Sodium-ion battery positive electrode material, preparation method thereof, sodium-ion battery and electrical equipment

Abstract

The present invention relates to the technical field of batteries, and discloses a cathode material for a sodium-ion battery, a preparation method thereof, a sodium-ion battery, and an electricity-related device. The cathode material includes a matrix and a coating layer coated on the surface of the matrix. The matrix includes a layered oxide; the coating layer includes Na x Mn 1‑y M' y O z F β , where 0.6 < x < 0.8, 0 < y ≤ 0.05, 1.9 < z ≤ 2.1, 0 < β ≤ 0.05, and M' is selected from at least one of Ni, Fe, Co, Ti, Li, and Mn. For the cathode material for a sodium-ion battery provided by the present invention, on the one hand, the P2-phase coating layer has good structural stability and can also significantly improve the cycle performance of the battery. On the other hand, the coating layer can reduce the residual sodium on the surface of the matrix, can also provide charge compensation during the process of sodium ion extraction / insertion, provide a fast Na + diffusion channel, and alleviate the downward trend of the discharge medium voltage, so that the battery takes into account both capacity and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a cathode material for a sodium-ion battery, a preparation method thereof, a sodium-ion battery, and an electricity-related device. Background Art

[0002] In recent years, sodium-ion batteries have shown excellent development and application prospects in the fields of consumer electronics, electric vehicles, and large-scale energy storage. Due to the advantages of high capacity, simple preparation, and adjustable voltage range of sodium-layered oxides, they have received extensive attention and research in the academic and industrial circles. Coating modification is widely used and has significant effects on the cathode materials of sodium-layered oxides. Currently, oxides are usually used for coating, such as Fe2O3, NiO, Al2O3, etc., but the oxide coatings are easily eroded by hydrofluoric acid, affecting the coating modification effect. Summary of the Invention

[0003] The purpose of the present invention is to provide a cathode material for a sodium-ion battery, a preparation method thereof, a sodium-ion battery, and an electricity-related device, so as to improve the structural stability of the cathode material for a sodium-ion battery, reduce the surface residual alkali, and further improve the cycle performance of the battery, making the battery take into account both capacity and cycle performance.

[0004] To achieve the above purpose, in the first aspect of the present invention, a cathode material for a sodium-ion battery is provided. The cathode material includes a matrix and a coating layer coated on the surface of the matrix. The matrix includes a layered oxide; the coating layer includes Na x Mn 1-y M' y O z F β , where 0.6 < x < 0.8, 0 < y ≤ 0.05, 1.9 < z ≤ 2.1, 0 < β ≤ 0.05, and M' is selected from at least one of Ni, Fe, Co, Ti, Li, and Mn.

[0005] In some embodiments, the matrix includes a layered oxide with an O3 phase; optionally, the chemical general formula of the layered oxide is Na i MF α O j , where 0.6 < i < 1.1, 0 ≤ α ≤ 0.05, 1.9 < j ≤ 2.1, and M is selected from at least one of Ni, Fe, Mn, Co, Ti, Cu, Ca, Zn, Mg, Al, Y, Ce, Sr, Sn, Ba, La, and Li.

[0006] In some embodiments, the mass ratio of the P2 phase to the O3 phase is (0.01 - 0.05):1.

[0007] In some embodiments, the cathode material satisfies at least one of the following conditions:

[0008] a. The concentration of fluorine element in the matrix is less than that in the coating layer;

[0009] b. The chemical general formula of the coating layer is Na x Mn 1-y M' y O z F β , where 0.6 < x < 0.7, 0 < y ≤ 0.02, 1.9 < z ≤ 2. , 0 < β ≤ 0.02, and M' is selected from at least one of Mn, Co, and Li;

[0010] c. The average thickness of the coating layer is 5 - 50 nm;

[0011] d. The D50 of the positive electrode material is 3 - 20 μm;

[0012] e. The mass of the coating layer accounts for 1 - 5% of the mass of the matrix.

[0013] The second aspect of the present invention provides a method for preparing a positive electrode material for a sodium - ion battery as described in the first aspect, and the method includes:

[0014] Performing a first sintering on a first mixture including a manganese - containing compound, a fluoride containing M', and the matrix to obtain the positive electrode material.

