Sodium ion positive electrode material and preparation method thereof

Abstract

The invention discloses a sodium ion positive electrode material. The general formula of the sodium ion positive electrode material is Na < 0.67 > MO < 2-x > Fx, a part of oxygen atoms in Na0. 67MO2 are substituted by fluorine, and a P phase / tunnel phase composite phase is provided; wherein M represents a transition metal, and x is 0.7 or less and greater than 0. The preparation method of the sodium ion positive electrode material comprises the following steps: mixing a transition metal source precursor, a sodium source and a fluorine source, and carrying out calcination reaction for 12-18 hours at 800-1000 DEG C in an oxygen-containing atmosphere to obtain the sodium ion positive electrode material. The sodium ion positive electrode material provided by the invention not only maintains high capacity of a P phase, but also has high structural stability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery positive electrode materials, and in particular to a sodium ion positive electrode material and a preparation method thereof. Background Art

[0002] Sodium-ion batteries have the advantages of wide distribution of sodium resources, high abundance and low cost, and play a vital role in power grid energy storage systems. However, there are still challenges in exploring efficient cathode materials. A variety of cathode materials have been developed, including transition metal oxides, polyanion materials and Prussian blue analogs. Among them, layered transition metal oxides have been widely studied due to their simple synthesis, diverse composition, high theoretical specific capacity and reliable electrochemical performance. 0.67 Layered oxide cathode materials represented by MnO2 have attracted much attention due to their extremely high theoretical capacity, low cost, environmental friendliness and good electrochemical reversibility. 0.67 MnO2 still faces irreversible structural changes / phase transitions, poor cycle stability, and air / water instability during cycling, such as rapid capacity decay due to transition metal layer slip and the Jahn-Taylor effect. 0.44 Tunnel-type oxide materials represented by MnO2 have unique S-shaped channels and are very stable in structure. They can even be used in aqueous electrolytes and have significant cycle stability as positive electrode materials for sodium-ion batteries. However, limited sodium storage sites result in low capacity (theoretical specific capacity is 121 mAh g -1 ), which hinders its practical application. Tunnel oxides and layered oxides have different crystal structures, which determine their different electrochemical properties. Therefore, it is of great significance to construct a cathode material that can have both the high specific capacity of the layered structure and the high stability of the tunnel structure. Summary of the invention

[0003] In order to solve the above problem, 0.67 The capacity of battery positive electrode materials represented by MnO2 decays rapidly, and Na 0.44 In order to solve the problem that the overall capacity of battery positive electrode materials represented by MnO2 is relatively low, the present invention provides a sodium ion positive electrode material and a preparation method thereof. The sodium ion positive electrode material is modified by fluorine-doped anions to introduce a tunnel phase into the traditional P-phase battery positive electrode material, thereby constructing a positive electrode material composite of the P-phase and the tunnel phase, which not only maintains the high capacity of the P-phase, but also achieves high structural stability.

[0004] The sodium ion positive electrode material of the present invention has the general formula Na 0.67 MO 2-x F x ; It is the use of fluorine to Na0.67 It is obtained by substituting some oxygen atoms in MO2 and has a composite phase of P phase / tunnel phase; wherein M represents a transition metal and x is less than 0.7 and greater than 0.

[0005] The above-mentioned M is selected from at least one of Ni, Fe, Cu, Co, Cr, Zn, Ti, V, Nb and Mn.

[0006] Through fluorine doping modification, the material surface can acquire new physical, chemical and other new functions, thereby greatly improving the material's dispersibility and compatibility with other substances.

[0007] The present invention also provides a method for preparing the above-mentioned sodium ion positive electrode material, which comprises mixing a transition metal source precursor, a sodium source, and a fluorine source, and calcining the mixture at 800° C. to 1000° C. for 12 h to 18 h in an oxygen-containing atmosphere.

[0008] The transition metal source precursor is selected from at least one of transition metal hydroxides, transition metal salts, and transition metal oxides, and the transition metal element is selected from at least one of Ni, Fe, Cu, Co, Cr, Zn, Ti, V, Nb, and Mn. The transition metal source precursor is preferably a manganese salt or a manganese oxide; when it is a manganese salt, it is selected from at least one of manganese carbonate, acetate, nitrate, chloride, sulfate, borate, or phosphate; when it is a manganese oxide, it is selected from at least one of manganese oxide, dimanganese trioxide, manganese dioxide, and trimanganese tetraoxide.

[0009] The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate and sodium hydroxide.

[0010] The fluorine source is selected from at least one of lithium fluoride, aluminum fluoride, sodium fluoride and calcium fluoride.

[0011] The molar ratio of sodium ions in the sodium source, transition metal elements in the transition metal source precursor, and fluorine ions in the fluorine source is 0.67 to 0.72:1:0.01 to 0.35.

