraulic button battery sealing machine to obtain a lithium-carbon dioxide button battery.

[0050] The button cell was placed in a test bottle filled with carbon dioxide gas for rate and cycle tests. The current density in the rate test was 50, 100, 200, 300, 400 and 500 mA / g, and the end capacity was 500 mAh / g; the current density in the cycle test was 250 mA / g, and the end capacity was also 500 mAh / g. In the rate test, the battery charging voltage was between 3.4 V and 4.3 V.

Claims

1. A method for preparing molybdenum as a positive electrode of a lithium-carbon dioxide battery, characterized in that: The following steps are involved: Step a. Mix concentrated acid and deionized water in a volume ratio of 1 to 5 to form an acid solution; Step b. adding the molybdenum source compound to the prepared acid solution and ultrasonically dissolving the molybdenum source compound in the acid solution for 2-5 minutes; Step c. Add the acid solution in which the molybdenum source compound is completely dissolved in step b to the reactor and conduct a hydrothermal reaction in an oven; Step d. The reaction temperature of the oven in step c is 180°C, the reaction time is 20-24h, and the molybdenum source oxide precipitate is obtained, filtered and dried for standby use; Step e. The molybdenum source oxide obtained in step d is heated in a tubular furnace in an atmosphere of reducing gas and inert gas, the heating temperature is 900-1200° C., the reaction time is 12 h, to obtain elemental molybdenum, wherein the reducing gas is hydrogen and the inert gas is nitrogen or argon; Step f. Take a molybdenum element and a binder in a mass ratio of 8:2 and mix them in a grinding mortar, grind them evenly for 20 minutes to fully mix the components, and evenly apply them on a carbon material substrate as a positive electrode of a lithium-carbon dioxide battery.

2. The method for preparing a single molybdenum substance as a positive electrode of a lithium-carbon dioxide battery according to claim 1, characterized in that: In step a, the concentrated acid is concentrated nitric acid, concentrated hydrochloric acid or concentrated sulfuric acid.

3. The method for preparing a single molybdenum substance as a positive electrode of a lithium-carbon dioxide battery according to claim 1, characterized in that: The molybdenum source compound in step b is ammonium molybdate or sodium molybdate.

4. The method for preparing a single molybdenum substance as a positive electrode of a lithium-carbon dioxide battery according to claim 1, characterized in that: The molybdenum source oxide in step d is molybdenum trioxide.

5. The method for preparing a single substance of platinum as a positive electrode of a lithium-carbon dioxide battery according to claim 1, characterized in that: The binder in step f is polyvinylidene fluoride, and the carbon material substrate is carbon cloth or carbon paper.

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