[0015] In some embodiments, the method satisfies at least one of the following conditions:

[0016] (1) The manganese - containing compound is selected from at least one of MnCO3, MnO, Mn2O3, MnO2, Mn2O7, and Mn3O4;

[0017] (2) M' in the fluoride containing M' is selected from at least one of Ni, Fe, Co, Ti, Li, and Mn;

[0018] (3) The temperature of the first sintering is 400 - 700 °C, and the time is 4 - 8 h; optionally, the temperature of the first sintering is 500 - 600 °C, and the time is 6 - 8 h;

[0019] (4) The heating rate of the first sintering is 1 - 5 °C / min; optionally, the heating rate of the first sintering is 1 - 3 °C / min;

[0020] (5) The matrix is polycrystalline particles or single - crystal particles;

[0021] (6) The mass ratio of the coating layer to the matrix in the first mixture is (0.01 - 0.05):1.

[0022] In some embodiments, the matrix is ​​obtained by second sintering a second mixture including a sodium source and a metal M source.

[0023] In some implementations, the method satisfies at least one of the following conditions:

[0024] A. The sodium source is selected from at least one of sodium carbonate, sodium hydroxide, and sodium bicarbonate;

[0025] B. The metal M source is selected from at least one of the following: oxides containing metal M, hydroxides containing metal M, and carbonates containing metal M;

[0026] C. The M in the metal M source is selected from at least one of Ni, Fe, Mn, Co, Ti, Cu, Ca, Zn, Mg, Al, Y, Ce, Sr, Sn, Ba, La, and Li;

[0027] D. The second sintering temperature is 800-1100℃, and the time is 10-15h;

[0028] E. The heating rate for the second sintering is 1-3℃ / min;

[0029] F. The molar ratio of sodium to metal M in the second mixture is (0.6-1.1):1.

[0030] A third aspect of the present invention provides a sodium-ion battery comprising the sodium-ion battery cathode material described in the first aspect.

[0031] A fourth aspect of the present invention provides an electrical device comprising the sodium-ion battery described in the third aspect.

[0032] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages:

[0033] The sodium-ion battery cathode material provided by this invention has the following advantages: Firstly, the P2 phase coating layer exhibits good structural stability, and the formed F-Mn bonds can both reduce the dissolution of manganese caused by hydrogen fluoride corrosion in the electrolyte and inhibit Mn dissolution. 3+ The lattice distortion caused by the Ginger-Taylor effect can significantly improve the cycle performance of the battery. On the other hand, the coating layer can reduce the residual sodium on the surface of the substrate and provide charge compensation and rapid Na+ extraction / insertion during sodium ion extraction / insertion. + The diffusion channel, along with mitigating the voltage drop trend during discharge, allows the battery to balance capacity and cycle performance. Attached Figure Description

[0034] Figure 1This is a comparison chart of the discharge specific capacity of batteries assembled with the cathode materials obtained in Embodiment 1, Comparative Example 1, and Comparative Example 3 provided by the present invention, at discharge rates of 0.1C, 0.2C, and 1C within a voltage range of 2.0-4.3V.

[0035] Figure 2 This is a comparison chart of the discharge voltage of batteries assembled with the cathode materials obtained in Example 1 and Comparative Example 4 of the present invention within a voltage range of 2.0-4.3V at discharge rates of 0.1C, 0.2C, and 1C.

[0036] Figure 3 This is a SEM image of the cathode material obtained in Example 1 of the present invention;

[0037] Figure 4 This is the XRD pattern of the cathode material obtained in Example 1 of the present invention;

[0038] Figure 5 The XRD pattern of sodium fluoromanganate obtained from the control group provided by the present invention is an example.

[0039] Figure 6 This is a cross-sectional EPMA diagram of the cathode material obtained in Example 1 of the present invention;

[0040] Figure 7 This is a cross-sectional electron microscope image of the cathode material obtained in Embodiment 1 of the present invention;

[0041] Figure 8 This is a fluorine element analysis point selection diagram of the cross-section EDS of the cathode material obtained by Example 1 of the present invention. Detailed Implementation

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] As described above, the first aspect of the present invention provides a cathode material for a sodium-ion battery. The cathode material includes a matrix and a coating layer coated on the surface of the matrix. The matrix includes a layered oxide; the coating layer includes Na x Mn 1-y M' y O z F β , where 0.6 < x < �.8, 0 < y ≤ 0.05, 1.9 < z ≤ 2.1, 0 < β ≤ 0.05, and M' is selected from at least one of Ni, Fe, Co, Ti, Li, and Mn.

