A P2-type tungsten-doped sodium-ion battery cathode material and its preparation method

Abstract

The present invention discloses a cathode material for a P2-type tungsten-doped sodium-ion battery and a preparation method thereof. The chemical expression of the cathode material is Na a Ni b Mn c W n O2, where 0.67 ≤ a ≤ 0.80, 0.15 ≤ b ≤ 0.35, 0.60 ≤ c ≤ 0.80, 0.01 ≤ n ≤ 0.03, and a + b + c = 1. The present invention proposes to use manganese dioxide as part of the manganese source, and a method combining multi-stage sintering and cooling to dope the W element into the crystal bulk of the material, stabilize the internal structure of the material, reduce the occurrence of phase transformation under high-rate test conditions, and improve the initial capacity and rate performance of the material.

Description

Technical Field

[0001] The present invention belongs to the field of chemical power sources, and particularly relates to a P2-type tungsten-doped sodium-ion battery cathode material and a preparation method thereof. Background Art

[0002] Since researchers discovered in the late 1970s that Na+ can be reversibly inserted / extracted in the layered oxide NaxCoO2, more and more research has been conducted on sodium-ion battery cathode materials. Sodium-ion battery cathode materials mainly include oxides, polyanions, Prussian blue compounds, and organic compounds, etc. Among them, due to the layered oxide materials in oxides having outstanding advantages such as a periodic layered structure, simple preparation method, high specific capacity and voltage, etc., they have received extensive attention from researchers.

[0003] However, currently, layered oxide cathode materials are mainly divided into two types: P2 phase and O3 phase. For O3-phase cathode materials, due to the relatively high sodium ion content (x≈1), they have excellent theoretical capacity and high initial Coulomb efficiency. However, during the charge and discharge process, O3-phase cathode materials have problems such as multiple complex phase transitions and poor rate performance. This is because the slip of the TMO2 layer in O3-phase materials does not require the breaking of the TM—O bond, resulting in the easy formation of stacking faults under high temperature and high pressure. The poor rate performance is due to the fact that sodium ion migration in the O3 phase occurs in the TMO6 octahedral coordination environment, and its diffusion barrier is often large, thus affecting the rate performance. P2-phase cathode materials have a more stable structure and better rate performance. This is because the layer spacing of the sodium ion diffusion channel in the P2-phase structure is larger, and compared with the structure of O3-phase materials, the sodium ion diffusion energy barrier is lower. And when the P2-phase structure transforms into other phase structures, it is necessary to break the TM—O bond, which only occurs under high temperature and high pressure, and the phase transition is more difficult to occur, so it is relatively more stable than other phase structures. However, the P2-phase materials have a lower capacity, which is not conducive to their large-scale development in the actual application process.

[0004] The beneficial effects of tungsten doping on transition metal oxides (LiMO2, where M is Ni, Co, Al, Mn) for lithium-ion batteries have been reported in the prior art. Tungsten doping can improve the capacity of the nickel-rich layered oxide cathode material for lithium-ion batteries. For example, in Document 1: Nafiseh Zaker, Botton. Probing the Mysterious Behavior of Tungsten as a Dopant Inside Pristine Cobalt-Free Nickel-Rich Cathode Materials[J]. Adv. Funct. Mater. 2023, 2211178. W-doped LiNiO2 (LNO) particles were prepared by mechanical fusion and coprecipitation methods to detect changes in the structure and position of W. In-depth characterization results were used to reveal the preferred position of W, its form, and possible W variants in the new doped LiNiO2 (LNO) cathode material.

[0005] Document 2: Mechanism of Action of the Tungsten Dopant in LiNiO2 Positive Electrode Materials. Adv. Energy Mater. 2021. J. R. Dahn et al. from Dalhousie University in Canada prepared W-doped LiNiO2 cathode materials by coprecipitation using WO3, Ni(OH)2, and LiOH·H2O as precursors and studied the mechanism of action of W doping in improving the electrode capacity retention rate.

[0006] Document 3: High-Energy W-Doped Li[Ni 0.95 Co 0.04 Al 0.01 O2 Cathodes for Next-Generation Electric Vehicles. Energy Storage Materials. 2020. Yang-Kook Sun et al. from Hanyang University in Korea explored the electrochemical performance of the tungsten-doped Li[Ni 0.95 Co 0.04 Al 0.01 O2 cathode (W-NCA95). The microstructurally modified W-NCA95 has a high initial capacity of 242 mAh g -1 (0.1C) and still retains 77.4% of its initial capacity after 1000 cycles, while the retention rate of Li[Ni 0.95 Co 0.04 Al 0.01 O2 is only 14.5%.

