Doped sodium manganate positive electrode material and preparation method and application thereof

Abstract

The invention relates to a doped sodium manganate positive electrode material and a preparation method and application thereof, and belongs to the technical field of sodium ion batteries. The chemical formula of the doped sodium manganate positive electrode material is Na < x > Can < n > Mn < y > Al < m > O < 2 >, n is less than or equal to 0.05, 0lt; m < = 0.1, and y + m = 1; the main crystal structure of the doped sodium manganate positive electrode material is an O-phase layer; and the O-phase layer is calcium-aluminum-doped sodium manganate and has high theoretical specific capacity. Calcium is used as a sodium-site doping modification element, and sodium-site doping can enhance the structural strength, stabilize the material structure and reduce phase change, so that the cycle performance can be improved; aluminum is a manganese-doped modified element, and manganese doping can stabilize the material structure, so that the effect of improving the cycling stability is achieved; and multi-position co-doping modification can play a synergistic role, so that the performance is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a doped sodium manganate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of energy technologies, efficient and safe energy storage technologies have become a hot topic in current research. As a new type of electrochemical energy storage technology, sodium-ion batteries are considered to be the best and most promising complementary products to current lithium-ion batteries due to a series of advantages such as easy extraction, low price, greenness, safety, environmental protection, and sustainable development. They are also one of the most promising systems for large-scale electrochemical energy storage in the future. In recent years, significant progress has been made in the research and application of sodium-ion battery cathode materials, which not only improves the energy density and cycle life of the batteries but also promotes the wide application of sodium-ion batteries in fields such as electric vehicles, energy storage systems, and smart grids.

[0003] Currently, the relatively mature and gradually commercialized cathode materials in the industry are layered oxide materials such as sodium nickel iron manganate and sodium nickel manganate. However, such materials contain expensive nickel elements and usually require pre-synthesis of precursors, resulting in high costs and ultimately relatively high selling prices of the finished products, thus losing the cost advantage of sodium-ion batteries to a certain extent. Another type of polyanion-type material with great application prospects, such as sodium iron sulfate and sodium iron pyrophosphate, although the raw material costs are low, their tap density is relatively low, which will lead to a low volumetric energy density of the battery cells, thus affecting the overall performance of the batteries. Therefore, they still face many challenges in practical applications. Sodium manganate, as a nickel-free sodium-ion cathode material, is gradually attracting the attention of researchers. Its raw material costs are low and the tap density of the finished product is relatively high. However, in the actual production and application process, there are still certain deficiencies in the capacity and cycle performance of this material. Therefore, it is of great significance to develop a sodium manganate cathode material with low cost, high tap density, and excellent electrochemical performance. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a doped sodium manganate cathode material, a preparation method thereof, and an application thereof. Due to the problem of poor cycle stability of the pure phase, the present invention uses calcium as the doping and modifying element at the sodium site and aluminum as the doping and modifying element at the manganese site to prepare a layered oxide cathode material mainly composed of O-phase sodium manganate, which has better electrochemical performance and air stability. Through the synergistic effect of co-doping at the sodium site and the manganese site, its cycle performance is optimized and the attenuation rate of the capacity is slowed down.

[0005] The first object of the present invention is to provide a doped sodium manganate cathode material, and the chemical formula of the doped sodium manganate cathode material is Na x Ca n Mn y Alm O2, where: 0.8 ≤ x ≤ 1.2, 0 < n ≤ 0.05, 0 < m ≤ 0.1, y + m = 1; the main crystal structure of the doped sodium manganese oxide cathode material is the O-phase layer; the O-phase layer is calcium-aluminum doped sodium manganese oxide.

[0006] The second object of the present invention is to provide a preparation method of the doped sodium manganese oxide cathode material, comprising the following steps: ball milling and sintering a sodium source, a manganese source, a calcium source and an aluminum source to obtain the doped sodium manganese oxide cathode material.

[0007] In one embodiment of the present invention, the sodium source is selected from sodium carbonate and / or sodium bicarbonate.

[0008] In one embodiment of the present invention, the manganese source is selected from one or more of manganese carbonate, manganese dioxide, manganese tetroxide and manganese oxide.

[0009] In one embodiment of the present invention, the calcium source is selected from one or more of calcium oxide, calcium hydroxide and calcium carbonate.

[0010] In one embodiment of the present invention, the aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide and aluminum carbonate.

[0011] In one embodiment of the present invention, the rotation speed of the ball milling is 200 rpm - 500 rpm, and the time is 3 h - 6 h.

[0012] In one embodiment of the present invention, during the ball milling process, the mass ratio of the polyurethane balls to the total material is (0.5 - 2):1.

[0013] In one embodiment of the present invention, the heating rate of the sintering is 1 °C / min - 5 °C / min, the temperature is 800 °C - 1000 °C, and the time is 5 h - 10 h.