[0046] For the cathode material for a sodium-ion battery provided by the present invention, on the one hand, the P2-phase coating layer has good structural stability. The formed F-Mn bond can not only reduce the dissolution of manganese elements caused by the erosion of hydrogen fluoride in the electrolyte, but also inhibit the lattice distortion caused by the Jahn-Teller effect of Mn 3+ , which can significantly improve the cycle performance of the battery. On the other hand, the coating layer can reduce the residual sodium on the surface of the matrix, and can also provide charge compensation, provide a fast Na + diffusion channel, and alleviate the downward trend of the discharge mid-voltage during the sodium ion extraction / insertion process, so that the battery takes into account both capacity and cycle performance.

[0047] In some embodiments, the matrix includes a layered oxide with an O3 phase; optionally, the chemical general formula of the layered oxide is Na i MF α O j , where 0.6 < i < <�.1, 0 ≤ α ≤ 0.05, 1.9 < j ≤ 2.1, and M is selected from at least one of Ni, Fe, Mn, Co, Ti, Cu, Ca, Zn, Mg, Al, Y, Ce, Sr, Sn, Ba, La, and Li; the O3-phase matrix can provide sufficient initial Na + reserves to achieve a higher charge-discharge specific capacity; in addition, when the matrix contains a small amount of fluorine element, it can not only avoid capacity reduction, but also improve the cycle stability at high voltages.

[0048] In some embodiments, the mass ratio of the P2 phase to the O3 phase is (0.01-0.05):1. For example, it can be 0.010, 0.015, 0.020, 0.025, 0.030, 0.035, 0.040, 0.045, 0.050 or any value between (0.01-0.05):1; the sodium-ion battery cathode material obtained by this embodiment has more excellent electrochemical performance. Through creative research, the present invention finds that when the proportion of the P2 phase is within the foregoing range, it is more conducive to effectively blocking the damage of the electrolyte to the material structure, and it will not cause an increase in impedance and a deterioration in rate performance due to a relatively high proportion of the P2 phase. Therefore, the present invention preferably limits the mass ratio of the P2 phase to the O3 phase to (0.01-0.05):1.

[0049] In some embodiments, the cathode material satisfies at least one of the following conditions:

[0050] a. The concentration of fluorine element contained in the matrix is less than the concentration of fluorine element contained in the coating layer; a large amount of fluorine element doping in the coating layer can inhibit the oxygen loss caused by the high-voltage O 2- / O - redox reaction, relieve the downward trend of the discharge medium voltage, and at the same time, a small amount of fluorine element doping in the matrix core avoids capacity reduction.

[0051] b. The chemical general formula of the coating layer is Na x Mn 1-y M' y O z F β , where 0.6 < x < 0.7, 0 < y ≤ 0.02, 1.9 < z ≤ 2.1, 0 < β ≤ 0.02, and M' is selected from at least one of Mn, Co, and Li; in this embodiment, the sodium-ion battery cathode material obtained by the present invention has more excellent electrochemical performance.

[0052] c. The average thickness of the coating layer is 5-50 nm; for example, it can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or any value between 5-50 nm. When the average thickness of the coating layer is within a suitable range, it can not only improve the coating uniformity, thereby enhancing the isolation effect between the matrix and the electrolyte, but also ensure the capacity of the cathode material.

[0053] d. The D50 of the cathode material is 3-20 μm; for example, it can be 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm or any value between 3-20 μm;

[0054] e. The mass of the coating layer accounts for 1-5% of the mass of the matrix; for example, it can be 1%, 2%, 3%, 4%, 5% or any value between 1-5%.

[0055] It should be noted that, in this invention, the fluorine concentration in the matrix and the fluorine concentration in the coating layer refer to the relative content of fluorine in the matrix, and the fluorine concentration in the coating layer refers to the relative content of fluorine in the coating layer, which can be measured by EDS spot scanning and EPMA detection.

[0056] In this invention, D50 is the particle size corresponding to a cumulative particle size distribution percentage of 50%.

[0057] As previously described, a second aspect of the present invention provides a method for preparing a sodium-ion battery cathode material as described in the first aspect, the method comprising:

[0058] The cathode material is obtained by first sintering a first mixture comprising a manganese-containing compound, a fluoride containing M', and the matrix.

[0059] In some embodiments, the first sintering is carried out in an oxygen-containing atmosphere; optionally, the oxygen-containing atmosphere is air or oxygen.

