Vanadium manganese sodium phosphate positive electrode material, battery and electrode plate

Abstract

The invention discloses a vanadium-manganese-sodium phosphate positive electrode material, which is a vanadium-manganese-sodium phosphate positive electrode material with a Mn / V disordered mixed arrangement structure, and the chemical formula of the vanadium-manganese-sodium phosphate positive electrode material is Na4MnV (PO4) 3. A plurality of pore structures are arranged on the surface. The sodium ion battery assembled by the vanadium manganese sodium phosphate positive electrode material prepared by the invention shows excellent performance. The specific discharge capacity of the first circle can reach 93.3 mAh g <-1 > under the 0.1 C multiplying power, and the specific discharge capacity is 72.80 mAh g <-1 > and the capacity retention ratio is 82.06% after 100 cycles under the 0.5 C multiplying power. Under the high rate of 10C, the specific discharge capacity can still reach 53.70 mAh g <-1 >. The positive electrode material shows relatively high specific capacity and excellent cycling stability and rate capability.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion positive electrode materials, and in particular to a sodium manganese vanadium phosphate positive electrode material, a battery and an electrode sheet. Background Art

[0002] Lithium-ion battery technology has achieved large-scale commercial applications in portable electronic devices and electric vehicles, and plays an increasingly important role in social life. However, the scarcity of lithium resources, geographical limitations, and high mining costs have kept its production costs high. Sodium-ion batteries have significant competitive advantages due to their abundant reserves and low costs.

[0003] The cathode material determines the overall performance of sodium-ion batteries. Therefore, the development of high-performance cathode materials is of great significance to the development of sodium-ion battery technology. For the cathode materials of sodium-ion batteries, they currently mainly include material systems such as transition metal oxides, Prussian blue compounds and polyanion compounds. Among them, polyanion materials with NASICON structure have fast sodium ion transmission channels and good structural stability and thermal stability, which have attracted widespread attention. Na3V2(PO4)3, as a typical NASICON structure polyanion cathode material, has a high theoretical capacity and good cycle stability. However, the high cost and toxicity of vanadium have greatly restricted the development of Na3V2(PO4)3 cathode materials. In response to this, Goodenough et al. partially replaced vanadium with inexpensive and environmentally friendly manganese to synthesize Na4MnV(PO4)3 cathode materials with lower cost and higher working voltage. However, due to the introduction of manganese, the synthesized Na4MnV(PO4)3 cathode material has the problems of fast capacity decay and poor rate performance.

[0004] Therefore, in order to inhibit the capacity decay of Na4MnV(PO4)3 material, improve its cycle stability and rate performance, and promote the commercial development of sodium manganese vanadium phosphate positive electrode material, the present invention is proposed. Summary of the invention

[0005] In order to solve the above problems, the present invention aims to provide a sodium manganese vanadium phosphate positive electrode material, a battery and an electrode sheet. The positive electrode material V / Mn has a disordered mixed structure. The sodium ion battery assembled using the sodium manganese vanadium phosphate positive electrode material prepared by the present invention exhibits excellent performance. At a rate of 0.1C, the first cycle discharge capacity can reach 93.3mAh g -1 After 100 cycles at 0.5C rate, the discharge capacity is 72.80 mAh g -1 The capacity retention rate is 82.06%. At a high rate of 10C, the discharge capacity can still reach 53.70mAh g -1The cathode material exhibits high specific capacity, excellent cycle stability and rate performance.

[0006] The present invention is achieved through the following technical solutions:

[0007] A sodium manganese vanadium phosphate positive electrode material is a sodium manganese vanadium phosphate positive electrode material with a disordered Mn / V mixed structure, and its chemical formula is Na4MnV(PO4)3. Its surface has multiple pore structures.

[0008] The sodium manganese vanadium phosphate cathode material precursor is rapidly Joule heated under the protection of an inert atmosphere, the rapid Joule heating temperature is 700-900°C, and the heating time is 5-120s.

