Coated sodium ion battery positive electrode material and preparation method and application thereof

Abstract

The present invention discloses a coated sodium ion battery positive electrode material and a preparation method and application thereof, wherein the coated sodium ion battery positive electrode material comprises a sodium ion battery positive electrode material; and a coating layer, wherein the coating layer is composed of Na x Al y Mg z M 1‑y‑z The O2 coating material is formed by covering the surface of the sodium ion battery positive electrode material, wherein 0 < x ≤ 4, 0 < y < 1, 0 < z < 1, y + z ≤ 1, and charge balance is satisfied. In the present invention, by coating the sodium ion battery positive electrode material, the safety of the sodium ion battery positive electrode material is improved, and the rate performance and wide temperature cycle stability of the sodium ion battery, especially the high temperature cycle stability, of the sodium ion battery are simultaneously improved, which can further promote the application of sodium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and specifically relates to a coated sodium ion battery positive electrode material and a preparation method thereof, and also relates to the application of the coated sodium ion battery positive electrode material in the preparation of sodium ion batteries. Background Art

[0002] Sodium-ion batteries (NIBs) are rechargeable secondary batteries that operate similarly to lithium-ion batteries, primarily transferring charge through the insertion and extraction of sodium ions between the positive and negative electrodes. Sodium is an abundant element in the Earth's crust, more abundant and widely distributed than lithium. This gives NIBs an advantage in raw material costs. With the increasing demand for large-scale energy storage systems, NIBs are gaining increasing attention. Furthermore, compared to lithium-ion batteries, NIBs exhibit better adaptability to high and low temperatures and offer improved safety.

[0003] However, sodium-ion batteries have a relatively low energy density. Furthermore, their cycling stability, especially at high temperatures, is poor, limiting their development. Cathode materials, as one of the key materials in sodium-ion batteries, can be modified through methods such as doping and coating to address these issues.

[0004] However, the current modification schemes make it difficult to ensure high discharge capacity of sodium-ion battery cathode materials while taking into account the stability of the cycling process. The existing modification processes either sacrifice the discharge capacity of sodium-ion battery cathode materials, or ensure the discharge capacity but have very limited improvement on the cycling stability of the cathode materials, especially the wide-temperature cycling stability. Summary of the Invention

[0005] In view of this, the primary purpose of the present invention is to provide a coated sodium ion battery positive electrode material, using Na x Al y Mg z M 1-y-z O2 is used to coat the surface of the positive electrode material of the sodium ion battery, thereby improving the safety of the positive electrode material of the sodium ion battery, and at the same time improving the rate performance and wide temperature cycle stability of the sodium ion battery, especially the high temperature cycle stability.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention first provides a coated sodium ion battery positive electrode material, comprising:

[0008] Sodium ion battery cathode materials;

[0009] and a coating layer, the coating layer being composed of Na x Aly Mg z M 1-y-z The O2 coating material is formed by covering the surface of the sodium ion battery positive electrode material, wherein 0<x≤4, 0<y<1, 0<z<1, y+z≤1 and the charge balance is satisfied.

[0010] In a further embodiment, the positive electrode material of the sodium ion battery is a layered transition metal oxide, a polyanion compound or a Prussian blue compound.

[0011] In a further embodiment, the positive electrode material of the sodium ion battery is a layered transition metal oxide.

[0012] Further solution, the Na x Al y Mg z M 1-y-z In the O2 coating material, M is at least one of Zn, Cu, Nb, Ta, Si, Ge, Ti, Sn, Mo, Zr, and Ga.

[0013] The present invention further provides a method for preparing the coated sodium ion battery positive electrode material as described above, comprising the following steps:

[0014] Provides Na x Al y Mg z M 1-y-z The precursor Na of O2 coating material x Al y Mg z M 1-y-z Cl4;

[0015] The precursor Na x Al y Mg z M 1-y-z Cl4 and a sodium ion battery cathode material are uniformly mixed in an anhydrous environment to obtain a mixture;

[0016] The mixed material is sequentially subjected to low-temperature heat treatment, hydrolysis and high-temperature calcination to prepare a coated sodium ion battery positive electrode material.

