Preparation method and application of positive electrode material

Abstract

The invention discloses a preparation method and application of a positive electrode material, and the preparation method comprises the following steps: adding a metal vanadium oxide and an organic acid into deionized water, carrying out a heating reaction, stirring, and cooling to obtain a first mixed solution; adding sodium phosphate and a carbon source into the first mixed solution, and reacting to obtain a second mixed solution; adding n-propyl alcohol into the second mixed solution, stirring and drying to obtain a solid compound; and preheating the solid compound in inert gas, heating to an annealing temperature, calcining, and cooling to obtain the sodium vanadium phosphate and carbon flower composite positive electrode material. According to the sodium vanadium phosphate and carbon flower positive electrode material, the electronic conductivity can be improved, the surface area is increased, the contact area between an electrode and an electrolyte is increased, and the electrochemical performance can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, in particular to a preparation method of a positive electrode material and application thereof. BACKGROUND

[0002] Among the battery systems, the sodium battery positive electrode material mainly includes layer oxides (i.e. sodium metal oxides), Prussian blue and polyanions. Among these materials, polyanions (phosphate positive electrodes) perform well in safety and stability, and are superior to layer oxides. Prussian blue has a problem of crystal water, and researchers are now making every effort to break through the technology. Compared with sodium metal oxides, phosphate positive electrodes exhibit extremely significant electrochemical stability and thermal stability, which is extremely beneficial to improving the cycle stability of the battery.

[0003] Up to now, many phosphate positive electrode materials, such as sodium vanadium fluorophosphate, sodium titanium phosphate and sodium vanadium phosphate (NVP), have been proved to be promising active materials. Among these materials, NVP is a typical compound related to Na+ super ionic conductor (NASICON). Due to its open framework structure with large ion transmission tunnels, it exhibits a high ion (Li+, Na+) mobility. However, NVP also has two obvious shortcomings. Firstly, its theoretical specific capacity is relatively low, about 117.6 mAh / g, which seriously restricts the improvement of the energy density of the full battery; secondly, its low electronic conductivity seriously affects its electrochemical performance, resulting in low electron transmission efficiency during charging and discharging, thereby limiting its performance in practical application. SUMMARY

[0004] In order to overcome the defects in the prior art, the first purpose of the present application is to provide a preparation method of a positive electrode material, the second purpose of the present application is to provide a positive electrode comprising the positive electrode material, the third purpose of the present application is to provide a sodium ion battery comprising the positive electrode material, and the fourth purpose of the present application is to provide an electric device.

[0005] To achieve the above purposes, the technical scheme adopted by the present application is as follows:

[0006] In a first aspect, a preparation method of a positive electrode material comprises the following steps:

[0007] Step one, metal vanadium oxide and organic acid are added to deionized water, heated and reacted, stirred and cooled to obtain a first mixed solution;

[0008] Step two, sodium phosphate and a carbon source are added to the first mixed solution, and a second mixed solution is obtained after reaction;

[0009] Step 3: Add n-propanol to the second mixed solution, stir, and dry to obtain a solid compound;

[0010] Step four: Preheat the solid compound in an inert gas, then heat it to the annealing temperature, calcine it, and then cool it to obtain sodium vanadium phosphate@carbon flower cathode material.

[0011] This invention synthesizes a phosphate cathode material, sodium vanadium phosphate@carbon flower composite material, with a "flower-like" structure through liquid-phase reaction and high-temperature annealing under the action of sugars. This flower-like structure utilizes conductive carbon to improve electronic conductivity. The increased surface area of ​​the flower-like structure enhances the contact area between the electrode and electrolyte. Furthermore, the petal-like structure reduces the distance between particles, shortening the diffusion distance and effectively improving electrochemical performance. The synthesized sodium vanadium phosphate@carbon flower composite material exhibits high capacity, excellent cycle stability, and outstanding rate performance in a coin cell system.

[0012] Preferably, the vanadium oxide is one or more of vanadium pentoxide, vanadium tripentoxide, vanadium heptaoxide, vanadium nonoxide, and vanadium tridecaoxide.

[0013] Preferably, the organic acid is one or more of oxalic acid, malonic acid, glutaric acid, and tartaric acid.

