CN104701531B - In-situ carbon-coated hexagonal K0.7[Fe0.5Mn0.5]O2 nanomaterial and its preparation method and application - Google Patents

Abstract

The invention relates to an in-situ carbon-coating hexagon K0.7[Fe0.5Mn0.5]O2 nano material as well as a preparation method and an application thereof. The material can serve as a sodium-ion battery positive active material which is formed by coating K0.7[Fe0.5Mn0.5]O2 hexagonal nano crystals with graphitized carbon layers; the diameter of the hexagonal nano crystals is 100-350nm; the thickness of the graphitized carbon layers is 6-10nm. The in-situ carbon-coating hexagon K0.7[Fe0.5Mn0.5]O2 nano material has the beneficial effects that the nano material with relatively uniform shape is finally prepared by combining methods of drying solutions and calcinating atmosphere; the material serves as a sodium-ion battery positive material active substance and shows relatively high specific discharge capacity and excellent cycling stability; on the other hand, the process is simple; the in-situ carbon-coating hexagon K0.7[Fe0.5Mn0.5]O2 nano material is prepared by simply drying and calcinating the solution; the energy consumption is relatively low.

Description

In-situ carbon-coated hexagonal K0.7[Fe0.5Mn0.5]O2 nanomaterial and its preparation method and application

technical field

The invention belongs to the technical field of nanomaterials and electrochemistry, and in particular relates to an in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanometer material and a preparation method thereof. The material can be used as a positive electrode active material of a sodium ion battery.

Background technique

With the development of science and technology and the rapid growth of population, the consumption of energy in the new century is also increasing, the depletion of non-renewable resources such as oil, coal and natural gas, it is urgent to find clean energy to make up for the gap in energy demand, and at the same time require clean Continuity and sustainability of energy to meet usage requirements. In the existing mainstream energy system, petroleum and coal are non-renewable energy sources, and they will produce a large amount of harmful substances such as CO ₂ and SO ₂ in the process of use and consumption, which will bring serious damage to the environment on which human beings depend. destroy. This prompts people to pay more attention to the establishment of a new and efficient energy supply system, which should meet the requirements of the environment while ensuring sustainable economic growth. Among them, the development of new energy and renewable clean energy is one of the most effective ways to solve these problems, and new energy materials are the basis and core to realize the development and utilization of new energy and support its development. In many new energy systems, such as wind energy, solar energy, biomass energy, etc., they all have discontinuous characteristics. If they are to be effectively integrated into the grid system, energy conversion and storage devices are indispensable.

Sodium ion battery is a new type of energy storage device developed in the past ten years. Compared with lithium ion battery, it has the characteristics of abundant earth resource storage and low cost. It is considered to be the main force of the next generation of large-scale energy storage device. At present, layered transition metal oxides, layered structure elements, and phosphate systems are mainly used as electrode materials. With the deepening of research, it is gradually found that layered transition metal oxide electrode materials are not only low in cost, but also have high specific capacity, which is a kind of better positive electrode material for sodium ion batteries. However, layered transition metal oxides are difficult to obtain due to the pure phase, and their shape is difficult to nanoflowers and poor conductivity, so that it is difficult to fully exert their high capacity, so we need to use in-situ coating of conductive substances , while improving its electronic conductivity, inhibiting the secondary agglomeration of its grains and improving its electrochemical performance. So far, in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials have not been reported.

Contents of the invention

The object of the present invention is to provide an in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial and a preparation method thereof, the preparation process is simple, the energy consumption is low, the yield is high, and the obtained In situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials have good electrochemical performance as cathode materials for sodium-ion batteries.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is: the preparation method of in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials, comprising the following steps:

1) Add potassium source, iron source, manganese source and carbon source together into deionized water, and stir at a certain temperature until the solution is light yellow and transparent;

2) Move the solution obtained in step 1) to a water bath and stir to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and evaporate to dryness at a constant temperature;

4) The solid obtained in step 3) is then quickly transferred to high temperature and baked to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining under air conditions;

6) The product obtained in step 5) is then transferred to argon for calcination to obtain an in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial.

According to the above scheme, the potassium source in step 1) is any one of KNO ₃ , K ₂ CO ₃ , K ₂ SO ₄ and KCl or a mixture thereof; the iron source is Fe(NO ₃ ) ₃ . Any one of 9H ₂ O and Fe ₂ (SO ₄ ) ₃ .7H ₂ O or their mixture; the manganese source is any one of Mn(CH ₃ COO) ₂ and MnCO ₃ or their mixture ; The carbon source is any one of oxalic acid and citric acid or their mixture.