[0014] In one embodiment of the present invention, the sintering is carried out in an air atmosphere and an oxygen atmosphere to ensure that the raw materials react fully, and the gas flow rate is 100 mL / min - 300 mL / min.

[0015] The third object of the present invention is to provide a sodium ion battery cathode, comprising the doped sodium manganese oxide cathode material.

[0016] The technical solution of the present invention has the following advantages compared with the prior art:

[0017] (1) The main component of the doped sodium manganate cathode material of the present invention is the O-phase NaMnO₂, which has a high theoretical specific capacity. Calcium is used as the doping and modification element at the sodium site. Doping at the sodium site can enhance the structural strength, stabilize the material structure, and reduce the occurrence of phase transitions, thus improving the cycling performance; aluminum is used as the doping and modification element at the manganese site. Doping at the manganese site can also stabilize the material structure, achieving the effect of improving the cycling stability; multi-site co-doping and modification can play a synergistic role to further improve the performance.

[0018] (2) The raw materials used for the doped sodium manganate cathode material of the present invention are low in cost. It does not use any nickel-containing precursors or additives, nor does it use materials containing expensive metals, strictly controlling the raw material cost.

[0019] (3) The tap density of the doped sodium manganate cathode material of the present invention reaches 3.3 g / cm 3 , and compared with the polyanion cathode material with comparable specific energy, it can provide a higher volume energy density for the battery cell. When used in sodium-ion batteries, it can obtain excellent volume energy density and cycling stability performance, with good economic benefits.

[0020] (4) The preparation method of the present invention has a simple process, is easy to operate, and is easy to realize industrial production. Moreover, the production process is pollution-free and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention in combination with the drawings, wherein:

[0022] Figure 1 is the SEM image of the doped sodium manganate cathode material prepared in Example 1 of the present invention;

[0023] Figure 2 is the XRD pattern of the doped sodium manganate cathode material prepared in Example 1 of the present invention;

[0024] Figure 3 is the charge-discharge curve of the button cell made of the doped sodium manganate cathode material prepared in Example 1 of the present invention at 0.2C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following further illustrates the present invention in combination with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the examples given are not used as a limitation to the present invention.

[0026] In the present invention, unless otherwise specified, the technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the technical field to which the present invention pertains.

[0027] In the present invention, unless otherwise specified, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0028] In the present invention, unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods without special instructions, and the materials, reagents, etc. used can be obtained from commercial channels without special instructions.

[0029] In the present invention, unless otherwise specified, when the terms "comprise" and / or "include" are used in the specification of the present invention, they indicate the presence of the stated features, wholes, steps, operations, raw materials or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, raw materials, components or combinations thereof.

[0030] Example 1

[0031] The doped sodium manganese oxide cathode material and its preparation method of this embodiment specifically include the following steps:

[0032] Weigh 31.10 g of sodium carbonate, 68.14 g of manganese carbonate, 0.31 g of alumina and 0.60 g of calcium carbonate and place them in a zirconia ball milling jar. Add about 100 g of polyurethane balls, and use a ball mill to ball mill at 300 rpm for 3 h to obtain a mixed powder;

[0033] Place the mixed powder in a muffle furnace and calcine it at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain a doped sodium manganese oxide cathode material mainly composed of the O phase, Na 0.98 Ca 0.01 Mn 0.99 Al 0.01 O2.

[0034] Comparative Example 1

[0035] Basically the same as Example 1, the difference is that no aluminum or calcium doping is carried out, and it specifically includes the following steps:

[0036] Weigh 31.10 g of sodium carbonate and 68.83 g of manganese carbonate and place them in a zirconia ball milling jar. Add about 100 g of polyurethane balls, and use a ball mill to ball mill at 300 rpm for 3 h to obtain a mixed powder;

[0037] Place the mixed powder in a muffle furnace and calcine it at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain a sodium manganese oxide cathode material, Na 0.98 MnO2.

[0038] Comparative Example 2

[0039] Basically the same as Example 1, except that no aluminum doping is carried out, and the specific steps are as follows:

[0040] Weigh 31.10 g of sodium carbonate, 68.83 g of manganese carbonate and 0.60 g of calcium carbonate and place them in a zirconia ball milling tank. Add about 100 g of polyurethane balls and use a ball mill to mill at 300 rpm for 3 h to obtain a mixed powder;

[0041] Place the mixed powder in a muffle furnace and calcine at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain the doped sodium manganese oxide cathode material Na 0.98 Ca 0.01 MnO2.

