Coated positive electrode layered oxide material for sodium-ion battery and modification method of coated positive electrode layered oxide material

Abstract

The invention discloses a sodium ion battery coated positive electrode layered oxide material and a modification method thereof, and belongs to the technical field of sodium ion batteries. The positive electrode material comprises a sodium-based positive electrode layered oxide main body and a coating layer which is formed on the surface of the main body and is composed of 2, 5-thiophene diborate. The modification method comprises the following steps: dissolving 2, 5-thiophene diborate in an N-methyl pyrrolidone (NMP) solvent to obtain a modified solution; dispersing a sodium-based positive electrode layered oxide main body material prepared in advance into the modified solution, and carrying out in-situ neutralization reaction through ultrasonic treatment; and separating, drying and grinding the reacted solid product to obtain the coated positive electrode layered oxide material. According to the method, a stable coating layer is constructed on the surface of a sodium-based positive electrode layered oxide main body through a liquid phase method, and the coating layer can neutralize residual alkali on the surface of the main body and inhibit an interface side reaction, so that the structural stability, the cycle performance and the rate capability of the positive electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion batteries, and in particular relates to a sodium-ion battery coated positive electrode layered oxide material and its modification method. Background Technology

[0002] With the continuous growth of global demand for clean energy, the development and utilization of renewable energy sources such as solar and wind power have received widespread attention. However, these renewable energy sources are characterized by intermittency and instability, requiring efficient energy storage technologies to ensure stable output and enable large-scale application. Lithium-ion rechargeable batteries have achieved remarkable success due to their advantages of high energy density and long cycle life.

[0003] With the increasing demand for energy storage, the scarcity of lithium resources and the high price of lithium compounds have limited the further development of energy storage technology. Sodium and lithium belong to the same group of elements and exhibit similar "rocking chair" electrochemical charge-discharge behavior in battery operation. Their similar working principles make them the most powerful alternative to lithium-ion batteries in large-scale energy storage technology.

[0004] As a key factor determining the performance of sodium-ion batteries, the research on cathode materials is crucial to promoting the development of sodium-ion batteries. At present, sodium-ion battery cathode materials are mainly divided into three categories: transition metal oxide systems, polyanion and Prussian blue analog systems.

[0005] Sodium-ion battery cathode layered oxide materials possess advantages such as high theoretical specific capacity, high conductivity, and simple fabrication process. Introducing iron and manganese into the transition metal layer can suppress structural collapse. However, with increasing cycle life, irreversible structural changes can still lead to a decline in overall cycle performance and rate capability. Therefore, it is urgent to address the fundamental structural stability and air stability issues at the material level.

[0006] Surface coating can improve structural and aerodynamic stability. A common method is to perform secondary processing on the base material and the coating material to obtain the coating. However, conventional coating methods are usually physical sintering, which consumes a certain amount of energy and requires strict control over the dimensions of the base material, making it difficult to obtain an ideal coating.

[0007] To address the aforementioned problems with cathode layered oxide materials, existing improvement methods mainly involve surface coating. This involves liquid-phase coating of the layered oxide, allowing the coating material to react effectively and fully with the host material without the need for secondary sintering. This reduces energy consumption, minimizes interfacial side reactions, removes residual alkali from the host material's surface, and improves the material's air stability and cycle stability.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] Technical issues: Sodium-ion battery layered oxide cathode materials suffer from structural instability, side reactions with the electrolyte, and poor air stability due to residual alkali on the surface during cycling, which limits their cycle life and rate performance.

[0010] Technical solution: To address the aforementioned technical problems, this invention provides a sodium-ion battery coated positive electrode layered oxide material, comprising: a sodium-based positive electrode layered oxide body; wherein the positive electrode material is a sodium-based positive electrode layered oxide and a thiophene 2,5-diborate coating material.

