Layered manganese-based positive electrode material with air stability for sodium-ion battery as well as preparation method and application of layered manganese-based positive electrode material

Abstract

The invention relates to a sodium ion battery layered manganese-based positive electrode material with air stability, and a preparation method and application thereof, and belongs to the technical field of sodium ion battery positive electrode materials. The chemical formula of the material is Na < 0.67 > Mn < x > Al < y > B < z > O < 2 >. According to the invention, a composite structure with Al < 3 + > in bulk phase enrichment and B < 3 + > in surface enrichment is constructed in a P2-Na0. 67MnO2 positive electrode material system through one-time solid-phase powder sintering, and the composite structure avoids Na < + > separation, carbonate and hydrated phase generation and crystal cracking caused by water molecule intercalation when the positive electrode material is exposed in air; and the crystal structure stability of the positive electrode material in air is obviously improved, so that the sodium ion battery layered manganese-based positive electrode material with air stability is obtained.

Description

Technical Field

[0001] The present invention relates to a sodium ion battery layered manganese-based positive electrode material with air stability, a preparation method and uses thereof, and belongs to the technical field of sodium ion battery positive electrode materials. Background Art

[0002] With the continuous expansion of the demand for distributed and large-scale electrochemical energy storage systems, sodium-ion batteries, which have the advantages of abundant raw material resources, low prices, and production equipment and production experience that are compatible with lithium-ion batteries, have received widespread attention from the scientific and industrial communities. The electrochemical properties of sodium-ion battery positive electrode materials play a vital role in the performance of the final full-battery device. Among the many sodium-ion battery positive electrode materials, layered transition metal oxides have the advantages of high specific capacity, controllable component and structural design, and simple preparation methods. Among them, the P2 phase structure positive electrode material Na 0.67 MnO2 has the advantages of high specific capacity, high reversibility of charge compensation, cheap and non-toxic raw materials. However, when it is exposed to air, Na + It is easy to break away from the crystal structure and react with water vapor and CO2 in the air to produce carbonates and hydrates. The irreversible destruction of the crystal structure and the generation of impurities seriously affect the use of positive electrode materials in sodium ion batteries. The poor air stability problem seriously limits the use of Na 0.67 Large-scale application of MnO2.

[0003] Currently, research on improving air stability focuses on methods such as doping with elements with high redox potentials, crystal structure design, and surface coating, and while some results have been achieved, these methods generally suffer from high costs, complex processes, and reduced electrochemical performance of the cathode materials, leaving room for further optimization and improvement. Therefore, there is an urgent need to develop a method for improving the air stability of layered manganese-based cathode materials for sodium-ion batteries that is simple to process, uses inexpensive raw materials, and does not compromise the electrochemical performance of the cathode materials. Summary of the Invention

[0004] The present invention is a solid phase powder sintering in P2-Na 0.67 Al was constructed in the MnO2 cathode material system. 3+ Bulk-enriched B 3+ The surface-enriched composite structure avoids the release of Na and Mn, the production of carbonate and hydrate phases, and the crystal cracking caused by water molecule intercalation when the positive electrode material is exposed to air, significantly improving the crystal structure stability of the positive electrode material in air, thereby obtaining an air-stable layered manganese-based positive electrode material for sodium ion batteries.

[0005] A layered manganese-based cathode material for sodium ion batteries with air stability has the following chemical composition: Na 0.67 Mnx Al y B z O₂; 0.8 < x < 1.0; 0 < y < 0.2; 0 < z < 0.1; Its morphology is a layered material, the B element is located in the surface layer of the material, the thickness of the surface layer is 5 - 50 nm, and the Al element is enriched in the bulk phase.

[0006] The layered material has a width of 0.5 - 1.5 μm and a thickness of 0.2 - 1.8 μm.

[0007] A preparation method of a layered manganese - based cathode material for a sodium - ion battery with air stability is prepared by a high - temperature solid - state powder sintering method, including the following steps: Step 1, mix a sodium source, a manganese source, and an aluminum source, and after ball - milling, obtain a precursor powder; Step 2, mix the precursor powder with a boron source, grind it, and then carry out a calcination treatment to obtain the cathode material.

[0008] The sodium source is sodium carbonate, the manganese source is manganese(III) oxide, the aluminum source is aluminum oxide, and the boron source is boric acid.

[0009] During the calcination treatment, the heating rate is 1 - 10 °C / min.

[0010] During the calcination treatment, it needs to be maintained at 800 - 1000 °C for 10 - 20 h.

[0011] During the ball - milling treatment, ball - mill at 100 - 500 rpm for 5 - 10 h.

