Method for synthesizing iron-manganese-based layered oxide positive electrode material of sodium-ion battery by oxalic acid dispersion solid-phase method

Abstract

The invention discloses a method for synthesizing a sodium-ion battery iron-manganese-based layered oxide positive electrode material by an oxalic acid dispersion solid-phase method, and belongs to the field of sodium-ion battery iron-manganese-based positive electrode materials. In order to solve the problems that a P2 type manganese-based layered oxide positive electrode material is low in capacity, poor in cycle performance and rate capability and the like, in the method, oxalic acid and deionized water are firstly added for ball milling, then high-temperature calcination is performed in a tubular furnace, a target product is finally obtained, the first discharge capacity of the material reaches 200-215mAh / g under the rate of 0.2 C, and the second discharge capacity of the material reaches 200-215mAh / g under the rate of 0.2 C; according to the present invention, the first coulombic efficiency is more than 100%, the capacity retention rate after 50 cycles is 51%, the positive electrode material synthesized by using the method has characteristics of high first cycle discharge specific capacity, good rate capability and stability, the synthesis method and the process are simple, the price is low, the method can be used for industrial production, and the new solution is provided for the development of the sodium ion battery layered oxide positive electrode material.

Description

Technical Field

[0001] The present invention belongs to the field of iron-manganese-based positive electrode materials for sodium ion batteries, and provides a preparation method capable of commercializing layered oxide Fe-Mn positive electrode materials, and having a simple process and being green and environmentally friendly. Background Art

[0002] With the rapid growth in demand for renewable energy storage and electric vehicles, traditional lithium-ion batteries face some challenges, such as the limited and uneven distribution of lithium resources. Sodium is abundant in the earth's crust and its resources are almost unlimited, making sodium-ion batteries an attractive alternative energy storage technology. Sodium-ion batteries have similar working principles to lithium-ion batteries, both of which are based on the insertion and deintercalation of ions between the positive and negative electrodes to achieve charging and discharging. However, since the radius of sodium ions (0.102nm) is larger than that of lithium ions (0.076nm), this requires the development of new electrode materials suitable for the insertion and deintercalation of sodium ions.

[0003] In the research and development of sodium-ion batteries, the exploration of positive electrode materials is a key link. Layered oxide structure is a widely studied positive electrode material system. Iron-manganese-based layered oxides are developed on the basis of multiple element combinations and structural optimization. Early research focused on imitating the structure of lithium-ion battery positive electrode materials, but due to the different characteristics of sodium ions, layered oxides suitable for sodium ion embedding were gradually developed. Through continuous improvement of the synthesis methods of iron-manganese-based materials (such as high-temperature solid-phase method, sol-gel method, etc.), as well as fine regulation of material composition (such as changing the iron-manganese ratio, doping with other elements) and microstructure (such as controlling grain size, interlayer spacing, etc.), the electrochemical properties of the materials are improved, so that they can better meet the requirements of sodium-ion batteries in terms of energy density, cycle life and rate performance. Compared with some lithium-ion battery positive electrode materials, sodium-ion battery layered oxide iron-manganese-based positive electrode materials have better thermal stability. Under extreme conditions such as high temperature, its structural changes are relatively small, reducing safety risks such as battery thermal runaway, which is very important for the safe operation of large-scale energy storage systems.

[0004] Iron and manganese are both abundant elements on earth, and their raw material costs are lower than some rare metals in lithium-ion battery cathode materials. This resource advantage makes sodium-ion battery layered oxide iron-manganese-based cathode materials more economically feasible in large-scale energy storage applications. Iron-manganese-based cathode materials have high theoretical specific capacity. Various oxidation states of iron and manganese (such as Fe 2+ / Fe 3+ , Mn 3+ / Mn 4+) can provide more electron transfer, which helps to improve the energy density of the battery. At the same time, this material can maintain good cycle stability to a certain extent. Through reasonable doping and surface modification, it can suppress problems such as structural collapse and phase change of the material during the charge and discharge process. Summary of the invention

[0005] The purpose of the present invention is to design a synthesis method for synthesizing layered oxide Fe-Mn-based positive electrode materials for sodium ion batteries. By regulating the microstructure of the synthesis method, the discharge specific capacity and cycle stability of the synthesized layered oxide Fe-Mn-based positive electrode materials are improved. In order to achieve the commercial use requirements of layered oxide Fe-Mn-based positive electrode materials for sodium ion batteries, a preparation method suitable for industrialization and green environmental protection is provided.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for synthesizing an iron-manganese-based layered oxide positive electrode material for a sodium ion battery by an oxalic acid dispersion solid phase method comprises the following steps:

[0008] Step 1. According to the chemical formula Na 0.8 Li 0.1 Fe 0.2 Mn 0.7 Atomic ratio of O2 Weigh four metal oxides Na2CO3, Li2CO3, Fe2O3, and MnO2 in sequence and put them into a mortar, grind them manually for about 30 min to evenly mix the four metal oxides;

[0009] Step 2. Weigh a certain amount of oxalic acid, which is 1.5 times the molar amount of the TM metal layer (Li+Fe+Mn), and add it to the mixed sample obtained in step 1, and mix it evenly again.