[0011] The present invention also provides a method for preparing the above-mentioned material, comprising: (1) Preparation of sodium-based crystalline oxide host material; (2) Dissolve 2,5-diborate thiophene in an appropriate amount of N-methylpyrrolidone (NMP) to obtain the desired modified solution, disperse the sodium-based positive electrode layered oxide host material in the modified solution, and react at room temperature and under ultrasonic conditions for 4-8 hours to obtain a solid-liquid mixture; (3) Separate the solid-liquid mixture obtained in step (2) and collect the solid product; (4) The solid product is dried under vacuum at 80-120°C for 12-24 hours to obtain the initial product, and the initial product is ground to obtain the final product.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: 1. A chemical liquid phase method is used to neutralize the residual alkali (such as NaOH, Na2CO3) on the surface of the main material with the organic acid in the solution, thereby removing the residual alkali on the surface of the main material and forming a coating layer on the surface of the main material. This achieves the technical effect of good structural stability and air stability of sodium-ion battery cathode material, as well as better cycle rate performance.

[0013] 2. This invention forms a thiophene 2,5-diboronate coating layer on the surface of a layered oxide. The coated cathode material exhibits high chemical stability under operating voltage, significantly suppresses interfacial side reactions, and accelerates Na… + This improves the diffusion rate, thus enhancing rate capability and cycling performance.

[0014] 3. This invention constructs a stable thiophene 2,5-diboronic acid coating layer on the surface of sodium-based crystalline oxides using a simple chemical liquid-phase method and ultrasonic stirring. This coating layer can accelerate the formation of Na+. +The diffusion rate can significantly suppress interfacial side reactions, which is beneficial to improving the structural stability, air stability, cycling and rate performance of sodium-based crystalline oxide materials. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 The XRD pattern of the positive electrode layered oxide material provided in Example 1 of this invention; Figure 2 The SEM image of the positive electrode layered oxide material provided in Example 1 of this invention; Figure 3 The XRD pattern of the positive electrode layered oxide material provided in Embodiment 2 of the present invention; Figure 4 The SEM image of the positive electrode layered oxide material provided in Example 2 of this invention; Figure 5 The XRD pattern of the positive electrode layered oxide material provided in Example 3 of this invention; Figure 6 The SEM image of the positive electrode layered oxide material provided in Example 3 of this invention; Figure 7 The XRD pattern of the positive electrode layered oxide material provided in Example 4 of this invention; Figure 8 The SEM image of the positive electrode layered oxide material provided in Example 4 of this invention; Figure 9 This is a comparison chart of the cycle performance obtained from the experimental examples of this invention; Figure 10 This is a comparison chart of the rate performance obtained from the experimental examples of this invention; Figure 11 This is a comparison chart of the cycling performance obtained from the experimental examples of this invention after being placed in the air for 1 day; Figure 12 This is a bar chart comparing the charge transfer resistance (Rct) obtained by fitting the electrochemical impedance spectroscopy (EIS) of different embodiments of the present invention (0.5%, 1%, 1.5%, 2% coating amount) with that of Comparative Example 1 (uncoated) material; Figure 13 A bar chart comparing the pH values ​​of suspensions obtained after soaking the material powders of different embodiments of the present invention and Comparative Example 1 in deionized water; Figure 14 The graphs show the relationship between capacity retention and coating amount after 200 cycles at 1C for different embodiments of the present invention and Comparative Example 1. Detailed Implementation

[0017] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0018] According to a first aspect of the present invention, a method for modifying a layered oxide material for a sodium-ion battery cathode is provided, comprising the following steps: The positive electrode layered oxide material is ultrasonicated in a modification solution and then vacuum dried to obtain the modified sodium-ion battery positive electrode layered oxide material. In this invention, a modified solution containing organic acid is used to coat the positive electrode layered oxide material, thereby neutralizing the residual alkali on the material surface and achieving surface coating of the material without the need for secondary sintering.

[0019] In summary, the modification method provided by this invention is not only simple to operate and has a high success rate, making it suitable for large-scale production, but also solves the technical problems of poor structural stability and air stability, as well as poor cycle rate performance, of sodium-ion battery cathode materials in the prior art.

