A preparation method of a cathode material for an aqueous electrolyte

Abstract

The present invention belongs to the technical field of electrochemical energy storage devices, and particularly relates to a preparation method of a positive electrode material for an aqueous electrolyte, specifically: first, ammonium dihydrogen phosphate, a reducing agent, and a carbon source are added to an aqueous solution, and heated and stirred until the solute is completely dissolved. Then, sodium carbonate, ammonium metavanadate, iron nitrate, and sodium tungstate are added, and heating and stirring are continued until the solute is completely dissolved. Then, it is heated in a water bath until the water is completely evaporated, and then vacuum dried, ground, and sintered in a tube furnace to obtain carbon-coated sodium ion fast conductor crystal powder. Finally, it is mixed with a conductive agent and a binder to form a positive electrode of an aqueous sodium ion battery; the positive electrode material prepared by the present invention has the characteristics of excellent stability, energy storage performance, cycle performance, low material cost, and high safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage devices, and particularly relates to a preparation method of a cathode material for an aqueous electrolyte. Background Art

[0002] Sodium-ion batteries have been in the battery research system for a long time. However, due to the excellent performance of lithium-ion batteries, the development of sodium-ion batteries lags behind that of lithium-ion batteries. But as lithium-ion batteries have reached the saturation stage, the disadvantages of developing a large number of lithium-ion batteries have gradually emerged. Problems such as the scarcity of lithium-ion battery resources, uneven resource distribution, and high development difficulty have made the energy industry urgently seek green and resource-rich battery materials.

[0003] In recent years' research, sodium-ion batteries have received extensive attention. Among them, sodium and lithium belong to the same main group elements, making substances have certain similarities in physical and chemical properties. Sodium also has abundant natural abundance, low price, and intercalation chemical properties similar to lithium, and is considered a promising candidate to supplement lithium-ion batteries. However, at present, explosion incidents of organic polymer batteries are common, and the extremely high energy density is a double-edged sword. Therefore, many current studies are dedicated to researching safer aqueous batteries to fill the gap in the large-scale energy storage field. Among them, sodium superionic conductor structure materials are well-known for their channels for rapid sodium-ion diffusion. The typical material of this structure, sodium vanadium phosphate, theoretically has high ionic conductivity and high stability. However, sodium vanadium phosphate will undergo serious dissolution during charge and discharge in an aqueous environment, which greatly limits the application of this material in aqueous sodium-ion batteries.

[0004] The patent with the publication number CN111082162A discloses an aqueous sodium-ion battery, and the cathode active material is potassium-ion doped sodium vanadium phosphate particles coated with a carbon layer and a carbon-nitrogen layer. Among them, doping potassium ions can play a role in supporting the crystal structure. Specifically, since the radius of potassium ions is larger than that of sodium ions, a small amount of potassium ions doped in the sodium vanadium phosphate crystal will increase the structural stability during the insertion and extraction of sodium ions; the coated carbon layer and carbon-nitrogen layer can play a role in increasing the conductivity of sodium vanadium phosphate. However, in this scheme, the electrolyte suitable for the active material is composed of sodium hypochlorite, acetonitrile, and water, and both acetonitrile and sodium hypochlorite are substances that are unfriendly to the environment and organisms.

[0005] The patent with the publication number CN107895789A discloses a microsphere nanomaterial of sodium vanadium phosphate coated with reduced graphene oxide, its preparation method and application. With a graphene layer as the coating layer, it greatly reduces the dissolution of active substances and also improves the conductivity of the material. However, this solution uses graphene, which greatly increases the cost, and graphene cannot inhibit the dissolution problem in an aqueous environment. This application uses glucose as a carbon source with transition metal doping, which reduces the cost while ensuring the stability of sodium vanadium phosphate.

[0006] The patent with the publication number CN114864929A discloses a preparation method of a modified micro-nano structured cathode material for sodium-ion batteries. This invention mainly uses the ball milling method to prepare sodium iron phosphate, and the chemical formula of sodium iron phosphate is NaFePO 4 , a typical olivine crystal structure material. However, sodium iron phosphate with an olivine structure does not have the property of fast sodium ion conduction. Its main application field is traditional organic batteries, and its weak ion transport rate makes it unsuitable for the aqueous battery environment.