[0017] In a further embodiment, the precursor Na x Al y Mg z M 1-y-z The mass ratio of Cl4 and sodium ion battery positive electrode material powder is a:100-a, where a is a positive number less than 5.

[0018] In a further embodiment, the precursor Na x Al y Mg z M1-y-z Cl4 was prepared by ball milling.

[0019] In a further embodiment, the ball milling process is as follows: NaCl, AlCl3, MgCl2 and MCl n The precursor Na x Al y Mg z M 1-y-z Cl4; wherein 0<x≤4, 0<y<1, 0<z<1, y+z≤1 and charge balance is satisfied; n is a positive integer and 2≤n≤6.

[0020] In a further embodiment, the temperature of the low-temperature heat treatment is 170° C. to 200° C., and the holding time is 2 to 5 hours.

[0021] In a further embodiment, the hydrolysis process is to mix the product after low-temperature heat treatment with concentrated ammonia water with a pH of 10 to 13 and stir for 10 to 24 hours, and then dry it completely.

[0022] In a further embodiment, the high-temperature calcination process is carried out in an air atmosphere at a calcination temperature of 400° C. to 500° C. and a holding time of 2 to 10 hours.

[0023] The present invention further provides a sodium ion battery positive electrode, comprising the coated sodium ion battery positive electrode material as described above or the coated sodium ion battery positive electrode material prepared by the preparation method described above.

[0024] The present invention further provides a sodium ion battery comprising the sodium ion battery positive electrode described above.

[0025] Beneficial effects of the present invention:

[0026] In the present invention, Na is coated on the surface of the positive electrode material of the sodium ion battery. x Al y Mg z M 1-y-z O2 materials help stabilize the structure of sodium-ion battery cathode materials during the charge and discharge process, reducing structural damage caused by volume expansion and contraction. They can also impart good chemical and thermal stability to sodium-ion batteries, improving the safety of sodium-ion battery cathode materials.

[0027] Coating material Na x Al y Mg z M 1-y-zO2 also has the following significant advantages: (1) it can reduce the side reactions between the cathode material and the electrolyte, thus improving the cycle stability and rate performance of sodium-ion batteries; (2) it helps the diffusion of sodium ions in the cathode material, thus improving the ion transport performance of the cathode material; (3) it has high thermal stability, which can improve the cycle stability of sodium-ion batteries under a wide temperature range, especially at high temperatures. This has promoted the development of sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is Na in Example 1 of the present invention 1.5 Al 0.5 Mg 0.5 O2 coated Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode and uncoated Na in comparative example 1 0.67 Ni 0.33 Mn 0.67 Rate performance test results of O2 positive electrode.

[0029] Figure 2 is Na in Example 1 of the present invention 1.5 Al 0.5 Mg 0.5 O2 coated Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode and uncoated Na in comparative example 1 0.67 Ni 0.33 Mn 0.67 O2 positive cycle performance test results. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0032] The first aspect of the present invention provides a coated sodium ion battery positive electrode material, comprising:

[0033] Sodium ion battery cathode materials;

[0034] and a coating layer, the coating layer being composed of Na x Al y Mg z M 1-y-zThe O2 coating material is formed by covering the surface of the sodium ion battery positive electrode material, wherein 0<x≤4, 0<y<1, 0<z<1, y+z≤ and the charge balance is satisfied.