[0010] Step 3. Put the sample obtained after uniform mixing in step 2 into a ball mill, then add a certain amount of deionized water into the ball mill, the mass of the deionized water is 1 / 6 of the mass of oxalic acid, and then ball mill for 3 hours at a speed of 450 rpm in the ball mill;

[0011] Step 4. Place the sample obtained in step 3 in a forced air oven and dry at 80°C for 3 h;

[0012] Step 5. Place the sample obtained in step 4 in a tubular furnace and calcine it at 300°C for 3 hours, then heat it to 750°C and calcine it for 12 hours to obtain a reddish-brown powdery Fe-Mn-based oxide positive electrode material.

[0013] The present invention has the following advantages:

[0014] 1. This method involves simple manual grinding and mixing and ball mill mixing during operation, and then high-temperature calcination to obtain the target product. The synthesis process of this method is relatively simple and the operation is easy to control.

[0015] 2. The synthesis process of this method does not contain other toxic and harmful reagents, is non-hazardous, and is safer and more environmentally friendly.

[0016] 3. The raw materials used in this experiment are abundant in reserves, low in price and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Process flow chart for preparing Fe-Mn based layered oxide positive electrode materials for sodium ion batteries.

[0018] Figure 2 XRD pattern of Fe-Mn based layered oxide positive electrode material for preparation of sodium ion battery.

[0019] Figure 3 SEM image of Fe-Mn based layered oxide cathode material for sodium ion batteries.

[0020] Figure 4 This is the first charge and discharge curve of the Fe-Mn-based positive electrode material based on layered oxide for sodium ion batteries at a rate of 0.2C.

[0021] Figure 5 Cycling performance diagram of Fe-Mn based layered oxide cathode material for sodium ion batteries at 0.2C rate. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1

[0024] According to the designed Na 0.8 Li 0.1 Fe 0.2 Mn 0.7The atomic ratio of O2 is: weigh Na2CO3, Li2CO3, Fe2O3, and MnO2, four metal oxides, and put them into a mortar in turn. Grind them manually and evenly mix the four metal oxides. Weigh a certain amount of oxalic acid (18.915 g), and the amount of oxalic acid is 1.5 times the molar amount of TM metal layer (Li+Fe+Mn). Put it into a mortar and mix and grind it evenly with the other four metal oxides. Put the ground sample into a ball mill, add a certain amount of small balls, the ratio of the mass of the small balls to the mass of the ground sample is 3:2, then add deionized water, the mass of the deionized water is 1 / 6 of the mass of oxalic acid, put the ball mill into a ball mill, set the ball mill parameters to 450rpm, 3h. The ball-milled material was taken out, placed in a forced air drying oven, and dried at 80°C for 3 h. 1.5 g of the dried material was first calcined at 300°C for 3 h in a tubular furnace under air atmosphere, then heated to 750°C and calcined for 12 h. The temperature was cooled down to room temperature along with the furnace to obtain a powdered sample of Fe-Mn based positive electrode material.

[0025] The above Fe-Mn positive electrode material was subjected to XRD phase analysis. Figure 2 As shown, it can be seen that the diffraction peak of the sample corresponds to the characteristic diffraction peak of PDF#27-0751, and the prepared sample belongs to the P63 / mmc space group. Figure 3 The SEM image of the sample of Example 1 shows that the synthesized material has an irregular layered structure. The material was used as the positive electrode active material, dissolved in NMP (N-methylpyrrolidone) with a conductive agent (acetylene black) and a binder (PVDF) to prepare a positive electrode sheet, with a mass ratio of positive electrode active material: conductive agent: binder = 80:10:10; the sodium sheet was used as the negative electrode, and assembled into a 2032 button battery for constant current charge and discharge test, with a test voltage of 1.5-4.5V and a current of 24m A / g. The prepared iron-manganese-based positive electrode material has an initial discharge specific capacity of 210m Ah / g, and has good cycle stability after 50 cycles (such as Figure 4 , Figure 5 shown).

[0026] Matters not covered by the present invention are known technologies.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for synthesizing an iron-manganese-based layered oxide positive electrode material for a sodium ion battery by an oxalic acid dispersed solid phase method, characterized in that: The following steps are involved: Step 1. According to the chemical formula Na 0.8 Li 0.1 Fe 0.2 Mn 0.7 O2 atomic ratio Weigh Na2CO3, Li2CO3, Fe2O3, and MnO2 four metal oxides in turn and put them into a mortar, grind and evenly mix the four metal oxides; Step 2. Add oxalic acid to the mixed sample obtained in step 1 and mix well; Step 3. Put the sample obtained in step 2 into a ball mill for ball milling; Step 4. Place the mixture obtained in step 3 in a blast oven and dry it at 80°C; Step 5. The sample obtained in step 4 is placed in a tube furnace and calcined at 750 degrees for 12 hours to obtain a reddish brown powdery Fe-Mn based oxide positive electrode material; In step 2, the molar ratio of TM metal layer (Li+Fe+Mn) to oxalic acid is 1:1.5; In step 3, deionized water is added, the mass of the deionized water is 1 / 6 of the mass of the oxalic acid, and then ball milling is performed, and the ball milling speed is 450 rpm for 3 hours; In step 5, the sample needs to be calcined in a tube furnace at 300°C for 3 h, and then heated to 750°C for 12 h.

2. The method for synthesizing an iron-manganese-based layered oxide positive electrode material for sodium ion batteries by an oxalic acid dispersed solid phase method according to claim 1, characterized in that: In step 4, the drying temperature is 80° C. and the drying time is 3 h.

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