[0009] The preparation method of sodium manganese vanadium phosphate positive electrode material precursor comprises the following steps: 1) heating and stirring a mixed solution of a sodium source, a manganese source, a vanadium source, a phosphorus source and citric acid at a constant temperature to obtain a wet gel; 2) drying the wet gel obtained in step 1) to obtain a precursor; the sodium source is one or more of sodium carbonate, sodium acetate, sodium bicarbonate or sodium dihydrogen phosphate; the manganese source is one or more of manganese acetate tetrahydrate, manganese carbonate and manganese nitrate hexahydrate; the vanadium source is one or more of ammonium metavanadate and vanadium pentoxide; the phosphorus source is one or more of sodium dihydrogen phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0010] In step 1), the sodium source, manganese source, vanadium source and phosphorus source are measured in a molar ratio of Na:Mn:V:P of 4:1:1:3; the ratio of citric acid to the total molar number of Mn and V elements is 3:2.

[0011] Step 1) The temperature of constant temperature heating is 70-90° C., the stirring speed is 250-400 rpm, and the heating time is 4-8 h.

[0012] In step 2), the temperature for drying the wet gel is 80-100° C. and the drying time is 10-18 hours.

[0013] An electrode sheet comprises the sodium manganese vanadium phosphate positive electrode material mentioned above.

[0014] A sodium ion battery comprises the electrode sheet as described above.

[0015] The principles of the present invention include:

[0016] The sodium vanadium manganese phosphate positive electrode partially replaces V with Mn, which reduces the cost and improves the working potential. However, the introduction of Mn also converts the sodium insertion and extraction process of the material into a two-step reaction, resulting in fast capacity decay and poor rate performance of the material. The present invention uses rapid Joule heating to quickly increase and decrease the temperature of the material during the sintering process to prepare a sodium vanadium manganese phosphate positive electrode material with a V / Mn disordered mixed structure. The disordered mixed structure of transition metal elements causes the two voltage platforms in the sodium vanadium manganese phosphate positive electrode charge and discharge curve to merge into one voltage platform, indicating that its reaction mechanism has changed, that is, the original two-step reaction is converted into a one-step reaction. On the one hand, this can reduce the volume change of the positive electrode material during the cycle, inhibit its capacity decay, and help improve the cycle stability of the material; on the other hand, compared with the two-step reaction, the one-step reaction process can significantly reduce the sodium ion diffusion energy barrier, has a faster sodium ion diffusion rate, and is conducive to improving the rate performance of the material. At the same time, the surface of the sodium vanadium manganese phosphate positive electrode material prepared by the present invention has a rich pore structure. The porous morphology can significantly increase the active specific surface area involved in the electrochemical reaction, allowing more active substances to participate in the electrode reaction, providing more channels for the diffusion of sodium ions, helping to maintain the efficient operation of the battery under high-rate charge and discharge conditions and improving the battery's rate performance.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] 1. The present invention provides a sodium vanadium manganese phosphate positive electrode material with a V / Mn disordered mixed structure, which changes the reaction mechanism of the material into a one-step reaction, thereby improving the reaction efficiency. The one-step reaction process is conducive to slowing down capacity decay and improving the cyclic stability of the material. It can also accelerate ion diffusion, improve electrode reaction kinetics, and enhance the rate performance of the material. Moreover, the porous morphology of the sodium vanadium manganese phosphate positive electrode material of the present invention can increase the electrochemically active specific surface area, facilitate the infiltration of the electrolyte, and further enhance the electrochemical performance of the material.

[0019] 2. The sodium ion battery assembled using the sodium manganese vanadium phosphate positive electrode material prepared by the present invention exhibits excellent performance. At a rate of 0.1C, the first cycle discharge capacity can reach 93.3 mAh g -1 After 100 cycles at 0.5C rate, the discharge capacity is 72.80 mAh g -1 The capacity retention rate is 82.06%. At a high rate of 10C, the discharge capacity can still reach 53.70mAh g -1 The cathode material exhibits high specific capacity, excellent cycle stability and rate performance.