[0035] In the present invention, Na x Al y Mg z M 1-y-z The O2 coating material covers the surface of the positive electrode material of the sodium ion battery to form a coating layer. x Al y Mg z M 1-y-z O2 has a high electrical conductivity and can form a stable SEI layer on the negative electrode surface, which can improve the overall conductivity of the positive electrode material, thereby improving the charge and discharge efficiency of the sodium ion battery, effectively promoting the migration or diffusion of sodium ions in the coating layer, improving the ion transport performance of the positive electrode material, and improving the charge and discharge efficiency. x Al y Mg z M 1-y-z O2 can reduce the side reactions between the cathode material and the electrolyte. It also has good thermal stability, which can improve the rate performance of sodium ion batteries and the cycle stability under wide temperature (room temperature 25°C and high temperature 65°C), especially the cycle stability under high temperature. x Al y Mg z M 1-y-z O2 helps stabilize the structure of the positive electrode material during the charging and discharging process, reduces structural damage caused by volume expansion and contraction, has good chemical stability and thermal stability, and can improve the safety of the positive electrode material.

[0036] In the present invention, the sodium ion battery cathode material may be any of the sodium ion battery cathode materials known to those skilled in the art, without particular limitation, and may be, for example, a layered transition metal oxide, a polyanion compound, or a Prussian blue compound.

[0037] The layered transition metal oxide described in this article is composed of MO6 octahedrons arranged in layers, with sodium ions located between the layers of the octahedrons. x MeO2 (0<x≤1), Me is a common transition metal element, including at least one of vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Mg), nickel (Ni), and copper (Cu). Layered transition metal oxide positive electrodes are divided into P type and O type, with O3 type and P2 type being the main types. Specific examples include Na 0.67 Ni 0.33 Mn 0.67 O2、Na 0.67 Fe0.5 Mn 0.5 O2 or NaNi 0.33 Fe 0.33 Mn 0.33 O2, but not limited to it.

[0038] The polyanionic compounds described herein generally refer to cathode materials composed of sodium, a transition metal, and anions. Common anions include phosphate, pyrophosphate, fluorophosphate, and sulfate. Specific examples include, but are not limited to, NaFeP2O7 or Na4V2(PO4)3.

[0039] The Prussian blue compounds described herein are cathode materials composed of sodium, a transition metal, and cyanide. They have a face-centered cubic crystal structure, with sodium ions located within three-dimensional channels and coordinated pores, thus providing a favorable migration path. A specific example is NaFe2[Fe3(CN)6], but is not limited thereto.

[0040] In some specific embodiments of the present invention, the sodium ion battery positive electrode material is a layered transition metal oxide.

[0041] Further solution, the Na x Al y Mg z M 1-y-z In the O2 coating material, M is at least one of Zn, Cu, Nb, Ta, Si, Ge, Ti, Sn, Mo, Zr, and Ga. By introducing the M element into the coating material, the high-temperature performance of the coated sodium-ion battery cathode material described herein can be further improved. Moreover, these elements will not enter the interior of the base material but will only be coated on the surface of the base material, thereby having no adverse effect on the performance of the base material itself.

[0042] The second aspect of the present invention provides a method for preparing the coated sodium ion battery positive electrode material according to the first aspect of the present invention, comprising the following steps:

[0043] Provides Na x Al y Mg z M 1-y-z The precursor Na of O2 coating material x Al y Mg z M 1-y-z Cl4;

[0044] The precursor Na x Al y Mg z M 1-y-zCl4 and a sodium ion battery cathode material are uniformly mixed in an anhydrous environment to obtain a mixture;

[0045] The mixed material is sequentially subjected to low-temperature heat treatment, hydrolysis and high-temperature calcination to obtain a coated sodium ion battery positive electrode material.

[0046] In the present invention, the precursor Na x Al y Mg z M 1-y-z After Cl4 is mixed with the positive electrode material of sodium ion battery, the precursor Na x Al y Mg z M 1-y-z Due to the low melting point of Cl4, the precursor is melted on the surface of the sodium ion battery cathode material in a low temperature and oxygen-free environment to achieve uniform coating; and the Cl4 in the coated material is removed by hydrolysis. - Finally, high-temperature calcination is performed to produce a coated sodium-ion battery cathode material. This coating method is simple to operate, has low energy consumption, can form a uniform coating layer, and the coating layer composition is easily controlled. Furthermore, the coating process is highly universal and can be applied to mainstream sodium battery cathode materials currently on the market.

