High-entropy layered oxide positive electrode material for sodium ion battery and preparation method of high-entropy layered oxide positive electrode material

Abstract

The invention provides a high-entropy layered oxide positive electrode material for a sodium ion battery and a preparation method of the high-entropy layered oxide positive electrode material. The chemical general formula of the material is Na < 0.67 > Cu < x > Co < y > Ni < z > Fe Mn < w > O < x >, the material has a P2 type layered crystal structure, the configuration entropy reaches 1.61 R, and high-voltage irreversible phase change can be inhibited; the preparation method adopts a high-energy ball milling-high-temperature solid-phase sintering method and comprises the following steps: firstly, drying a metal source raw material with a specific ratio at 70-85 DEG C for 1-5 hours, and grinding until the particle size is less than 150 microns; carrying out ball milling for 11-13 hours at the speed of 350-450rpm according to the mass ratio of the raw materials to the ball milling beads of 1: (18-22) to obtain a precursor; finally, raising the temperature to 900-1000 DEG C at the speed of 1-3 DEG C / min in an air atmosphere, keeping the temperature for 8-12 hours, and keeping the temperature at 150-250 DEG C for 1-4 hours during cooling to obtain a pure-phase product; the first discharge capacity of the material is about 148mAh / g, the capacity retention rate after 200 cycles reaches 89%, and the material is simple in process, low in cost and suitable for the field of large-scale energy storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion battery materials, and particularly relates to a high-entropy layered oxide positive electrode material for sodium ion batteries and a preparation method thereof. BACKGROUND

[0002] Sodium ion batteries have broad application prospects in large-scale energy storage due to abundant sodium resources and low cost. The positive electrode material is the key to determine the performance of sodium ion batteries. Sodium-based layered transition metal oxides, especially sodium manganese oxides, have attracted extensive attention due to their high theoretical capacity. However, these materials undergo severe structural phase transition and Jahn-Teller effect during charge and discharge, resulting in poor cycle stability and rapid capacity decay, which seriously restricts their practical application.

[0003] Sodium-based layered transition metal oxides have been widely studied in large-scale energy storage and low-speed transportation due to their simple preparation method, easy technology transformation, high energy density, high reversible specific capacity, high rate performance and reversible sodium ion extraction / insertion capability. However, the phase transition occurring during charge and discharge leads to poor cycle life, which cannot meet the development needs of sodium ion batteries applied to new energy vehicles with long endurance (>1000km). The theoretical capacity of sodium manganese oxide NaMnO2 positive electrode material is as high as 243mAh / g, and manganese element is environmentally friendly and abundant in resources, which becomes a candidate for the next generation of high-energy-density sodium ion battery positive electrode materials. However, NaMnO2 faces serious structural stability problems during charge and discharge due to Jahn-Teller effect, leading to rapid capacity decay and restricting its further development. The existing performance optimization path is to change the crystal structure of NaMnO2 by adjusting the sintering temperature to prepare alpha-NaMnO2 (<700℃), beta-NaMnO2 (~1000℃) and other layered structures to improve the structural stability, but the improvement effect is limited. SUMMARY

[0004] In view of this, the present application provides a high-entropy layered oxide positive electrode material for sodium ion batteries and a preparation method thereof, which solves the above problems.

[0005] The technical scheme of the present application is as follows: a high-entropy layered oxide positive electrode material for sodium ion batteries, the chemical general formula of the material is Na 0.67 Cu x Co y Ni z Fe u Mn w O xwherein x is in the range of 0.05-0.1, y, z, u are each in the range of 0.05-0.15, and satisfy x+y+z+u≤0.4, w is in the range of 0.6-0.7, and the material has a P2-type layered crystal structure.

[0006] Preferably, the chemical formula of the material is Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x、 Na 0.67 Cu 0.08 Co 0.08 Ni 0.08 Fe 0.08 Mn 0.68 O x or Na 0.67 Cu 0.05 Co 0.12 Ni 0.08 Fe 0.15 Mn 0.6 O x .

