Preparation method of carbon-coated polyanionic sodium ion battery cathode material

Abstract

The application provides a preparation method of a carbon-coated polyanionic sodium ion battery positive electrode material. By optimizing the transition metal proportion, the electronic structure of the material is adjusted. The introduction of the surface conductive carbon layer provides a fast electron transmission channel and improves the apparent electrochemical diffusion coefficient of the electrode material. The positive electrode particle size is optimized, so that the reversible capacity and the cycle life of the material are simultaneously and significantly improved. Through simple solid-phase mixing and a multi-step calcination and grinding process, the obtained material has good consistency and low cost. The prepared sodium ion battery positive electrode material has excellent performance and is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to sodium-ion battery electrode material preparation technology, and more specifically, to a carbon-coated polyanionic sodium-ion battery cathode material and its preparation method. Background Technology

[0002] With the continuous development of electrochemical energy storage technology, lithium-ion batteries have been widely used in electric vehicles, portable electronic devices, and large-scale energy storage systems due to their high energy density, high operating voltage, excellent cycle stability, and high safety. However, the abundance and uneven distribution of lithium in the Earth's crust, coupled with its persistently high extraction costs, pose a significant constraint on the long-term supply of lithium resources. Therefore, developing resource-sustainable and cost-effective alternative electrochemical energy storage systems has become an important research direction in this field. Sodium-ion batteries, due to their similarity to lithium-ion batteries in charge storage mechanisms and the abundant and widely distributed natural reserves of sodium, are considered a promising alternative technology for large-scale application. Among the many sodium-ion battery cathode material systems, polyanionic compounds have attracted widespread attention due to their high structural stability, adjustable operating voltage, and good thermal safety. Pyrophosphate materials, as an important class of polyanionic cathode materials, have been extensively studied.

[0003] Specifically, sodium iron pyrophosphate (Na2FeP2O7) exhibits high rate performance and a reversible capacity of approximately 80 mAh / g. Studies show that embedding Na2FeP2O7 nanoparticles into a carbon matrix effectively enhances its electronic conductivity, retaining approximately 83% of its initial discharge capacity after 10,000 cycles at 10 C. In contrast, pure Na2FeP2O7 without carbon composite exhibits significantly poorer cycle stability, typically retaining only about 70% of its initial capacity after the first 20 cycles. Similarly, sodium manganese pyrophosphate (Na2MnP2O7) shows improved rate performance relative to Na / Na... + At a voltage of 3.8 V, it can provide a reversible capacity of approximately 90 mAh / g, and after 30 cycles at a C / 20 scan rate, the capacity retention reaches 96%, demonstrating a higher charge-discharge voltage plateau and reversible capacity potential. However, due to the low intrinsic electronic conductivity of manganese-based materials, the rate performance of Na2MnP2O7 is significantly limited, making it difficult to meet the requirements of practical applications for fast charge-discharge capabilities.

[0004] Although iron- and manganese-based pyrophosphates each have their own performance characteristics, there are still technical contradictions that are difficult to balance among the capacity, rate performance, and cycle stability of single transition metal pyrophosphate cathode materials. In addition, the current systematic research on pyrophosphate cathode materials with iron / manganese mixed occupancy is not sufficient. In particular, how to simultaneously improve the comprehensive electrochemical performance through the synergistic regulation of optimizing the transition metal ratio and carbon coating process is still a technical problem亟待解决 in this field. The deficiencies of the above-mentioned prior art have restricted the commercialization process of such materials as sodium-ion battery cathode materials. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a preparation method of a carbon-coated polyanionic sodium-ion battery cathode material.

[0006] To achieve the above purpose, the technical solution of this invention is as follows: (1) Mix a sodium source, a phosphorus source, a manganese source, and an iron source according to a stoichiometric ratio to obtain mixture I; (2) Calcinate mixture I in an inert atmosphere at a calcination temperature of 250-400°C for 2-5 hours, and then grind it to obtain mixture II; (3) Calcinate mixture II in an inert atmosphere at a calcination temperature of 600-800°C for 5-12 hours, and then grind it to obtain Na2Fe x Mn y P2O7 powder, where 0 < x < 1, 0 < y < 1, and x + y = 1; (4) Mix the Na2Fe x Mn y P2O7 powder with a carbon source and add ethanol for ball milling, and obtain mixed powder III after drying; (5) Anneal mixed powder III in an inert atmosphere at an annealing temperature of 500-800°C for 4-10 hours, and obtain a carbon-coated polyanionic sodium-ion battery cathode material after cooling.