[0007] The patent with the publication number CN109650348A discloses a transition metal chalcogenide nanosheet material, its preparation method, a battery anode material, a secondary battery and its application. This invention prepares a layered oxide by dissolving a transition metal salt and obtains a sheet material after sulfidation. However, this solution mainly modifies by coating, and it is difficult to balance the ion channels and stability in coating modification.

[0008] The patent with the publication number CN109755565A discloses a cathode material for sodium-ion batteries doped with transition metals, its preparation and application. This patent adjusts the properties of Na 3 V 2 (PO 4 ) 2 F 3 / C by regulating transition metals. However, sodium vanadium phosphate fluoride is a relatively good cathode material in organic batteries. Due to its extremely high redox voltage, which exceeds the electrolysis voltage of water, it is difficult to be applied in the field of aqueous batteries.

[0009] In summary, avoiding the dissolution of the cathode active material in a large amount of free water can not only improve the utilization rate of the active material, but also avoid the corrosion of the anode caused by the dissolution effect, prevent side reactions of the dissolved substances on the positive and negative electrodes, etc. In addition, an ideal cathode material should also have a high deintercalation potential, a high deintercalation capacity, mild electrode process kinetics, high reversibility of intercalation and deintercalation, and fewer reaction processes. Therefore, it is of great significance to study a cathode active material that is insoluble or hardly soluble in an aqueous electrolyte and has stable and excellent electrochemical performance. Summary of the Invention

[0010] In view of the deficiencies of the prior art, the present invention provides a method for preparing a positive electrode material for an aqueous electrolyte.

[0011] This is achieved specifically through the following technical solutions:

[0012] A method for preparing a positive electrode material for an aqueous electrolyte comprises the following steps:

[0013] (1) adding ammonium dihydrogen phosphate, a reducing agent and a carbon source into water, and heating and stirring until the solute is completely dissolved to obtain a transparent solution;

[0014] (2) Add metal salt to the transparent solution and continue heating and stirring until the solute is completely dissolved;

[0015] (3) heating the solution obtained in step (2) in a water bath and stirring until the water is completely evaporated;

[0016] (4) The sample after dehydration is vacuum dried at 120°C-140°C to obtain a loose block sample;

[0017] (5) Grind the block sample into powder in a grinding mortar;

[0018] (6) Place the powdered sample in a tube furnace and sinter it for more than 6 hours at 700°C-800°C in a protective gas atmosphere to form a carbon-coated sodium ion fast conductor crystal powder, thus obtaining the positive electrode material Na 3 V 1.5-x Fe 0.5 W x (PO 4 ) 3 ;

[0019] (7) The carbon-coated sodium ion fast conductor crystal powder is mixed with a conductive agent and a binder to form an aqueous sodium ion battery positive electrode.

[0020] In step (1), the molar ratio of the diammonium phosphate, the reducing agent and the carbon source is 3:(7-14):(1-3); preferably, the molar ratio of the diammonium phosphate, the reducing agent and the carbon source is 3:7:1.

[0021] The carbon source is one or more of citric acid, glucose and polyvinyl alcohol.

[0022] The reducing agent is oxalic acid.

[0023] The metal salts are sodium carbonate, ammonium metavanadate, ferric nitrate and sodium tungstate.

[0024] The molar ratio of ammonium dihydrogen phosphate, sodium carbonate, ammonium metavanadate, ferric nitrate and sodium tungstate in the solution obtained in step (2) is 30:15:15-X:5:X, wherein the range of X is 0<x≤5.

[0025] Preferably, the molar ratio of ammonium dihydrogen phosphate, sodium carbonate, ammonium metavanadate, iron nitrate and sodium tungstate in the obtained solution is 30:15:13:5:2.

[0026] The amount of water used is weighed according to 15 liters of water added per mole of ammonium metavanadate.

[0027] The temperature of the water bath heating is 80 °C.

[0028] The protective gas is any one or more of argon, nitrogen, helium, neon.

[0029] Preferably, the temperature of the vacuum drying is 120 °C.

[0030] Preferably, the time of the vacuum drying is 12 h.

[0031] Preferably, the time of the sintering is 8 h.

[0032] The positive electrode material Na 3 V 1.5-x Fe 0.5 W x (PO 4 ) 3 is sodium vanadium phosphate doped with iron and tungsten, wherein the chemical formula of sodium vanadium phosphate is Na 3 V 2 (PO 4 ) 3 .

