A high-sodium-content sodium manganate positive electrode material, a preparation method and application thereof

Abstract

The application belongs to the technical field of sodium-ion battery cathode material preparation, and particularly relates to a high-sodium-content sodium manganate cathode material and a preparation method and application thereof; the high-sodium-content sodium manganate material is prepared by using a simple and feasible solid-phase method, raw materials are first subjected to ball milling and pre-sintering treatment, so that the raw materials are mixed more uniformly to obtain a sodium manganate precursor, then the precursor is pressed into a round sheet, the particles are in closer contact, and the area available for reaction is more, then the surface phase and internal uniform heating of the precursor are realized by using a microwave heating mode, so that the reaction is more consistent at the same rate, and the generation of a heterogeneous phase is avoided. The preparation process can be scaled up in industry at equal proportions, the rate performance of the two prepared materials is relatively excellent, the discharge capacity is about 110 mAh / g at 0.1C, the discharge capacity is about 100 mAh / g at 0.2C, when the rate is increased to 5C, the capacity is still about 40 mAh / g, and the material has a good application prospect in the field of sodium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material preparation technology, specifically relating to a sodium manganate cathode material with high sodium content, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries have attracted widespread attention due to their abundant resources, low cost, and safety and reliability; however, their low energy density greatly limits their application in the power energy field. The cathode material is one of the key limiting factors determining the energy density and power density of sodium-ion batteries. Sodium manganate (NMO) is a typical cathode material for sodium-ion batteries, such as Na... 0.44 MnO2, with its stable structure, can be used as a sodium-ion cathode material in aqueous solution. However, its low sodium content results in insufficient sodium intercalation capacity. The amount of sodium in sodium manganate directly determines the amount of Na+ that can participate in the reaction in sodium-ion batteries. + The current methods for preparing sodium manganate materials either involve low sodium content or employ complex liquid-phase methods, which are insufficient to meet the demands of modern sodium-ion batteries. Therefore, increasing the sodium content in sodium manganate materials is crucial for improving battery energy density. Finding a simple and easy way to prepare sodium-rich sodium manganate materials is a pressing issue that needs to be addressed.

[0003] Patent CN 114180633 B reports a solid-liquid combined method for preparing Na with a sodium content of 0.7%. 0.7 MnO 2.05 The materials and preparation process are cumbersome, and the yield is low, which is not conducive to large-scale industrial production. Patent CN110921713 A also utilizes a solid-liquid combined method to prepare a Na₂O₃ with a smooth surface and a sodium content of 0.7%. 0.7 MnO 2.05The materials and preparation process are equally cumbersome, and the discharge capacity is not high, which is also unfavorable for large-scale industrial production. Patent CN108063239 A uses a hydrothermal method to prepare a network structure of sodium manganate nanoparticles. The preparation process is more complex than the previous two patents, and large-scale production is extremely difficult. Patent CN106800312B discloses a solid-phase preparation method of sodium manganite (Na2MnO3), a high-voltage positive electrode material for sodium secondary batteries. It involves grinding and mixing a manganese source compound and a sodium source compound in a certain stoichiometric ratio. The resulting mixture is transferred to a tube furnace and reacted at a high temperature of 400~700℃ under inert gas protection, followed by cooling to room temperature. The precursor is then ground, washed with distilled water until neutral, dried, and ground again to obtain the target product, sodium manganite. However, this patent uses sodium hydroxide, sodium acetate, sodium sulfate, sodium nitrate and sodium chloride as sodium sources. None of these sodium sources are suitable for preparing sodium manganate materials with sodium ions. It is questionable whether the prepared sodium manganate material can have a Na / Mn ratio ≥2. Moreover, the XRD of this patent shows a lot of impurity peaks. Furthermore, the preparation method is to simply grind the sodium and manganese sources and then directly calcine them at high temperature with conventional resistance wire. The performance of the product obtained is not ideal. Summary of the Invention

[0004] To address the shortcomings and drawbacks of the existing technology, the present invention aims to provide a sodium manganate cathode material with high sodium content, its preparation method, and its application.

[0005] The technical solution adopted in this invention is:

[0006] 1. A method for preparing a sodium manganate cathode material with high sodium content, comprising the following steps:

[0007] (1) Mix sodium carbonate (Na2CO3) and manganese dioxide (MnO2) in a molar ratio of 0.8~1.1:1.6~2 and ball mill for 30~60 minutes, then take out the mixed powder;

[0008] (2) The mixed powder is pre-fired at 200~400℃, kept at the temperature for 2~4 hours, and then naturally cooled to room temperature. The powder is then removed and ground to obtain sodium manganate precursor powder.