[0014] Preferably, the molar ratio of the vanadium oxide to the organic acid is 1:(1-5).

[0015] Preferably, the amount of deionized water used is 10 mL to 50 mL.

[0016] Preferably, the heating reaction temperature in step one is 50℃~100℃, and the stirring time is 0.5h~2h.

[0017] More preferably, the vanadium oxide in step one is vanadium pentoxide, and the organic acid is oxalic acid. The molar ratio of vanadium pentoxide to the organic acid is 1:1.2. The amount of deionized water used is 40 mL. The heating temperature is 70 °C, and the stirring time is 2 h.

[0018] Preferably, the sodium phosphate salt is one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium trimetaphosphate.

[0019] Preferably, the carbon source is one or more of glucose, sucrose, citric acid, starch, and polyvinyl alcohol.

[0020] Preferably, the molar ratio of the sodium phosphate salt to the carbon source is (4-10):1, and the molar ratio of the carbon source to the vanadium oxide is 1:(1-4).

[0021] Preferably, the sodium phosphate salt, the carbon source and the first mixed solution are reacted for 5 minutes to 30 minutes.

[0022] Further preferably, in the second step, the sodium phosphate salt is sodium dihydrogen phosphate, the carbon source is glucose, the molar ratio of sodium dihydrogen phosphate to glucose is 5:1, and the molar ratio of glucose to vanadium oxide is 1:2.

[0023] Preferably, the amount of n-propanol is 20 mL to 80 mL.

[0024] Preferably, in the third step, the n-propanol and the second mixed solution are stirred for 5 minutes to 30 minutes, the drying temperature is 50°C to 100°C, and the drying time is 1 hour to 4 hours.

[0025] Further preferably, the amount of n-propanol is 40 mL, the stirring time is 30 minutes, the drying temperature is 70°C, and the drying time is 2 hours.

[0026] Preferably, the inert gas includes one or more of nitrogen, argon and helium.

[0027] Preferably, in the fourth step, the preheating temperature is 300°C to 500°C, the preheating time is 2 hours to 8 hours, the temperature is raised to 600°C to 900°C at a rate of 2°C / min to 10°C / min, and the annealing time is 6 hours to 12 hours.

[0028] Further preferably, in the fourth step, the inert gas is nitrogen, the preheating temperature is 400°C, the preheating time is 4 hours, the temperature is raised at a rate of 5°C / min, the annealing temperature is 750°C, and the annealing time is 10 hours.

[0032] The fourth step is used to control the formation of the final "flower-like" morphology of the positive electrode material.

[0033] In a second aspect, a positive electrode of a sodium ion battery includes the sodium vanadium phosphate@carbon flower composite positive electrode material prepared by the above preparation method.

[0034] The preparation method of the positive electrode of the sodium ion battery includes the following steps:

[0035] The sodium vanadium phosphate@carbon flower composite positive electrode material, acetylene black (SP) and polyvinylidene fluoride (PVDF) are mixed in an N-methyl pyrrolidone (NMP) solution at a certain mass ratio, the solid content of the suspension is adjusted, and then the suspension is coated on a current collector to form the positive electrode.

[0036] Preferably, the mass ratio of the sodium vanadium phosphate@carbon flower composite positive electrode material, acetylene black (SP) and polyvinylidene fluoride (PVDF) is 8:1:1.

[0037] Preferably, the solid content of the suspension is 50% to 70%.

[0038] Preferably, the preparation of the positive electrode by coating the suspension on the current collector comprises: coating the suspension on the aluminum foil, then drying in a blast oven, and cutting into a predetermined size of the positive electrode by a sheet cutter.

[0039] Preferably, the temperature of the blast oven is 80 to 110℃, and the drying time in the blast oven is 0.5 to 3h.

[0040] Preferably, the positive electrode can be provided as a round piece with a diameter of 12 to 14mm.

[0041] In a third aspect, a sodium ion battery comprises the sodium vanadium phosphate@carbon flower composite positive electrode material prepared by the preparation method.

