Preparation method of carbon-coated sodium chromite material and application of carbon-coated sodium chromite material prepared by method

Abstract

The invention relates to a preparation method of a carbon-coated sodium chromite material and application of the carbon-coated sodium chromite material prepared by the method, and the preparation method comprises the following steps: (1) weighing a chromium source, a sodium source and a carbon source, respectively heating and drying, and uniformly mixing to obtain mixed powder; (2) putting the mixed powder into a ball mill for ball milling, and then preparing into sheets; (3) calcining in an inert atmosphere to obtain a sodium chromite precursor; (4) performing ball milling in a ball mill, and stirring in a carbon source saturated solution; (5) baking the stirred materials at a high temperature; and (6) calcining the baked product in an inert atmosphere. The preparation method is simple, low in cost and free of redundant by-products, comprehensive and complete carbon coating of the sodium chromite material is achieved through a distributed carbon coating method, side reactions are effectively prevented, the formed carbon coating layer is good in uniformity, and the service life of the sodium chromite material is prolonged. The sodium ion battery prepared from the material has high specific capacity, good rate capability and excellent cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and specifically to a preparation method of a carbon-coated sodium chromite material and the application of the carbon-coated sodium chromite material prepared by this method. Background Art

[0002] The abundance of lithium in the earth's crust is only about 0.0017%, and it is unevenly distributed, with 50% concentrated in South America. Different from lithium, sodium is one of the elements with relatively high content in the earth's crust and is widely distributed in the ocean. Therefore, the rich sodium resources are the main factors that have attracted much attention for sodium-ion batteries in large-scale energy storage applications. In addition to the problem of lithium resources, the reserves of other elements commonly used in lithium-ion batteries, such as nickel and cobalt, in the earth's crust are also relatively low. In contrast, the elements commonly used in sodium-ion batteries, such as iron, manganese, and aluminum (positive and negative current collectors), have relatively high reserves in the earth's crust. These characteristics help to reduce the material cost of sodium-ion batteries and make their large-scale production not restricted by geographical factors, which is conducive to the sustainable development of large-scale energy storage.

[0003] In 1982, the electrochemical performance of O3-NaCrO2 was reported. In the voltage range of 2.5 - 3.6 V, the average working voltage was 3.02 V, and the reversible specific capacity was 110 mAh / g. In lithium ions, LiCrO2 has no electrochemical activity. The structural evolution process of O3-NaCrO2 during charge and discharge is O3 - O’3 - P’3. If the sodium content is further reduced, it will lead to irreversible migration of Cr from the transition metal layer to the Na layer. Subsequently, through single coating, the specific capacity of O3-NaCrO2 can be increased to 120 mAh / g, and the cycle performance and rate performance of the material can also be improved.

[0004] The applicant of the present invention disclosed a carbon-coated sodium chromite material, its preparation method and application in Chinese Patent Publication No. CN 115863609A. Using a chromium source and a sodium source as the main raw materials, a complexing agent is used to form a colloid, and after dehydration, primary decarbonization and secondary decarbonization are carried out, and the carbon-coated sodium chromite material is obtained by sintering. This patented technology only uses a single carbon coating technology. As a positive electrode material for sodium-ion batteries, the discharge specific capacity of the obtained carbon-coated sodium chromite material is less than 110 mAh / g at a 1C charge and discharge rate. Therefore, developing a preparation method of a carbon-coated sodium chromite material so that the prepared carbon-coated sodium chromite has a high specific capacity, good electrochemical stability and cycle performance is an urgent problem to be solved at present. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of a carbon-coated sodium chromite material and the application of the carbon-coated sodium chromite material prepared by this method in view of the problems such as the small discharge specific capacity of the carbon-coated sodium chromite material prepared by the prior art. The present invention uses a chromium source, a sodium source and a carbon source as the main raw materials, and adopts a method of distributed carbon coating to sinter and obtain a carbon-coated sodium chromite material. The preparation method of the present invention is simple, low in cost and has no redundant by-products. Through the method of distributed carbon coating, the carbon coating of the sodium chromite material is realized comprehensively and completely, which not only effectively prevents the occurrence of side reactions, but also has good uniformity of the formed carbon coating layer. The sodium ion battery prepared by using this material has a high specific capacity, good rate performance and excellent cycle stability performance.

[0006] To achieve the above object, the present invention adopts the following technical solutions.