[0060] In some implementations, the method satisfies at least one of the following conditions:

[0061] (1) The manganese-containing compound is selected from at least one of MnCO3, MnO, Mn2O3, MnO2, Mn2O7, and Mn3O4;

[0062] (2) The M' in the M'-containing fluoride is selected from at least one of Ni, Fe, Co, Ti, Li, and Mn;

[0063] (3) The temperature of the first sintering is 400-700℃ and the time is 4-8h; optionally, the temperature of the first sintering is 500-600℃ and the time is 6-8h.

[0064] (4) The heating rate of the first sintering is 1-5℃ / min; optionally, the heating rate of the first sintering is 1-3℃ / min.

[0065] (5) The matrix is ​​a polycrystalline particle or a single crystal particle;

[0066] (6) The mass ratio of the coating layer to the matrix in the first mixture is (0.01-0.05):1.

[0067] It should be noted that, in this invention, the matrix being polycrystalline particles refers to secondary spheres composed of primary particles with significant crystal interfaces, while the matrix being monocrystalline particles refers to plate-like grains without significant crystal interfaces, which can be measured by SEM.

[0068] In some embodiments, the matrix is ​​obtained by second sintering a second mixture including a sodium source and a metal M source.

[0069] In some embodiments, the second sintering is carried out in an oxygen-containing atmosphere; optionally, the oxygen-containing atmosphere is air or oxygen.

[0070] In some optional embodiments of this application, the method satisfies at least one of the following conditions:

[0071] A. The sodium source is selected from at least one of sodium carbonate, sodium hydroxide, and sodium bicarbonate;

[0072] B. The metal M source is selected from at least one of the following: oxides containing metal M, hydroxides containing metal M, and carbonates containing metal M;

[0073] C. The M in the metal M source is selected from at least one of Ni, Fe, Mn, Co, Ti, Cu, Ca, Zn, Mg, Al, Y, Ce, Sr, Sn, Ba, La, and Li;

[0074] D. The second sintering temperature is 800-1100℃, and the time is 10-15h;

[0075] E. The heating rate for the second sintering is 1-3℃ / min;

[0076] F. The molar ratio of sodium to metal M in the second mixture is (0.6-1.1):1.

[0077] In this invention, there are no particular limitations on the preparation methods of the oxides, hydroxides, and carbonates containing metal M. Those skilled in the art can make selections based on known techniques. This invention will not elaborate further here, but will provide some specific preparation methods in the examples below.

[0078] The above method obtains the P2 phase Na by first sintering the matrix with a manganese-containing compound and a fluoride containing M'. y MnM' z O 2-β F β The sodium-ion battery cathode material is a layered oxide coated with O3 phase. This in-situ coating process is simple to operate, easy to control, has a short process flow, and causes less environmental pollution. The prepared coating layer is uniformly distributed and completely covered.

[0079] As previously stated, a third aspect of the present invention provides a sodium-ion battery comprising the sodium-ion battery cathode material described in the first aspect.

[0080] As previously described, a fourth aspect of the present invention provides an electrical device including the sodium-ion battery described in the third aspect.

[0081] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials are all commercially available products.

[0082] Example 1

[0083] This embodiment prepares a sodium-ion battery cathode material, and the preparation steps are as follows:

[0084] (1) Preparation of precursor (hydroxide containing metal M): With a Ni:Mn:Ti:Mg molar ratio of 0.40:0.52:0.05:0.03, nickel sulfate, manganese sulfate, titanium sulfate, and magnesium sulfate were dissolved in 1000 mL of water to obtain a mixed solution with a metal ion concentration of 1 mol / L. Then, 50 mL of 20 wt% ammonia water and 80 mL of 38 wt% sodium hydroxide solution were added to carry out a precipitation reaction. After solid-liquid separation, the solid product was washed and dried to obtain a precursor Ni with a D50 of 3.5 μm. 0.40 Mn 0.52 Ti 0.05 Mg 0.03 (OH)2; The precipitation reaction conditions are: temperature 70℃, time 50h;

[0085] (2) Matrix preparation: In the presence of air, the precursor obtained in step (1) was mixed with Na2CO3 at a molar ratio of n(Na) / n(M) of 1.03, and then subjected to a second sintering to obtain an O3 phase matrix Na. 0.86 Ni 0.40 Mn 0.52 Ti 0.05 Mg 0.03 O2; The conditions for the second sintering are: heating rate of 1℃ / min, temperature of 980℃, and time of 15h;

[0086] (3) Preparation of sodium-ion battery cathode material: In the presence of air atmosphere, 100g of the matrix obtained in step (2), 0.8g of manganese tetroxide and 0.2g of manganese fluoride are mixed and subjected to first sintering to obtain sodium-ion battery cathode material S1; The conditions for the first sintering are: temperature of 550℃, time of 6h and heating rate of 2℃ / min.