[0020] In a preferred embodiment, the organic coating material is thiophene 2,5-diboronate; wherein the amount of coating material can be 0.5%-3% of the molar amount of the positive electrode layered oxide material, for example, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 3%, but is not limited thereto, and can be further preferably 0.5%-2%.

[0021] The types and amounts of organic coating layers selected in this invention are more conducive to further improving the effect of coating the layered oxide material of sodium-ion battery cathode, which can fully neutralize the residual alkali on the surface of the main material, and is more conducive to further improving the air stability and rate performance of the material.

[0022] In a preferred embodiment, the alcohol solvent includes, but is not limited to, at least one of methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, isobutanol, sec-butanol, tert-butanol, n-pentanol, sec-pentanol, n-octanol, sec-octanol, and n-hexanol.

[0023] In this invention, the ultrasonication time of the modified solution can be 0.5-1 h, and the ultrasonication time of the material can be 3-4 h; or, the ultrasonication time of the modified solution can be 1-2 h, and the ultrasonication time of the material can be 4-8 h.

[0024] In this invention, typical but non-limiting temperature conditions for vacuum drying are, for example, 80°C, 90°C, 100°C, 110°C, and 120°C; typical but non-limiting time conditions for vacuum drying are, for example, 12h, 15h, 18h, 21h, and 24h.

[0025] According to a second aspect of the present invention, a sodium-ion battery cathode layered oxide material modified by any of the above-described modification methods is provided.

[0026] The modified sodium-ion battery cathode layered oxide material provided by this invention has high specific capacity and air stability, as well as excellent cycle performance and rate performance.

[0027] According to a third aspect of the present invention, a sodium-ion battery is provided, comprising the above-described sodium-ion battery positive electrode layered oxide material.

[0028] The sodium-ion battery of this invention exhibits good air stability, high cycle performance and rate performance, and excellent electrochemical performance.

[0029] In addition to the positive electrode sheet containing the positive electrode material of the present invention, the above-mentioned sodium-ion battery further includes an electrolyte and a separator. Electrolytes are generally obtained by dissolving sodium salts in organic solvents; The sodium salts that can be used include at least one of NaPF6 and NaClO4; The organic solvents used are mainly anhydrous solvents, including at least one of carbonates (ethylene carbonate, propylene carbonate and diethyl carbonate, etc.), 1,2-dimethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; Available membranes include at least one of single-layer polypropylene membranes, polyethylene membranes, polyethylene / polypropylene / polyethylene composite membranes, cellulose nonwoven membranes, and glass fiber.

[0030] According to a fourth aspect of the present invention, a sodium-ion battery as described above is provided, which can increase the capacity of portable electronic devices, improve the battery life of low-speed transportation tools, and demonstrate outstanding application value with high rate performance and long cycle stability.

[0031] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0032] Example 1 A method for modifying a layered oxide material for a sodium-ion battery cathode includes the following steps: (1) Weigh Na2CO3 (5% excess) and Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 was hand-ground in a mortar for 1 hour to obtain a precursor, which was then treated in a muffle furnace at 900°C in air for 12 hours. After cooling to room temperature, the resulting black powder was ground for later use.

[0033] (2) Thiophene 2,5-diborate and N-methylpyrrolidone (NMP) were mixed and sonicated for 0.5 h to obtain a modified solution; The amount of thiophene 2,5-diboronate used is 1 mol% of the positive electrode layered oxide material. (3) Disperse the positive electrode layered oxide material obtained in step (1) in the modified solution in step (2) and sonicate it at room temperature for 4 hours. After the reaction is completed, perform solid-liquid separation by centrifugation or filtration and collect the solid product.

[0034] (4) The solid product obtained in step (3) was vacuum dried at 120℃ for 20h, and then ground to obtain a 2,5-diboronic acid thiophene-coated positive electrode layered oxide material. Its XRD pattern is shown in [reference needed]. Figure 1 Its SEM image is shown below. Figure 2 .