[0007] A preparation method of a carbon-coated sodium chromite material of the present invention includes the following steps: (1) Weigh the chromium source, sodium source and carbon source in proportion and place them in an oven at a temperature of 80 - 110 °C for heating and drying for 2 - 4 h. After mixing evenly, a mixed powder is obtained; the molar ratio of the chromium source to the sodium source is 1:(1 - 1.03), and the addition amount of the carbon source is 5 - 12% of the total mass of the sodium source and the chromium source; (2) Place the mixed powder in a ball mill under a pressure of 20 - 35 MPa for ball milling for 4 - 10 h, and then press it into a mixed powder tablet under a pressure of 2000 - 3500 Mpa; (3) Place the mixed powder tablet in an inert atmosphere for calcination for 5 - 12 h, the calcination temperature is 800 - 950 °C, and the heating rate is 3 - 10 °C / min to obtain a sodium chromite precursor; (4) Place the obtained sodium chromite precursor in a ball mill for ball milling, and then place it in a saturated carbon source solution for stirring. The addition amount of the carbon source in the saturated carbon source solution is 10% - 25% of the mass of the sodium chromite precursor; (5) Place the stirred material in a high temperature of 80 - 110 °C for baking for 2 - 5 h; (6) Place the baked product in an inert atmosphere for calcination for 0.5 - 2.5 h, the calcination temperature is 600 - 700 °C, and the carbon-coated sodium chromite material is obtained.

[0008] In step (1) of the present invention, the chromium source is any one or at least two combinations of chromium monoxide, chromium sesquioxide, and chromium dioxide, preferably chromium sesquioxide; the sodium source is any one or at least two combinations of sodium sulfate, sodium carbonate, sodium chloride, sodium hydroxide, sodium acetate, sodium oxalate, and sodium nitrate, preferably sodium carbonate; the carbon source is any one or at least two combinations of polyvinylpyrrolidone, ascorbic acid, glucose, sucrose, citric acid, polyaniline, graphene, reduced graphene oxide, and carbon nanotubes, preferably citric acid.

[0009] In the present invention, the particle sizes of the chromium source, sodium source, and carbon source are 10 - 1000 μm.

[0010] In the present invention, the inert atmosphere includes any one or at least two combinations of nitrogen, argon, neon, or helium, preferably nitrogen.

[0011] In the carbon source solution of the present invention, the solute is the carbon source, that is, any one or at least two combinations of polyvinylpyrrolidone, ascorbic acid, glucose, sucrose, citric acid, polyaniline, graphene, reduced graphene oxide, and carbon nanotubes, preferably citric acid; the solvent is any one or at least two combinations of methanol, ethanol, and propanol, preferably ethanol.

[0012] The present invention also provides an application of the carbon-coated sodium chromite material prepared by the preparation method of the carbon-coated sodium chromite material.

[0013] In the present invention, the carbon-coated sodium chromite material is used as a positive electrode material for sodium-ion batteries to test the charge and discharge performance. At a 1C charge and discharge rate, the discharge specific capacity is 130 mAh / g - 132 mAh / g. After 300 cycles, the capacity retention rate is ≥91%.

[0014] Compared with the prior art, the present invention has the following advantages: (1) The present invention uses a chromium source, a carbon source, and a sodium source to prepare a carbon-coated sodium chromite material for the positive electrode of a sodium-ion battery. During the whole process of the preparation method, there is no emission of toxic gases, liquids, or solids, which is green and environmentally friendly.

[0015] (2) The raw materials involved in the present invention have low costs and the preparation process is simple, which is suitable for large-scale industrial production.

[0016] (3) The carbon-coated sodium chromite material for the positive electrode of the sodium-ion battery prepared by the present invention shows far higher performance than other positive electrode materials for sodium-ion batteries (sodium nickel iron manganate, Prussian blue-based materials), and shows great potential in the application fields of energy storage devices and low-speed electric vehicles.

[0017] (4) By means of distributed carbon coating, an inner carbon coating is formed through the first calcination, and an outer dense carbon layer is generated through solution impregnation during the second calcination. Comprehensive and complete carbon coating of the sodium chromite material is achieved, which not only effectively prevents the occurrence of side reactions but also has good uniformity of the formed carbon coating layer. The obtained sodium-ion battery has a high specific capacity, good rate performance, and excellent cycle stability performance. Description of the Drawings

[0018] Figure 1 SEM diagram of the carbon-coated sodium chromite material obtained in Example 1 of the present invention; Figure 2 XRD diagram of the carbon-coated sodium chromite material obtained in Example 1 of the present invention; Figure 3 Voltage-specific capacity curve of the sodium-ion battery assembled with the carbon-coated sodium chromite obtained in Example 1 of the present invention as the positive electrode material at a charge-discharge rate of 1C; Figure 4 Specific capacity-cycle number curve of the sodium-ion battery assembled with the carbon-coated sodium chromite obtained in Example 1 of the present invention as the positive electrode material at a charge-discharge rate of 1C. Detailed Embodiments

[0019] In order to better explain the present invention and facilitate understanding of its technical solutions, the present invention will be further elaborated below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments of the present invention are only for illustrative purposes and do not limit the present invention. Embodiment