[0042] Comparative Example 3

[0043] Basically the same as Example 1, except that no calcium doping is carried out, and the specific steps are as follows:

[0044] Weigh 31.10 g of sodium carbonate, 68.14 g of manganese carbonate and 0.31 g of aluminum oxide and place them in a zirconia ball milling tank. Add about 100 g of polyurethane balls and use a ball mill to mill at 300 rpm for 3 h to obtain a mixed powder;

[0045] Place the mixed powder in a muffle furnace and calcine at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain the doped sodium manganese oxide cathode material Na 0.98 Mn 0.99 Al 0.01 O2.

[0046] Comparative Example 4

[0047] Basically the same as Example 1, except that the calcium doping is replaced by magnesium doping and the aluminum doping is replaced by iron doping, and the specific steps are as follows:

[0048] Weigh 31.10 g of sodium carbonate, 68.14 g of manganese carbonate, 0.48 g of iron oxide and 0.50 g of magnesium carbonate and place them in a zirconia ball milling tank. Add about 100 g of polyurethane balls and use a ball mill to mill at 300 rpm for 3 h to obtain a mixed powder;

[0049] Place the mixed powder in a muffle furnace and calcine at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain the doped sodium manganese oxide cathode material Na 0.98 Mg 0.01 Mn 0.99 Fe 0.01 O2.

[0050] Comparative Example 5

[0051] Basically the same as Example 1, except that on the basis of calcium doping, magnesium doping is added, and on the basis of aluminum doping, iron doping is added. The specific steps are as follows:

[0052] Weigh 31.10 g of sodium carbonate, 67.45 g of manganese carbonate, 0.48 g of iron oxide, 0.31 g of aluminum oxide, 0.60 g of calcium carbonate and 0.50 g of magnesium carbonate and place them in a zirconia ball milling jar. Add about 100 g of polyurethane balls and use a ball mill to mill at 300 rpm for 3 h to obtain a mixed powder;

[0053] Place the mixed powder in a muffle furnace and calcine at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain the doped sodium manganese oxide cathode material Na 0.98 Ca 0.01 Mg 0.01 Mn 0.98 Al 0.01 Fe 0.01 O2.

[0054] Comparative Example 6

[0055] Basically the same as Example 1, except for the sodium content. The specific steps are as follows:

[0056] Weigh 21.34 g of sodium carbonate, 68.14 g of manganese carbonate, 0.31 g of aluminum oxide and 0.60 g of calcium carbonate and place them in a zirconia ball milling jar. Add about 100 g of polyurethane balls and use a ball mill to mill at 300 rpm for 3 h to obtain a mixed powder;

[0057] Place the mixed powder in a muffle furnace and calcine at 900 °C for 8 h, with a heating rate of 3 °C / min and a compressed air intake of 150 mL / min, to obtain the doped sodium manganese oxide cathode material Na 0.67 Ca 0.01 Mn 0.99 Al 0.01 O2.

[0058] Comparative Example 7

[0059] Weigh 10.22 g of anhydrous sodium sulfate, 18.35 g of ferrous sulfate monohydrate and 1.30 g of carbon nanotubes and place them in a vacuum ball milling jar. At the same time, add 10 mm zirconia balls with a mass ratio of 15:1, fill the tank with nitrogen, and mill at 300 r / min for 6 h to obtain a mixed powder;

[0060] Transfer the mixed powder into a tubular furnace and carry out calcination treatment under the protection of a nitrogen atmosphere. The calcination temperature is 350 °C, the heating rate is 2.5 °C / min, the holding time is 10 h, and then it is naturally cooled to obtain the sodium iron sulfate cathode material Na 2.4 Fe 1.8 (SO4)3 / C.

[0061] Comparative Example 8

[0062] Weigh 7.42 g of anhydrous sodium pyrophosphate, 15.14 g of ferrous oxalate, 6.45 g of ammonium dihydrogen phosphate, 1.45 g of anhydrous glucose and 90 g of anhydrous ethanol and place them in a vacuum ball milling tank. At the same time, add 5 mm zirconia balls with a mass ratio of 10:1 and ball mill at 300 r / min for 12 h. After ball milling, place it in a vacuum drying oven and dry at 80 °C for 12 h to obtain a mixed powder;

[0063] Transfer the mixed powder into a tubular furnace and carry out calcination treatment under the protection of a nitrogen atmosphere. First, pre-sinter at 350 °C for 6 h, then raise the temperature to 550 °C and calcine for 8 h. The heating rate is 3 °C / min, and then it is naturally cooled to obtain the sodium iron pyrophosphate phosphate cathode material Na4Fe3(PO4)2P2O7 / C.

