Iron-based layered oxide sodium-ion battery cathode material and preparation method and application thereof

Abstract

The application discloses an iron-based layered oxide sodium-ion battery positive electrode material and a preparation method thereof. x Fe y Mn z A a B b C c O2, wherein x+y+z+a+b+c=1, y>1 / 3, a+b+c<0.1, A is at least one of Mg, Al, Sn and Ti, B is at least one of Y, Zr, Nb, Mo and Ta, C is at least one of Li, Co and Zn, and the element B is doped in the surface and the bulk phase, and the content of the element B in the surface is higher than that in the bulk phase. The product preparation method is simple in process, raw materials are easy to obtain and low in price, and is suitable for large-scale production. The application realizes simultaneous modification of the interface and the bulk phase, enhances the interface and bulk phase structure stability of the material, and through co-doping of high electron conductivity elements, improves the sodium ion diffusion kinetics of the material, and effectively improves the cycle performance and rate performance of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of chemical power sources, and particularly relates to preparation and application of a Fe-based layered oxide sodium-ion battery cathode material. BACKGROUND

[0002] With the increasingly serious energy crisis and environmental problems, developing efficient and environmentally friendly energy storage technology to realize the rational storage and use of renewable new energy has become a hot issue of widespread concern in the field of electrochemical energy storage. In the field of electrochemical energy storage, lithium-ion batteries are the most widely used secondary batteries at present. However, the lithium resource reserves are limited and unevenly distributed, and the cost of lithium-ion batteries increases year by year. This hinders lithium-ion batteries from becoming large-scale electrochemical energy storage devices. In contrast, sodium-ion batteries have gradually become a research hotspot for large-scale energy storage devices in recent years due to their abundant sodium resource reserves, wide sources and low cost.

[0003] Among the common types of sodium-ion battery cathode materials, transition metal layered oxides have good commercial application prospects due to their high specific capacity and simple synthesis method. In particular, high-iron-based layered oxide cathodes have the advantages of low cost and high energy density, and have the development potential of large-scale energy storage applications. However, due to the migration, dissolution and catalytic decomposition of Fe, the mechanical properties are poor, and the cycle stability and rate performance are poor, which cannot meet the needs of practical applications. In addition, the low service life increases the degree of electrical cost. Therefore, the structure stability of the interface and bulk phase can be improved by multi-element synergistic doping, and the sodium ion diffusion kinetics can be improved, thereby obtaining an iron-based layered oxide cathode material.

[0004] CN202110982228 discloses an iron-based layered oxide cathode active material, a preparation method and application thereof, but the method for realizing surface doping is relatively complex, and the rare earth element with a large ionic radius is not used to utilize the intrinsic tendency distribution site. After being doped into the bulk phase, the lattice will be distorted, which is not conducive to the structure stability. In contrast, the intrinsic characteristics of the doped elements tend to segregate on the surface or uniformly distribute in the bulk phase. One-step synthesis realizes the synergistic modification of the interface and bulk phase, which can more effectively improve the interface and bulk phase structure stability of the sodium-ion battery cathode material. Therefore, by multi-element synergistic doping, the interface, bulk phase stability and sodium ion diffusion kinetics are significantly improved, and the iron-based layered oxide cathode with high capacity, excellent rate and cycle stability and enhanced mechanical properties is of great significance. SUMMARY

[0005] In view of this, the application solves the above problems by enhancing mechanical properties through the method of interface body phase synergistic doping, directly doping elements during the synthesis process, the preparation method is simple, and by selecting elements that tend to surface segregation and elements that tend to uniform distribution in the bulk phase and elements with high electronic conductivity, the intrinsic characteristics of the doping elements that tend to surface segregation or uniform distribution in the bulk phase can be utilized, the interface and bulk phase are synergistically modified, the interface and bulk phase structure stability of the sodium electrode material is more effectively improved, and the electronic conductivity and sodium ion diffusion kinetics of the material are also improved, effectively improving the long cycle performance and rate performance of the material.

[0006] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions:

[0007] An iron-based layered oxide sodium ion battery cathode material, characterized in that the chemical formula of the iron-based layered oxide sodium ion battery cathode material is: NaNi x Fe y Mn z A a B b C c O2, wherein x+y+z+a+b+c=1, y>1 / 3, a+b+c<0.1, A is at least one of Mg, Al, Sn, and Ti, B is at least one of Y, Zr, Nb, Mo, and Ta, C is at least one of Li, Co, and Zn, and the B element is doped in the surface and the bulk phase, and the content in the surface is greater than that in the bulk phase.