[0087] Example 2

[0088] This embodiment prepares a sodium-ion battery cathode material. The preparation method is basically the same as that in Example 1. The difference is that in step (3) of this embodiment, the amount of manganese tetroxide is 3.2g and the amount of manganese fluoride is 0.8g.

[0089] Sodium-ion battery cathode material S2 was prepared.

[0090] Example 3

[0091] This embodiment prepares a sodium-ion battery cathode material. The preparation method is basically the same as that in Example 1. The difference is that in step (3) of this embodiment, lithium fluoride of equal mass is used to replace manganese fluoride.

[0092] Sodium-ion battery cathode material S3 was prepared.

[0093] Example 4

[0094] This embodiment prepares a sodium-ion battery cathode material. The preparation method is basically the same as that in Example 1. The difference is that in step (3) of this embodiment, cobalt fluoride of equal mass is used to replace manganese fluoride.

[0095] Sodium-ion battery cathode material S4 was prepared.

[0096] Example 5

[0097] (1) Matrix preparation: Sodium carbonate, nickel oxide, manganese carbonate, and titanium dioxide were thoroughly ground in an agate mortar in a molar ratio of 1.03:0.50:0.35:0.15, and a second sintering was carried out in the presence of air to obtain the Na matrix. 1.0 Ni 0.50 Mn 0.35 Ti 0.15 O2; The conditions for the second sintering are: heating rate of 1℃ / min, temperature of 960℃, and time of 15h;

[0098] (2) Preparation of sodium-ion battery cathode material: In the presence of air, 100g of the matrix obtained in step (1), 0.8g of manganese tetroxide and 0.2g of manganese fluoride are mixed and subjected to first sintering to obtain the sodium-ion battery cathode material S5; the conditions for the first sintering are: temperature of 550℃, time of 6h and heating rate of 2℃ / min.

[0099] Example 6

[0100] This embodiment prepares a sodium-ion battery cathode material. The specific preparation steps are as follows:

[0101] (1) Preparation of precursor (hydroxide containing metal M): With a Ni:Fe:Mn molar ratio of 0.33:0.33:0.33, nickel sulfate, ferric sulfate, and manganese sulfate were dissolved in 1000 mL of water to obtain a mixed solution with a metal ion concentration of 1 mol / L. Then, 50 mL of 20 wt% ammonia solution and 80 mL of 38 wt% sodium hydroxide solution were added to carry out a precipitation reaction. After solid-liquid separation, the solid product was washed and dried to obtain a precursor Ni with a D50 of 3.5 μm. 0.33 Fe 0.33 Mn 0.33 (OH)2; the precipitation reaction conditions are: temperature 70℃, time 55h;

[0102] (2) Matrix preparation: In the presence of air, the precursor obtained in step (1) was mixed with Na2CO3 at a molar ratio of n(Na) / n(M) of 1.03, and then subjected to a second sintering to obtain the Na matrix. 1.0 Ni 0.33 Fe 0.33 Mn 0.33 O2; The conditions for the second sintering are: heating rate of 1℃ / min, temperature of 960℃, and time of 15h;

[0103] (3) Preparation of sodium-ion battery cathode material: In the presence of air atmosphere, 100g of the matrix obtained in step (2), 0.8g of manganese tetroxide and 0.2g of manganese fluoride are mixed and subjected to first sintering to obtain the sodium-ion battery cathode material S6; The conditions for the first sintering are: temperature of 550℃, time of 6h and heating rate of 2℃ / min.

[0104] Example 7

[0105] This embodiment prepares a sodium-ion battery cathode material. The preparation method is basically the same as that in Example 1. The difference is that in step (3) of this embodiment, the amount of manganese tetroxide is 4g and the amount of manganese fluoride is 1g.

[0106] Sodium-ion battery cathode material S7 was prepared.