[0047] In the present invention, the precursor Na x Al y Mg z M 1-y-z Cl4 was prepared by ball milling. Specifically, the process of the ball milling method is as follows: NaCl, AlCl3, MgCl2 and MCl n According to the molar ratio of x:y:z:1-yz, the precursor Na x Al y Mg z M 1-y-z Cl4; wherein n is a positive integer and 2≤n≤6.

[0048] In the present invention, the precursor Na x Al y Mg z M 1-y-z The mass ratio of Cl4 and the sodium ion battery positive electrode material is a:100-a, where a is a positive number less than 5, for example, it can be any mass ratio of 1:99, 1.5:98.5, 2:98, 3:97, 3.5:96.5, 4:96, 4.5:95.5, etc.

[0049] Furthermore, the low temperature heat treatment mentioned in this article refers to the treatment temperature just enough to make the coated precursor Na x Al yMg z M 1-y-z Cl4 melts and does not have any effect on the sodium ion battery cathode material in the matrix, such as causing the state change or reaction of the sodium ion battery cathode material. Generally, according to the precursor Na x Al y Mg z M 1-y-z The melting point of Cl4 is adjusted and optimized. In some specific embodiments of the present invention, the temperature of the low-temperature heat treatment is 170°C to 200°C, and the holding time is 2 to 5 hours.

[0050] Furthermore, Cl ions in the coated precursor can be removed by hydrolysis. Specifically, in the present invention, the hydrolysis process is to mix the product after low-temperature heat treatment with concentrated ammonia water at a pH of 10 to 13, stir for 10 to 24 hours, and then dry it completely. Specific drying conditions can be conventional in the art, for example, drying at 80°C to 150°C.

[0051] The specific reaction process is as follows:

[0052] Na x Al y Mg z M 1-y-z Cl4+NH3·H2O→Na x Al y Mg z M 1-y-z O2+HCl+NH3.

[0053] Furthermore, the high-temperature calcination process is in an air atmosphere, with a calcination temperature of 400° C. to 500° C. and a holding time of 2 to 10 hours.

[0054] A third aspect of the present invention provides a sodium ion battery positive electrode, comprising the coated sodium ion battery positive electrode material described above or the coated sodium ion battery positive electrode material prepared using the preparation method described above. It is understood that the sodium ion battery positive electrode also includes additives such as a conductive agent and a binder, as well as materials such as a positive electrode current collector. However, since these can all be conventional compositions of positive electrodes in the art, there are no particular limitations.

[0055] A fourth aspect of the present invention provides a sodium ion battery comprising the aforementioned sodium ion battery cathode. It is understood that the sodium ion battery further comprises a negative electrode, a separator, and an electrolyte, but since these can all employ conventional components of sodium ion batteries in the art, there are no particular limitations.

[0056] The present invention is described below by means of specific examples. It should be noted that the following specific examples are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0057] Example 1

[0058] This embodiment provides a Na 1.5 Al 0.5 Mg 0.5 O2 coated P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode material, the specific preparation method is as follows:

[0059] S1. Add NaCl, AlCl3, and MgCl2 into a ball mill at a molar ratio of 1.5:0.5:0.5 and mill at a speed of 500 r / min for 10 h. While mixing evenly, the product can be crushed to obtain a precursor Na with a particle size of 500 nm. 1.5 Al 0.5 Mg 0.5 Cl4;

[0060] S2, P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 cathode powder and precursor Na 1.5 Al 0.5 Mg 0.5 Cl4 was mixed in a mortar in an inert atmosphere at a mass ratio of 98:2. The mixed sample was heated to 200°C in a vacuum tube and kept warm for 2 hours. 1.5 Al 0.5 Mg 0.5 Cl4 will melt and evenly coat the surface of the cathode material to obtain a fast ion conductor Na 1.5 Al 0.5 Mg 0.5 Cl4 coated P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode;

