Sodium metaaluminate coated sodium ion layered oxide positive electrode material, preparation method and application

Abstract

The invention belongs to the technical field of sodium ion battery positive electrode materials, and relates to a sodium metaaluminate coated sodium ion layered oxide positive electrode material and a preparation method and application thereof, and the chemical expression of the positive electrode material is NaAlO2 (at) NaxTMO2, the surface of the layered oxide is uniformly coated with the coating layer, and TM in NaxTMO2 comprises one or more of transition metals Ni, Co, Mn, Cu, Zn, Mg, Fe, Al, Cr, Ti and Zr. In the preparation method, a direct solid-phase coating method which is simple, convenient and easy to operate is used, a well sintered layered oxide positive electrode material and a coating material sodium metaaluminate are mixed and ground, and then medium-high temperature secondary sintering is carried out. The invention aims to design and develop a modified positive electrode material capable of improving the interface stability and the structure stability aiming at the poor cycling stability of the existing sodium ion layered oxide positive electrode material, so that the electrochemical performance of a sodium ion battery is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for sodium-ion batteries, and relates to a sodium-ion layered oxide cathode material coated with sodium metaaluminate, and its preparation method and application. Background Art

[0002] Due to the low abundance and uneven distribution of lithium elements in the earth's crust, the widespread application of lithium-ion batteries has raised concerns about lithium resources. In contrast, China has rich sodium resources, which can relieve the pressure of limited lithium resources, and sodium-ion batteries have a similar working principle and structure to lithium-ion batteries. Therefore, sodium-ion batteries are considered to be a promising supplementary alternative to lithium-ion batteries, especially in the fields of large-scale energy storage systems and low-speed electric vehicles.

[0003] Among all components, the cathode material is a key factor determining the performance of the battery, and also largely determines the cost of the battery. Among common sodium-ion battery cathode materials, layered transition metal oxides are the most promising ideal sodium battery cathode materials for large-scale application because of their simple synthesis process, high specific capacity, and affordable price; however, the unsatisfactory cycle stability is a major obstacle to their large-scale industrialization.

[0004] The reason for its unsatisfactory cycle stability is as follows: during the cycling process, due to the repeated insertion and extraction of sodium ions, the stability of the material's layered structure decreases or even undergoes irreversible phase transformation; in addition, the harmful side reactions between the material surface and the electrolyte will also lead to the deterioration of the interface stability. Therefore, to improve the performance, these two aspects of problems should be addressed.

[0005] The invented sodium-ion layered oxide cathode material coated with sodium metaaluminate effectively improves the stability of the material structure and interface during the cycling process, and thus optimizes the electrochemical performance of the battery. Summary of the Invention

[0006] Aiming at the problem of poor cycle performance of the existing layered oxide cathode for sodium-ion batteries, the present invention adopts a simple solid-phase sintering coating method to obtain a cathode material with uniformly coated sodium metaaluminate on the surface, effectively suppressing the degradation problems of the material bulk phase and interface during the cycling process, and achieving a significant improvement in cycle stability.

[0007] The present invention is realized through the following technical solutions.

[0008] In the first aspect, the present invention provides a cathode material for a sodium-ion battery, wherein the sodium-ion cathode material includes a sodium-ion layered oxide material, and sodium metaaluminate coated on at least part of the surface of the sodium-ion layered oxide material.

[0009] In some embodiments, the sodium-ion layered oxide material Na xTMO2 includes at least one of O3-type sodium ion layered oxide materials, P2-type sodium ion layered oxide materials, and P2 / O3 composite phase sodium ion layered oxide materials. Among them, M is one or more of the transition metal elements Ni, Co, Mn, Cu, Zn, Mg, Fe, Al, Cr, Ti, Zr; the sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium fluoride, sodium hydroxide; 0 < x ≤ 1.

[0010] In some embodiments, the surface coating material is sodium metaaluminate, wherein the thickness of the coating layer is 2 - 30 nm, and the mass of the coating layer accounts for 0.5% - 5% of the mass of the sodium ion layered oxide cathode material.

[0011] In a second aspect, the present invention provides a preparation method of the sodium ion cathode material as described in the first aspect, and the preparation method includes:

[0012] Mix the sodium ion battery layered oxide material and sodium metaaluminate to obtain a premix, and calcine the premix to obtain the sodium ion cathode material with sodium metaaluminate coated on the sodium ion layered oxide material.

[0013] In some embodiments, the preparation method of the sodium ion layered oxide material includes:

[0014] After uniformly mixing the metal source precursor and the sodium source, perform a calcination reaction to obtain the sodium ion battery layered oxide material.

[0015] In some embodiments, the metal source precursor is at least one of metal oxides and metal hydroxides.