[0008] Further, 0.5>y>1 / 3, 0.03>a>0.01, 0.03>b>0.01, and 0.02>c>0.05; in a preferred embodiment of the application, the iron-based layered oxide sodium ion battery cathode material is NaNi 0.25 Fe 0.45 Mn 0.25 Al 0.01 Y 0.01 Co 0.03 O2.

[0009] Further, the iron-based layered oxide sodium ion battery cathode material of the application has the B element doped in the surface and the bulk phase, and the content in the surface is greater than that in the bulk phase.

[0010] Further, the iron-based layered oxide sodium ion battery cathode material satisfies that in the XPS spectrum of the B element, the ratio of the surface intensity (etching depth 0 nm) to the intensity of etching 90 nm is between 1.5 and 5, and preferably between 1.82 and 2.07.

[0011] The second object of the present application is to provide a preparation method of the above-mentioned iron-based layered oxide sodium-ion battery cathode material, comprising the following steps:

[0012] (S1) adding a sodium source, a nickel source, an iron source, a manganese source, an element A source, and an element C source (i.e. all metal sources except the element B source), and uniformly mixing to obtain a mixture I;

[0013] (S2) performing first calcination on the mixture I at 400-600°C, adding an element B source after cooling, and uniformly mixing to obtain a mixture II;

[0014] (S3) performing second calcination on the mixture II at 800-1200°C, and obtaining the iron-based layered oxide sodium-ion battery cathode material after cooling.

[0015] Further, the sodium source is at least one selected from sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium hydroxide, sodium oxide, sodium peroxide, and sodium nitrite; the nickel source, the iron source, and the manganese source are selected from oxides, hydroxides, sulfates, nitrates, carbonates, acetates, and oxalates of nickel, iron, and manganese; or the nickel source, the iron source, and the manganese source are nickel-iron-manganese hydroxide precursors. The element A source and the element C source are at least one selected from oxides, hydroxides, sulfates, nitrates, carbonates, acetates, and oxalates of the doped element A and element C; and the element B source is at least one selected from oxides, hydroxides, sulfates, nitrates, carbonates, acetates, and oxalates of the element B.

[0016] Further, the sodium source, the nickel source, the iron source, the manganese source, the element A source, the element B source, and the element C source are added according to the stoichiometric ratio of the product, and the sodium source is added in excess of 5-10% in terms of molar ratio. The excess sodium source is to compensate for the loss of sodium during calcination.

[0017] Further, the uniformly mixing method includes but is not limited to ball milling, high-speed mixing, and mechanical grinding; and the ball milling is preferred, with a ball milling speed of 200-1000 rpm and a ball milling time of 1-20 h.

[0018] Further, the first calcination time is 1-10 h, preferably 3-5 h; and the second calcination time is 5-40 h, preferably 10-15 h.

[0019] The calcination atmosphere is at least one selected from oxygen, air, nitrogen, and argon.

[0020] The iron-based layered oxide sodium-ion battery positive electrode material provided by the application can effectively realize the surface and bulk phase co-modification of the doping element B, compared with the bulk phase inert element doping, the surface inert element doping modification can effectively improve the stability of the material while not losing the capacity, and is a more optimal modification selection. Since the radii of the fifth and sixth period transition metal elements are relatively large, when they are doped into the bulk phase, they will cause large lattice distortion, and therefore the configuration free energy of the doping into the bulk phase is high and unstable from the thermodynamic point of view. On the other hand, from the kinetic point of view, since the ion radius is large, the diffusion kinetics is relatively slow, and it is relatively difficult to uniformly diffuse into the bulk phase of the particles during the synthesis process, and therefore the element is enriched on the surface to play a surface modification role. The slow diffusion rate of the fifth and sixth period elements in the second step of calcination with the B source makes it difficult for them to uniformly diffuse into the interior of the large particles generated after the first calcination, and therefore the surface enrichment of the elements is realized.

[0021] The application has the following beneficial effects:

[0022] Firstly, the iron-based positive electrode material prepared by the application uses inexpensive Fe as the main active element, has the advantage of low cost, and Fe 3+ / 4+ The active redox potential and specific capacity of the active electric pair are high, and it is suitable for application in high-energy-density positive electrode materials.

[0023] Secondly, the iron-based positive electrode material prepared by the application has stable interface and bulk phase structures, improves the stability and electrochemical performance of the material structure in the cycle process, effectively improves the long cycle performance of the material, and at the same time, the material has high electronic conductivity, improves the sodium ion diffusion kinetics in the charging and discharging process, and effectively improves the rate performance of the material.