[0061] S3. Put Na 1.5 Al 0.5 Mg 0.5 Cl4-coated P2-type Na 0.67 Ni 0.33 Mn 0.67 The O2 positive electrode material was added into 1 mol / L concentrated ammonia water with a liquid-solid ratio of 1:20 and the temperature was set at 40℃ and stirred for 24 hours for hydrolysis.1.5 Al 0.5 Mg 0.5 Cl4 reacts to form Na 1.5 Al 0.5 Mg 0.5 O2; then put the hydrolyzed sample into a blast drying oven and dry it for 24 hours until the concentrated ammonia solution is completely dried to obtain the hydrolyzed Na 1.5 Al 0.5 Mg 0.5 O2 coated P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode;

[0062] S4, the Na 1.5 Al 0.5 Mg 0.5 O2 coated P2 type Na 0.67 Ni 0.33 Mn 0.67 The O2 positive electrode was placed in a muffle furnace and heated to 600℃ and kept warm for 4h to obtain Na 1.5 Al 0.5 Mg 0.5 O2 surface coated with P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode material.

[0063] Comparative Example 1

[0064] This comparative example adopts the same implementation as Example 1, with the only difference being that no coating layer is formed.

[0065] Example 2

[0066] This embodiment adopts the same implementation method as that of embodiment 1, except that: in step S2, P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 cathode powder and precursor Na 1.5 Al 0.5 Mg 0.5 The mass ratio of Cl4 is 99:1. Other process conditions and steps are the same as those in Example 1.

[0067] Example 3

[0068] This embodiment adopts the same implementation method as that of embodiment 1, except that: in step S2, P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 cathode powder and precursor Na 1.5 Al 0.5 Mg0.5 The mass ratio of Cl4 is 96:4. Other process conditions and steps are the same as those in Example 1.

[0069] Comparative Example 2

[0070] This comparative example adopts the same implementation as Example 1, with the only difference being that the coating layer formed is NaAlO2. Other process conditions and steps are the same as those in Example 1.

[0071] The specific preparation method of the coated sodium ion battery positive electrode material in this comparative example is as follows:

[0072] S1. Add NaCl and AlCl3 in a molar ratio of 1:1 into a ball mill and mill at a speed of 500 r / min for 10 h. While mixing, the product can be crushed to obtain a precursor NaAlCl4 with a particle size of 500 nm.

[0073] S2, P2 type Na 0.67 Ni 0.33 Mn 0.67 The O2 cathode powder and the precursor NaAlCl4 were mixed evenly in a mortar in an inert atmosphere at a mass ratio of 98:2. The mixed sample was heated to 200 ° C in a vacuum test tube and kept warm for 2 hours. At this time, NaAlCl4 will melt and evenly coat the surface of the cathode material to obtain a fast ion conductor NaAlCl4 coated P2 type Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode;

[0074] S3, NaAlCl4 coated P2 type Na 0.67 Ni 0.33 Mn 0.67 The O2 positive electrode material was added to 1 mol / L concentrated ammonia water with a liquid-solid ratio of 1:20 and stirred at 40 °C for 24 hours for hydrolysis. During the process, ammonia water reacted with NaAlCl4 to generate NaAlO2. The hydrolyzed sample was then placed in a blast drying oven and dried for 24 hours until the concentrated ammonia solution was completely dried to obtain the hydrolyzed NaAlO2-coated P2-type Na 0.67 Ni 0.33 Mn 0.67 O2 positive electrode;

[0075] S4, the hydrolyzed and dried NaAlO2 is coated with P2 type Na 0.67 Ni 0.33 Mn 0.67 The O2 positive electrode was placed in a muffle furnace and heated to 600℃ and kept warm for 4h to obtain NaAlO2 surface coated with P2 type Na 0.67 Ni 0.33 Mn 0.67O2 positive electrode material.

