Rapid preparation method and application of high-capacity medium-manganese phosphate positive electrode material

Abstract

According to the rapid preparation method and application of the high-capacity medium-manganese phosphate positive electrode material, citric acid serves as a first carbon source and a reducing agent, hydroxylated carbon nanotubes serve as a second carbon source, and carboxyl on the carbon nanotubes can be bonded with metal ions, so that the material can be better attached to the carbon nanotubes. A precursor is obtained through a sol-gel method, and then high-temperature rapid sintering is carried out through Joule heating to obtain a final material. Joule heating has the characteristics of simple operation and relatively high energy consumption efficiency, meanwhile, synchronous implementation of formation of a coating carbon layer through citric acid decomposition and formation of a material phase is realized, a uniform carbon coating layer is obtained, and when the obtained material is used as a sodium ion battery identification material, excellent specific capacity and good cycling stability are shown. According to the manganese phosphate positive electrode material, the discharge capacity is up to 153 mAh / g at 0.2 C, the capacity retention rate reaches 87.8% after 1500 times of high-rate 10C circulation, and reference significance can be provided for development of sodium ion battery positive electrode materials and design of high-capacity commercial sodium ion batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage devices and electrode materials, and particularly relates to a rapid preparation method of a high-capacity medium-manganese phosphate positive electrode material and application thereof. The material is prepared by a sol-gel method, and then high-temperature rapid sintering is performed by using joule heating to obtain the final material. When the material obtained by the application is applied to a sodium ion battery positive electrode material, the material exhibits high specific capacity and cycle stability. BACKGROUND

[0002] Energy storage batteries, as important basic equipment and technical support for solving energy storage problems, are showing a rapid development trend. Compared with traditional lithium ion battery technology, sodium ion batteries as a new type of energy storage technology have attracted widespread attention from technology workers and enterprises in recent years. Sodium resources are abundant and widely distributed, and the cost is low, so sodium ion batteries have a significant cost advantage in large-scale energy storage technology. The positive electrode material, as a key component of sodium ion batteries, plays a decisive role in the capacity, cycle stability and safety of the full battery. Therefore, the development of high-performance positive electrode materials is of great significance for promoting the widespread application of sodium ion batteries.

[0003] Sodium vanadium phosphate (Na3V2(PO4)3) has a typical sodium super ionic conductor (NASICON) structure and is considered to be an extremely attractive positive electrode material for sodium ion batteries. In the structure of Na3V2(PO4)3, VO6 octahedra and PO4 tetrahedra share apex oxygen to form a stable "lantern" three-dimensional structure framework, so that there are a large number of ion channels for sodium ion transmission in the structure, and the working platform is as high as 3.4 V. Generally, the charge and discharge voltage range of this positive electrode material is 2-3.8 V, and only V 3+ / V 4+ redox couples are exhibited, which cannot fully utilize the advantage of vanadium having multiple valence states. However, the high price and toxicity of vanadium limit its large-scale application. In 2016, Goodenough et al. obtained a Na4MnV(PO4)3 positive electrode material by partially replacing vanadium with manganese, which has high abundance and a higher redox potential. The Mn 2+ / Mn 3+ voltage platform exists, which can increase the working voltage to 3.5 V. However, the Na4MnV(PO4)3 positive electrode material with high manganese content causes Jahn-Teller effect of Mn 3+ in the structure when it is in a charged state, which causes lattice distortion of the Mn / VO6 octahedron in the structure, resulting in rapid degradation of the structure and rapid capacity decay during the cycle. By reducing the content of manganese in the Na4MnV(PO4)3 material, a Na 3.5 Mn 0.5 V 1.5 (PO4)3 material with medium manganese content is obtained, which can alleviate the Mn 3+The lattice distortion generated by the Jahn-Teller effect of V 4+ / V 5+ Redox couples, further improve the working voltage of the material.

[0004] The conventional preparation methods of phosphate positive electrode materials include solid phase method, hydrothermal / solvothermal method and spray drying method, etc., but these methods have complex process, long reaction time and high energy consumption. In recent years, Joule heating is a new preparation technology developed, which has the characteristics of fast heating rate, and the temperature is quickly raised to the required temperature within a few seconds, and the decomposition of citric acid and the formation of material phase are realized synchronously during the preparation process, which effectively prevents the aggregation or shedding of the carbon layer and realizes the uniform coating of the carbon layer. SUMMARY

[0005] The present application is directed to the Na 3.5 Mn 0.5 V 1.5 The present application provides a rapid preparation method of high-capacity medium-manganese phosphate positive electrode material and its application, and the specific steps are as follows:

[0006] (1) ultrasonically disperse a proper amount of carboxylated carbon nanotubes in 30 mL of deionized water;

[0007] (2) according to the stoichiometric ratio, stir and dissolve citric acid monohydrate and V2O5 in 50 mL of deionized water, and place in an 80 ℃ oil bath for magnetic stirring and dissolution;