[0107] Example 8

[0108] This embodiment prepares a sodium-ion battery cathode material, and its preparation method is basically the same as that in Example 1. The difference is that in this embodiment, the first sintering temperature is 700°C.

[0109] Sodium ion cathode material S8 was prepared.

[0110] control group

[0111] In this control group, manganese tetroxide, manganese fluoride, and sodium carbonate were mixed and sintered in the presence of air. The sintering conditions were: temperature 550℃, time 6h, and heating rate 2℃ / min, to obtain sodium fluoromanganate. Figure 6 The XRD pattern of sodium fluoride-doped manganate prepared for this control group is shown.

[0112] Comparative Example 1

[0113] This comparative example prepares a sodium-ion battery cathode material, and its preparation method is basically the same as that of Example 1, except that in step (3), 1g of P2 phase Na is used. 0.66 Cu 0.35 Mn 0.65 O 1.98 F 0.02 Replace 0.8g of manganese tetroxide and 0.2g of manganese fluoride in Example 1.

[0114] Material DS1 was prepared.

[0115] Comparative Example 2

[0116] This comparative example prepares a sodium-ion battery cathode material. The preparation method is basically the same as that of Example 1. The difference is that in step (3), 1g of aluminum oxide is used to replace 0.8g of manganese tetroxide and 0.2g of manganese fluoride in Example 1.

[0117] Material DS2 was prepared.

[0118] Comparative Example 3

[0119] This comparative example prepares a sodium-ion battery cathode material, and its preparation method is basically the same as that of Example 1, except that in step (3), 1g of O3 phase Na is used. 0.98 Cu 0.5 Mn 0.5 O 1.98 F 0.02 Replace 0.8g of manganese tetroxide and 0.2g of manganese fluoride in Example 1.

[0120] Material DS3 was prepared.

[0121] Comparative Example 4

[0122] This comparative example uses the substrate prepared in Example 1 as the positive electrode material DS4 for comparison.

[0123] Comparative Example 5

[0124] This comparative example uses the substrate prepared in Example 5 as the positive electrode material DS5 for comparison.

[0125] Comparative Example 6

[0126] This comparative example uses the substrate prepared in Example 6 as the positive electrode material DS6 for comparison.

[0127] The cathode materials prepared in the above embodiments and comparative examples were tested, specifically:

[0128] 1. Particle size (D50) was tested using a Malvern 3000 laser particle size analyzer, referring to standard GB / T19077-2016;

[0129] 2. XRD was measured by an X-ray diffractometer, in accordance with the standard GA / T 2079-2023. The crystal structure of each sample was tested using a Rigaku SmartLab 9kW X-ray diffractometer (XRD, Cu Kα), with a scanning range of 5-80° and a scanning rate of 8° / min.

[0130] 3. The coating thickness is measured by cross-sectional electron microscopy of the cathode material: select 5 locations along the edge of the cathode material particle profile and measure the coating thickness at the corresponding 5 locations. Calculate the average thickness as the coating thickness.

[0131] The specific results are shown in Table 1.

[0132] Table 1

[0133]

[0134] Test Example 1

[0135] The pH value and residual sodium content of the cathode materials obtained in the above embodiments and comparative examples were tested using the following methods:

[0136] (1) pH test: Take 5g of sample and 45g of deionized water into a 50mL graduated conical flask, stir magnetically for 10min and then perform pH test; the pH electrode liquid level is between 1 / 3 and 2 / 3, and the test solution temperature is 25±1℃.

[0137] (2) Residual sodium test: Take 10g of sample and 90g of deionized water, place them in a magnetic stirrer and stir for 10min, then filter with a vacuum circulating water pump; take the supernatant and test it with a potentiometric titrator, and calculate the residual sodium content based on the volume values ​​corresponding to the two isoelectric points on the titration curve of the potentiometric titrator.

[0138] The test results are shown in Table 2.

[0139] Table 2

[0140] pH value <![CDATA[Na + (wt%)]]> Example 1 12.18 0.324 Example 2 12.11 0.285 Example 3 12.15 0.338 Example 4 12.17 0.365 Example 5 12.17 0.318 Example 6 12.19 0.336 Example 7 12.05 0.241 Example 8 12.18 0.342 Comparative Example 1 12.20 0.552 Comparative Example 2 12.01 0.338 Comparative Example 3 12.17 0.533 Comparative Example 4 12.22 0.502 Comparative Example 5 12.35 0.491 Comparative Example 6 12.31 0.527

[0141] As can be seen from the results in Table 2, the sodium-ion battery cathode material obtained by this invention has a lower residual sodium content compared to the uncoated substrate surface.