[0007] Preferably, a preparation method of a high-entropy layered oxide positive electrode material for sodium ion batteries comprises the following steps: (1) raw material pretreatment: dry and grind the metal source raw material; (2) high-energy ball milling to prepare a precursor: mix the pretreated raw material with ball milling beads and perform high-energy ball milling to obtain a uniformly mixed precursor; (3) high-temperature solid-phase sintering: heat the precursor to 900-1000℃ at a heating rate of 1-3℃ / min in an air atmosphere, and keep the temperature for 8-12 hours, and then perform cooling treatment to obtain a high-entropy layered oxide positive electrode material, which is a pure phase product P2-type positive electrode material.

[0008] More preferably, the metal source raw material in step (1) comprises the following weight components: anhydrous sodium carbonate 3.5-4.0g, manganese monoxide 4.0-4.5g, nano copper oxide 0.4-1.0g, cobalt monoxide 0.5-1.0g, nickel hydroxide 0.6-1.2g, and ferrous oxide 0.6-1.1g.

[0009] More preferably, the nano copper oxide has a particle size of 50-100nm, the ferrous oxide has a purity of ≥99.5%, and the nickel hydroxide is β-type nickel hydroxide.

[0010] More preferably, the drying in step (1) is oven drying at 70-85℃ for 1-5 hours.

[0011] More preferably, the grinding particle size in step (1) is < 150 μm.

[0012] More preferably, the mass ratio of the raw material to the ball milling beads after the treatment in step (2) is 1:18-22, the ball milling rotation speed is 350-450 rpm, the ball milling time is 11-13 hours, and after the ball milling, the precursor is stored in a vacuum environment at 50-70℃.

[0013] More preferably, the heating rate in step (3) is 2℃ / min, the sintering temperature is 950℃, and the holding time is 10 hours.

[0014] More preferably, the cooling treatment in step (3) is natural cooling, and when the temperature is cooled to 150-250℃, the holding time is 1-4 hours, and then the temperature is cooled to room temperature.

[0015] Compared with the prior art, the present application has the following beneficial effects: The present application uses manganese sodium oxide as a template, synthesizes a new type of high-entropy layered sodium manganese oxide compound by doping transition metal elements, expands the sodium manganese oxide compound into a new type of high-entropy material, the configuration entropy is 1.61R, effectively improves the stability in air, and inhibits the irreversible phase transition under high pressure.

[0016] The present application can prepare pure-phase, well-crystallized layered oxides by a high-energy ball milling-high-temperature solid-phase sintering method, which is simple in process, low in cost, and suitable for large-scale preparation. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The SEM image of the material prepared in Example 1 of the present application is shown in Figure 1. 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x The SEM image of the material prepared in Example 1 of the present application is shown in Figure 1. Figure 2 The XRD pattern of the material prepared in Example 1 of the present application is shown in Figure 2. Figure 3 The XRD pattern of the material prepared in Example 2 of the present application is shown in Figure 3. Figure 4 The XRD pattern of the material prepared in Example 3 of the present application is shown in Figure 4. Figure 5 The EDS surface distribution map of the material prepared in Example 1 of the present application is shown in Figure 5. Figure 6 The charge-discharge curve of the material prepared in Example 1 of the present application as a positive electrode of a sodium ion battery is shown in Figure 6. Figure 7 The material prepared in Example 1 of the present application and the traditional Na 0.7 MnO 2.05 Comparison chart of long cycle performance of the material. DETAILED DESCRIPTION

[0018] In order to better understand the technical content of the present application, the following specific examples are provided to further illustrate the present application.

[0019] The experimental methods used in the examples of the present application are conventional methods unless otherwise specified.

[0020] The materials, reagents, etc. used in the examples of the present application can be obtained commercially unless otherwise specified.

[0021] Example 1: Preparation of Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x Weigh by mass: anhydrous sodium carbonate (Na2CO3) 3.8g, manganese monoxide (MnO) 4.2g, nano copper oxide (CuO) 0.75g, cobalt monoxide (CoO) 0.75g, nickel hydroxide (Ni(OH)2) 1.0g, iron monoxide (FeO) 0.75g.

[0022] Preparation method: (1) Put the above raw materials into a 80℃ oven and dry for 3 hours, then grind into fine powder after taking out.

[0023] (2) Put the powder and ball milling beads into a ball milling tank according to the mass ratio of 1:20, and ball mill at 400rpm for 12 hours. Immediately transfer to a 60℃ vacuum oven after taking out.

[0024] (3) Put the precursor into a corundum crucible and put it into a muffle furnace, heat to 950℃ at a rate of 2℃ / min under air atmosphere, and keep for 10 hours.