[0007] Preferably, in step (1), the stoichiometric ratio is determined according to the molar ratio of Fe to Mn in the target product Na2Fe x Mn y P2O7, where 0 < x < 1, 0 < y < 1, and x + y = 1.

[0008] Preferably, the inert atmosphere in steps (2), (3), and (5) is an argon atmosphere or a nitrogen atmosphere.

[0009] Preferably, in step (4), the carbon source is a common organic sugar.

[0010] Preferably, in step (4), the ball milling speed is 200~500 rpm and the ball milling time is 10~15 hours.

[0011] A sodium-ion battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a carbon-coated polyanion sodium-ion battery positive electrode material prepared by any of the above preparation methods. Beneficial effects

[0012] This invention designs and prepares a mixed transition metal pyrophosphate, Na₂Fe. x Mn y For P2O7 cathode materials, this invention proposes a synergistic strategy of adjusting the iron / manganese molar ratio (x / y) and surface carbon coating to systematically solve the technical contradiction that single iron-based or manganese-based pyrophosphate cathode materials struggle to simultaneously achieve high capacity, rate performance, and cycle stability. Specifically, this invention optimizes the transition metal ratio to adjust the electronic structure of the material, promoting Mn content during charge and discharge processes. 3+ / Mn 4+ with Fe 2+ / Fe 3+ The efficient synergistic participation of the redox couple effectively broadens the charge compensation window and enhances the stability of the crystal structure during sodium insertion / extraction, thereby simultaneously and significantly improving the material's reversible capacity and cycle life. Simultaneously, the introduction of a conductive carbon layer on the surface provides a rapid electron transport channel, optimizes the cathode particle size, and improves the apparent electrochemical diffusion coefficient of the electrode material, overcoming the inherent defect of low intrinsic electronic conductivity in polyanionic materials. The synergistic effect of these two mechanisms achieves a comprehensive improvement in the electrode material's capacity, rate performance, and long-term cycling stability.

[0013] The preparation method provided by this invention utilizes widely available and inexpensive raw materials, combining simple solid-phase mixing with multi-step calcination and grinding processes to successfully construct a uniform conductive carbon coating layer in situ on the surface of active material particles. This process route avoids complex or high-cost synthesis steps, is simple to operate, and is controllable. The resulting final product exhibits good batch-to-batch consistency, excellent and stable electrochemical performance, significant cost advantages, and scalability, making it highly suitable for large-scale industrial production. Attached Figure Description

[0014] Figure 1 The diagram shows the synthesis steps of Example 1. Some steps in the diagram have been omitted and do not correspond one-to-one with the step numbers in the previous part of the specification, but the overall process is the same.

[0015] Figure 2 Rate maps of batteries assembled from the cathode materials prepared in Comparative Example 1, Comparative Example 2, Example 1, Example 2 and Example 3 at different current densities.

[0016] Figure 3 Cyclic data at 1.0C current density for batteries assembled with the cathode materials prepared in Comparative Example 1, Comparative Example 2, Example 1, Example 2 and Example 3. Detailed Implementation

[0017] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0018] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, and instruments used in the embodiments, unless otherwise specified, can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0019] In the following embodiments or comparative examples: Assembly of button cell: At room temperature, the working electrode is first prepared by mixing the materials prepared in the examples or comparative examples with conductive agent and binder in a ratio of 7:2:1 to prepare a uniform slurry; then, the slurry is uniformly coated onto aluminum foil with a scraper and dried under vacuum at 100°C for 12 hours to obtain the working electrode; finally, the aluminum foil coated with the sample is pressed into a small disc with a diameter of 1.1 cm using a punching machine as the positive electrode, sodium sheet as the negative electrode material, and 1.0 M NaClO4 carbonate electrolyte to prepare a button half cell.