[0042] The sodium ion battery can be a button cell prepared from the above positive electrode. Specifically, the assembly process of the button cell is as follows: in an argon glove box (water content <1ppm, oxygen content <1ppm), taking a sodium sheet as a counter electrode, assembling the round piece into a button cell with a model of CR2032 or CR2024 according to the assembly mode of the button cell, and injecting a 1M NaPF6 solution, the solvent of which is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. The sealed battery is activated at 25 to 45℃ for 2 to 12h, and then tested according to the set steps. The specific steps of the test are as follows: standing for 2h→0.1C rate charging, 3.5V cutoff voltage→standing for 10min→0.005A constant voltage charging, current cutoff→0.1C constant current discharging, 2.0V cutoff voltage→standing for 10min→0.1C rate charging, 3.5V cutoff voltage→standing for 10min→0.005A constant voltage charging, current cutoff→0.1C constant current discharging, 2V cutoff voltage→standing for 10min→0.1C rate charging, 3.5V cutoff voltage→standing for 10min.

[0043] In a fourth aspect, an electric device comprises the above sodium ion battery.

[0044] Thanks to the above technical solutions, the present application has the following advantages compared with the prior art:

[0045] 1.The phosphate positive electrode material sodium vanadium phosphate@carbon flower composite material with a "flower-like" structure system is synthesized by a liquid phase reaction and high-temperature annealing under the action of a saccharide. The flower-like structure system uses conductive carbon to improve the electronic conductivity. The flower-like structure system has an increased surface area, an increased contact area between the electrode and the electrolyte, and a reduced distance between the overall particles, which shortens the diffusion distance and effectively improves the electrochemical performance. The synthesized sodium vanadium phosphate@carbon flower composite material exhibits high capacity, excellent cycle stability and excellent rate performance in a coin cell system.

[0046] 2.The method for synthesizing the "flower-like" coated sodium vanadium phosphate material by using conductive carbon is simple and easy to operate, the reaction conditions are easy to control, the requirements for equipment are low, the production cost and operation difficulty are reduced, and the method is suitable for large-scale industrial production and has potential commercial application prospects.

[0047] 3.The synthesized sodium vanadium phosphate@carbon flower composite material can be used as a positive electrode material of a sodium ion battery and can also be used as a negative electrode material in a lithium battery structure system, and has good ion deintercalation effect.

[0048] In order to make the above and other objects, features and advantages of the present application more apparent, the following preferred embodiments are described in detail, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0050] Figure 1 is a schematic diagram of the preparation process of the positive electrode material in embodiment 1 of the present application;

[0051] Figure 2 is a schematic diagram of sodium vanadium phosphate and sodium vanadium phosphate@carbon flower in embodiment 1 of the present application;

[0052] Figure 3 is an XRD pattern of sodium vanadium phosphate and sodium vanadium phosphate@carbon flower composite material in embodiment 2 of the present application;

[0053] Figure 4 is a Raman spectrum of sodium vanadium phosphate and sodium vanadium phosphate@carbon flower composite material in embodiment 2 of the present application;

[0054] Figure 5 is a graph of the relationship between capacity and voltage in embodiment 2 of the present application;

[0055] Figure 6 This is a graph showing the relationship between the magnification and capacity in Embodiment 2 of the present invention;

[0056] Figure 7 These are SEM images of sodium vanadium phosphate@carbon flower composite material and sodium vanadium phosphate in Example 2 of this invention. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] Example 1:

[0059] A method for preparing a positive electrode material includes the following steps:

[0060] Step 1: Weigh vanadium pentoxide and oxalic acid in a molar ratio of 1:1.2, with a total mass of 80g. Add the weighed vanadium pentoxide and oxalic acid to 40mL of deionized water, heat to 70℃, then stop heating and stir for 2 hours. After cooling, the first mixed solution is obtained.

[0061] Step two: Weigh sodium dihydrogen phosphate and glucose in a molar ratio of 5:1, ensuring that the molar ratio of glucose to vanadium pentoxide is 1:2. Add the weighed sodium dihydrogen phosphate and glucose to the first mixed solution, and react for 30 minutes to obtain the second mixed solution.

[0062] Step 3: Measure 40 mL of n-propanol and add it to the second mixed solution, stir for 30 min, and then dry the solution at 70 °C to obtain a solid compound.