[0076] Example 4

[0077] This embodiment provides a Na 1.5 Al 0.5 Mg 0.5 O2 coated O3 type NaNi 0.33 Fe 0.33 Mn 0.33 O2 positive electrode material, the specific preparation method is as follows:

[0078] S1, same as Example 1;

[0079] S2, O3 type NaNi 0.33 Fe 0.33 Mn 0.33 O2 cathode powder and precursor Na 1.5 Al 0.5 Mg 0.5 Cl4 was mixed in a mortar in an inert atmosphere at a mass ratio of 98:2. The mixed sample was heated to 200°C in a vacuum tube and kept warm for 2 hours. 1.5 Al 0.5 Mg 0.5 Cl4 will melt and evenly coat the surface of the cathode material to obtain a fast ion conductor Na 1.5 Al 0.5 Mg 0.5 Cl4-coated O3-type NaNi 0.33 Fe 0.33 Mn 0.33 O2 positive electrode;

[0080] S3, same as Example 1;

[0081] S4, the Na 1.5 Al 0.5 Mg 0.5 O2 coated O3 type NaNi 0.33 Fe 0.33 Mn 0.33 The O2 positive electrode was placed in a muffle furnace and heated to 600℃ and kept warm for 4h to obtain Na 1.5 Al 0.5 Mg 0.5 O2 surface coated with O3 type NaNi 0.33 Fe 0.33 Mn 0.33 O2 positive electrode material.

[0082] Comparative Example 3

[0083] This comparative example adopts the same implementation as Example 4, with the only difference being that no coating layer is formed.

[0084] Example 5

[0085] This embodiment adopts the same implementation as that of embodiment 1, except that the positive electrode material of the sodium ion battery used is P2 type Na 0.67 Fe 0.5 Mn 0.5 O2, and its precursor Na 1.5 Al 0.5 Mg 0.5 The mass ratio of Cl4 is 98:2. The other process conditions and steps are the same as those in Example 1. The prepared coated sodium ion battery positive electrode material is Na 1.5 Al 0.5 Mg 0.5 O2-coated P2-type Na 0.67 Fe 0.5 Mn 0.5 O2 positive electrode.

[0086] Example 6

[0087] This embodiment adopts the same implementation as that of embodiment 1, except that the positive electrode material of the sodium ion battery used is Na3V2(PO4)3 positive electrode, and the positive electrode material thereof is the same as the precursor Na 1.5 Al 0.5 Mg 0.5 The mass ratio of Cl4 is 98:2. The other process conditions and steps are the same as those in Example 1. The prepared coated sodium ion battery positive electrode material is Na 1.5 Al 0.5 Mg 0.5 O2-coated Na3V2(PO4)3 cathode.

[0088] Comparative Example 4

[0089] This comparative example adopts the same implementation as Example 6, with the only difference being that no coating layer is formed.

[0090] Example 7

[0091] This embodiment adopts the same implementation as that of embodiment 1, except that the positive electrode material of the sodium ion battery used is NaFe2[Fe3(CN)6] positive electrode, and the positive electrode is the same as the precursor Na 1.5 Al 0.5 Mg 0.5 The mass ratio of Cl4 is 98:2. The other process conditions and steps are the same as those in Example 1. The prepared coated sodium ion battery positive electrode material is Na 1.5 Al 0.5 Mg 0.5 O2-coated NaFe2[Fe3(CN)6] cathode.

[0092] Comparative Example 5

[0093] This comparative example adopts the same implementation as Example 7, with the only difference being that no coating layer is formed.

[0094] Examples 8-12

[0095] Examples 8-12 all adopt the same implementation as Example 1, with the only difference being that the coating materials used are different from those in Example 1, as shown in Table 1. Each coating material is prepared in the same manner as in Example 1 after preparing its specific composition.