According to the above scheme, the potassium source, iron source, and manganese source are prepared according to the K:Fe:Mn element molar ratio of 7:5:5; step 1) the K ⁺ ion concentration range in the solution is 7/20- 7/10mol/L.

According to the above scheme, the water bath temperature in step 2) is 50-80°C; the constant temperature in step 3) is 60-90°C; the baking temperature in step 4) is 120-200°C.

According to the above scheme, the stirring time described in step 1) is 2-6 hours; the stirring time described in step 2) is 6-12 hours; the drying time described in step 3) is 8-12 hours; the described drying time of step 4) The baking time is 8-12h;;.

According to the above scheme, the calcination temperature in step 5) is 200-500°C and the time is 2-4 hours; the calcination temperature in step 6) is 600-1000°C and the time is 8-12 hours.

The in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained by any of the above preparation methods is formed by coating K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ hexagonal nanocrystals with a graphitized carbon layer, The diameter of the hexagonal nanocrystal is 100-350nm, and the thickness of the graphitized carbon layer is 6-10nm.

The application of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanometer material as a positive electrode active material for a sodium ion battery.

The present invention combines the method of solution drying and atmosphere calcination, uses organic acid as the carbon source, and then sinters and carbonizes the in-situ coating, and finally obtains the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanometer material . The results show that the hexagonal material prepared by this method has uniform morphology, and the graphitized carbon layer is evenly coated on the surface. The hexagonal structure can effectively shorten the diffusion distance of sodium ions in the electrolyte and provide continuous ion transfer channels. The graphitized carbon layer can greatly improve the conductivity of the material, and can act as a buffer, which can provide the space required for the volume expansion and contraction of the active material during the intercalation and extraction of sodium ions, and prevent the gap between the hexagonal grains. Self-agglomeration occurs, and the electrolyte can penetrate through the carbon layer to the surface of the hexagonal nanocrystals, which can also reduce the dissolution of active substances. Therefore, the preparation process of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial provided by the present invention is simple and efficient, avoiding the use of harsh experimental conditions such as hydrothermal, and reducing its synthesis cost. , which greatly improves the electrochemical performance of sodium-ion batteries, and at the same time improves its cycle stability and rate performance, and solves the shortcomings of layered transition metal oxide system cathode materials such as poor conductivity and easy agglomeration, so that its electrochemical performance is very good It has great development potential in the field of sodium ion battery application.

The beneficial effects of the present invention are: the present invention combines the method of solution drying and atmosphere calcination, uses organic acid as carbon source, and then sinters and carbonizes in-situ coating to inhibit the growth and agglomeration of crystal grains, and finally obtains a more uniform morphology In situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials. As an active material for the positive electrode material of a sodium ion battery, it exhibits a high discharge specific capacity and good cycle stability; secondly, the process of the present invention is simple, and after simple solution drying and calcination, the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanometer material with low energy consumption. The mass of the obtained graphitized carbon in the coaxial structure accounts for 5.0-9.0% of the total mass of the raw materials, which is beneficial to market promotion.

As a cathode material for sodium-ion batteries, at a current density of 100mA/g, its discharge specific capacity is 169.4mAh/g, and at a high current density of 1000mA/g, after 800 cycles, the capacity retention rate is as high as 78.2%. This result indicates that the in situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials have excellent sodium storage properties and are potential applications for sodium-ion batteries.

Description of drawings

Figure 1 is the XRD pattern of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Figure 2 is the Raman spectrum of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

3 is a TG diagram of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Figure 4 is the FT-IR image of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

5 is an SEM image of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Fig. 6 is an element distribution diagram of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

7 is a TEM image of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Figure 8 is the HRTEM image of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Fig. 9 is a rate performance diagram of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

10 is a cyclic voltammetry curve of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Fig. 11 is a low-rate cycle performance diagram of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention;

Fig. 12 is a high-rate cycle performance graph of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial in Example 1 of the present invention.

detailed description

In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

Example 1:

In-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ] O ₂ nanometer preparation method, which comprises the following steps:

1) Add 7.0mmol KNO ₃ , 5.0mmol Fe(NO ₃ ) ₃ .9H ₂ O, 5.0mmol Mn(CH ₃ COO) ₂ and 6.0g oxalic acid into 20mL deionized water, stir at 25°C until solution Light yellow transparent;