[0007] Patent CN116779828A discloses a preparation method of a modified sodium-ion layered cathode material with the chemical formula Na x Cu a+e Ni b+f M' (1-a-b-c) M" c W d O 2+4d , with a layer of Cu e Ni f WO4 heterojunction coated on its surface, rather than doping with W element.

[0008] Patent CN116741984A discloses a cathode material for sodium-ion batteries, and the coating layer is a tungsten-containing compound. In this patent, the tungsten element is only coated on the surface of the cathode substrate, rather than being doped into the bulk phase.

[0009] However, for sodium-ion layered oxide cathode materials, one of the difficulties in tungsten doping is that it is difficult to dope it into the bulk phase of the material. Different from other substitutional doping, W element doping is difficult to replace any metal site, and it often enters in the form of an amorphous phase and enriches on the crystal phase surface. This results in the inability of traditional methods to dope tungsten into the crystal interior, thus limiting its application in sodium-ion battery cathode materials. Summary of the Invention

[0010] In order to solve the problems of uneven doping and difficulty in deep doping into the bulk phase existing in tungsten doping of P2-phase cathode materials, the present invention dopes W element inside the bulk phase structure of the material through appropriate raw materials, as well as multiple calcination and cooling processes, so as to achieve the purpose of improving the material capacity and rate performance. To achieve the above invention purpose, the present invention provides the following technical solutions:

[0011] A P2-type tungsten-doped sodium-ion battery cathode material with the chemical formula Na a Ni b Mn c W n O2, where 0.67 ≤ a ≤ 0.80, 0.15 ≤ b ≤ 0.35, 0.60 ≤ c ≤ 0.80, 0.01 ≤ n ≤ 0.03, and a + b + c = 1.

[0012] Furthermore, the D50 of the cathode material of the P2-phase high-capacity sodium-ion battery of the present invention is 0.5 - 1.5 μm larger than that of the nickel-manganese precursor. W doping is difficult to replace the metal site and will not be doped into the crystal structure. Instead, it mostly adheres to the surface of the primary particles to form a "coating", which hinders the growth of primary grains. Therefore, the D50 of the P2-type tungsten-doped sodium-ion battery cathode material obtained by conventional W doping process is relatively small, smaller than the size of the nickel-manganese precursor. However, through the specific manganese source and multiple sintering and cooling processes of the present invention, uniform doping of W in the crystal lattice of the cathode material is achieved. Therefore, a P2-type tungsten-doped sodium-ion battery cathode material with a larger D50 can be obtained, and its size is 0.5 - 1.5 μm larger than that of the nickel-manganese precursor. The nickel-manganese precursor generally refers to nickel-manganese hydroxide, and its chemical formula is Ni d Mn e (OH)2.

[0013] During the charge and discharge process of the layered oxide cathode material of the sodium-ion battery, the internal crystal structure will collapse, and the unit cell volume changes greatly, resulting in a decrease in the electrochemical stability of the material. By selecting the method of multi-stage sintering and cooling of manganese dioxide, W element is doped into the layered oxide cathode material to improve the capacity and rate performance of the material. Through the multi-stage sintering process, W element can be doped into the material, and then through the cooling process, the W element doped into the interior is prevented from being discharged to the grain boundary surface, affecting the growth of primary particles.

[0014] The second object of the present invention is to provide a preparation method of the P2-type tungsten-doped sodium-ion battery cathode material, which includes the following steps:

[0015] (S1) Mixing: Weigh the sodium source, nickel-manganese precursor, and tungsten source according to the chemical formula Na a Ni b Mn c W n O2, and mix the weighed raw materials evenly;

[0016] (S2) First-stage sintering: The mixture obtained in step (S1) is calcined in a muffle furnace, heated to 600 - 700 °C, kept at this temperature for 5 - 8 h, and then cooled to 200 - 300 °C to obtain intermediate product 1;

[0017] (S3) Second-stage sintering: Then, the intermediate product 1 obtained in (S2) is heated to 800 - 1000 °C, kept at this temperature for 10 - 15 h, and then cooled to room temperature again to obtain intermediate product 2;

[0018] (S4) Third-stage sintering: The intermediate product 2 obtained in (S3) is subjected to sodium supplementation treatment, mixed evenly, then heated to 600 - 800 °C in a muffle furnace, kept at this temperature for 4 - 6 h, and then cooled to obtain the P2-type tungsten-doped sodium-ion battery cathode material Na a Nib Mn c W n O₂。

[0019] Furthermore, the sodium source is selected from at least one of sodium oxide, sodium peroxide, sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium oxalate; the nickel-manganese precursor is a hydroxide and / or oxide of nickel and manganese. For example, the chemical formula of nickel-manganese hydroxide is Ni d Mn e (OH)₂, where 0.15 ≤ d ≤ 0.35 and 0.65 ≤ e ≤ 0.85.