[0009] (3) Press the precursor powder into small round tablets with a diameter of 1~2 cm and a thickness of 1~2 cm using a tablet press, with a pressure of 1KN~2KN;

[0010] (4) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace and calcine at 700~900℃ for 6~12 hours with a microwave power of 500~1500 W, calcine in an oxygen atmosphere, and cool naturally to room temperature.

[0011] (5) Take out the product from step (4), grind it into powder, pass it through a 200-mesh sieve, and obtain sodium manganate material 1 with high sodium content;

[0012] (6) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace and calcine at 700~900℃ for 6~12 hours with a microwave power of 500~1500 W, set to calcine in an air atmosphere, and let them cool naturally to room temperature.

[0013] (7) Take out the product from step (6), grind it into powder, pass it through a 200-mesh sieve, and obtain sodium manganate material 2 with high sodium content.

[0014] Upon testing, sodium manganate material 1 was found to be pure phase Na. 0.7 MnO 2.05 Sodium manganate material 2 is Na 0.7 MnO 2.05 A mixture of NaMnO2 and NaMnO2.

[0015] 2. Application of sodium manganate material prepared by the above method in sodium-ion batteries:

[0016] One of the two sodium manganate materials mentioned above was used as the positive electrode active material, and mixed with Super P, CNTS, and PVDF (5% by mass solution) in a mass ratio of 80:6:4:10 to prepare the positive electrode sheet. A sodium metal sheet was used as the negative electrode, and a CR2025 coin cell was prepared using a 1 mol / L NaPF6 / EC:DMC electrolyte system. Charge-discharge performance was tested, with a discharge cutoff voltage of 2.0 V and a charge cutoff voltage of 4.0 V.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention employs a simple and easy-to-implement solid-state method to prepare sodium manganate materials with high sodium content. First, the raw materials are ball-milled and pre-calcined to ensure more uniform mixing, yielding a sodium manganate precursor. This precursor is then pressed into discs to increase particle contact and provide a larger reaction area. Microwave heating is then used to achieve uniform heating of the precursor's surface and interior, ensuring a more consistent reaction rate and preventing the formation of impurity phases. High-temperature solid-state methods, due to their faster reaction rates at high temperatures, result in shorter reaction times, purer materials, larger crystals, and better crystallinity. This patent utilizes microwave media for high-temperature calcination, resulting in more uniform heating of the reactants and a more complete reaction. The resulting material exhibits excellent crystallinity, providing a foundation for high capacity and high-rate discharge in the cathode material. The preparation process can be scaled up industrially on a proportional scale. Moreover, two sodium manganate materials can be obtained simultaneously on the same production line by simply changing the calcination atmosphere, which is the first time in this field. While significantly reducing production costs, the obtained sodium-rich sodium manganate material has the characteristics of high capacity and good rate performance when applied to sodium-ion batteries, and has a very good application prospect in the field of sodium-ion batteries. Attached Figure Description

[0019] Figure 1 The images show the XRD patterns of the two sodium manganate materials obtained in Example 1.

[0020] Figure 2 The images show the SEM and mapping images of the two sodium manganate materials obtained in Example 1.

[0021] Figure 3 The first discharge curves of the two sodium manganate materials obtained in Example 1 are shown.

[0022] Figure 4 The graph shows the rate performance of the two sodium manganate materials obtained in Example 1. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] Example 1

[0025] 1. A method for preparing a sodium manganate cathode material with high sodium content, comprising the following steps:

[0026] (1) Weigh out 0.08 mol of sodium carbonate (Na2CO3) and 0.16 mol of manganese dioxide (MnO2), with an additional 5% wt. of Na2CO3. Mix and ball mill for 40 minutes, then remove the mixed powder.

[0027] (2) The mixed powder was pre-fired in air at 300°C for 2 hours, then cooled naturally to room temperature. The powder was then removed and ground to obtain sodium manganate precursor powder.

[0028] (3) Press the sodium manganate precursor into round tablets with a diameter of 1 cm and a thickness of 1 cm using a tablet press, and set the pressure to 1.5 KN;

[0029] (4) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace for calcination, set the temperature to 800℃, calcination time to 6 hours, microwave power to 1000W, set the atmosphere to oxygen and air respectively, and cool naturally to room temperature.