2) Move the solution obtained in step 1) to an 80° C. water bath and stir for 4 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry at a constant temperature of 80°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 180°C and baked for 12 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining at 300°C for 3 hours in air;

6) Step 5) was transferred to 600, 800 and 1000° C. for calcination under argon gas conditions for 8 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon _- coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O nanomaterial invented in this experiment as an example, it was determined by an X-ray diffractometer, as shown in Figure 1, and the X-ray diffraction pattern (XRD) It shows that the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials calcined at different temperatures have the same peak positions, and the products have higher crystallinity. As shown in Figure 2, Raman analysis shows that the carbon in the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials calcined at different temperatures is graphitized carbon. As shown in Figure 3, thermogravimetric analysis shows that the carbon content of the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials calcined at different temperatures are 5.0%, 7.0% and 9.0%, respectively. As shown in Figure 4, the FT-IR test results show that the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at different temperatures have the same valence bond structure. As shown in Fig. 5, field emission scanning electron microscopy (FESEM) tests show that the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at 800°C have relatively uniform morphology and good dispersion. Preferably, the diameter of the hexagons is about 100-350 nm. However, the morphology of K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at 600°C is relatively chaotic, and the grains have not grown completely. The K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at Severe agglomeration occurred among the polygonal particles. As shown in FIG. 6 , K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at different temperatures are uniformly distributed among three elements K, Fe and Mn. As shown in Figure 7, transmission electron microscopy (TEM) shows more clearly the specific structure of in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials, which consist of graphitized carbon layers covering hexagonal It is made of K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanocrystal grains, and the thickness of the coated carbon layer is about 5-8nm. As shown in Figure 8, obvious lattice fringes can be found under a high-magnification transmission electron microscope (HRTEM), and the inner hexagonal nanocrystals are single crystals. As shown in Table 1, the inductively coupled plasma test results show that the element ratios of K, Fe and Mn in the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at different calcination temperatures are very high. Closer to 7:5:5.

The in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial is used as the positive electrode active material of the sodium ion battery, and the remaining steps of the sodium ion battery assembly method are the same as the usual preparation method. The sodium-ion battery was assembled as follows, using in-situ carbon _- coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O nanomaterials as the active material, acetylene black as the conductive agent, polytetrafluoroethylene as the binder, and the active material The mass ratio of acetylene black and polyvinylidene fluoride is 70:20:10; after they are fully mixed in proportion, add a small amount of isopropanol, grind evenly, and press an electrode sheet about 0.5mm thick on the roller machine; press well The positive electrode sheet was dried in an oven at 80° C. for 24 hours before use. The concentration of 1mol/cm ³ NaClO ₄ solution is used as the electrolyte, the solvent is ethylene carbonate and dimethyl carbonate mixed with a mass ratio of 1:1, and the metal sodium sheet is used as the negative electrode, and the battery is charged between 1.5-4.0V Chemical performance test.

As shown in Figure 9, the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at 800 °C have excellent rate performance, and at a current density of 100 mA/g, the initial Capacity is higher than 600°C and 1000°C products. After continuous magnification test, its magnification recovery rate is also the highest.

As shown in Figure 10, the CV curves of in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials have no obvious redox peaks during charge and discharge.

As shown in Fig. 11, the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials were charged and discharged at 800°C with the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials as an example, the constant current charge and discharge test results at 100mA/g show that the first discharge specific capacity can reach 169.4mAh/g, and the capacity retention rate after 200 cycles can reach 75.1% . Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained at 600°C as an example, the constant current charge and discharge test results at 100mA/g show that its first discharge specific capacity It was 140.7mAh/g, and the capacity retention reached 66.8% after 100 cycles. Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained at 1000°C as an example, the constant current charge and discharge test results at 100mA/g show that its first discharge specific capacity It was 156.1mAh/g, and the capacity retention reached 63.9% after 100 cycles. Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained at 800°C as an example, the constant current charge and discharge test results at 200mA/g show that the initial capacity is 137.8 mAh/g, the capacity retention rate reaches 86.1% after 300 cycles. Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained at 800°C as an example, the constant current charge and discharge test results at 500mA/g show that after 250 cycles The capacity has almost no attenuation, and taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained at 600°C as an example, the constant current charge and discharge test results at 500mA/g show that , the capacity retention rate after 100 cycles is only 14.9%.