[0033] In step (7), the mass ratio of the carbon-coated sodium ion fast conductor crystal powder, the conductive agent and the binder is 8:1:1.

[0034] In the above preparation process, by doping two transition metal elements of iron and tungsten, the stability of the electrode material in water is greatly improved, so that it can be applied in the field of aqueous sodium ion batteries.

[0035] Beneficial effects:

[0036] (1) The positive electrode material prepared by the present invention has high stability, uses iron nitrate and sodium tungstate as doping materials, and the electrolyte is sodium sulfate solution, with low material cost, high safety and environmental friendliness.

[0037] (2) The positive electrode material prepared by the present invention can have excellent energy storage properties at a large current of 1 A / g.

[0038] (3) The positive electrode material prepared by the present invention has excellent cycle performance, and the battery capacity retention rate is ≥90% in 50 cycles.

[0039] (4) The positive electrode material prepared by the present invention has a high specific capacity, with a capacity of about 65 mAh / g. Description of the Drawings

[0040] Figure 1 is the preparation flow chart of the positive electrode material Na 3 V 1.5-x Fe 0.5 W x (PO 4 ) 3 in Example 4;

[0041] Figure 2 is the XRD pattern of the positive electrode material obtained in Example 4;

[0042] Figure 3 is the cyclic capacity percentage graph of the positive electrode materials prepared in Example 1 and Example 2;

[0043] Figure 4 is the positive electrode material Na 3 V 1.5-x Fe 0.5 W x (PO 4 ) 3 cyclic capacity graph in Example 4;

[0044] Figure 5 is the cyclic capacity graph of the positive electrode materials prepared in Example 1, Example 2, Example 3, and Example 4;

[0045] Figure 6 is the comparison graph of the color of the initial electrolyte and the electrolyte after 50 cycles after the positive electrodes prepared in Example 1 - 4 are assembled. Detailed Description of the Invention

[0046] The following further details the specific embodiments of the present invention, but the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of this embodiment still falls within the scope protected by the claims of the present invention.

[0047] Example 1

[0048] A method for preparing a positive electrode material NVP for aqueous electrolyte, comprising the following steps:

[0049] (1) Weigh according to the molar ratio of ammonium dihydrogen phosphate, oxalic acid, and citric acid of 3:7:1. Add ammonium dihydrogen phosphate, oxalic acid, and citric acid to water, and heat and stir until the solute is completely dissolved to obtain a transparent solution;

[0050] (2) adding sodium carbonate and ammonium metavanadate to the transparent solution in a molar ratio of ammonium dihydrogen phosphate: sodium carbonate: ammonium metavanadate = 6:3:4, and continuing heating and stirring until the solute is completely dissolved;

[0051] (3) heating the solution obtained in step (2) in a water bath at 80° C. with stirring until the water is completely evaporated;

[0052] (4) The sample after dehydration was vacuum dried at 120°C for 12 h to obtain a loose block sample;

[0053] (5) Grinding the bulk sample into powder;

[0054] (6) placing the powdered sample in a tube furnace and sintering it at 700°C for 6 h in a neon atmosphere to form a carbon-coated sodium ion fast conductor crystalline powder, thus obtaining the positive electrode material NVP;

[0055] (7) The carbon-coated sodium ion fast conductor crystal powder is mixed with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain an aqueous sodium ion battery positive electrode.

[0056] Example 2

[0057] A method for preparing a positive electrode material for an aqueous electrolyte comprises the following steps:

[0058] (1) Weighing diammonium phosphate, oxalic acid, and glucose in a molar ratio of 3:7:1, adding diammonium phosphate, oxalic acid, and glucose into water, and heating and stirring until the solute is completely dissolved to obtain a transparent solution;

[0059] (2) Weighing the molar ratio of ammonium dihydrogen phosphate: sodium carbonate: sodium tungstate: ammonium metavanadate = 30:15:X:20-X, adding sodium carbonate, ammonium metavanadate and sodium tungstate into the transparent solution, and continue heating and stirring until the solute is completely dissolved; the specific molar ratio of sodium tungstate to ammonium metavanadate is set to 6 groups, as shown in Table 1

[0060] Table 1

[0061] Item Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Sodium tungstate: Ammonium metavanadate 10:10 9:11 7:13 5:15 3:17 1:19