[0063] Step four: Place the dried solid compound in a nitrogen high-temperature furnace and preheat at 400℃ for 4 hours. Increase the temperature to 750℃ at a rate of 5℃ / min and maintain this annealing temperature for 10 hours. Then cool the sample and remove it to obtain the target product, sodium vanadium phosphate@carbon flower composite cathode material.

[0064] See Figure 2 The diagram shows a comparison between commercially available sodium vanadium phosphate (lithium source 136B) and the target product, sodium vanadium phosphate@carbon flower composite cathode material. As can be seen from the diagram, the sodium vanadium phosphate@carbon flower composite material in this embodiment has a larger surface area compared to sodium vanadium phosphate.

[0065] This embodiment also discloses the steps for preparing the positive electrode of a sodium-ion battery using the above-mentioned target product:

[0066] Step one, mix the target product (sodium vanadium phosphate@carbon flower composite material) in example 1, acetylene black (SP) and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 in N-methyl pyrrolidone (NMP) solution, adjust the solid content of the suspension to 60%.

[0067] Step two, coat the suspension on aluminum foil, put it in a 100℃ air oven for 2h, take it out, and cut it into a 12mm diameter disc with a disc cutter.

[0068] The example also discloses the steps of preparing a sodium ion battery using the above positive electrode:

[0069] Step one, in an argon glove box (water content <1 ppm, oxygen content <1 ppm), assemble CR2032 button cells according to the button cell assembly method, and the negative electrode is a sodium sheet.

[0070] Step two, inject 1M NaPF6 electrolyte (its solvent is a volume ratio of 1:1 ethylene carbonate (EC) and dimethyl carbonate (DMC)) and seal. The sealed cell is activated at 45℃ for 5h.

[0071] Step three, conduct button cell test. Button cell test steps: stand for 2h → rate charge 0.1C, voltage 3.5V cutoff → stand for 10min → constant voltage charge, current 0.005A cutoff → constant current discharge 0.1C, voltage 2.0V cutoff → stand for 10min → rate charge 0.1C, voltage 3.5V cutoff → stand for 10min → constant voltage charge, current 0.005A cutoff → constant current discharge 0.1C, voltage 2V cutoff → stand for 10min → rate charge 0.1C, voltage 3.5V cutoff → stand for 10min.

[0072] Comparative example 1:

[0073] A mature commercial sodium vanadium phosphate (lithium source 136B) purchased is used as a positive electrode material, and a battery is prepared according to the steps in example 1. The difference is that the positive electrode includes a total mass of 60% sodium vanadium phosphate, 30% acetylene black and 10% polytetrafluoroethylene (PTFE), and the battery uses a lithium sheet as a negative electrode.

[0074] Example 2:

[0075] The batteries prepared in the above example 1 and comparative example 1 are tested as follows:

[0076] XRD and in-situ XRD measurements are performed using a D8 Advance X-ray diffractometer equipped with a non-monochromatic Cu Kα X-ray source to study the crystal structure.

[0077] Carbon content analysis was performed by Elementar Vario EL cube elemental analyzer.

[0078] Raman spectrum test was performed by Avantes spectrometer.

[0079] SEM test was performed on sodium vanadium phosphate@carbon flower composite and sodium vanadium phosphate.

[0080] Referring to Figure 3 As shown in the XRD pattern, the phase purity and crystallinity of sodium vanadium phosphate@carbon flower composite were characterized by XRD pattern. All the diffraction peaks can be easily attributed to sodium vanadium phosphate with NASICON structure having R3c space group (rhombohedral cell), and no other phase was detected, which confirmed that the phase purity of sodium vanadium phosphate@carbon flower composite was very high.

[0081] Referring to Figure 4 As shown in the Raman spectrum, at 1339 cm -1 (D band, disordered induced phonon mode) and 1593 cm -1 (Graphite G band), which indicated that the deposited carbon was partially graphitized, which might be attributed to the carbonization of C2O4 2− anion during the annealing process. In addition, based on the elemental analysis of C, H and N, the carbon content of the sample of sodium vanadium phosphate@carbon flower composite annealed at 750°C was 5.2, which ensured that the material had excellent conductive performance.

[0082] The galvanostatic charge-discharge cycling behavior was studied using a multi-channel battery test system (LAND CT2001A) in the potential range of 1.0-4.3 / 2.5-4.3 / 1.0-2.5 V vs. Li+ / Li.