As shown in Figure 12, the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained at 800°C were subjected to 800 cycles at a higher current density of 1000mA/g , and their capacity retention rates are as high as 78.2%.

Table 1 ICP test results of in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials obtained in Example 1 at different temperatures

Example 2:

1) Add 3.5mmol K ₂ CO ₃ , 2.5mmol Fe ₂ (SO ₄ ) ₃ .9H ₂ O, 2.5mmol Mn ₂ CO ₃ and 2.0g citric acid into 20mL deionized water and stir at 25°C until The solution is light yellow and transparent;

2) Move the solution obtained in step 1) to a 60° C. water bath and stir for 6 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry it at a constant temperature of 60°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 120°C and baked for 10 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining at 400°C for 3 hours in air;

6) Step 5) was moved to 600° C. for calcination under argon for 12 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained in this example as an example, the constant current charge and discharge test results at 100mA/g show that its first discharge specific capacity can reach 160.8mA/g, the capacity retention rate reaches 88.2% after 100 cycles.

Example 3:

1) 3.5mmol KNO ₃ , 1.75mmol K ₂ SO ₄ , 2.5mmol Fe(NO ₃ ) ₃ .9H ₂ O, 1.25mmol Fe ₂ (SO ₄ ) ₃ .7H ₂ O, 2.5mmol Mn(CH ₃ COO) ₂ , 1.25mmol Mn ₂ CO ₃ , 2.0g oxalic acid and 2.0g citric acid were added to 40mL deionized water, and stirred at 25°C until the solution was light yellow and transparent;

2) Move the solution obtained in step 1) to a water bath at 50° C. and stir for 6 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry it at a constant temperature of 90°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 200°C and baked for 10 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4). Then calcined at 500°C for 2 hours in air;

6) Step 5) was moved to 1000° C. for calcination under argon gas for 10 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained in this example as an example, the constant current charge and discharge test results at 200mA/g show that its first discharge specific capacity can reach 137.8mAh/g, the capacity retention rate reaches 86.1% after 300 cycles.

Example 4:

1) Add 3.5mmol K ₂ SO ₄ , 2.5mmol Fe ₂ (SO ₄ ) ₃ .7H ₂ O, 2.5mmol Mn ₂ CO ₃ and 4.0g citric acid into 30mL deionized water, and stir at 25°C until The solution is light yellow and transparent;

2) Move the solution obtained in step 1) to an 80° C. water bath and stir for 6 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry it at a constant temperature of 75°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 150°C and baked for 9 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining at 400°C for 2.5 hours in air;

6) Step 5) was moved to 800° C. for calcination under argon for 9 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained in this example as an example, the constant current charge and discharge test results at 500mA/g show that its first discharge specific capacity can reach 114.9mAh/g, the capacity retention rate reaches 92.3% after 200 cycles.

Example 5:

1) Add 14.0mmol KNO ₃ , 10.0mmol Fe(NO ₃ ) ₃ .9H ₂ O, 10.0mmol Mn(CH ₃ COO) ₂ and 5.0g citric acid into 40mL deionized water and stir at 25°C until The solution is light yellow and transparent;

2) Move the solution obtained in step 1) to a water bath at 50° C. and stir for 6 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry at a constant temperature of 80°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 160°C and baked for 12 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining at 350°C for 3.5 hours under air condition.

6) Step 5) was moved to 700° C. for calcination under argon for 12 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained in this example as an example, the constant current charge and discharge test results at 100mA/g show that its first discharge specific capacity can reach 170.5mAh/g, the capacity retention rate reaches 81.2% after 100 cycles.

Embodiment 6:

1) Add 7.0mmol KNO ₃ , 2.5mmol Fe ₂ (SO ₄ ) ₃ .7H ₂ O, 2.5mmol Mn ₂ CO ₃ , 2.0g oxalic acid and 2.0g citric acid into 20mL deionized water, at 25°C Stir until the solution is light yellow and transparent;

2) Move the solution obtained in step 1) to a 65° C. water bath and stir for 6 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry it at a constant temperature of 75°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 170°C and baked for 12 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining at 450°C for 3.5 hours in air;

6) Step 5) was moved to 900° C. for calcination under argon gas for 10.5 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained in this example as an example, the constant current charge and discharge test results at 100mA/g show that its first discharge specific capacity can reach 159.8mAh/g, the capacity retention rate reaches 80.9% after 100 cycles.