[0020] Preferably, the nickel-manganese precursor includes manganese sesquioxide; more preferably, the manganese in manganese sesquioxide accounts for 40-50% of the manganese in the nickel-manganese precursor. The inventors unexpectedly found that the presence of a part of manganese sesquioxide in the nickel-manganese precursor can allow more doping of tungsten into the bulk phase, while using manganese dioxide cannot achieve such a purpose. The possible reason is that manganese sesquioxide and tungsten acid compounds are more likely to form a eutectic melt of manganese tungstate and enter the bulk phase of the material.

[0021] Furthermore, in step (S4), the sodium supplementation treatment is to supplement 5-8% of the sodium source in terms of Na to make up for the loss of sodium during the first two sintering processes.

[0022] Furthermore, the calcination atmosphere is oxygen or air, the heating rate is 2-10 °C / min, and the cooling rate during cooling is 20-40 °C / min.

[0023] The present invention also provides a sodium-ion battery, and the positive electrode of the sodium-ion battery includes the above-mentioned P2-type tungsten-doped sodium-ion battery positive electrode material.

[0024] The beneficial effects of the present invention are as follows:

[0025] First, the present invention mixes the raw materials evenly through a one-step dry process, with a simple process, easy to operate, and convenient for large-scale production.

[0026] Second, for the positive electrode material prepared by the present invention, the doped element W can alleviate the structural collapse problem caused by the dissolution of transition metals during charge and discharge.

[0027] Third, the W element doping and its doping method of the present invention can effectively improve the capacity and rate performance of the battery, providing a new development idea for the research of layered oxide sodium-ion battery positive electrode materials. Description of the Drawings

[0028] Figure 1 It is the SEM image of the positive electrode material prepared in Example 1.

[0029] Figure 2It is the SEM image of the cathode material prepared in Example 3.

[0030] Figure 3 It is the SEM image of the cathode material prepared in Example 4.

[0031] Figure 4 It is the SEM image of the cathode material prepared in Comparative Example 1.

[0032] Figure 5 It is the SEM image of the cathode material prepared in Comparative Example 2. Detailed implementation manners

[0033] The sodium-ion layered oxide cathode material containing doped element W according to the present invention will be further described below in conjunction with specific examples and the specification. However, it should be understood that the protection scope of the present invention is not limited to the following examples.

[0034] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0035] Ni used in the embodiments of the present invention 0.5 Mn 0.5 (OH)2 has a D50 of about 5 μm.

[0036] Prepare P2-Na in Example 1 0.67 Ni 0.35 Mn 0.64 W 0.01 O2 layered cathode material

[0037] (S1) Weigh 0.335 mol of Na2CO3, 0.7 mol of Ni 0.5 Mn 0.5 (OH)2, 0.145 mol of Mn2O3, and 0.01 mol of H2WO4 and mix them evenly in a mixer;

[0038] (S2) First-stage sintering: Place the powder obtained in step (S1) in a muffle furnace for calcination, with a heating rate of 2 °C / min. After heating to 600 °C, hold for 8 hours, and then cool to 200 °C at a rate of 20 °C / min to obtain intermediate product 1;

[0039] (S3) Second-stage sintering: Then heat the intermediate product 1 obtained in (S2) to 1000 °C at a heating rate of 2 °C / min, hold for 10 h, and then cool to room temperature at a cooling rate of 20 °C / min to obtain intermediate product 2;

[0040] (S4) Three-stage sintering: The intermediate product 2 obtained in (S3) is subjected to 5% sodium supplementation treatment, and after mixing evenly, it is heated in a muffle furnace at a heating rate of 2 °C / min to 600 °C, kept warm for 6 h, and then cooled at a cooling rate of 20 °C / min to room temperature to obtain the W-doped P2-phase sodium layered metal oxide cathode material Na 0.67 Ni 0.35 Mn 0.64 W 0.01 O2. Its SEM image is as shown in Figure 1 and its D50 is about 6.3 μm, which is 1.3 μm larger than the D50 of Ni 0.5 Mn 0.5 (OH)2.