[0012] A sodium - ion battery, whose cathode material is the above - mentioned layered manganese - based cathode material for a sodium - ion battery. Brief Description of the Drawings

[0013] Figure 1 : Powder X - ray diffraction pattern of Example 1 Figure 2 : Powder X - ray diffraction pattern of Comparative Example 1 Figure 3 : Scanning electron micrograph of Example 1 Figure 4 : Scanning electron micrograph of Comparative Example 1 Figure 5 : Element distribution map of Example 1 Figure 6 : Surface boron element distribution map of Example 1 Figure 7 : Scanning transmission electron microscopy EELS line - scan spectrum of Example 1 Figure 8 : Charge - discharge curve of the first cycle of Example 1 at a current density of 20 mA / g Figure 9: Charge-discharge curve of Comparative Example 1 in the first cycle at a current density of 20 mA / g Figure 10 : Rate performance test curves of Example 1 and Comparative Example 1 Figure 11 : Cycling test curves of Example 1 and Comparative Example 1 at a current density of 500 mA / g in the voltage range of 1.8 - 4.3 V Figure 12 : Cycling test curves of Example 1 and Comparative Example 1 at a current density of 1 A / g in the voltage range of 2 - 4 V Figure 13 : Powder X-ray diffraction patterns of Example 1 before and after exposure to air for 14 days Figure 14 : Powder X-ray diffraction patterns of Comparative Example 1 before and after exposure to air for 14 days Figure 15 : Scanning electron microscope images of Example 1 after exposure to air for 14 days Figure 16 : Scanning electron microscope images of Comparative Example 1 after exposure to air for 14 days Figure 17 : Scanning transmission electron microscope images and elemental distribution maps of Example 1 after exposure to air for 14 days Figure 18 : Scanning transmission electron microscope images and elemental distribution maps of Comparative Example 1 after exposure to air for 14 days Figure 19 : Charge-discharge curves of the first 20 cycles of Example 1 after exposure to air for 14 days at a current density of 50 mA / g Figure 20 : Charge-discharge curves of the first 20 cycles of Comparative Example 1 after exposure to air for 14 days at a current density of 50 mA / g Figure 21 : Rate performance test curves of Example and Comparative Example 1 after exposure to air for 14 days Figure 22 : XRD patterns of the material obtained in Comparative Example 2 Figure 23 : XRD patterns of the material obtained in Comparative Example 3 Detailed implementation manners

[0014] Example 1 The materials prepared by the high-temperature solid-phase powder sintering method use Na2CO3, Mn2O3 and Al2O3 as raw materials. According to the corresponding molar ratio, they are ball-milled at 300 rpm for 5 h, and the wet-milling aid is anhydrous ethanol. The precursor powder is dried at 80 °C. The obtained precursor powder is mixed with H3BO3 in the corresponding molar ratio and manually ground in a mortar for 1 h. The obtained powder is placed in a muffle furnace for calcination, heated to 900 °C at a rate of 5 °C / min, calcined for 12 h, and naturally cooled to prepare the cathode material Na 0.67 B 0.05 Mn 0.88 Al 0.12 O2. The test results of the materials by powder X-ray diffraction are as follows Figure 1 , and the space group is P 63 / mmc, which is a P2-phase cathode material without impurities.

[0015] Comparative Example 1 The materials prepared by the high-temperature solid-phase powder sintering method use Na2CO3 and Mn2O3 as raw materials. According to the corresponding molar ratio, they are ball-milled at 300 rpm for 5 h, and the wet-milling aid is anhydrous ethanol. The precursor powder is dried at 80 °C. The obtained precursor powder is placed in a muffle furnace for calcination, heated to 900 °C at a rate of 5 °C / min, calcined for 12 h, and naturally cooled to prepare the cathode material Na 0.67 MnO2. The test results of the materials by powder X-ray diffraction are as follows Figure 2 , and the space group is P 63 / mmc, which is a P2-phase cathode material without impurities.

[0016] Comparative Example 2 Na 0.67 B 0.05 The preparation of MnO2 materials is the same as that in Example 1, using the solid-phase method and synthesizing under the same roasting preparation. The test results of powder X-ray diffraction are as follows Figure 22 , and the arrow indicates impurities. It does not have a P2-phase crystal structure and there are oxide impurities at the same time.

[0017] Comparative Example 3 Na 0.67 Mn 0.85 Al 0.15 The preparation of O2 materials is the same as that in Example 1, using the solid-phase method and synthesizing under the same roasting preparation. The test results of powder X-ray diffraction are as follows Figure 22 , and the arrow indicates impurities. It has a P2-phase crystal structure but there are oxide impurities.

[0018] Combining Example 1 and Comparative Examples 2 and 3, it can be seen that only when the P2 phase containing Al and B doping is simultaneously prepared in the material can the oxide without impurities and the P2 phase be ensured at the same time.