[0020] 3. The sodium manganese vanadium phosphate positive electrode material provided by the present invention partially replaces vanadium by manganese, effectively reducing the cost, and at the same time alleviating the toxicity problem of vanadium in the Na3V2(PO4)3 positive electrode material, with good environmental benefits. The preparation method of the present invention is simple, the raw materials are abundant and easy to obtain, the cost is low, and during the material sintering process, the heating time is extremely short, which greatly reduces the energy consumption and has great commercial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0022] Figure 1 : X-ray diffraction patterns of the positive electrode materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0023] Figure 2 : Scanning electron microscope photograph of the positive electrode material prepared in Example 1 of the present invention.

[0024] Figure 3 : Scanning electron microscope photograph of the positive electrode material prepared in Comparative Example 1 of the present invention.

[0025] Figure 4 : The first charge and discharge curve of the positive electrode material prepared in Example 1 of the present invention at a rate of 0.1C.

[0026] Figure 5 : The first charge and discharge curve of the positive electrode material prepared in Comparative Example 1 of the present invention at a rate of 0.1C.

[0027] Figure 6 : Cyclic performance diagram of the positive electrode materials prepared in Examples 1-4 and Comparative Example 1 of the present invention.

[0028] Figure 7 : Rate performance diagram of the positive electrode materials prepared in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] According to the Na:Mn:V:P molar ratio of 4:1:1:3, sodium carbonate, manganese acetate tetrahydrate, ammonium metavanadate, sodium dihydrogen phosphate were weighed and added to deionized water, and citric acid was added as a chelating agent at a ratio of 2:3 to the total amount of Mn and V elements to obtain a mixed solution. The obtained mixed solution was heated at 80°C in a constant temperature water bath and magnetically stirred at a speed of 300rpm for 4h to obtain a wet gel, and then the wet gel was transferred to a blast drying oven and dried at 80°C for 12h to obtain a dry gel. The obtained dry gel was collected and ground into powder to obtain a precursor.

[0032] The obtained precursor powder was placed in a rapid Joule heating furnace, argon gas was introduced for protection, the temperature was raised to 750°C within 0.5s, heated for 30s, and then cooled to room temperature in 10s, finally obtaining a sodium vanadium manganese phosphate positive electrode material with the chemical formula Na4MnV(PO4)3.

[0033] Figure 1 The X-ray diffraction spectrum of the prepared positive electrode material is a Na4MnV(PO4)3 positive electrode material with a NASICON structure, which has no obvious impurities and high purity. At the same time, the half-peak width of the diffraction peak is wide, indicating that the size of the crystal particles is small. Figure 2 The SEM image of the obtained material shows that the primary particle size of the material is small and the surface has a rich pore structure, which is conducive to the infiltration of the electrolyte, increases the electrochemical active specific surface area, and enhances the electrochemical performance of the material.

[0034] The prepared positive electrode material is ground and mixed with acetylene black conductive agent and polyvinylidene fluoride binder in a mass ratio of 70:15:15, dissolved in N-methylpyrrolidone, and stirred for degassing to obtain a uniformly mixed slurry. The slurry is coated on aluminum foil and dried in a vacuum oven at 80°C. The dried electrode film is cut into pieces by a punching machine to obtain electrode sheets. Using a metal sodium sheet as the counter electrode, glass fiber as the diaphragm, and 1M NaClO4 dissolved in PC (5% FEC added) as the electrolyte, a CR2032 button battery is assembled for electrochemical performance testing, and the voltage window is 2-3.8V. Figure 3 As shown in Figure 2, at a current density of 11 mA / g, the initial discharge capacity of the battery is 93.3 mAh g -1 , showing a large voltage platform, indicating that its sodium insertion and extraction process is a one-step reaction.

[0035] Example 2

[0036] Compared with Example 1, the difference lies in the sintering method, which is as follows:

[0037] The precursor was prepared by the method described in Example 1. The precursor powder was placed in a rapid Joule heating furnace, argon gas was introduced for protection, and the heating mode was set to cyclic pulse heating, that is, the temperature was raised to 750°C within 0.5s, heated for 5s, cooled for 4s, and then the temperature was raised to 750°C again in 0.5s, heated for 5s, and cyclically heated 6 times, with a total heating time of 30s, and finally cooled to room temperature to obtain the positive electrode material.