[0012] The oxygen-containing atmosphere is an oxygen atmosphere or an air atmosphere, preferably an oxygen atmosphere. The mixing methods mainly include the following categories: mechanical mixing, solid phase reaction, hydrothermal, sol-gel, precipitation and deposition; among them, the solid phase reaction method is the simplest and most convenient for synthesis and is most suitable for commercialization, but the current solid phase reaction method is often used in combination with the sol-gel method or precipitation method for surface coating, or through secondary sintering, the entire process is still relatively cumbersome, and it is easy to have problems such as uneven and loose coating, so the mixing method is preferably mechanical mixing, especially ball milling mixing.

[0013] The present invention also provides a battery, wherein the positive electrode material in the battery comprises the above-mentioned sodium ion positive electrode material, or the sodium ion positive electrode material prepared using the above-mentioned method for preparing the sodium ion positive electrode material.

[0014] Beneficial effect: The positive electrode material for sodium ion battery of the present invention introduces a tunnel phase into the traditional P-phase battery positive electrode material by modifying the positive electrode material with fluorine doping anions, thereby constructing a composite phase of the P-phase and the tunnel phase. The positive electrode material for sodium ion battery of the present invention not only maintains the high capacity of the P-phase, but also achieves high structural stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 XRD spectra of samples prepared in Examples 1, 2, 3, 4 and Comparative Example 1 of the present invention; Figure 2 The first cycle charge and discharge curves of the samples prepared in Comparative Example 1 and Example 1 at a current density of 0.1 A / g; Figure 3 100-cycle long cycle diagram of samples prepared in Comparative Example 1 and Example 1 at a current density of 0.1 A / g; Figure 4 The SEM images of the samples obtained in Example 1 and the comparative example of the present invention are shown in FIG. DETAILED DESCRIPTION

[0016] The present invention will now be further described in detail by way of examples in conjunction with the accompanying drawings, but the present invention is not limited to the examples.

[0017] In the following examples, the transition metal source precursors are Mn2O3 as a manganese source, Na2CO3 as a sodium source, and NaF as a fluorine source; the mass of the manganese source and the sodium source is calculated according to the layered transition metal oxide Na 0.67 MnO 2-X F X The amount of fluorine source added is calculated based on the percentage of the mass of the fluorine source to the total mass of Mn2O3 and Na2CO3.

[0018] Example 1 0.5 mol of Mn2O3, 0.265 mol of Na2CO3, and 0.14 mol of NaF (molar ratio of Na:Mn:F=0.67:1:0.14) (wherein the Na source is 2% excess) were ball milled (400 r / min, 6 h), mixed evenly, and then heated at 900°C for 15 h in an oxygen atmosphere. After cooling, 0.8 mol of composite phase fluorinated transition metal oxide powder Na was actually obtained. 0.67 MnO 1.86 F 0.14 .

[0019] Example 2 0.5 mol of Mn2O3, 0.3 mol of Na2CO3, and 0.07 mol of NaF (molar ratio of Na:Mn:F=0.67:1:0.07) (wherein the Na source is 2% excess) were ball milled (400 r / min, 6 h), mixed evenly, and then heated at 900°C for 15 h in an oxygen atmosphere. After cooling, 0.8 mol of composite phase fluorinated transition metal oxide powder Na was actually obtained. 0.67 MnO 1.93 F 0.07 .

[0020] Example 3 0.5 mol of Mn2O3, 0.195 mol of Na2CO3, and 0.28 mol of NaF (molar ratio of Na:Mn:F=0.67:1:0.28) (wherein the Na source is 2% excess) were ball milled (400 r / min, 6 h), mixed evenly, and then heated at 900°C for 15 h in an oxygen atmosphere. After cooling, 0.8 mol of composite phase fluorinated transition metal oxide powder Na was actually obtained. 0.67 MnO 1.72 F 0.28 .

[0021] Example 4 0.5 mol of Mn2O3, 0.16 mol of Na2CO3, and 0.35 mol of NaF (molar ratio of Na:Mn:F=0.67:1:0.35) (wherein the Na source is 2% excess) were ball milled (400 r / min, 6 h), mixed evenly, and then heated at 900°C for 15 h in an oxygen atmosphere. After cooling, 0.8 mol of composite phase fluorinated transition metal oxide powder Na was actually obtained. 0.67 MnO 1.65 F 0.35 .

[0022] Comparative Example 0.335 mol of Na2CO3 and 0.5 mol of Mn2O3 (molar ratio of Na:Mn=0.67:1) (wherein the Na source is 5% excess) were ball milled (400 r / min, 6 h), mixed evenly, and then heated at 900°C for 15 h in an oxygen atmosphere. After cooling, 1 mol of layered transition metal oxide powder Na was actually obtained. 0.67 MnO2. The materials obtained in Examples 1-4 and Comparative Examples were subjected to XRD testing, and the results are as follows: Figure 1 shown.

[0023] from Figure 1It can be seen that the samples of Examples 1-4 have characteristic peaks of P phase and tunnel phase, proving that the bulk phase of the positive electrode material obtained by the method of the present invention is mainly composed of P phase and tunnel phase, and as the mass of the fluorine source increases, the peak of the tunnel phase becomes stronger and stronger, and the proportion of the tunnel phase in the material increases.