[0096] Performance Testing

[0097] The coated sodium ion battery positive electrode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 5 were prepared into sodium ion button batteries to test the electrochemical performance. The preparation method of sodium batteries is as follows:

[0098] The coated sodium ion battery positive electrode material, acetylene black and PVDF are added to a ball mill in a mass ratio of 8:1:1 and ball milled for 30 minutes to form a uniform slurry. A certain amount of NMP needs to be added as a diluent before mixing. After mixing, the slurry is evenly coated on the current collector aluminum foil and assembled with the diaphragm, electrolyte and negative electrode to form a button battery.

[0099] The specific assembly process: Sodium metal serves as the negative electrode, a prepared sodium cathode serves as the positive electrode, and a glass microfiber filter (grade GF / A; Whatman) serves as the separator. Each button cell is pipetted with 80 μL of sodium ion electrolyte and sealed. The entire assembly process must be performed in an argon-filled glove box, with the water and oxygen content controlled below 0.01 ppm.

[0100] 1. Room temperature long cycle test: Long cycle and rate tests were performed on the NEWARE battery test system, with constant current charge and discharge cycles and rates performed in the voltage range of 2.5-4.5V. The electrochemical test temperature was set to 25°C. Before the cycle, the battery was charged and discharged three times at a constant current of 0.1C to form a stable SEI film, and then cycled 200 times at 1C. The rate test was performed at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 10C for five times each to test the discharge capacity at different current densities. Finally, the battery was returned to 0.1C for five cycles to observe the battery's return performance after the high rate test.

[0101] 2. High-temperature long-cycle test: Long-cycle testing was performed on a NEWARE battery testing system. Before testing, a constant-current charge-discharge cycle was performed three times at room temperature with a voltage range of 2.5-4.5V to form a stable SEI film. The battery was then transferred to a high-temperature chamber (65°C) and cycled at a current density of 0.5C for 50 cycles.

[0102] The test results are shown in Table 1 and Figure 1-2 As shown in Table 1, the capacity retention rate of 200 cycles at 1C at room temperature (25°C), the discharge capacity at 10C rate at room temperature (25°C), and the capacity retention rate of 50 cycles at 0.5C at high temperature (65°C) are shown.

[0103] Table 1 Sodium ion battery performance test results

[0104]

[0105] Figure 1 and Figure 2 The test results of the rate performance and cycle performance of the coated sodium ion battery positive electrode material in Example 1 and the uncoated sodium ion battery positive electrode material in the comparative example at room temperature of 25°C are shown. It can be seen that by coating the coating material of the present invention, the rate performance and cycle stability at room temperature of 25°C are significantly improved. Furthermore, it can be seen from the test results in Table 1 that the coated sodium ion battery positive electrode material in the present invention not only has a higher discharge capacity, but also improves the wide temperature cycle performance, and the cycle stability at room temperature of 25°C and high temperature of 65°C is improved.

[0106] Based on the above results, it can be seen that the coated sodium ion battery positive electrode material provided in the present invention can improve the wide temperature cycle performance of sodium ion batteries while ensuring the rate performance, thereby further promoting the development of sodium ion batteries.

[0107] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A coated sodium ion battery cathode material, characterized in that: include: Sodium ion battery cathode materials; and a coating layer, the coating layer being composed of Na x Al y Mg z M 1-y-z The O2 coating material is formed by covering the surface of the sodium ion battery positive electrode material, wherein x=1.5, y=0.5, z=0.25 or 0.5, y+z≤1 and the charge balance is satisfied; M is Cu.

2. A coated sodium ion battery positive electrode material, characterized in that include: Sodium ion battery cathode materials; and a coating layer, the coating layer being composed of Na x Al y Mg z M 1-y-z The O2 coating material is formed by covering the surface of the sodium ion battery positive electrode material, wherein x=1, y=0.4, z=0.4, y+z≤1 and the charge balance is satisfied; M is Nb.