[0020] A preparation method of a carbon-coated sodium chromite material in this embodiment includes the following steps: (1) Weigh 1.43 g of chromium(III) oxide powder with a mesh size of 100, 1.0 g of sodium carbonate powder with a mesh size of 100, and 0.243 g of citric acid powder with a mesh size of 100. Heat and dry them at 110 °C for 2 h respectively to reduce the moisture content in the three to less than 800 ppm. First, mix the chromium(III) oxide powder and sodium carbonate powder evenly and then mix them with the citric acid powder evenly to obtain a mixed material; (2) Place the mixed material and the milling balls in a ball mill under a pressure of 20 MPa and mill for 4 h. The particle size of the milled mixed material is 300 mesh; under a pressure of 2000 MPa, press the mixed material into tablets; (3) Place the tablets in a tubular furnace with a heating rate of 3 °C / min, a temperature of 800 °C, and a nitrogen atmosphere and calcine for 5 h to obtain a sodium chromite precursor; (4) After ball milling the sodium chromite precursor in a ball mill, place it in a saturated citric acid ethanol solution and stir evenly; (5) Bake the above solid-liquid mixture at 110 °C for 2 h; (6) Calcinate the baked product at 600 °C in a nitrogen atmosphere for 0.5 h to obtain the carbon-coated sodium chromite material.

[0021] The carbon-coated sodium chromite material prepared in this example was subjected to SEM and XRD tests respectively. See Figure 1 and Figure 2 . From Figure 1 , it can be seen that the obtained carbon-coated sodium chromite material is flaky particles. From Figure 2 , it can be seen that the obtained carbon-coated sodium chromite material has a layered oxide crystal structure.

[0022] The carbon-coated sodium chromite prepared in this example was assembled into a sodium-ion battery as the positive electrode material. The voltage-specific capacity curve at a charge-discharge rate of 1C is shown in Figure 3 , and the specific capacity-cycle number curve at a charge-discharge rate of 1C is shown in Figure 4 . It can be seen from Figure 3 that at a charge-discharge rate of 1C, the discharge specific capacity is 130 mAh / g - 132 mAh / g. It can be seen from Figure 4 that after 300 cycles, the capacity retention rate ≥ 91%. Example

[0023] A preparation method of a carbon-coated sodium chromite material in this example includes the following steps: (1) Weigh 1.43 g of chromium dioxide powder with a mesh size of 150, 1.0 g of sodium chloride powder with a mesh size of 150, and 0.34 g of polyvinylpyrrolidone powder with a mesh size of 150. Heat and dry them at 80 °C for 4 h respectively to reduce the moisture content in the three to below 800 ppm. First, mix the chromium dioxide powder and sodium chloride powder evenly and then mix them with the polyvinylpyrrolidone powder evenly to obtain a mixed material; (2) Place the mixed material and the ball milling balls in a ball mill under a pressure of 25 MPa and ball mill for 5 h. The particle size of the ball-milled mixed material is 300 mesh; under a pressure of 2500 MPa, press the mixed material into a tablet; (3) Place the tablet in a tubular furnace with a heating rate of 3 °C / min, a temperature of 900 °C, and a nitrogen atmosphere and calcine for 6 h to obtain a sodium chromite precursor; (4) Ball mill the sodium chromite precursor and then place it in a saturated polyvinylpyrrolidone solution and stir evenly; (5) Bake the above solid-liquid mixture at 80 °C for 5 h; (6) Place the baked product in a nitrogen atmosphere at 650 °C and calcine for 2.0 h to obtain carbon-coated sodium chromite. Example

[0024] A preparation method of a carbon-coated sodium chromite material according to this embodiment includes the following steps: (1) Weigh 1.49 g of chromium(II) oxide powder with a mesh size of 200, 1.0 g of sodium acetate powder with a mesh size of 150, and 0.35 g of ascorbic acid powder with a mesh size of 150. Heat and dry them at 90 °C for 3 h respectively to reduce the moisture content in the three to less than 800 ppm. First, mix the chromium(II) oxide powder and sodium acetate powder evenly, and then mix them evenly with the ascorbic acid powder to obtain a mixed material; (2) Place the mixed material and grinding balls in a ball mill under a pressure of 35 MPa and ball mill for 4 h. The particle size of the ball-milled mixed material is 300 mesh; under a pressure of 3000 MPa, press the mixed material into a tablet; (3) Place the tablet in a tubular furnace with a heating rate of 3 °C / min, a temperature of 950 °C, and a nitrogen atmosphere and calcine for 5 h to obtain a sodium chromite precursor; (4) Place the sodium chromite precursor in a ball mill, and then place it in a saturated ascorbic acid solution and stir evenly; (5) Bake the above solid-liquid mixture at 90 °C for 4 h; (6) Place the baked product in a nitrogen atmosphere at a temperature of 700 °C and calcine for 2.0 h to obtain carbon-coated sodium chromite. Example