[0025] (4) After sintering, naturally cool, keep at 200℃ for 2 hours, then cool to room temperature, get black block-shaped product, grind after that is the target positive electrode material.

[0026] Example 2: Preparation of Na 0.67 Cu 0.08 Co 0.08 Ni 0.08 Fe 0.08 Mn 0.68 O x Weigh the following by weight: 3.8g anhydrous sodium carbonate (Na2CO3), 4.4g manganese monoxide (MnO), 0.6g nano copper oxide (CuO, particle size 50-100nm), 0.6g cobalt oxide (CoO), 0.6g β-type nickel hydroxide (Ni(OH)2), and 0.6g ferrous oxide (FeO, purity ≥99.5%).

[0027] The preparation method is the same as in Example 1.

[0028] Example 3: Preparation of Na 0.67 Cu 0.05 Co 0.12 Ni 0.08 Fe 0.15 Mn 0.6 O x Weigh the following by weight: 3.8g anhydrous sodium carbonate (Na2CO3), 4.2g manganese monoxide (MnO), 0.4g nano copper oxide (CuO, particle size 50-100nm), 0.9g cobalt oxide (CoO), 0.6g β-type nickel hydroxide (Ni(OH)2), and 1.1g ferrous oxide (FeO, purity ≥99.5%).

[0029] The preparation method is the same as in Example 1.

[0030] Test The microstructure, crystal structure, and elemental distribution uniformity of the battery cathode material of this invention were characterized using scanning electron microscopy and X-ray diffraction.

[0031] After testing, by Figure 1 It can be seen that the pure phase product P2-Na obtained by the high-energy ball milling-high-temperature solid-state sintering method in Example 1 of this invention is... 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x The material particles exhibit a regular hexagonal layered structure with uniform size, ranging from 2 to 10 μm, indicating good crystallinity.

[0032] from Figure 2 It can be known that Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x XRD patterns of materials and P2-Na 0.7 MnO 2.05The standard PDF card of the phase structure is matched, and no extra impurity diffraction peak appears, which proves that the material structure is a pure phase P2 type (space group P63 / mmc) transition metal oxide. The diffraction peak is very sharp, indicating that it has good crystallinity.

[0033] Figure 3 Na 0.67 Cu 0.08 Co 0.08 Ni 0.08 Fe 0.08 Mn 0.68 XRD pattern of the O material. The pattern is completely matched with the standard PDF card of P2 type-Na 0.7 MnO 2.05 The standard PDF card of the phase structure is completely matched, and no extra impurity diffraction peak appears, which proves that the material is successfully synthesized into a pure phase P2 type structure. The diffraction peak in the pattern is sharp and symmetrical, indicating that the material has good crystallinity, and the multi-element doping does not destroy the P2 type layered crystal structure, further verifying the reliability of the preparation process of the application.

[0034] Figure 4 Na 0.67 Cu 0.05 Co 0.12 Ni 0.08 Fe 0.15 Mn 0.6 O x XRD pattern of the material. From the pattern, it can be seen that the diffraction peak position is matched with the standard PDF card of P2 type-Na 0.7 MnO 2.05 The standard PDF card is highly matched, and no impurity phase diffraction peak appears, which proves that the material is a pure phase P2 type layered crystal structure. The diffraction peak is sharp and clear, and the peak width is narrow, indicating that the material has high crystallinity and regular crystal arrangement. Even if the doping ratio of Cu, Co and Fe is adjusted, a pure phase P2 type structure can still be stably formed, which reflects the rationality of the composition design of the material and the stability of the process.

[0035] Figure 5 It can be seen that Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x The Na, Cu, Co, Ni, Fe, Mn and O elements in the material are highly uniform in the material, and there is no segregation phenomenon, which indicates that they have completely reacted to form the corresponding product, proving the effectiveness of high-energy ball milling and the uniformity of the product.

[0036] The positive electrode material of Example 1 was prepared into an electrode sheet and assembled into a CR2032 type button half-cell for testing the charge-discharge performance and long cycle stability.

[0037] Figure 6 It can be seen that the material has a first discharge capacity of about 148 mAh / g as a positive electrode of a sodium ion battery, has a high sodium storage activity. At the same time, it has obvious charge-discharge platforms, a discharge platform of about 3.5 / 2.3 / 1.8 V, a charge platform of about 2.2 / 2.6 / 3.7 V, stable cycle performance, and can still maintain a discharge specific capacity of 130.5 mAh / g after 200 cycles.