[0083] Referring to Figure 5 As shown from the specific capacity data, the specific capacity of sodium vanadium phosphate@carbon flower composite was increased from 103.5 mAh / g to 182.3 mAh / g compared with ordinary sodium vanadium phosphate, greatly improving the energy density.

[0084] Referring to Figure 6 As shown, the rate performance can be seen that sodium vanadium phosphate@carbon flower composite has excellent rate performance compared with sodium vanadium phosphate, which can deliver a capacity of 140 mAh / g at 10C.

[0085] Referring to Figure 7 As shown, SEM test was performed on sodium vanadium phosphate@carbon flower composite and sodium vanadium phosphate. Among them Figure 7 (a) is the SEM image of sodium vanadium phosphate@carbon flower composite, Figure 7(b) is a SEM image of sodium vanadium phosphate. As can be seen from the figure, the sodium vanadium phosphate@carbon flower composite material prepared by the method of the application has a flower-like structure, which is obviously different from the existing sodium vanadium phosphate in morphology.

[0086] The principles and implementation manners of the application are described by using specific examples, and the above examples are only used to help understand the method and core idea of the application; meanwhile, for those skilled in the art, according to the idea of the application, the specific implementation manners and application ranges will be changed, and the above description should not be understood as limiting the application.

Claims

1. A method for producing a positive electrode material, characterized by, The method comprises the following steps: adding metal vanadium oxide and organic acid into deionized water, heating, stirring, cooling to obtain a first mixed solution; adding sodium phosphate salt and carbon source into the first mixed solution, and reacting to obtain a second mixed solution; adding n-propanol into the second mixed solution, stirring, and drying to obtain a solid compound; preheating the solid compound in inert gas, then heating to annealing temperature, calcining, and cooling to obtain a sodium vanadium phosphate-carbon flower composite positive electrode material.

2. The method according to claim 1, wherein: the metal vanadium oxide is one or more of vanadium pentoxide, trivanadium pentoxide, trivanadium heptoxide, tetravanadium nonoxide, and hexavanadium tridec oxide; the organic acid is one or more of oxalic acid, malonic acid, glutaric acid, and tartaric acid; the molar ratio of the metal vanadium oxide to the organic acid is 1: (1-5).

3. The preparation method according to claim 1, characterized in that, the heating temperature is 50-100°C, and the stirring time is 0.5-2h.

4. The method of claim 1, wherein, the metal vanadium oxide is vanadium pentoxide, and the organic acid is oxalic acid; the molar ratio of the vanadium pentoxide to the oxalic acid is 1:1.2; the heating temperature is 70°C, and the stirring time is 2h.

5. The method according to claim 1, wherein: the sodium phosphate salt is one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium trimetaphosphate; the carbon source is one or more of glucose, sucrose, citric acid, starch, and polyvinyl alcohol; the molar ratio of the sodium phosphate salt to the carbon source is (4-10):1, and the molar ratio of the carbon source to the metal vanadium oxide is 1: (1-4); the reaction time of the sodium phosphate salt, the carbon source, and the first mixed solution is 5-30min.

6. The preparation method according to claim 1, characterized in that, the sodium phosphate salt is sodium dihydrogen phosphate, the carbon source is glucose, the molar ratio of the sodium phosphate salt to the carbon source is 5:1, and the molar ratio of the glucose to the metal vanadium oxide is 1:

2.

7. The method according to claim 1, wherein: the amount of n-propanol is 20-80mL; the stirring time of the n-propanol and the second mixed solution is 5-30min, the drying temperature is 50-100°C, and the drying time is 1-4h.

8. The method of claim 1, wherein, the inert gas includes one or more of nitrogen, argon, and helium; the preheating temperature is 300-500°C, the preheating time is 2-8h, the heating rate is 2-10°C / min, the annealing temperature is 600-900°C, and the annealing time is 6-12h.

9. A positive electrode of a sodium-ion battery, characterized by, The sodium vanadium phosphate-carbon flower composite positive electrode material prepared by the method of any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The sodium vanadium phosphate-carbon flower composite positive electrode material prepared by the method of any one of claims 1-8.

11. An electrical device, characterized by The electric device includes the sodium ion battery of claim 10.

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