[0064] Test Example 1

[0065] Carry out SEM and XRD characterization on the doped sodium manganate cathode material mainly composed of the O phase prepared in Example 1. The results are as follows Figure 1 and Figure 2 shown. From Figure 1 it can be seen that the morphology of the doped sodium manganate cathode material is in the shape of long strip rods, with distinct edges and corners and regular shapes, which is consistent with the orthorhombic crystal system with the main component of the O phase structure. From Figure 2 it can be seen that the composition of the doped sodium manganate cathode material is mainly the O phase NaMnO2. The theoretical capacity of the O phase material is relatively high, so it can exhibit good electrical properties. In addition, Figure 2 there are also a small number of impurity phase peaks shown in

[0066] Test Example 2

[0067] Fabricate button cells with the cathode materials prepared in Example 1 and Comparative Examples 1-6 to test the electrical properties. Among them, the weight ratio of the cathode components is cathode material: conductive agent (acetylene black): binder (PVDF) = 90:5:5; the anode uses a sodium sheet, the electrolyte is NaClO4, and the test temperature of the button cell is 25 °C. The results are as follows Figure 3 and Table 1 show:

[0068] Table 1

[0069]

[0070] From Figure 3 As can be seen from Table 1, for the doped sodium manganate cathode material of Example 1 under the condition of 0.2C rate, the charge specific capacity reaches 164.79 mAh / g, the discharge specific capacity reaches 140.95 mAh / g, the discharge plateau is about 2.7V, and the multiple inflection points in the charge-discharge curve indicate the existence of multiple phase transitions, which is consistent with the situation of multiple valence changes and phase transitions during the charge-discharge process of manganese-based materials. Compared with Comparative Example 1 without doping, and Comparative Examples 2 and 3 with single-site sodium doping or manganese doping respectively, the discharge specific capacity of Example 1 with co-doping of sodium site and manganese site does not differ significantly, but the cyclic capacity retention rate is much higher, increasing from 71.95% to 96.12%, indicating that the co-doping of sodium site and manganese site can play a synergistic role and further improve the cyclic performance. The cathode materials prepared by doping with other elements in Comparative Example 4 and multi-site co-doping in Comparative Example 5 are inferior in electrical properties, indicating that a better cathode material can be prepared by simply performing double-site single-element co-doping with calcium and aluminum. Comparative Example 6 is to prepare a doped sodium manganate cathode material mainly in the P phase by adjusting the sodium ratio, which differs greatly from Example 1 in terms of capacity, indicating that the O-phase-based doped sodium manganate cathode material of the example has more value for mass production and application.

[0071] Test Example 3

[0072] The single-point compaction density test at 300 MPa was carried out on the cathode materials prepared in Example 1 and Comparative Examples 7-8 respectively by using a powder compaction density meter, and the pressure was maintained for 10 s, and the obtained powder compaction data were recorded; the charge-discharge performance test referred to Test Example 2, and the test results are shown in Table 2:

[0073] Table 2

[0074]

[0075] As can be seen from Table 2, the 1C specific energy (the product of specific capacity and discharge voltage) of the cathode materials in Comparative Examples 7-8 is equivalent to that of Example 1, but the compaction density is only about two-thirds of that of Example 1, which means that more cathode materials of Example 1 can be accommodated under the same volume, that is, the volume energy density is higher.

[0076] Obviously, the above examples are only for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A doped sodium manganate cathode material, characterized in that, The chemical formula of the doped sodium manganate cathode material is Na x Ca n Mn y Al m O2, where: 0.8 ≤ x ≤ 1.2, 0 < n ≤ 0.05, 0 < m ≤ 0.1, y + m = 1; the main crystal structure of the doped sodium manganate cathode material is the O-phase layer; the O-phase layer is calcium-aluminum-doped sodium manganate.

2. A method for preparing the doped sodium manganate cathode material according to claim 1, characterized in that, It includes the following steps: ball-milling and sintering a sodium source, a manganese source, a calcium source, and an aluminum source to obtain the doped sodium manganate cathode material described above.

3. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that, The sodium source is selected from sodium carbonate and / or sodium bicarbonate.

4. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that, The manganese source is selected from one or more of manganese carbonate, manganese dioxide, manganese tetroxide, and manganese oxide.

5. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that, The calcium source is selected from one or more of calcium oxide, calcium hydroxide, and calcium carbonate.

6. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that, The aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide, and aluminum carbonate.

7. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that The rotation speed of the ball-milling is 200 rpm - 500 rpm, and the time is 3 h - 6 h.

8. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that, The heating rate of the sintering is 1 °C / min - 5 °C / min, the temperature is 800 °C - 1000 °C, and the time is 5 h - 10 h.

9. The preparation method of the doped sodium manganate cathode material according to claim 2, characterized in that, The sintering is carried out in an air atmosphere and an oxygen atmosphere, and the gas flow rate is 100 mL / min - 300 mL / min.

10. A positive electrode of a sodium-ion battery, characterized in that, It includes the doped sodium manganate cathode material described in claim 1.

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