[0019] Comparison of SEM Characterization Results The scanning electron microscope image of the cathode material powder in the example is as follows Figure 3 , with a particle size width of 1 ± 0.2 μm, a thickness of 1 ± 0.5 μm, an obvious layered structure, clear and sharp particle edges, a large number of active crystal planes exposed, and extremely high crystallinity. The scanning electron microscope image of the cathode material powder in the comparative example is as follows Figure 4 , with a particle size width of 3 ± 1 μm, a thickness of 0.5 ± 0.2 μm, an obvious layered structure, relatively clear particle edges, a large number of small irregular particles, less active crystal planes exposed, and general crystallinity.

[0020] Element Distribution Characteristics The scanning transmission electron microscope EDS test results of the cathode material powder in the example are as follows Figure 5 and Figure 6 , and the elements Na, Mn, Al, and O are evenly distributed in the material particles, and the B element is concentrated in the surface area of the material particles. The scanning transmission electron microscope EELS test results of the cathode material powder in Example 1 are as follows Figure 7 , and the B element is distributed from the surface to about 15 nm in the bulk of the material particles. It is proved that in the Na 0.67 MnO2 cathode material system of Example 1, a composite structure with Al 3+ bulk-phase enrichment of B 3+ and surface enrichment is constructed.

[0021] Electrochemical Performance Test Using N-methylpyrrolidone as the solvent, a slurry was prepared in the ratio of cathode material: acetylene black: polyvinylidene fluoride = 8:1:1. The obtained slurry was coated on a 15-μm-thick aluminum foil, dried in vacuum at 120 °C, and then cut into a 12-mm-diameter circular piece as the positive electrode plate. Metallic sodium was used as the negative electrode, glass fiber was used as the separator, and a 1.0 M NaClO4PC + 5% FEC electrolyte was used to assemble a 2032 coin cell in an argon-protected glove box. The electrochemical performance test was carried out using a LAND electrochemical test system at room temperature of 25 °C.

[0022] As Figure 8 , the charge-discharge curve of Example 1 at a current density of 20 mA / g in the first cycle, with a voltage window of 1.5 - 4.5 V and a reversible specific capacity of 184.3 mAh / g. As Figure 9 , the charge-discharge curve of Comparative Example 1 at a current density of 20 mA / g in the first cycle, with a voltage window of 1.5 - 4.5 V and a reversible specific capacity of 184.5 mAh / g. As Figure 10 , the rate performance test results of Example 1 and Comparative Example 1, with a voltage window of 1.5 - 4.5 V. At a high current density of 2 A / g, the reversible specific capacity of Example 1 is 73.1 mAh / g, and that of Comparative Example 1 is 25.7 mAh / g. As Figure 11, The cyclic test results of Example 1 and Comparative Example 1 at a current density of 500 mA / g in the voltage range of 1.8 - 4.3 V. After 200 charge-discharge cycles, the cyclic capacity retention rate of Example 1 was 76.6%, and that of Comparative Example 1 was 46.7%. As Figure 12 , The cyclic test results of Example 1 and Comparative Example 1 at a current density of 1 A / g in the voltage range of 2 - 4 V. After 1000 charge-discharge cycles, the cyclic capacity retention rate of Example 1 was 80.1%, and after 552 charge-discharge cycles, the cyclic capacity retention rate of Comparative Example 1 was 79.8%.

[0023] Air stability test Take 0.5 g of the cathode material powder of Example 1 and Comparative Example 1 respectively, and expose them in the air for 14 days. The environmental temperature is 25 °C and the relative humidity is 55%. The comparison of powder X-ray diffraction tests of the cathode material powder of Example 1 before and after exposure in the air is as Figure 13 , After being exposed in the air for 14 days, the P2-phase crystal structure is retained, the crystallinity hardly changes, and no characteristic peaks of carbonate and hydrate are seen. The comparison of powder X-ray diffraction tests of the cathode material powder of Comparative Example 1 before and after exposure in the air is as Figure 14 , After being exposed in the air for 14 days, although the P2-phase crystal structure is retained, the characteristic peaks become wider and the intensity decreases, indicating that the crystallinity becomes worse. At the same time, the characteristic peaks of carbonate and hydrate appear. As Figure 15 , The scanning electron microscope image of the cathode material powder of Example 1 after being exposed in the air for 14 days. The layered structure hardly changes, the particle edges are relatively clear, the crystallinity is relatively good, and no cracks appear in the particles. As Figure 16 , The scanning electron microscope image of the cathode material powder of Comparative Example 1 after being exposed in the air for 14 days. The particle edges are irregular, small particles appear on the surface, the crystallinity becomes worse, and cracks are generally present and large inside the particles. As Figure 17 , The scanning transmission electron microscope image and EDS test results of the cathode material powder of Example 1 after being exposed in the air for 14 days. The crystal particles are complete without cracks, the edges are clear, and the Na, Mn, Al, and O elements are evenly distributed. As Figure 18 , The scanning transmission electron microscope image and EDS test results of the cathode material powder of Comparative Example 1 after being exposed in the air for 14 days. A large number of cracks appear in the crystal particles, the edges are blurred, the distribution of Na, Mn, and O elements is uneven, and sodium carbonate appears locally.