[0142] Test Example 2

[0143] The electrochemical performance of the cathode materials obtained in the above embodiments and comparative examples was tested using the following methods:

[0144] (1) Preparation of positive electrode sheet: Weigh the positive electrode material, conductive agent (Super P) and binder (polyvinylidene fluoride PVDF) in a mass ratio of 85:10:5 and place them in a weighing bottle. Add an appropriate amount of dispersing solvent (N-methylpyrrolidone NMP), stir evenly and coat it on aluminum foil. Then dry, roll and slice to make the required positive electrode sheet.

[0145] (2) Sodium-ion battery assembly and testing: All batteries used CR2032 button cells. The batteries were assembled in the following order: positive electrode shell, gasket, positive electrode sheet prepared in step (1) above, separator, electrolyte, sodium metal negative electrode, gasket, spring sheet, and negative electrode shell. Then, the batteries were sealed in a button cell sealing machine. After being removed and left to stand for a period of time, the electrochemical performance was tested on the Blue Battery Testing System. The voltage range was set to 2.0-4.3V, the test rate was 0.1C (1C = 150mAh / g) for 2 cycles of activation, then 0.2C for 2 cycles of activation, and finally 1C for 50 cycles. The test temperature was 25±1℃.

[0146] The test results are shown in Table 3.

[0147] Table 3

[0148] 1C initial discharge capacity mAh / g <![CDATA[1C-50 th Capacity retention rate % Example 1 157.00 97.03 Example 2 153.23 97.28 Example 3 156.71 96.48 Example 4 156.69 96.36 Example 5 148.77 88.25 Example 6 150.60 90.49 Example 7 152.87 97.48 Example 8 152.02 97.54 Comparative Example 1 150.01 93.24 Comparative Example 2 156.58 92.01 Comparative Example 3 154.89 91.88 Comparative Example 4 157.95 91.29 Comparative Example 5 149.35 84.80 Comparative Example 6 151.53 84.11

[0149] As can be seen from the results in Table 3, the sodium-ion battery cathode material with the coating provided by this invention exhibits superior overall electrochemical performance when applied to coin cells.

[0150] Figure 1 The figures show the discharge specific capacity of batteries assembled with the cathode materials obtained in Comparative Examples 1-3 and Example 1 at 0.1C, 0.2C, and 1C rates within a voltage range of 2.0-4.3V. It can also be seen from the figures that the discharge specific capacity of batteries assembled with the cathode materials obtained in Example 1 decreases more slowly at 1C rate, and the cycle stability is better.

[0151] Figure 2 The discharge voltage of the batteries assembled with the cathode materials obtained in Example 1 and Comparative Example 4 is shown in the figure at discharge rates of 0.1C, 0.2C, and 1C within a voltage range of 2.0-4.3V. As can be seen from the figure, the discharge voltage of Example 1 decreases more slowly compared with Comparative Example 4.

[0152] Test Example 3

[0153] Figure 3 This is a SEM image of the sodium-ion battery cathode material obtained in Example 1 of the present invention. Figure 3 It can be seen that the cathode material is a single crystal with a relatively smooth surface, indicating that the P2 phase coating layer is evenly distributed. This is beneficial for isolating the substrate from the electrolyte and reducing the dissolution of transition metal ions.

[0154] Figure 4 The XRD pattern of the sodium-ion battery cathode material obtained in Embodiment 1 of this invention is shown below. Figure 4 It can be seen that the cathode material is a mixed phase of P2 and O3. To further verify that the coating layer of the sodium-ion battery cathode material obtained in this invention has a P2 phase structure, this invention uses fluorine-doped sodium manganate generated by the reaction of manganese tetroxide, manganese fluoride, and sodium carbonate as a control. Figure 5 The XRD pattern of sodium fluoromanganate obtained from the control group is shown below. Figure 5 It can be identified as fluorine-doped sodium manganate in the P2 phase.

[0155] Figure 6 The image shown is a cross-sectional EPMA diagram of the sodium-ion battery cathode material obtained in Example 1. Figure 6 It is known that a large amount of fluorine is concentrated at the edge of the material; the strong Mn-F bond can both reduce the dissolution of manganese caused by hydrogen fluoride corrosion and alleviate the Mn... 3+ The lattice distortion caused by the Ginger-Taylor effect.