[0041] The obtained P2-Na 0.67 Ni 0.35 Mn 0.64 W 0.01 O2 layered oxide cathode material, conductive additive SP, and binder PVDF are mixed in a mass ratio of 90:5:5 and dissolved in NMP. After stirring, a uniform slurry is obtained. Then, the slurry is evenly coated on the surface of the aluminum foil using a 200-μm doctor blade, dried, and sliced to obtain the required electrode sheet.

[0042] Example 2

[0043] The operation steps are the same as those in Example 1, except that "H2WO4" in step (1) is changed to an equimolar amount of Na2WO4.

[0044] Example 3

[0045] Prepare the P2-Na 0.67 Ni 0.28 Mn 0.70 W 0.02 O2 layered cathode material

[0046] (S1) Weigh 0.335 mol of Na2CO3, 0.56 mol of Ni 0.5 Mn 0.5 (OH)2, 0.21 mol of Mn2O3, and 0.02 mol of H2WO4 and mix them evenly in a mixer.

[0047] (S2) One-stage sintering: The powder obtained in step (S1) is calcined in a muffle furnace at a heating rate of 10 °C / min. After heating to 700 °C, it is kept warm for 6 hours and then cooled to 200 °C at a rate of 20 °C / min to obtain intermediate product 1;

[0048] (S3) Two-stage sintering: Then, the intermediate product 1 obtained in (S2) is heated to 900 °C at a heating rate of 10 °C / min, held for 15 h, and then cooled to room temperature at a cooling rate of 20 °C / min to obtain intermediate product 2;

[0049] (S4) Three-stage sintering: The intermediate product 2 obtained in (S3) is subjected to 5% sodium supplementation treatment, and after being mixed evenly, it is heated to 700 °C at a heating rate of 10 °C / min in a muffle furnace, held for 6 h, and then cooled at a cooling rate of 20 °C / min to room temperature to obtain the W-doped P2-phase sodium-ion layered metal oxide cathode material P2-Na 0.67 Ni 0.28 Mn 0.70 W 0.02 O2. The SEM image of the prepared cathode material is as Figure 2 shown, and its D50 is about 6.1 μm, which is 1.1 μm larger than that of Ni 0.5 Mn 0.5 (OH)2.

[0050] The obtained P2-Na 0.67 Ni 0.35 Mn 0.63 W 0.02 O2 layered oxide cathode material, conductive additive SP, and binder PVDF are mixed and dissolved in NMP in a mass ratio of 90:5:5, and a uniform slurry is obtained through stirring. Then, the slurry is evenly coated on the surface of the aluminum foil using a 200-μm blade, dried, and sliced to obtain the required electrode sheet.

[0051] Example 4

[0052] Other conditions are the same as those in Example 1. The difference is that in (S1), 0.145 mol of Mn2O3 is replaced with a mixture of 0.07 mol of Mn2O3 and 0.15 mol of MnO2. The SEM image of the prepared cathode material is as Figure 3 shown, and its D50 is about 5.6 μm, which is 0.6 μm larger than that of Ni 0.5 Mn 0.5 (OH)2.

[0053] Prepare P2-Na 0.67 Ni 0.35 Mn 0.64 W 0.01 O2 layered cathode material

[0054] Other conditions are the same as those in Example 1. The difference is that in (S1), 0.145 mol of Mn2O3 is replaced with 0.29 mol of MnO2. Its SEM image is as Figure 4 shown, and D50 is about 4.5 μm.

[0055] Comparative Example 2

[0056] Other conditions were the same as in Example 1, and the difference was that after step (S1), it was as follows:

[0057] (S2) One-stage sintering: The powder obtained in step (S1) was placed in a muffle furnace for calcination, with a heating rate of 2 °C / min. After heating to 1000 °C, it was held for 20 hours, and then cooled to room temperature at a cooling rate of 20 °C / min to obtain P2-Na 0.67 Ni 0.35 Mn 0.64 W 0.01 O2 layered cathode material. Its SEM image is as Figure 5 shown, and D50 is about 4.3 μm.

[0058] Electrochemical performance test of application example

[0059] Electrochemical performance test: Using the electrode sheets obtained in the examples and comparative examples as the positive electrode, glass fiber as the separator, sodium metal sheet as the negative electrode, and 1 mol / L NaClO4 (PC + 5% FEC) as the electrolyte to assemble a button cell. The test voltage range was 2.5 - 4.15 V, 0.2C discharge test, and 1.0C cycle test. The electrochemical performances of the button cells corresponding to the materials of the examples and comparative examples of the present invention were tested, and the results are shown in Table 1:

[0060] Table 1 Electrochemical performance

[0061]

[0062] It can be seen from the test results of each example in Table 1 of the half-cell that after doping the layered cathode material with metal W, the first-cycle discharge capacity of the battery has a large increase. The rate performance of 1.0 / 0.2C has also been improved significantly. This shows that W element doping can effectively improve the capacity and rate performance of the material. When doping W element by one-stage sintering method, or when there is not enough Mn2O3 in the manganese source, W cannot be successfully doped into the crystal structure. More often, it adheres to the surface of the primary particles to form a "coating", which hinders the growth of primary grains and at the same time increases the resistance of the particles to microcracks.