[0024] The charge-discharge curves of the cathode material powder of Example 1 in the first 20 cycles at a current density of 50 mA / g after being exposed in the air for 14 days are as Figure 19, the voltage window is 1.8 - 4.3 V, the discharge specific capacity in the first cycle is 145.6 mAh / g, and the capacity retention rate is 88.2% after 20 charge-discharge cycles. The charge-discharge curves of the cathode material powder in Comparative Example 1 for the first 20 cycles at a current density of 50 mA / g after being exposed to air for 14 days are as Figure 20 , the voltage window is 1.8 - 4.3 V, the discharge specific capacity in the first cycle is 145.5 mAh / g, and the capacity retention rate is 68.9% after 20 charge-discharge cycles. As Figure 21 , the rate performance test results of the cathode material powders of Example 1 and Comparative Example 1 after being exposed to air for 14 days. The voltage window is 1.5 - 4.5 V. At a current density of 20 mA / g, the reversible specific capacity of Example 1 is 170.3 mAh / g, and the capacity retention rate compared with that before exposure to air is 92.4%. The reversible specific capacity of Comparative Example 1 is 157.3 mAh / g, and the capacity retention rate compared with that before exposure to air is 85.3%. At a current density of 500 mA / g, the reversible specific capacity of Example 1 is 79 mAh / g, and the reversible specific capacity of Comparative Example 1 is 1.1 mAh / g.

[0025] Combining the results of various characterization tests and electrochemical performance tests, the air stability of Example 1 is significantly improved compared with that of Comparative Example 1. The Al 3+ bulk phase enriched with B 3+ surface enriched composite structure avoids the extraction of Na + when the cathode material is exposed to air, as well as the generation of carbonate and hydrated phases, and the crystal cracking caused by the intercalation of water molecules, significantly improving the crystal structure stability of the cathode material in air, and obtaining a sodium-ion battery layered manganese-based cathode material with air stability.

Claims

1. A layered manganese-based cathode material for sodium-ion batteries with air stability, characterized in that, It has the following chemical composition: Na 0.67 Mn x Al y B z O2; 0.8 < x < 1.0; 0 < y < 0.2; 0 < z < 0.1; Its morphology is a layered material, the B element is located in the surface layer of the material, the thickness of the surface layer is 5 - 50 nm, and the Al element is enriched in the bulk phase.

2. The layered manganese-based cathode material for sodium-ion battery with air stability according to claim 1, characterized in that, The layered material has a width of 0.5 - 1.5 μm and a thickness of 0.2 - 1.8 μm.

3. The preparation method of the layered manganese-based cathode material for sodium-ion batteries with air stability according to claim 1, characterized in that, It is prepared by a high-temperature solid-phase powder sintering method, including the following steps: Step 1: Mix the sodium source, manganese source, and aluminum source, and after ball milling, obtain the precursor powder; Step 2: Mix the precursor powder with the boron source, grind it, and then perform a calcination treatment to obtain the cathode material.

4. The preparation method of the layered manganese-based cathode material for sodium-ion battery with air stability according to claim 1, characterized in that, The sodium source is sodium carbonate, the manganese source is manganese dioxide, the aluminum source is aluminum oxide, and the boron source is boric acid.

5. The preparation method of the layered manganese-based cathode material for sodium-ion batteries with air stability according to claim 1, characterized in that, During the calcination treatment, the heating rate is 1 - 10 °C / min.

6. The preparation method of the layered manganese-based cathode material for sodium-ion batteries with air stability according to claim 1, characterized in that, During the calcination treatment, it needs to be maintained at 800 - 1000 °C for 10 - 20 h.

7. The preparation method of the layered manganese-based cathode material for sodium-ion batteries with air stability according to claim 1, characterized in that, During the ball milling treatment, ball milling is carried out at 100 - 500 rpm for 5 - 10 h.

8. A sodium-ion battery, the cathode material of which is the layered manganese-based cathode material for sodium-ion batteries described in claims 1 - 2.

9. Use of the layered manganese-based cathode material for sodium-ion batteries described in claim 1 in the preparation of the cathode of a sodium-ion battery.

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