[0030] (5) Take out the product from step (4), grind it into powder, and pass it through a 200-mesh sieve to obtain sodium manganate material 1 and sodium manganate material 2 with high sodium content.

[0031] Upon testing, sodium manganate material 1 was found to be pure phase Na. 0.7 MnO 2.05 Sodium manganate material 2 is Na 0.7 MnO 2.05 A mixture of NaMnO2 and NaMnO2.

[0032] 2. Application of sodium manganate material prepared by the above method in sodium-ion batteries:

[0033] The above two sodium manganate materials, Super P, CNTS, and PVDF (5% PVDF solution) were mixed in a mass ratio of 80:6:4:10 to prepare the positive electrode. A sodium metal sheet was used as the negative electrode, and a CR2025 coin cell was prepared using a 1 mol / L NaPF6 / EC:DMC electrolyte system. Charge-discharge performance was tested, with a discharge cutoff voltage of 2.0 V and a charge cutoff voltage of 4.0 V.

[0034] Example 2

[0035] 1. A method for preparing a sodium manganate cathode material with high sodium content, comprising the following steps:

[0036] (1) Weigh out 0.1 mol of sodium carbonate (Na2CO3) and 0.2 mol of manganese dioxide (MnO2), with an additional 5% wt. of Na2CO3. Mix and ball mill for 30 minutes, then remove the mixed powder.

[0037] (2) The mixed powder was pre-fired in air at 200°C for 3 hours, then naturally cooled to room temperature. The powder was then removed and ground to obtain sodium manganate precursor powder.

[0038] (3) Press the sodium manganate precursor into round tablets with a diameter of 1.5 cm and a thickness of 1.5 cm using a tablet press, and set the pressure to 1.5 KN;

[0039] (4) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace for calcination, set the temperature to 700℃, calcination time to 10 hours, microwave power to 500W, set the atmosphere to oxygen and air respectively, and cool naturally to room temperature.

[0040] (5) Take out the product from step (4), grind it into powder, and pass it through a 200-mesh sieve to obtain sodium manganate material 1 and sodium manganate material 2 with high sodium content.

[0041] Upon testing, sodium manganate material 1 was found to be pure phase Na. 0.7 MnO 2.05 Sodium manganate material 2 is Na 0.7 MnO 2.05 A mixture of NaMnO2 and NaMnO2.

[0042] Example 3

[0043] 1. A method for preparing a sodium manganate cathode material with high sodium content, comprising the following steps:

[0044] (1) Weigh out 0.16 mol of sodium carbonate (Na2CO3) and 0.3 mol of manganese dioxide (MnO2), with an additional 5% wt. of Na2CO3. Mix and ball mill for 60 minutes, then remove the mixed powder.

[0045] (2) The mixed powder was pre-fired in air at 400°C for 4 hours, then naturally cooled to room temperature. The powder was then removed and ground to obtain sodium manganate precursor powder.

[0046] (3) Press the sodium manganate precursor into round tablets with a diameter of 2 cm and a thickness of 2 cm using a tablet press, and set the pressure to 2 KN;

[0047] (4) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace for calcination, set the temperature to 900℃, calcination time to 12 hours, microwave power to 1500W, and set them to oxygen atmosphere and air atmosphere for calcination respectively, and let them cool naturally to room temperature.

[0048] (5) Take out the product from step (4), grind it into powder, and pass it through a 200-mesh sieve to obtain sodium manganate material 1 and sodium manganate material 2 with high sodium content.

[0049] Upon testing, sodium manganate material 1 was found to be pure phase Na. 0.7 MnO 2.05 Sodium manganate material 2 is Na 0.7 MnO 2.05 A mixture of NaMnO2 and NaMnO2.

[0050] I. Performance Testing

[0051] The sodium manganate materials 1 and 2 prepared by the method in Example 1 were subjected to XRD analysis, SEM and mapping analysis, discharge test and rate performance test, respectively. The XRD test scan rate was 1.3° / min, ranging from 10° to 90°; the initial charge-discharge test rate was 0.1C, and the voltage range was 2.0V to 4.0V; the rate test voltage range was 2.0V to 4.0V.

[0052] 1. XRD Analysis

[0053] like Figure 1 As shown, the sodium content of the prepared sodium manganate materials is all 0.7% or higher. Among them, pure phase Na was obtained by calcination under an oxygen atmosphere. 0.7 MnO 2.05 Calcination in air produces Na. 0.7 MnO 2.05 The mixture of NaMnO2 and oxygen atmosphere indicates that a pure phase material is more readily obtained under oxygen atmosphere.