[0025] A preparation method of a carbon-coated sodium chromite material according to this embodiment includes the following steps: (1) Weigh 1.0 g of chromium(IV) oxide powder with a mesh size of 100, 1.59 g of sodium oxalate powder with a mesh size of 100, and 0.37 g of polyaniline with a mesh size of 100. Heat and dry them at 100 °C for 3 h respectively to reduce the moisture content in the three to less than 800 ppm. First, mix the chromium(IV) oxide powder and sodium oxalate powder evenly, and then mix them evenly with the polyaniline to obtain a mixed material; (2) Place the mixed material and grinding balls in a ball mill under a pressure of 30 MPa and ball mill for 8 h. The particle size of the ball-milled mixed material is 300 mesh; under a pressure of 3500 MPa, press the mixed material into a tablet; (3) Place the tablet in a tubular furnace with a heating rate of 3 °C / min, a temperature of 850 °C, and a nitrogen atmosphere and calcine for 8 h to obtain a sodium chromite precursor; (4) Place the sodium chromite precursor in a ball mill, and then place it in a saturated polyaniline solution and stir evenly; (5) Bake the above solid-liquid mixture at 100 °C for 4 h; (6) Place the baked product in a nitrogen atmosphere at a temperature of 650 °C and calcine for 1.5 h to obtain carbon-coated sodium chromite.

[0026] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of carbon-coated sodium chromite material, characterized in that, It includes the following steps: (1) Weigh the chromium source, sodium source and carbon source proportionally and place them at a temperature of 80 - 110 °C for heating and drying for 2 - 4 h. After mixing evenly, a mixed powder is obtained; the molar ratio of the chromium source to the sodium source is 1:(1 - 1.03), and the addition amount of the carbon source is 5 - 12% of the total mass of the sodium source and the chromium source; (2) Place the mixed powder in a ball mill with a pressure of 20 - 35 MPa for ball milling for 4 - 10 h, and then press it into a mixed powder tablet at a pressure of 2000 - 3500 Mpa; (3) Place the mixed powder tablet in an inert atmosphere for calcination for 5 - 12 h, the calcination temperature is 800 - 950 °C, and the heating rate is 3 - 10 °C / min to obtain a sodium chromite precursor; (4) Place the obtained sodium chromite precursor in a ball mill for ball milling, and then place it in a saturated carbon source solution for stirring. The addition amount of the carbon source in the saturated carbon source solution is 10% - 25% of the mass of the sodium chromite precursor; (5) Place the stirred material in a high temperature of 80 - 110 °C for baking for 2 - 5 h; (6) Place the baked product in an inert atmosphere for calcination for 0.5 - 2.5 h, the calcination temperature is 600 - 700 °C, and the carbon-coated sodium chromite material is obtained.

2. The preparation method of a carbon-coated sodium chromite material according to claim 1, wherein: In the step (1), the chromium source is any one or at least two combinations of chromium(II) oxide, chromium(III) oxide, chromium(IV) oxide, preferably chromium(III) oxide; the sodium source is any one or at least two combinations of sodium sulfate, sodium carbonate, sodium chloride, sodium hydroxide, sodium acetate, sodium oxalate, sodium nitrate, preferably sodium carbonate; the carbon source is any one or at least two combinations of polyvinylpyrrolidone, ascorbic acid, glucose, sucrose, citric acid, polyaniline, graphene, reduced graphene oxide, carbon nanotubes, preferably citric acid.

3. The preparation method of a carbon-coated sodium chromite material according to claim 1, characterized in that: The particle sizes of the chromium source, sodium source and carbon source are 10 - 1000 μm.

4. The preparation method of a carbon-coated sodium chromite material according to claim 1, characterized in that: The inert atmosphere includes any one or at least two combinations of nitrogen, argon, neon or helium, preferably nitrogen.

5. The preparation method of a carbon-coated sodium chromite material according to claim 1, characterized in that: The solute in the carbon source solution is the carbon source, that is, any one or at least two combinations of polyvinylpyrrolidone, ascorbic acid, glucose, sucrose, citric acid, polyaniline, graphene, reduced graphene oxide, carbon nanotubes, preferably citric acid; the solvent is any one or at least two combinations of methanol, ethanol, propanol, preferably ethanol.

6. Application of the carbon-coated sodium chromite material prepared by the preparation method of the carbon-coated sodium chromite material according to any one of claims 1 - 5.

7. Use of the carbon-coated sodium chromite material prepared by the preparation method of the carbon-coated sodium chromite material according to claim 6, characterized in that: The carbon-coated sodium chromite material is used as a positive electrode material for a sodium-ion battery to test the charge and discharge performance. At a 1C charge and discharge rate, the discharge specific capacity is 130 mah / g - 132 mah / g. After 300 cycles, the capacity retention rate ≥ 91%.

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