[0020] The Blue Electric system is used to detect electrochemical performance. The test voltage range is 2.0 V-4.5 V, the test temperature is 30℃, and the test current density is 0.1C-50.0C (1.0C=100 mA / g). Example 1

[0021] Sodium carbonate, diammonium hydrogen phosphate, manganese oxalate, and ferrous oxalate were thoroughly mixed in a molar ratio of 1:2:0.1:0.9 to obtain mixture I. Mixture I was placed in a tube furnace and calcined for the first time in an argon atmosphere at 350°C for 3 hours. After calcination, the mixture was ground to obtain mixture II. Mixture II was then placed in a tube furnace again and calcined for the second time in an argon atmosphere at 650°C for 6 hours. After grinding, Na₂Fe₂ was obtained. 0.9 Mn 0.1 P2O7 powder. Ethanol and glucose were added, and the resulting Na2Fe was obtained by high-energy ball milling. 0.9 Mn 0.1 P2O7 powder was carbon-coated and ball-milled at 300 rpm for 12 hours. After drying, mixed powder III was obtained. Mixed powder III was placed in a tube furnace and annealed in an argon atmosphere at 650°C for 6 hours. After cooling, the carbon-coated polyanion sodium-ion battery cathode material of Example 1 was obtained. The rate capability and cycle performance of the assembled battery are as follows: Figure 2 and Figure 3 As shown. Example 2

[0022] After adjusting the carbon coating to 5% by mass, Example 2 with carbon coating can be obtained by following the steps of Example 1. The electrochemical performance of the obtained cathode material after being assembled into a battery is as follows: Figure 2 and Figure 3 As shown. Example 3

[0023] After adjusting the carbon coating to 7.5% by mass, Example 3 with carbon coating can be obtained by following the steps of Example 1. The electrochemical performance of the obtained cathode material after being assembled into a battery is as follows: Figure 2 and Figure 3 As shown. Comparative Example 1

[0024] Sodium carbonate, diammonium hydrogen phosphate, and ferrous oxalate were thoroughly mixed in a molar ratio of 1:2:1 to obtain mixture I. Mixture I was placed in a tube furnace and calcined for the first time in an argon atmosphere at 350°C for 3 hours. After calcination, the mixture was ground to obtain mixture II. Mixture II was then placed in a tube furnace again and calcined for the second time in an argon atmosphere at 650°C for 6 hours. After grinding, Na₂Fe₁P₂O₇ powder was obtained, which is Comparative Example 1. Comparative Example 2

[0025] Sodium carbonate, diammonium hydrogen phosphate, manganese oxalate, and ferrous oxalate were thoroughly mixed in a molar ratio of 1:2:0.1:0.9 to obtain mixture I. Mixture I was placed in a tube furnace and calcined for the first time in an argon atmosphere at 350°C for 3 hours. After calcination, the mixture was ground to obtain mixture II. Mixture II was then placed in a tube furnace again and calcined for the second time in an argon atmosphere at 650°C for 6 hours. After grinding, Na₂Fe₂ was obtained. 0.9 Mn 0.1 P2O7 powder, which is Comparative Example 2.

Claims

1. A method for preparing a carbon-coated polyanionic sodium-ion battery cathode material, characterized in that, Includes the following steps: (1) Sodium source, phosphorus source, manganese source and iron source are mixed in stoichiometric ratio to obtain mixture I; (2) The mixture I is calcined for the first time in an inert atmosphere at a temperature of 250-400°C for 2-5 hours, and then ground to obtain mixture II; (3) The mixture II is subjected to a second calcination in an inert atmosphere at a calcination temperature of 600-800 °C for a calcination time of 5-12 hours, and then ground to obtain Na2Fe x Mn y P2O7 powder, where 0 < x < 1, 0 < y < 1, and x + y = 1; (4) The Na2Fe x Mn y P2O7 powder was mixed with a carbon source and ethanol was added. The mixture was then ball-milled and dried to obtain mixed powder III. (5) The mixed powder III is annealed in an inert atmosphere at a temperature of 500-800°C for 4-10 hours. After cooling, carbon-coated polyanionic sodium-ion battery cathode material is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the stoichiometric ratio is determined according to the molar ratio of Fe to Mn in the target product Na2Fe x Mn y P2O7, where 0 < x < 1, 0 < y < 1, and x + y = 1.

3. The preparation method according to claim 1, characterized in that, The inert atmosphere in steps (2), (3), and (5) is either argon or nitrogen.

4. The preparation method according to claim 1, characterized in that, In step (4), the carbon source is a common organic sugar.

5. The preparation method according to claim 1, characterized in that, In step (4), the ball milling speed is 200~500 rpm and the ball milling time is 10~15 hours.

6. A carbon-coated polyanionic sodium-ion battery cathode material, characterized in that, It is prepared by any one of claims 1 to 6.

7. A sodium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode comprises the carbon-coated polyanion sodium-ion battery positive electrode material as described in claim 7.

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