[0024] The sample of the comparative example is composed of the P phase, and according to the comparison between the comparative example 1 and the examples 1-4, it can be proved that the fluorine ions successfully enter into the material. The materials obtained in Example 1 and Comparative Example 1 were subjected to SEM, and the results were as follows: Figure 4 As shown, Figure 4 a- Figure 4 c is the SEM image of the comparative example, Figure 4 d- Figure 4 i is the SEM image of Example 1.

[0025] It can be seen from the SEM image that the samples of the comparative example all have irregular plate-like morphology, while Example 1 after fluorination is a composite of P phase and tunnel phase. After the introduction of the tunnel phase, the structure of the coexistence of the two phases is more stable. At the same time, the introduction of fluoride ions shrinks the transition metal layer, widens the alkali metal layer, and improves the electrochemical performance.

[0026] It can be proved from the above that the present invention successfully synthesized the sodium-electrolyte layered transition metal oxide composite of P phase and tunnel phase through fluorination.

[0027] The prepared positive electrode material is uniformly mixed with superconducting carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP), and coated on the surface of aluminum foil, and then dried in a vacuum oven at 80°C for 10 hours to obtain a surface-coated layered transition metal oxide electrode.

[0028] The fluorinated layered transition metal oxide electrode was used as the positive electrode, the sodium metal sheet as the negative electrode, and 1.0 mol / LNaPF6 / propylene carbonate as the electrolyte. A half-cell was assembled in an argon atmosphere glove box to test the electrochemical properties of the fluorinated layered transition metal oxide electrode material, including specific capacity, cycle stability, and first coulombic efficiency. The test voltage range was 2~4V. The test results are shown in Figure 2. Figure 2 , Figure 3 shown.

[0029] Combination Figure 1 , Figure 4 It can be seen that the introduction of fluoride ions significantly improves the capacity of the material. The composite phase structure constructed by fluorination makes the material have good cycle performance. When 20 wt% sodium fluoride is added, the capacity is improved.

[0030] The present invention uses a local coordination chemical modulation strategy, Na 0.67MnO2 was used as a verification material to achieve precise regulation of the dynamic crystal structure evolution of the cathode material by fluorine substitution, which presented a new layered-tunnel composite structure and exhibited excellent sodium ion storage performance. - Coordinated O 2- The surrounding local environment promotes Na + Diffusion, smoothing the electrochemical curve. This work's exploration of the local coordination chemical modulation of composite cathode materials can provide important clues for achieving SIBs with high energy density and long cycle life. The examples after fluorination are all composites of P phase and tunnel phase. After the introduction of the tunnel phase, the structure of the coexistence of the two phases is more stable. At the same time, the introduction of fluoride ions shrinks the transition metal layer, widens the alkali metal layer, and improves the electrochemical performance.

[0031] The above-mentioned technologies not specifically mentioned are all referred to the prior art.

[0032] With the above ideal examples of the present invention as inspiration, through the above description, relevant staff can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the contents of the specification.

Claims

1. A sodium ion positive electrode material, characterized in that: The general formula is Na 0.67 MO 2-x F x ; It is the use of fluorine to Na 0.67 The composite phase of P phase / tunnel phase is obtained by replacing some oxygen atoms in MO2; Here, M represents a transition metal, and x is 0.7 or less and greater than 0.

2. The sodium ion positive electrode material according to claim 1, characterized in that The M is selected from at least one of Ni, Fe, Cu, Co, Cr, Zn, Ti, V, Nb, and Mn.

3. The method for preparing the sodium ion positive electrode material according to claim 1 or 2, characterized in that: The transition metal source precursor, the sodium source and the fluorine source are mixed, and calcined at 800° C. to 1000° C. for 12 h to 18 h in an oxygen-containing atmosphere to obtain the product.

4. The method for preparing the sodium ion positive electrode material according to claim 3, characterized in that: The transition metal source precursor is selected from at least one of transition metal hydroxides, transition metal salts or transition metal oxides, and the transition metal element is selected from at least one of Ni, Fe, Cu, Co, Cr, Zn, Ti, V, Nb and Mn.

5. The method for preparing the sodium ion positive electrode material according to claim 3, characterized in that: The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium fluoride and sodium hydroxide.

6. The method for preparing the sodium ion positive electrode material according to claim 3, characterized in that: The fluorine source is selected from at least one of lithium fluoride, aluminum fluoride, sodium fluoride and calcium fluoride.

7. The method for preparing a sodium ion positive electrode material according to claim 3, characterized in that: The molar ratio of sodium ions in the sodium source, transition metal elements in the transition metal source precursor, and fluorine ions in the fluorine source is 0.67 to 0.72:1:0.01 to 0.

35.

8. The method for preparing a sodium ion positive electrode material according to claim 3, characterized in that: The oxygen-containing atmosphere is an oxygen atmosphere or an air atmosphere, and the mixing method is ball milling mixing.

9. A battery, characterized in that: The positive electrode material in the battery includes the sodium ion positive electrode material according to claim 1 or 2, or the sodium ion positive electrode material prepared by the method for preparing the sodium ion positive electrode material according to any one of claims 3-8.

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