[0008] (3) after all the dissolution in step (2), according to the stoichiometric ratio, sequentially add NaAc·3H2O, NaH2PO4 and Mn(Ac)2·4H2O, continue to stir for 30 minutes, then add the carbon nanotube suspension liquid in step (1), continue to stir to evaporate the water, then obtain a dry gel, and then vacuum dry at 100 ℃ for 12 hours to obtain a dried gel;

[0009] (4) grind the dry gel obtained in step (3) thoroughly to make it into a powder, then weigh an appropriate amount of the powder and press it into a tablet using a Ф15 mm mold, and then place the pressed tablet in a Joule heating device, quickly heat it to 950 ℃ for 10 seconds, and then heat it for 20 seconds to obtain a Na 3.5 Mn 0.5 V 1.5 (PO4)3 material.

[0010] The medium-manganese phosphate Na 3.5 Mn 0.5 V 1.5The (PO4)3 positive electrode material is synthesized by using Joule heating instead of a conventional tube furnace heating synthesis process, so that extremely high energy efficiency and second-level synthesis speed can be achieved. The method is simple and easy to implement, has fast synthesis speed, and has reference significance for synthesis of other electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is an X-ray diffraction pattern of the sample of Example 1 of the present application.

[0012] Figure 2 is a cyclic voltammogram of the electrode of Example 1 of the present application at a scan rate of 0.2 mV / s in a voltage range of 1.5-4.2 V.

[0013] Figure 3 is a comparison graph of the cyclic-discharge specific capacity of the electrodes of Example 1 and Comparative Example 1 of the present application at different rates.

[0014] Figure 4 is a comparison graph of the cyclic performance of the electrodes of Example 1 and Comparative Example 1 of the present application at a high rate of 10 C. DETAILED DESCRIPTION

[0015] Example 1

[0016] This embodiment is implemented on the premise of the technical solution of the present application. The following describes the preparation process of the 5 mmol target Na 3.5 Mn 0.5 V 1.5 (PO4)3 material in detail, but the protection scope of the present application is not limited to the following examples, and the specific steps are as follows:

[0017] (1) 0.15 g of carboxylated carbon nanotubes were ultrasonically dispersed in 30 mL of deionized water;

[0018] (2) Citric acid monohydrate and V2O5 were stirred and dissolved in 50 mL of deionized water according to the stoichiometric ratio, and the mixture was placed in an 80 ℃ oil bath and magnetically stirred to dissolve;

[0019] (3) After all the substances in step (2) were dissolved, NaAc·3H2O, NaH2PO4, and Mn(Ac)2·4H2O were added according to the stoichiometric ratio, and the mixture was continuously stirred for 30 minutes. Then, the carbon nanotube suspension was added, and the mixture was continuously stirred to evaporate the water, obtaining a dry gel. Then, the dry gel was vacuum dried at 100 ℃ for 12 hours, obtaining a dried gel;

[0020] (4) The xerogel obtained in step (3) was ground thoroughly until it became a powder, then 0.5 g of the powder was weighed and tableted into a Ф15 mm mold, the tablet was placed in a joule heating device, rapidly heated to 950 °C for 10 seconds, and then held at 950 °C for 20 seconds to obtain a NASICON-structured Na 3.5 Mn 0.5 V 1.5 (PO4)3material.

[0021] Comparative Example 1

[0022] The preparation process of Comparative Example 1 used a conventional tube furnace for high-temperature sintering, the front part was consistent with steps (1) to (3) of Example 1, except that the xerogel obtained in step (3) was ground into a powder, then placed in a tube furnace, heated to 400 °C at a rate of 5 °C / min in an argon atmosphere, and held for 2 hours. After the furnace was cooled, the powder was re-ground, then 0.6 g was weighed and tableted into a Ф12 mm mold, then placed in a tube furnace, heated to 700 °C at a rate of 5 °C / min in an argon atmosphere, then held for 6 hours. After the furnace was cooled, the powder was ground to obtain the sample of Comparative Example 1.

[0023] When making a sodium-ion battery positive electrode, the powders obtained in Example 1 and Comparative Example 1 were used as active materials, and the electrode was made according to a mass ratio of active material: Super P carbon (conductive agent): PVDF (binder) of 7:2:1. First, PVDF was placed in a beaker containing N-methyl pyrrolidone (NMP) and stirred magnetically until it was clear. The active material and super conductive carbon black were mixed, then taken out and placed in a glass beaker, stirred for 6 hours, and finally uniformly coated on a current collector aluminum foil, which was placed in a vacuum drying oven at 80 °C for 12 hours. After cooling, the slice was taken out and cut into a round piece with an area of 1.13 cm 2 , then the electrode sheet was compacted at a pressure of 4 MPa. The obtained electrode sheet was used as the working electrode, a piece of metallic sodium was used as the reference electrode, a glass fiber membrane (Whatman) was used as the separator, sodium perchlorate was dissolved in polycarbonate as the electrolyte, and 5wt% of fluoroethylene carbonate was used as the additive. The concentration of sodium perchlorate was 1 mol / L. -1 The CR2032 half-cell was assembled and sealed in an argon-filled glove box, and the oxygen and water contents inside were less than 0.1 ppm. The charge and discharge capacity was calculated based on the mass of the active material.