[0024] Thirdly, the iron-based positive electrode material prepared by the application has good mechanical properties, and the particles can remain intact during the cycle process, and almost no slippage or cracking phenomenon occurs.

[0025] Fourthly, the application first mixes and sinters other materials except the doping element B source, then adds the doping element B source after cooling, realizes the simultaneous doping of the element B in the bulk phase and the surface of the material through the slow diffusion speed and short sintering time, and the element B is more enriched on the surface of the material, thereby improving the electrochemical performance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The XRD spectrum of the positive electrode prepared in Example 1.

[0027] Figure 2 The SEM spectrum of the positive electrode prepared in Example 1.

[0028] Figure 3XPS spectra of Y element at different etching depths for Example 1.

[0029] Figure 4 XPS spectra of Y element at different etching depths for Comparative Example 1. DETAILED DESCRIPTION

[0030] The iron-based layered oxide sodium-ion battery cathode material described in the present application will be further described below in conjunction with specific examples and the accompanying drawings of the specification, but it should be understood that the protection scope of the present application is not limited to the following examples.

[0031] Unless otherwise defined, all the professional terms used below have the same meaning as understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific examples and are not intended to limit the protection scope of the present application.

[0032] Example 1

[0033] Preparation of NaNi 0.25 Fe 0.45 Mn 0.25 Al 0.01 Y 0.01 Co 0.03 O2 layered cathode material:

[0034] (S1) 0.105 mmol of sodium carbonate, 0.025 mmol of nickel-iron-manganese hydroxide precursor (NiFeMn(OH)2), 0.01 mmol of iron sesquioxide, 0.001 mmol of aluminum hydroxide, and 0.0015 mmol of cobalt sesquioxide were weighed and mixed, and ball-milled at a speed of 300 rpm for 1 hour;

[0035] (S2) The ground powder was placed in a magnetic boat and then placed in a muffle furnace for first calcination, with a heating rate of 5°C / min, and heated to 450°C and kept for 5 hours, and then cooled to room temperature. The product after first calcination was mixed with 0.001 mmol of yttrium acetate and ground;

[0036] (S3) The mixture was placed in a muffle furnace for second calcination, with a heating rate of 5°C / min, and heated to 1000°C and kept for 15 hours, and then cooled to room temperature to obtain the iron-based layered oxide sodium-ion battery cathode material;

[0037] (S4) The obtained cathode material, conductive additive SP, and binder PVDF were mixed in a weight ratio of 80:10:10, dissolved in solvent NMP, and stirred to obtain a uniform slurry. Then the slurry was uniformly coated on a carbon-coated aluminum foil using a 200 μm doctor blade, dried, and sliced to obtain a cathode electrode sheet.

[0038] Figure 1The XRD spectrum of the positive electrode material prepared in Example 1 can be seen that the doped modified material still maintains the structure of O3 phase, which can be classified as R3m type space group.

[0039] Figure 2 The SEM image of the positive electrode material prepared in Example 1 can be seen that the positive electrode material after multi-element synergistic doping modification is in the form of stacked sheet, and the particle size is uniform.

[0040] Figure 3 The XPS image of Y element at different etching depths in Example 1 can be seen that in the XPS spectrum of Y 3d, the ratio of surface intensity (etching depth 0 nm) to etching depth 90 nm intensity is 2.07.

[0041] Figure 4 The XPS image of Y element at different etching depths in Comparative Example 1 can be seen that in the XPS spectrum of Y 3d, the ratio of surface intensity (etching depth 0 nm) to etching depth 90 nm intensity is 1.33.

[0042] Example 2

[0043] The operation steps are the same as those in Example 1, except that 0.025 mmol of nickel-iron-manganese hydroxide precursor is replaced by 0.025 mmol of nickel oxide, 0.0125 mmol of ferric trioxide, and 0.025 mmol of manganese dioxide. 5 / 2 In the XPS spectrum of Y 3d, the ratio of surface intensity (etching depth 0 nm) to etching depth 90 nm intensity is 1.93.

[0044] Example 3

[0045] The operation steps are the same as those in Example 1, except that 0.001 mmol of aluminum hydroxide is replaced by 0.001 mmol of zinc oxide.

[0046] Example 4

[0047] The operation steps are the same as those in Example 1, except that 0.001 mmol of yttrium acetate is replaced by 0.001 mmol of zirconium oxide.