[0035] Example 2 (1) Weigh Na2CO3 (5% excess) and Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 was hand-ground in a mortar for 1 hour to obtain a precursor, which was then treated in a muffle furnace at 900°C in air for 12 hours. After cooling to room temperature, the resulting black powder was ground for later use.

[0036] (2) Thiophene 2,5-diborate and N-methylpyrrolidone (NMP) were mixed and sonicated for 0.5 h to obtain a modified solution; The amount of thiophene 2,5-diboronate used is 0.5 mol% of the positive electrode layered oxide material. (3) The positive electrode layered oxide material was sonicated in the modified solution for 4 h, and then vacuum dried at 120 °C for 20 h to obtain a positive electrode layered oxide material coated with thiophene 2,5-diboronate. Its XRD pattern is shown in [reference needed]. Figure 3 Its SEM image is shown below. Figure 4 .

[0037] Example 3 (1) Weigh Na2CO3 (5% excess) and Ni according to the stoichiometric ratio. 1 / 3 Fe1 / 3 Mn 1 / 3 (OH)2 was hand-ground in a mortar for 1 hour to obtain the precursor, which was then treated in a muffle furnace at 900°C in air for 12 hours. After cooling to room temperature, the resulting black powder was ground and used as the uncoated control sample.

[0038] (2) Thiophene 2,5-diborate and N-methylpyrrolidone (NMP) were mixed and sonicated for 0.5 h to obtain a modified solution; The amount of thiophene 2,5-diboronate used is 1.5 mol% of the positive electrode layered oxide material. (3) The positive electrode layered oxide material was placed in a modified solution and sonicated for 4 hours, then vacuum dried at 120°C for 20 hours to obtain a positive electrode layered oxide material coated with thiophene 2,5-diboronate. Its XRD pattern is shown in [reference needed]. Figure 5 Its SEM image is shown below. Figure 6 .

[0039] Example 4 (1) Weigh Na2CO3 (5% excess) and Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 was hand-ground in a mortar for 1 hour to obtain a precursor, which was then treated in a muffle furnace at 900°C in air for 12 hours. After cooling to room temperature, the resulting black powder was ground for later use.

[0040] (2) Thiophene 2,5-diborate and N-methylpyrrolidone (NMP) were mixed and sonicated for 0.5 h to obtain a modified solution; The amount of thiophene 2,5-diboronate used is 2 mol% of the positive electrode layered oxide material. (3) The positive electrode layered oxide material was placed in a modified solution and sonicated for 4 hours, then vacuum dried at 120°C for 20 hours to obtain a positive electrode layered oxide material coated with thiophene 2,5-diboronate. Its XRD pattern is shown in [reference needed]. Figure 7 Its SEM image is shown below. Figure 8 .

[0041] Comparative Example 1 Weigh Na₂CO₃ (5% excess) and Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 was hand-ground in a mortar for 1 hour to obtain a precursor, which was then treated in a muffle furnace at 900°C in air for 12 hours. After cooling to room temperature, the resulting black powder was ground for later use.

[0042] Experimental Example 1 Example 1 and Comparative Example 1: The material prepared in Example 1 was used as the positive electrode. A 1 mol / L NaPF6 PC:EMC = 1:1 with 2% FEC was used as the electrolyte, and glass fiber was used as the separator to assemble a 2025 coin cell. The battery performance was tested at 130 mA / g, and the results are shown in Tables 1, 2, and 3. Figure 9 , Figure 10 and Figure 11 .exist Figure 9 , Figure 10 and Figure 11 In the examples, Example 1 corresponds to a 1% thiophene 2,5-diboronic acid coating material, and Comparative Example 1 corresponds to NFM.

[0043] Table 1 Cyclic Comparison Chart

[0044] Table 2 Comparison Chart

[0045] Table 3. Comparison chart of cycles after being placed in the air for one day.