[0054] 2. SEM and Mapping Analysis

[0055] like Figure 2 As shown, pure phase Na 0.7 MnO 2.05 The material exhibits a blocky structure, and the mapping diagram shows that the sodium content is lower than that of the mixed material. (Na...) 0.7 MnO 2.05 The mixed material with NaMnO2 is elongated, with a length of more than 20µm, and the mapping diagram shows that it is rich in sodium.

[0056] 3. First discharge test

[0057] like Figure 3 As shown, pure phase Na 0.7 MnO 2.05 The material exhibits an initial discharge capacity of 116 mAh / g and a median voltage of 2.40 V. Na 0.7 MnO 2.05 The mixed material with NaMnO2 had an initial discharge capacity of 109 mAh / g and a median voltage of 2.66 V, which is slightly lower than that of pure Na. 0.7 MnO 2.05 The material has a median voltage that is 0.26V higher than the median voltage, indicating that increasing the sodium content in the material helps to improve the median discharge voltage.

[0058] 4x Performance Test

[0059] like Figure 4As shown, both materials exhibit excellent rate performance, with a discharge capacity of approximately 110 mAh / g at 0.1C and approximately 100 mAh / g at 0.2C. Even at a rate increased to 5C, the capacity remains around 40 mAh / g. Pure-phase Na 0.7 MnO 2.05 The material exhibits better discharge performance at high rates than the hybrid material, with a discharge capacity of approximately 30 mAh / g at 10C.

Claims

1. A method for preparing a sodium manganate cathode material with high sodium content, characterized in that, Includes the following steps: (1) Sodium carbonate and manganese dioxide are mixed in a molar ratio of 0.8~1.1:1.6~2, and the mixture is ball-milled and then the powder is taken out. (2) The mixed powder is pre-fired, naturally cooled to room temperature, and then ground to obtain sodium manganate precursor powder; the pre-fired powder is the mixed powder pre-fired in air at 200~400℃ for 2~4 hours. (3) Press the precursor powder into small round tablets with a diameter of 1~2 cm and a thickness of 1~2 cm using a tablet press, with a pressure of 1KN~2KN; (4) Place the small discs obtained in step (3) into a ceramic boat, calcine them in a microwave tube furnace, cool them to room temperature, grind them into powder, and pass them through a 200-mesh sieve to obtain sodium manganate cathode material with high sodium content; the calcine in step (4) is to place the small discs into a ceramic boat, transfer them to a microwave tube furnace, and calcine them at a temperature of 700~900℃ for 6~12 hours, with a microwave power of 500~1500 W, and calcine them under two different atmospheres; the two different atmospheres are oxygen atmosphere and air atmosphere, respectively. The sodium manganate material 1 with high sodium content is obtained by calcine under an oxygen atmosphere. The sodium manganate material 1 has a block structure and is pure phase Na 0.7 MnO 2.05 High-sodium-content sodium manganate material 2 was prepared by calcination in air atmosphere. Sodium manganate material 2 was in the form of long strips with a length of more than 20 µm and was Na... 0.7 MnO 2.05 A mixture of NaMnO2 and NaMnO2.

2. The method for preparing a high-sodium-content sodium manganate cathode material as described in claim 1, characterized in that, Specifically, the following steps are included: (1) Mix sodium carbonate and manganese dioxide in a molar ratio of 0.8~1.1:1.6~2 and ball mill for 30~60 minutes, then take out the mixed powder; (2) The mixed powder is pre-fired at 200~400℃, kept at the temperature for 2~4 hours, and then naturally cooled to room temperature. The powder is then removed and ground to obtain sodium manganate precursor powder. (3) Press the precursor powder into small round tablets with a diameter of 1~2 cm and a thickness of 1~2 cm using a tablet press, with a pressure of 1KN~2KN; (4) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace and calcine at 700~900°C for 6~12 hours with a microwave power of 500~1500 W. Calcine them in an oxygen atmosphere and let them cool naturally to room temperature. (5) Take out the product from step (4), grind it into powder, pass it through a 200-mesh sieve, and obtain sodium manganate material 1 with high sodium content; (6) Place the small round pieces obtained in step (3) into a ceramic boat, transfer them to a microwave tube furnace and calcine at 700~900℃ for 6~12 hours with a microwave power of 500~1500 W, set to calcine in an air atmosphere, and cool naturally to room temperature. (7) Take out the product from step (6), grind it into powder, pass it through a 200-mesh sieve, and obtain sodium manganate material 2 with high sodium content.

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