[0063] Figure 1 is the SEM image of the tungsten-doped cathode material obtained in Example 1; Figure 4 In Comparative Example 1, MnO2 was used as the manganese source and Mn2O3 was not added; Figure 5 while Comparative Example 2 is the W-doped P2-phase cathode material prepared by one-stage sintering method. After comparison, it can be found that the primary particles of the cathode materials in Comparative Example 1 and Comparative Example 2 are smaller. While for the W-doped cathode materials prepared by the methods of Example 1 and Example 3, the primary particle size is larger, indicating that W element has been doped into the crystal structure.

[0064] The present invention provides a cathode material for a P2-type tungsten-doped sodium-ion battery and a preparation method thereof. The preparation process is simple and can effectively improve the electrochemical performance of the layered oxide cathode material. It can be understood that in various embodiments of the present invention, although the present invention is described in detail in combination with specific electrolytes, separators, current collectors, active substances, binders, conductive additives, etc., the above is only to meet legal requirements and illustrate the composition of the sodium-ion battery. The present invention is not limited to the given embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention by using the specification of the present invention, or directly or indirectly applied in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A cathode material for a P2-type tungsten-doped sodium-ion battery, characterized in that, The chemical formula is Na a Ni b Mn c W n O2, where 0.67 ≤ a ≤ 0.80, 0.15 ≤ b ≤ 0.35, 0.60 ≤ c ≤ 0.80, 0.01 ≤ n ≤ 0.03, and b + c + n = 1; The positive electrode material of the P2-type tungsten-doped sodium ion battery is prepared by a preparation method including the following steps: (S1) Mixing: Weigh the sodium source, nickel-manganese precursor, and tungsten source according to the chemical formula Na a Ni b Mn c W n O2, and mix the weighed raw materials evenly; the nickel-manganese precursor includes manganese dioxide, and the manganese in the manganese dioxide accounts for 40-50% of the manganese in the nickel-manganese precursor; (S2) One-stage sintering: The mixture obtained in step (S1) is calcined in a muffle furnace, heated to 600-700 °C, kept warm for 5-8 h, and then cooled to 200-300 °C to obtain intermediate product 1; (S3) Two-stage sintering: Then, the intermediate product 1 obtained in (S2) is heated to 800-1000 °C, kept warm for 10-15 h, and then cooled to room temperature again to obtain intermediate product 2; (S4) Three-stage sintering: The intermediate product 2 obtained in (S3) is subjected to sodium supplementation treatment. After mixing evenly, it is heated to 600 - 800 °C in a muffle furnace, cooled after holding for 4 - 6 h to obtain the P2-type sodium-ion battery cathode material Na a Ni b Mn c W n O2.

2. The cathode material for a P2-type tungsten-doped sodium-ion battery according to claim 1, characterized in that, The D50 of the positive electrode material of the P2-type high-capacity sodium ion battery is 0.5-1.5 μm larger than that of the nickel-manganese precursor.

3. The cathode material for a P2-type tungsten-doped sodium-ion battery according to claim 1, characterized in that, The sodium source is selected from at least one of sodium oxide, sodium peroxide, sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium oxalate; the nickel-manganese precursor is a hydroxide and / or oxide of nickel and manganese, and the chemical formula of the nickel-manganese hydroxide is Ni d Mn e (OH)2, where 0.15 ≤ d ≤ 0.35 and 0.65 ≤ e ≤ 0.

85.

4. The cathode material for a P2-type tungsten-doped sodium-ion battery according to claim 1, characterized in that, In step (S4), the sodium supplementation treatment is to supplement 5-8% of the sodium source in terms of Na.

5. The cathode material for a P2-type tungsten-doped sodium-ion battery according to claim 1, characterized in that, The calcination atmosphere is oxygen or air, the heating rate is 2-10 °C / min, and the cooling rate during cooling is 20-40 °C / min.

6. A sodium-ion battery, characterized in that, The positive electrode of the sodium ion battery includes the positive electrode material of the P2-type tungsten-doped sodium ion battery according to any one of claims 1-5.

Images