[0048] Example 5

[0049] The operation steps are the same as those in Example 1, except that 0.003 mmol of cobalt trioxide is replaced by 0.0015 mmol of lithium carbonate.

[0050] Example 6

[0051] The operation steps are the same as those in Example 1, except that 0.001 mmol of aluminum hydroxide and 0.01 mmol of ferric trioxide are replaced by 0.003 mmol of aluminum hydroxide and 0.008 mmol of ferric trioxide.

[0052] Example 7

[0053] The operation steps are the same as those in Example 1, except that the first calcination is changed to calcination at 600℃ for 3h, and the second calcination is changed to calcination at 900℃ for 15h. The Y 3d 5 / 2 In the XPS spectrum of Y, the ratio of the surface intensity (etching depth 0nm) to the etching depth 90nm is 1.82.

[0054] Comparative Example 1

[0055] Preparation of NaNi 0.25 Fe 0.49 Y 0.01 Mn 0.25 O2 layered positive electrode material:

[0056] (S1) 0.105mmol of sodium carbonate, 0.025mmol of nickel-iron-manganese hydroxide precursor (NiFeMn(OH)2), 0.012mmol of iron sesquioxide, and 0.001mmol of yttrium acetate were weighed and mixed, and the mixture was ball-milled at a speed of 300rpm for 1h to obtain a mixture powder;

[0057] (S2) The mixture powder was placed in a magnetic boat and calcined in a muffle furnace at a heating rate of 5℃ / min, and after being raised to 450℃, it was kept at this temperature for 5h, and then the heating rate was 5℃ / min, and after being raised to 1000℃, it was kept at this temperature for 15h, and after cooling to room temperature, an iron-based layered oxide sodium-ion battery positive electrode material was obtained;

[0058] (S3) The obtained positive electrode material, conductive additive SP, and binder PVDF were mixed in a hand box at a weight ratio of 80:10:10, and then dissolved in a solvent NMP to obtain a uniform slurry, and then the slurry was uniformly coated on a carbon-coated aluminum foil using a 200μm doctor blade, dried, and sliced to obtain a positive electrode sheet.

[0059] Figure 4 is the XPS spectrum of Y element at different etching times in Comparative Example 1. It can be seen that the ratio of the surface intensity (etching 0min) to the etching depth 90nm is 1.33. 5 / 2

[0060] Application Example Testing of electrochemical performance

[0061] ​Electrochemical performance testing: Coin cells were assembled using the electrodes obtained in Examples 1-8 and Comparative Example 1 as positive electrodes, sodium metal sheets as negative electrodes, glass fiber as separators, and 1 mol / L NaClO4 (PC + 5% FEC) as the electrolyte. The positive electrode was activated for one cycle at a current density of 13 mA / g within the voltage range of 2.0–4.0 V, followed by two cycles at a current density of 26 mA / g, and then charge-discharge cycles at a current density of 130 mA / g. The electrochemical performance of the sodium batteries in the examples and comparative examples of this invention was tested, and the results are shown in Table 1.

[0062] Table 1 Electrochemical performance

[0063]

[0064] The capacity retention rate after 200 laps is relative to the 4th lap; the first three laps are part of the formation process.

[0065] As can be seen from the test results of the half-cells in Table 1 for each embodiment, after multi-element synergistic doping of the high-speed rail-based bulk cathode material, the first-cycle discharge specific capacity of the sodium battery decreased slightly, but the capacity retention rate after 200 cycles was significantly improved. For example, in Example 1, the diffusion rate of Y was slow due to the secondary calcination process, which involved the addition of yttrium acetate. Therefore, it was difficult for Y to be incorporated into the bulk phase during calcination, resulting in surface enrichment, as shown in the attached figure. Figure 3 XPS results show that a longer etching time indicates an increased etching depth, and the Y signal intensity gradually weakens with etching time. Surface doping with Y improves the stability of the interface structure, achieving a capacity retention of 86.8% after 200 cycles, compared to only 68.5% in Comparative Example 1. Furthermore, Example 1 maintains a capacity of 85.3 mAh / g at a high current density of 10C, while Comparative Example 1's capacity is only 22.9 mAh / g. It is worth noting that the elemental doping content needs to be appropriate, and the calcination conditions and synthesis methods also need to be carefully selected; otherwise, the electrochemical performance will be affected. In addition, the use of different elements for synergistic doping significantly improves the long-cycle performance and rate performance of the high-speed rail-based substrate cathode material.