[0016] Optionally, the metal elements in the metal source precursor include at least one of Ni, Co, Mn, Cu, Zn, Mg, Fe, Al, Cr, Ti, Zr.

[0017] In some embodiments, the temperature of the calcination reaction is 850°C - 1000°C, the time is 10 - 15 h, and the atmosphere of the calcination reaction is an air or oxygen atmosphere.

[0018] In some embodiments, the method for mixing the sodium ion battery layered oxide material and sodium metaaluminate includes manual grinding and planetary ball milling.

[0019] In some embodiments, the time for manual grinding is 20 - 60 min.

[0020] In some embodiments, the time for planetary ball milling is 2 - 24 h, and the rotation speed of planetary ball milling is 100 - 300 rpm.

[0021] In some embodiments, the calcination treatment temperature of the mixture is 400 - 700 °C, the time is 2 - 12 h, and the atmosphere is an air atmosphere.

[0022] In a third aspect, the present invention provides a battery, wherein the positive electrode material in the battery comprises the sodium ion positive electrode material as described in the first aspect.

[0023] The beneficial effects of the present invention are as follows:

[0024] The present invention adopts a simple and easily expandable solid-phase sintering coating method to coat a thin layer of sodium metaaluminate on the surface of the sodium ion layered oxide positive electrode material, which can weaken the side reaction between the surface of the positive electrode material and the electrolyte, improve the interfacial stability, inhibit the dissolution of transition metal ions, and effectively increase sodium ion conduction by utilizing the good sodium ion diffusion kinetics of sodium metaaluminate. At the same time, it also reduces the structural degradation of the layered oxide positive electrode material during the cycling process and improves the structural stability. Therefore, the present invention can effectively improve the electrochemical performance of sodium ion batteries. Description of the Drawings

[0025] Figure 1 It is an X-ray diffraction (XRD) pattern of the positive electrode materials prepared in Example 2 and Comparative Example 1.

[0026] Figure 2 It is an energy spectrum (EDS) pattern of the sodium metaaluminate-coated sodium ion layered oxide positive electrode material prepared in Example 2.

[0027] Figure 3 It is an electrochemical cycling performance graph of the batteries assembled in Example 2 and Comparative Example 1. Specific Embodiments

[0028] Next, the related technologies in the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0029] In all the examples or comparative examples:

[0030] (1) Preparation of sodium ion layered oxide material: Using metal source and sodium source as raw materials, calculating and weighing according to the stoichiometric ratio, mixing evenly, and cooling after heat treatment in an air or oxygen atmosphere to obtain the sodium ion layered oxide material.

[0031] In an alternative embodiment, the metal element in the metal source precursor comprises at least one of Ni, Co, Mn, Cu, Zn, Mg, Fe, Al, Cr, Ti, Zr.

[0032] In an alternative embodiment, the metal source precursor is at least one of metal oxides and metal hydroxides.

[0033] In an alternative embodiment, the sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium fluoride, and sodium hydroxide.

[0034] In an alternative embodiment, the temperature of the heat treatment is 850 °C to 1000 °C, the time is 10 - 15 h, and the atmosphere of the heat treatment is air or oxygen atmosphere.

[0035] (2) Preparation of sodium aluminate-coated sodium-ion layered oxide cathode material: Using the sodium-ion layered oxide material and sodium aluminate as raw materials, calculate and weigh according to the coating ratio, and mix evenly by manual grinding or planetary ball milling. After heat treatment in an air atmosphere and cooling, a sodium aluminate-coated sodium-ion layered oxide cathode material is obtained.

[0036] In an alternative embodiment, the method of mixing the sodium-ion battery layered oxide material and sodium aluminate is manual grinding or planetary ball milling.

[0037] In an alternative embodiment, the time of manual grinding is 20 - 60 min.

[0038] In an alternative embodiment, the time of planetary ball milling is 2 - 24 h, and the rotation speed of planetary ball milling is 100 - 300 rpm.

[0039] In an alternative embodiment, the calcination treatment temperature of the mixed material is 400 - 700 °C, the time is 2 - 12 h, and the atmosphere is air atmosphere.

[0040] (3) Button battery assembly and electrochemical performance test: At room temperature, the electrochemical performance test is carried out by a CR2032 button battery. The preparation process of the working electrode is as follows: First, mix the cathode material, conductive agent Super P, and binder PVDF prepared in the example or comparative example in a ratio of 8:1:1 in N-methylpyrrolidone to obtain a uniform slurry; then, evenly scrape the obtained slurry onto the aluminum foil and keep it in a vacuum drying oven at 100 °C for 12 h; finally, use a punching machine to press the aluminum foil coated with the sample into a small round piece with a diameter of 1.1 cm as the cathode. The anode material uses a sodium metal sheet. The electrolyte composition is 1M NaClO4 carbonate electrolyte (ethylene carbonate (EC) and propylene carbonate (PC) with a volume ratio of 1:1 plus 5% fluoroethylene carbonate (FEC)). The battery assembly is carried out in a glove box filled with argon gas atmosphere at room temperature. The charge-discharge test is completed under a Neware battery test system, the test voltage range is 2 - 4 V, the test temperature is room temperature, and the test current density is 130 mA / g.