3. A coated sodium ion battery positive electrode material, characterized in that include: Sodium ion battery cathode materials; and a coating layer, the coating layer being composed of Na x Al y Mg z M 1-y-z The O2 coating material is formed by covering the surface of the sodium ion battery positive electrode material, wherein x=1, y=0.5, z=0.25, y+z≤1 and the charge balance is satisfied; M is one of Zr, Ti, and Mo.

4. The coated sodium ion battery positive electrode material according to any one of claims 1 to 3, wherein The sodium ion battery positive electrode material is a layered transition metal oxide, a polyanion compound or a Prussian blue compound.

5. The coated sodium ion battery positive electrode material according to claim 4, wherein The sodium ion battery positive electrode material is a layered transition metal oxide.

6. A method for preparing a coated sodium ion battery positive electrode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: Provides Na x Al y Mg z M 1-y-z The precursor of O2 coating material Na x Al y Mg z M 1-y-z Cl4; The precursor Na x Al y Mg z M 1-y-z Cl4 and sodium ion battery cathode material powder are uniformly mixed in an anhydrous environment to obtain a mixture; The mixed material is sequentially subjected to low-temperature heat treatment, hydrolysis and high-temperature calcination to prepare a coated sodium ion battery positive electrode material.

7. The preparation method according to claim 6, wherein The precursor Na x Al y Mg z M 1-y-z The mass ratio of Cl4 and the sodium ion battery positive electrode material is a:100-a, where a is a positive number less than 5.

8. The preparation method according to claim 6, wherein The precursor Na x Al y Mg z M 1-y-z Cl4 was prepared by ball milling.

9. The preparation method according to claim 8, wherein The process of the ball milling method is as follows: NaCl, AlCl3, MgCl2 and MCl n According to the molar ratio of x:y:z:1-yz, the precursor Na x Al y Mg z M 1-y-z Cl4; wherein, x=1.5, y=0.5, z=0.25 or 0.5, y+z≤1 and satisfy charge balance; M is Cu; n is a positive integer and 2≤n≤6.

10. The preparation method according to claim 8, characterized in that The process of the ball milling method is as follows: NaCl, AlCl3, MgCl2 and MCl n According to the molar ratio of x:y:z:1-yz, the precursor Na x Al y Mg z M 1-y-z Cl4; wherein, x=1, y=0.4, z=0.4, y+z≤1 and satisfy charge balance; M is Nb; n is a positive integer and 2≤n≤6.

11. The preparation method according to claim 8, characterized in that The process of the ball milling method is as follows: NaCl, AlCl3, MgCl2 and MCl n According to the molar ratio of x:y:z:1-yz, the precursor Na x Al y Mg z M 1-y-z Cl4; wherein, x=1, y=0.5, z=0.25, y+z≤1 and satisfy charge balance; M is one of Zr, Ti, and Mo; n is a positive integer and 2≤n≤6.

12. The preparation method according to claim 6, wherein The temperature of the low-temperature heat treatment is 170° C. to 200° C., and the holding time is 2 to 5 hours.

13. The preparation method according to claim 6, characterized in that The hydrolysis process is to mix the product after low-temperature heat treatment with concentrated ammonia water with a pH of 10-13, stir for 10-24 hours, and then dry completely.

14. The preparation method according to claim 6, wherein The high-temperature calcination process is in an air atmosphere, with a calcination temperature of 400° C. to 500° C. and a holding time of 2 to 10 hours.

15. A sodium ion battery positive electrode, characterized in that Contains the coated sodium ion battery positive electrode material according to any one of claims 1 to 5 or the coated sodium ion battery positive electrode material prepared by the preparation method according to any one of claims 6 to 14.

16. A sodium ion battery, characterized in that: A sodium ion battery positive electrode comprising the sodium ion battery according to claim 15.

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