[0024] Figure 1 is the Na 3.5 Mn 0.5 V 1.5The X-ray diffraction pattern of the sample of Na3V2(PO4)3 shows all the diffraction peaks corresponding to the Na3V2(PO4)3 card of the NASICON structure, indicating that the sample synthesized by the rapid Joule heating is a pure phase compound with the NASICON structure.

[0025] Figure 2 is the cyclic voltammogram of the electrode of Example 1 of the present application at a scan rate of 0.2 mV s -1 The cyclic voltammogram of Example 1 of the present application at a scan rate of 0.2 mV s 2+ 3+ The cyclic voltammogram of Example 1 of the present application at a scan rate of 0.2 mV s 3+ 4+ The cyclic voltammogram of Example 1 of the present application at a scan rate of 0.2 mV s 2+ 3+ The cyclic voltammogram of Example 1 of the present application at a scan rate of 0.2 mV s 4+ 5+ The cyclic voltammogram of Example 1 of the present application at a scan rate of 0.2 mV s

[0026] Figure 3 is the comparison chart of the cyclic-discharge specific capacity of the electrode of Example 1 of the present application and the electrode of Comparative Example 1 at different rates, it can be seen that the discharge capacity of the electrode of Example 1 synthesized by the rapid Joule device is higher than that of the electrode of Comparative Example 1 prepared by the conventional tube furnace heating at each rate. At a rate of 0.2 C, the average discharge capacity of the electrode of Example 1 is as high as 153 mAh / g, which is much higher than the theoretical capacity of Na3V2(PO4)3 (117.6 mAh / g) and the discharge capacity of the electrode of Comparative Example 1 (144 mAh / g). Even at a high rate of 20 C, the average capacity is as high as 85 mAh / g.

[0027] Figure 4 is the cycle performance chart of the electrode of Example 1 of the present application and the electrode of Comparative Example 1 at a rate of 10 C, it can be seen from the chart that at a high rate of 10 C, the discharge specific capacity of the electrode of Example 1 is higher than that of the electrode of Comparative Example 1, and has a higher capacity retention rate. After 1500 cycles, the discharge capacity of the electrode of Example 1 is 83.7 mAh / g, and the capacity retention rate is about 87.8%, which is higher than the discharge capacity of 74.5 mAh / g and the capacity retention rate of 83% of the electrode of Comparative Example 1 after 400 cycles.​​​​

Claims

1. A rapid preparation method for high-capacity medium-manganese phosphate cathode material and its application, characterized in that: The chemical formula of the medium-manganese phosphate cathode material is Na. 3.5 Mn 0.5 V 1.5 (PO4)3.

2. The rapid preparation method of a high-capacity medium-manganese phosphate cathode material according to claim 1 and its application, characterized in that: The precursor was obtained by the sol-gel method, and then the final material was obtained by high-temperature rapid sintering using Joule heating.

3. A rapid preparation method for a high-capacity medium-manganese phosphate cathode material according to claims 1-2 and its application, characterized in that, Specific steps: (1) Disperse an appropriate amount of carboxylated carbon nanotubes ultrasonically in 30 mL of deionized water; (2) Dissolve citric acid monohydrate and V2O5 in 50 mL of deionized water according to the stoichiometric ratio, and then place them in an oil bath at 80 °C and stir magnetically to dissolve them. (3) After all the solution in step (2) is dissolved, add NaAc·3H2O, NaH2PO4 and Mn(Ac)2·4H2O in sequence according to the stoichiometric ratio and continue stirring for 30 minutes. Then add the carbon nanotube suspension in step (1) and continue stirring to evaporate the water to obtain a dry gel. Then dry it in a vacuum at 100 °C for 12 hours to obtain a dry gel. (4) Grind the dry gel obtained in step (3) thoroughly until it becomes powder. Then weigh an appropriate amount of powder and press it into a tablet using a Ф15mm mold. Place the pressed tablet in a Joule heating device and rapidly heat it to 950 ℃ in 10 seconds. Hold the temperature for 20 seconds to obtain Na with NASICON structure. 3.5 Mn 0.5 V 1.5 (PO4)3 material.

4. The preparation method and the obtained material according to claims 1-3, characterized in that: As a cathode material for sodium-ion batteries, it exhibits high capacity and good cycle stability.

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