[0041] Example 1

[0042] Weigh 0.005 g of sodium metaaluminate and 1 g of sodium-ion layered oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, manually grind and mix evenly in a mortar for 30 min, loosely spread the mixed powder on a crucible, place the crucible in a muffle furnace, and heat-treat at 600 °C for 5 h to obtain a sodium metaaluminate-coated sodium-ion layered oxide cathode material, denoted as 0.5 wt% NaAlO2-NFM.

[0043] Example 2

[0044] Weigh 0.01 g of sodium metaaluminate and 1 g of sodium-ion layered oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, manually grind and mix evenly in a mortar for 30 min, loosely spread the mixed powder on a crucible, place the crucible in a muffle furnace, and heat-treat at 600 °C for 5 h to obtain a sodium metaaluminate-coated sodium-ion layered oxide cathode material, denoted as 1.0 wt% NaAlO2-NFM.

[0045] Example 3

[0046] Weigh 0.02 g of sodium metaaluminate and 1 g of sodium-ion layered oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, manually grind and mix evenly in a mortar for 30 min, loosely spread the mixed powder on a crucible, place the crucible in a muffle furnace, and heat-treat at 600 °C for 5 h to obtain a sodium metaaluminate-coated sodium-ion layered oxide cathode material, denoted as 2.0 wt% NaAlO2-NFM.

[0047] Example 4

[0048] Weigh 0.005 g of sodium metaaluminate and 1 g of sodium-ion layered oxide cathode material Na 0.67 Ni 0.5 Mn 0.5 O2, use a planetary ball mill to ball-mill and mix evenly at a rotation speed of 150 rpm for 12 h, loosely spread the mixed powder on a crucible, place the crucible in a muffle furnace, and heat-treat at 500 °C for 8 h to obtain a sodium metaaluminate-coated sodium-ion layered oxide cathode material, denoted as 0.5 wt% NaAlO2-NM.

[0049] Example 5

[0050] Weigh 0.01 g of sodium metaaluminate and 1 g of sodium-ion layered oxide cathode material Na0.67 Ni 0.5 Mn 0.5 O₂, ball-mill and mix evenly at a rotation speed of 150 rpm for 12 h using a planetary ball mill. Loosely spread the mixed powder on a crucible, place the crucible in a muffle furnace, and heat-treat at 500 °C for 8 h to obtain a sodium aluminate-coated sodium-ion layered oxide cathode material, denoted as 1.0 wt% NaAlO₂-NM.

[0051] Example 6

[0052] Weigh 0.02 g of sodium aluminate and 1 g of sodium-ion layered oxide cathode material Na 0.67 Ni 0.5 Mn 0.5 O₂, ball-mill and mix evenly at a rotation speed of 150 rpm for 12 h using a planetary ball mill. Loosely spread the mixed powder on a crucible, place the crucible in a muffle furnace, and heat-treat at 500 °C for 8 h to obtain a sodium aluminate-coated sodium-ion layered oxide cathode material, denoted as 2.0 wt% NaAlO₂-NM.

[0053] Comparative Example 1

[0054] Set 0.03 mol of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O₂, using Na₂CO₃, NiO, Fe₂O₃ and Mn₂O₃ as raw materials, weigh according to the molar ratio of Na:Ni:Fe:Mn = 1.05:1 / 3:1 / 3:1 / 3 (the sodium source is in excess by 5%). Use a planetary ball mill, with absolute ethanol as the medium, ball-mill and mix evenly at a rotation speed of 300 rpm for 9 h. After suction filtration and drying, use a mold and pressure to press the obtained mixed powder into small round pieces. Place the small round pieces in a crucible, and place the crucible in a muffle furnace, heat-treat at 900 °C for 12 h to obtain a sodium-ion layered oxide cathode material, denoted as NFM.

[0055] Comparative Example 2

[0056] Set 0.03 mol of Na 0.67 Ni 0.5 Mn 0.5 O₂, using Na₂CO₃ and the precursor Ni 0.5 Mn 0.5 (OH)₂ as raw materials, weigh according to the molar ratio of Na:Ni:Mn = 0.7035:0.5:0.5 (the sodium source is in excess by 5%). Manually grind and mix evenly in a mortar for 30 min. Use a mold and pressure to press the obtained mixed powder into small round pieces. Place the small round pieces in a crucible, and place the crucible in a muffle furnace, heat-treat at 900 °C for 12 h to obtain a sodium-ion layered oxide cathode material, denoted as NM.