[0046] Depend on Figure 9 It can be seen that the battery's capacity at 1C is 118.44 mAh / g (compared to 131.69 mAh / g in Comparative Example 1), and the capacity retention rate after 200 cycles is still 83.08% (compared to 66.59% in Comparative Example 1), indicating that the material has very good cycle stability.

[0047] Depend on Figure 10 It can be seen that the battery capacity can reach 168.57mAh / g at 0.1C (compared to 165.82mAh / g in Comparative Example 1), and the capacity at 5C is 95.39mAh / g (compared to 86.58mAh / g in Comparative Example 1), indicating that it has very good rate performance.

[0048] Depend on Figure 11 It can be seen that after the material was placed in the air for one day, the battery capacity at 1C was 112.81 mAh / g (compared to 120.76 mAh / g of Comparative Example 1), and the capacity was only reduced by 4.7% compared with the battery that was not placed in the air for one day (compared to 8.3% of Comparative Example 1). After 100 cycles, the capacity retention rate was still 89.06% (compared to 78.88% of Comparative Example 1), indicating that it has very good air stability.

[0049] In summary, this invention utilizes a mixed solution of thiophene 2,5-diboronate and N-methylpyrrolidone to ultrasonically soak the positive electrode layered oxide, neutralizing the residual alkali on the surface of the main material and obtaining a positive electrode layered oxide material uniformly coated with thiophene 2,5-diboronate. This invention not only solves the problem of residual alkali on the surface of the positive electrode layered oxide material, but also generates a uniform and dense thiophene 2,5-diboronate coating layer, thereby improving the structural stability and air stability of the layered oxide positive electrode material, and enhancing its rate performance and cycle performance to meet the practical requirements of sodium-ion batteries.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium-ion battery coated positive electrode layered oxide material, characterized in that, include: The cathode material is a sodium-based layered oxide substrate and a thiophene 2,5-diboron oxide coating material.

2. The sodium-ion battery coated positive electrode layered oxide material according to claim 1, characterized in that, The chemical formula of the sodium-based oxide host material is NaM x O2, wherein 0≤x≤1, and element M is at least one of Ni, Fe, Mn, Co, Cu, Sc, Zn, Zr, Ti, Sn, Si, V, La, and Nb; the organic coating material is thiophene 2,5-diboronic acid with the chemical formula C4H5BO2S.

3. The sodium-ion battery coated positive electrode layered oxide material according to claim 1, characterized in that, The amount of the coating material is 0.5% to 2% of the mass of the sodium-based cathode layered oxide host material.

4. A method for preparing a sodium-ion battery coated cathode material according to any one of claims 1 to 3, characterized in that: The method includes the following steps: (1) Preparation of sodium-based crystalline oxide host material; (2) Dissolve 2,5-diborate thiophene in an appropriate amount of N-methylpyrrolidone (NMP) to obtain the desired modified solution, disperse the sodium-based positive electrode layered oxide host material in the modified solution, and react at room temperature and under ultrasonic conditions for 4-8 hours to obtain a solid-liquid mixture; (3) Separate the solid-liquid mixture obtained in step (2) and collect the solid product; (4) The solid product is dried under vacuum at 80-120°C for 12-24 hours to obtain the initial product, and the initial product is ground to obtain the final product.

5. The method for preparing the sodium-ion battery coated cathode material according to claim 4, characterized in that: In step (1), the preparation method of the sodium-based crystalline oxide host material is one of the following: high-temperature solid-state method, co-precipitation method, sol-gel method, and hydrothermal method.

6. The method for preparing the sodium-ion battery coated cathode material according to claim 4, characterized in that: In step (2), the solute of the modified solution is a soluble organic compound, and the solvent is any one of N-methylpyrrolidone, alcohol, etc.

7. The method for preparing the sodium-ion battery coated cathode material according to claim 4, characterized in that: In step (2), the sodium-based positive electrode layered oxide material is dispersed in the modified solution by ultrasonication, the reaction time is 4-8 hours, and the reaction temperature is room temperature.

Images