[0038] The preparation of the electrode film and button cell and the electrochemical testing method are the same as those in Example 1.

[0039] Example 3

[0040] Compared with Example 1, the difference lies in the sintering method, which is as follows:

[0041] The precursor was prepared by the method described in Example 1. The precursor powder was first placed in a tube furnace and heated at 350°C for 3h under an argon atmosphere at a heating rate of 5°C / min. It was then transferred to a rapid Joule heating furnace, argon was introduced for protection, the temperature was raised to 750°C within 0.5s, heated for 30s, and then cooled to room temperature in 10s to obtain the positive electrode material.

[0042] The preparation of the electrode film and button cell and the electrochemical testing method are the same as those in Example 1.

[0043] Example 4

[0044] Similar to Example 1, the difference is that the temperature is raised to 900° C. within 0.5 s.

[0045] Comparative Example 1

[0046] Compared with Example 1, the difference lies in the sintering method, which is as follows:

[0047] The precursor was prepared by the method described in Example 1. The precursor powder was placed in a tube furnace, heated to 750°C at a heating rate of 5°C / min in an argon atmosphere, kept at this temperature for 6 hours, then cooled to 200°C at a rate of 5°C / min, and then cooled naturally to obtain a positive electrode material.

[0048] The preparation of the electrode film and button cell and the electrochemical testing method are the same as those in Example 1.

[0049] By comparing Example 1 with Comparative Example 1, and Figure 4-7 It can be seen that compared with conventional heating methods, the positive electrode material prepared by rapid Joule heating in the present invention has higher specific capacity, excellent cycle stability and rate performance. At the same time, the preparation method of the present invention is simple, the source of raw materials is abundant, the cost is low, the heating time during the sintering process is extremely short, and the energy consumption during the sintering process is greatly reduced, which has great development prospects.

[0050] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sodium manganese vanadium phosphate positive electrode material, characterized in that: It is a sodium manganese vanadium phosphate positive electrode material with a disordered mixed structure of Mn / V, and its chemical formula is Na4MnV(PO4)3.

2. The positive electrode material according to claim 1, characterized in that Its surface has multiple pore structures.

3. The method for preparing the positive electrode material according to claim 1 or 2, characterized in that: The sodium manganese vanadium phosphate cathode material precursor is rapidly Joule heated under the protection of an inert atmosphere, with a heating rate of 0.5s to 700-900°C. The rapid Joule heating temperature is 700-900°C and the heating time is 5-120s.

4. The preparation method according to claim 3, characterized in that: The preparation method of sodium manganese vanadium phosphate positive electrode material precursor comprises the following steps: 1) heating and stirring a mixed solution of a sodium source, a manganese source, a vanadium source, a phosphorus source and citric acid at a constant temperature to obtain a wet gel; 2) drying the wet gel obtained in step 1) to obtain a precursor; the sodium source is one or more of sodium carbonate, sodium acetate, sodium bicarbonate or sodium dihydrogen phosphate; the manganese source is one or more of manganese acetate tetrahydrate, manganese carbonate and manganese nitrate hexahydrate; the vanadium source is one or more of ammonium metavanadate and vanadium pentoxide; the phosphorus source is one or more of sodium dihydrogen phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

5. The preparation method according to claim 4, characterized in that: In step 1), the sodium source, manganese source, vanadium source and phosphorus source are measured in a molar ratio of Na:Mn:V:P of 4:1:1:3; the ratio of citric acid to the total molar number of Mn and V elements is 3:

2.

6. The preparation method according to claim 4, characterized in that: Step 1) The temperature of constant temperature heating is 70-90° C., the stirring speed is 250-400 rpm, and the heating time is 4-8 h.

7. The preparation method according to claim 4, characterized in that: In step 2), the temperature for drying the wet gel is 80-100° C. and the drying time is 10-18 hours.

8. An electrode sheet, characterized in that: The invention comprises the sodium manganese vanadium phosphate positive electrode material as described in claim 1 or 2.

9. A sodium ion battery, characterized in that: Comprising the electrode sheet as claimed in claim 8.

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