[0038] Table 1. Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x The electrode sheet and the traditional Na 0.7 MnO 2.05 The cycle performance comparison of the electrode sheet

[0039] From the above Table 1 and Figure 7 Analysis can be obtained that the Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x The material has a first discharge capacity of about 148 mAh / g as a positive electrode of a sodium ion battery, and after 5 / 10 cycles, the reversible capacity is about ~ 148 mAh / g, the capacity retention rate is about 100%; after 50 cycles, the reversible capacity is about ~ 142 mAh / g, the capacity retention rate is about 96%; after 100 cycles, the reversible capacity is about ~ 139 mAh / g, the capacity retention rate is about 94%. Similarly, after 200 cycles, the reversible capacity is about ~ 131 mAh / g, the capacity retention rate is about 89%. In comparison, the traditional Na 0.7 MnO 2.05 The capacity of the electrode sheet after 5 / 10 / 50 / 100 / 200 cycles is only 178 / 172 / 145 / 106 / 68 mAh / g, and the capacity retention rate is only 100% / 97% / 81% / 60% / 38%. Therefore, thanks to the entropy increase strategy brought by multi-element doping, the Na 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O xThe phase change occurring in the charging and discharging process is effectively buffered, so that the cycle stability of the electrode sheet is effectively improved.

[0040] The above merely provides the preferred embodiments of the application, and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall fall within the protection scope of the application.

Claims

1. A high-entropy layered oxide cathode material for sodium-ion batteries, characterized in that, The chemical formula of the material is Na. 0.67 Cu x Co y Ni z Fe u Mn w O x The value of x ranges from 0.05 to 0.1, the values ​​of y, z, and u each range from 0.05 to 0.15, and x + y + z + u ≤ 0.4, the value of w ranges from 0.6 to 0.8, and the material has a P2 type layered crystal structure.

2. The high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 1, characterized in that, The chemical formula of the material is Na. 0.67 Cu 0.1 Co 0.1 Ni 0.1 Fe 0.1 Mn 0.6 O x Na 0.67 Cu 0.08 Co 0.08 Ni 0.08 Fe 0.08 Mn 0.68 O x Or Na 0.67 Cu 0.05 Co 0.12 Ni 0.08 Fe 0.15 Mn 0.6 O x .

3. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 1, characterized in that, Includes the following steps: (1) Raw material pretreatment: The metal source raw materials are dried and ground; (2) Preparation of precursor by high-energy ball milling: The pretreated raw material is mixed with the ball milling beads and subjected to high-energy ball milling to obtain a uniformly mixed precursor; (3) High-temperature solid-state sintering: The precursor is heated to 900-1000℃ in air at a heating rate of 1-3℃ / min and held for 8-12 hours. Then it is cooled to obtain a high-entropy layered oxide cathode material, which is the pure phase product P2 type cathode material.

4. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, The metal source materials in step (1) include the following weight components: 3.5-4.0g of anhydrous sodium carbonate, 4.0-4.5g of manganese monoxide, 0.4-1.0g of nano copper oxide, 0.5-1.0g of cobalt oxide, 0.6-1.2g of nickel hydroxide, and 0.6-1.1g of ferrous oxide.

5. The high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 4, characterized in that, The nano-copper oxide has a particle size of 50-100 nm, the ferrous oxide has a purity of ≥99.5%, and the nickel hydroxide is β-type nickel hydroxide.

6. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, In step (1), the drying process is carried out in an oven at 70-85℃ for 1-5 hours.

7. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, In step (1), the grinding particle size is <150μm.

8. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, The mass ratio of the raw material to the ball milling beads after step (2) is 1:18-22. The ball milling speed is 350-450 rpm and the ball milling time is 11-13 hours. After ball milling, the precursor is stored in a vacuum environment at 50-70℃.

9. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, Step (3) The heating rate is 2℃ / minute, the sintering temperature is 950℃, and the holding time is 10 hours.

10. The method for preparing a high-entropy layered oxide cathode material for sodium-ion batteries as described in claim 3, characterized in that, The cooling process in step (3) is natural cooling, and the temperature is maintained at 150-250°C for 1-4 hours, and then cooled to room temperature.

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