Embodiment 7:

1) Add 7.0mmol KNO ₃ , 5.0mmol Fe(NO ₃ ) ₃ .9H ₂ O, 5.0mmol Mn(CH ₃ COO) ₂ and 8.0g oxalic acid into 40mL deionized water, stir at 25°C until solution Light yellow transparent;

2) Move the solution obtained in step 1) to an 80° C. water bath and stir for 3 hours to obtain a brown-red transparent solution;

3) Transfer the solution obtained in step 2) into a petri dish, and dry it at a constant temperature of 70°C;

4) The solid obtained in step 3) is then quickly transferred to a high temperature of 200°C and baked for 8 hours to obtain a loose solid structure;

5) Grinding the product obtained in step 4), and then calcining at 300°C for 3 hours in air;

6) Step 5) was moved to 800° C. for calcination under argon for 10 hours to obtain in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterials.

Taking the in-situ carbon-coated hexagonal K _0.7 [Fe _0.5 Mn _0.5 ]O ₂ nanomaterial obtained in this example as an example, the constant current charge and discharge test results at 100mA/g show that its first discharge specific capacity can reach 167.2mAh/g, the capacity retention rate reaches 82.7% after 100 cycles.

Claims (7)

1. original position carbon coating hexagon k_0.7[fe_0.5mn_0.5]o₂The preparation method of nano material, comprises the steps:

1) potassium resource, source of iron, manganese source and carbon source are added in deionized water in the lump, stir at a certain temperature present to solution shallow Yellow transparent shape；Described carbon source is any one or their mixing in oxalic acid and citric acid；

2) by step 1) resulting solution moves on to stirred in water bath again, obtains brownish red clear solution；

3) by step 2) resulting solution is transferred in culture dish, is evaporated at a constant temperature；

4) by step 3) solid of gained and then be quickly transferred to baking under high temperature, baking temperature is 120-200 DEG C, obtains loose Solid structure；

5) by step 4) products therefrom grinding, then calcine under air conditionses；Described calcining heat is 200-500 DEG C, when Between be 2-4 hour；

6) by step 5) products therefrom moves on to and calcines under the conditions of argon, and described calcining heat is 600-1000 DEG C, and the time is 8-12 hour, obtains original position carbon coating hexagon k_0.7[fe_0.5mn_0.5]o₂Nano material.

2. original position carbon coating hexagon k according to claim 1_0.7[fe_0.5mn_0.5]o₂The preparation method of nano material, its Be characterised by: step 1) described in potassium resource be kno₃、k₂co₃、k₂so₄With any one in kcl or their mixing；Described Source of iron is fe (no₃)₃·9h₂O and fe₂(so₄)₃·7h₂Any one in o or their mixing；Described manganese source is mn (ch₃coo)₂And mnco₃In any one or their mixing.

3. original position carbon coating hexagon k according to claim 2_0.7[fe_0.5mn_0.5]o₂The preparation method of nano material, its It is characterised by: described potassium resource, source of iron, manganese source are joined for 7:5:5 according to k:fe:mn elemental mole ratios and taken；Step 1) described solution Middle k⁺Ion concentration range is 7/20-7/10mol/l.

4. original position carbon coating hexagon k according to claim 1_0.7[fe_0.5mn_0.5]o₂The preparation method of nano material, its Be characterised by: step 2) described in bath temperature be 50-80 DEG C；Step 3) described in constant temperature under temperature be 60-90 DEG C.

5. original position carbon coating hexagon k according to claim 4_0.7[fe_0.5mn_0.5]o₂The preparation method of nano material, its Be characterised by: step 1) described in mixing time be 2-6 hour；Step 2) described in mixing time 6-12 hour；Step 3) institute The time that is evaporated stated is 8-12 hour；Step 4) described in baking time be 8-12h.

6. the original position carbon coating hexagon k of the preparation method gained described in a kind of any one by claim 1-5_0.7 [fe_0.5mn_0.5]o₂Nano material, coats k by graphitization carbon-coating_0.7[fe_0.5mn_0.5]o₂The nanocrystalline formation of hexagon, described six The nanocrystalline a diameter of 100-350nm of side shape, the wherein thickness of graphitization carbon-coating are 6-10nm.

7. the original position carbon coating hexagon k described in claim 6_0.7[fe_0.5mn_0.5]o₂Nano material is as sodium-ion battery positive pole The application of active material.