[0156] Figure 7 The image shows a cross-sectional view of the sodium-ion cathode material provided in Embodiment 1 of the present invention. Five positions were randomly selected at the edge of the cross-section, and the thickness of the coating layer corresponding to these five positions was measured. The average thickness was calculated to be 12 nm. Figure 8 This is a fluorine element analysis point selection diagram of the cross-section EDS of the cathode material obtained by Example 1 of the present invention. The test results are shown in Table 4.

[0157] Table 4

[0158]

[0159] As can be seen from the table, the concentration of fluorine in the single-crystal particle matrix of the cathode material obtained by this invention is less than that in the coating layer. Here, Weight% represents the element weight percentage and Atomic% represents the atomic percentage. According to the data, the fluorine weight percentage and atomic percentage at sites 3 and 4 are both less than those at sites 1 and 2.

[0160] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A sodium-ion battery cathode material, characterized in that, The positive electrode material includes a matrix and a coating layer coated on the surface of the matrix, the matrix includes a layered oxide; the coating layer includes Na x Mn 1-y M' y O z F β , where 0.6 < x < 0.7, 0 < y ≤ 0.02, 1.9 < z ≤ 2.1, 0 < β ≤ 0.02, and M' is selected from at least one of Mn, Co, and Li; The substrate includes a layered oxide having an O3 phase; the chemical general formula of the layered oxide is Na i MF α O j , where 0.6 < i < 1.1, 0 ≤ α ≤ 0.05, 1.9 < j ≤ 2.1, and M is selected from at least one of Ni, Fe, Mn, Co, Ti, Cu, Ca, Zn, Mg, Al, Y, Ce, Sr, Sn, Ba, La, and Li.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The mass ratio of the P2 phase to the O3 phase is (0.01-0.05):

1.

3. The sodium-ion battery cathode material according to claim 1 or 2, characterized in that, The cathode material satisfies at least one of the following conditions: a. The concentration of fluorine in the matrix is ​​less than the concentration of fluorine in the coating layer; c. The average thickness of the coating layer is 5-50 nm; d. The D50 of the positive electrode material is 3-20 μm; e. The mass of the coating layer accounts for 1-5% of the mass of the substrate.

4. A method for preparing a sodium-ion battery cathode material as described in any one of claims 1-3, characterized in that, The method includes: The cathode material is obtained by first sintering a first mixture comprising a manganese-containing compound, a fluoride containing M', and the matrix. The manganese-containing compound is selected from at least one of MnCO3, MnO, Mn2O3, MnO2, Mn2O7, and Mn3O4; The M' in the M'-containing fluoride is selected from at least one of Mn, Co, and Li; The first sintering temperature is 400-700℃, and the time is 4-8h; The matrix is ​​obtained by second sintering a second mixture including a sodium source and a metal M source.

5. The method according to claim 4, characterized in that, The method satisfies at least one of the following conditions: (3) The temperature of the first sintering is 500-600℃ and the time is 6-8h; (4) The heating rate of the first sintering is 1-5℃ / min; (5) The matrix is ​​a polycrystalline particle or a single crystal particle; (6) The mass ratio of the coating layer to the matrix in the first mixture is (0.01-0.05):

1.

6. The method according to claim 5, characterized in that, The heating rate of the first sintering is 1-3℃ / min.

7. The method for preparing the sodium-ion battery cathode material according to claim 6, characterized in that, The method satisfies at least one of the following conditions: A. The sodium source is selected from at least one of sodium carbonate, sodium hydroxide, and sodium bicarbonate; B. The metal M source is selected from at least one of the following: metal M-containing oxides, metal M-containing hydroxides, and metal M-containing carbonates; C. The M in the metal M source is selected from at least one of Ni, Fe, Mn, Co, Ti, Cu, Ca, Zn, Mg, Al, Y, Ce, Sr, Sn, Ba, La, and Li; D. The second sintering temperature is 800-1100℃, and the time is 10-15h; E. The heating rate for the second sintering is 1-3℃ / min; F. The molar ratio of sodium to metal M in the second mixture is (0.6-1.1):

1.

8. A sodium-ion battery, characterized in that, Includes the sodium-ion battery cathode material according to any one of claims 1-3.

9. An electrical-related device, characterized in that, Including the sodium-ion battery as described in claim 8.

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