[0066] The application provides a modified design idea and a preparation method of an iron-based layered oxide sodium-ion battery positive electrode. Through multi-element synergistic doping, the synthesis process is simple, the modification effect is excellent, and the cycle stability and rate performance of the sodium-ion battery can be greatly improved. It can be understood that in various embodiments of the application, although the application is described in detail in combination with specific electrolyte, separator, current collector, active material, binder, conductive additive, etc., the above is only to meet the legal requirements and explain the composition of the sodium-ion battery, and the application is not limited to the given embodiments. Any modification, equivalent replacement and improvement made within the spirit and principles of the application, or directly or indirectly applied to other related technical fields, are also included in the patent protection scope of the application.

Claims

1. An iron-based layered-oxide sodium-ion battery cathode material, characterized in that, The chemical formula of the iron-based layered oxide sodium-ion battery cathode material is as follows: NaNi x Fe y Mn z A a B b C c O2, wherein x + y + z + a + b + c = 1, y > 1 / 3, a + b + c < 0.1, A is at least one of Mg, Al, Sn and Ti, B is at least one of Y, Zr, Nb, Mo and Ta, C is at least one of Li, Co and Zn, and the B element is doped in the surface and the bulk phase, and the content of the B element in the surface is greater than that in the bulk phase.

2. The iron-based layered oxide cathode material of claim 1, wherein, In the chemical formula, 0.5≥y≥1 / 3, 0.03≥a≥0.01, 0.03≥b≥0.01, 0.02≥c≥0.

05.

3. The iron-based layered oxide positive electrode material for sodium-ion batteries according to claim 1, characterized in that, The iron-based layered-oxide sodium-ion battery cathode material is NaNi 0.25 Fe 0.45 Mn 0.25 Al 0.01 Y 0.01 Co 0.03 O2.

4. The iron-based layered oxide cathode material of claim 1, wherein, The iron-based layered oxide sodium-ion battery positive electrode material satisfies that, in the XPS spectrum of the B element thereof, the ratio of the surface intensity at an etching depth of 0 nm to the intensity after etching for 90 nm is between 1.5 and 5.

5. The iron-based layered oxide cathode material of claim 4, wherein, The iron-based layered oxide sodium-ion battery positive electrode material satisfies that, in the XPS spectrum of the B element thereof, the ratio of the surface intensity at an etching depth of 0 nm to the intensity after etching for 90 nm is between 1.82 and 2.

07.

6. The method of producing the iron-based layered oxide cathode material for sodium-ion batteries according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: (S1) feeding a sodium source, a nickel source, an iron source, a manganese source, an element A source, and an element C source, and uniformly mixing to obtain a mixture I; (S2) performing first calcination on the mixture I at 400-600 DEG C, after cooling, adding an element B source, and uniformly mixing to obtain a mixture II; (S3) performing second calcination on the mixture II at 800-1200 DEG C, and obtaining the iron-based layered oxide sodium-ion battery positive electrode material after cooling.

7. The production method according to claim 6, wherein The sodium source is at least one selected from sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium hydroxide, sodium oxide, sodium peroxide, and sodium nitrite; the nickel source, the iron source, and the manganese source are selected from oxides, hydroxides, sulfates, nitrates, carbonates, acetates, and oxalates of nickel, iron, and manganese; or the nickel source, the iron source, and the manganese source are a nickel-iron-manganese hydroxide precursor; the element A source and the element C source are at least one selected from oxides, hydroxides, sulfates, nitrates, carbonates, acetates, and oxalates of the doped element A and element C; and the element B source is at least one selected from oxides, hydroxides, sulfates, nitrates, carbonates, acetates, and oxalates of the element B.

8. The preparation method according to claim 6, characterized in that, The sodium source, the nickel source, the iron source, the manganese source, the element A source, the element B source, and the element C source are fed according to the stoichiometric ratio of the product, and the sodium source is in excess of 5-10% in terms of the molar ratio.

9. The preparation method according to claim 6, characterized in that, The uniformly mixed manner includes ball milling, high-speed mixing, or mechanical grinding.

10. The method of claim 9, wherein, The uniformly mixed manner is ball milling, the ball milling speed is 200-1000 rpm, and the ball milling time is 1-20 h.

11. The preparation method according to claim 6, characterized in that, The first calcination time is 1-10 h, and the second calcination time is 5-40 h.

12. The method of claim 11, wherein, The first calcination time is 3-5 h, and the second calcination time is 10-15 h.

13. The method of claim 6, wherein the method further comprises, The calcination atmosphere is at least one selected from oxygen, air, nitrogen, and argon.

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