[0057] The XRD test results of the sodium metaaluminate-coated sodium-ion layered oxide cathode material show that, compared with the bulk cathode material of Comparative Example 1, the layered structure of the sodium metaaluminate-coated sodium-ion layered oxide cathode material has not changed.

[0058] The EDS test results of the sodium metaaluminate-coated sodium-ion layered oxide cathode material show that the sodium metaaluminate-coated sodium-ion layered oxide cathode material is distributed with Al element, indicating that sodium metaaluminate is coated on the surface of the bulk material.

[0059] For the battery assembled with the sodium metaaluminate-coated sodium-ion layered oxide cathode material, after 200 cycles, both the discharge specific capacity (79.62 mAh / g) and the capacity retention rate (67.35%) are significantly higher than those of the battery assembled with the uncoated bulk material (67.51 mAh / g, 53.61%); therefore, the present invention can effectively improve the cycling performance of sodium-ion batteries.

[0060] The above are only several embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. Sodium aluminate-coated sodium-ion layered oxide cathode material, characterized in that, The chemical formula of the positive electrode material is expressed as NaAlO2@Na x TMO2, where NaAlO2 is the coating layer, and Na x TMO2 is at least one of an O3-type sodium ion layered oxide material, a P2-type sodium ion layered oxide material, and a P2 / O3 composite phase sodium ion layered oxide material; the coating layer uniformly coats the surface of the sodium ion layered oxide.

2. The sodium metaaluminate-coated sodium-ion layered oxide cathode material according to claim 1, characterized in that The thickness of the coating layer is 2 to 30 nm, and the mass of the coating layer accounts for 0.5% to 5% of the mass of the sodium-ion layered oxide cathode material.

3. Preparation method of sodium aluminate-coated sodium ion layered oxide cathode material, characterized in that The preparation method is used to prepare the cathode material described in any one of claims 1 to 2, and the preparation method includes the following steps: Step 1: Manually grind or perform planetary ball milling on sodium aluminate powder and sodium-ion layered oxide cathode material Na x TMO2 to mix them evenly, obtaining mixture I; Step 2: Sinter the mixture I obtained in Step 1 at medium to high temperature in an air atmosphere to promote the tight combination of the coating material and the matrix material and optimize the microstructure to obtain a sintered product; Step 3: Manually grind the sintered product obtained in Step 2 to obtain a sodium-ion layered cathode material coated with sodium aluminate.

4. The preparation method according to claim 3, characterized in that, The preparation method of the sodium-ion layered oxide cathode material includes: mixing a metal source precursor and a sodium source evenly and then performing a calcination reaction to obtain the sodium-ion layered oxide cathode material.

5. The preparation method according to claim 4, characterized in that, The preparation method of the sodium-ion layered oxide cathode material satisfies at least one of the following conditions: (1) The metal source precursor is at least one of a metal oxide and a metal hydroxide; optionally, the metal element in the metal source precursor includes one or more of Ni, Co, Mn, Cu, Zn, Mg, Fe, Al, Cr, Ti, Zr; (2) The sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium fluoride, sodium hydroxide; (3) The molar ratio of sodium ions in the sodium source to the metal element in the metal source precursor is (0 to 1.0):1, excluding 0; (4) The temperature of the calcination reaction is 850 °C to 1000 °C, the time is 8 h to 15 h, and the atmosphere of the calcination reaction is an air or oxygen atmosphere.

6. The preparation method of the sodium aluminate-coated sodium-ion layered oxide cathode material according to claim 3, wherein, In Step 1, the manual grinding time is 20 to 60 min.

7. The preparation method of the sodium aluminate-coated sodium ion layered oxide cathode material according to claim 3, characterized in that, In Step 1, the planetary ball milling time is 2 to 24 h, and the planetary ball milling speed is 100 to 300 rpm.

8. The preparation method of the sodium aluminate-coated sodium ion layered oxide cathode material according to claim 3, characterized in that, In Step 2, the medium to high temperature sintering temperature is 400 to 700 °C, the sintering time is 2 to 12 h, and the sintering atmosphere is an air atmosphere.

9. The preparation method of the sodium aluminate-coated sodium-ion layered oxide cathode material according to claim 3, characterized in that In Step 3, the manual grinding time is 10 to 30 min.

10. A battery, characterized in that, The cathode material in the battery includes the sodium-ion layered oxide cathode material coated with sodium aluminate described in any one of claims 1 to 2.

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