[0062] (3) heating the solution obtained in step (2) in a water bath at 80° C. with stirring until the water is completely evaporated;

[0063] (4) The sample after dehydration was vacuum dried at 140°C for 12 h to obtain a loose block sample;

[0064] (5) Grinding the bulk sample into powder;

[0065] (6) Place the powdered sample in a tube furnace and sinter it at 800 °C for 6 h under a nitrogen atmosphere to form a carbon-coated sodium-ion fast conductor crystal powder, i.e., the positive electrode material NV. 1.9 W 0.1 P, NV 1.7 W 0.3 P, NV 1.5 W 0.5 P, NV 1.3 W 0.7 P, NV 1.1 W 0.9 P, NV 1 W 1 P;

[0066] (7) Mix the carbon-coated sodium-ion fast conductor crystal powder with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain the positive electrode of an aqueous sodium-ion battery.

[0067] Example 3

[0068] A method for preparing a positive electrode material for an aqueous electrolyte, comprising the following steps:

[0069] (1) Weigh ammonium dihydrogen phosphate, oxalic acid, and glucose in a molar ratio of 3:7:1. Add ammonium dihydrogen phosphate, oxalic acid, and glucose to water and heat with stirring until the solute is completely dissolved to obtain a transparent solution;

[0070] (2) Weigh ammonium dihydrogen phosphate: sodium carbonate: ammonium metavanadate: iron nitrate = 30:15:15:5 in molar ratio. Add sodium carbonate, iron nitrate, and ammonium metavanadate to the transparent solution and continue heating with stirring until the solute is completely dissolved;

[0071] (3) Heat the solution obtained in step (2) in a water bath at 80 °C with stirring until the water is completely evaporated;

[0072] (4) Vacuum dry the sample after removing water at 130 °C for 12 h to obtain a porous block sample;

[0073] (5) Grind the block sample into a powder;

[0074] (6) Place the powdered sample in a tube furnace and sinter it at 750 °C for 8 h under an argon atmosphere to form a carbon-coated sodium-ion fast conductor crystal powder, i.e., the positive electrode material NV. 1.5 Fe 0.5 P;

[0075] (7) Mix the carbon-coated sodium-ion fast conductor crystal powder with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain the positive electrode of an aqueous sodium-ion battery.

[0076] Example 4

[0077] A positive electrode material for an aqueous electrolyte and a method for preparing a positive electrode, comprising the following steps:

[0078] (1) Weighing diammonium phosphate, oxalic acid, and glucose in a molar ratio of 3:7:1, adding diammonium phosphate, oxalic acid, and glucose into water, and heating and stirring until the solute is completely dissolved to obtain a transparent solution;

[0079] (2) Weighing the sodium carbonate, ferric nitrate, ammonium metavanadate and sodium tungstate in a molar ratio of ammonium dihydrogen phosphate: sodium carbonate: ammonium metavanadate: ferric nitrate: sodium tungstate = 30:15:15-X:5:X, adding sodium carbonate, ferric nitrate, ammonium metavanadate and sodium tungstate into the transparent solution, and continuing to heat and stir until the solute is completely dissolved; the specific molar ratios of ammonium metavanadate, ferric nitrate and sodium tungstate are set to 5 groups, as shown in Table 2:

[0080] Table 2

[0081]

[0082] (3) heating the solution obtained in step (2) in a water bath at 80° C. with stirring until the water is completely evaporated;

[0083] (4) The sample after dehydration was vacuum dried at 130°C for 12 h to obtain a loose block sample;

[0084] (5) Grinding the bulk sample into powder;

[0085] (6) The powdered sample was placed in a tube furnace and sintered for 6 h at 750 °C in an argon atmosphere to form a carbon-coated sodium ion fast conductor crystal powder, thus obtaining the positive electrode material NV. 1.45 Fe 0.5 W 0.05 P. NV 1.4 Fe 0.5 W 0.1 P. NV 1.3 Fe 0.5 W 0.2 P. NV 1.2 Fe 0.5 W 0.3 P. NV 1.1 Fe 0.5 W 0.4 P;

[0086] (7) The carbon-coated sodium ion fast conductor crystal powder is mixed with a conductive agent and a binder in a mass ratio of 8:1:1 to obtain an aqueous sodium ion battery positive electrode.

[0087] Experimental Example 1

[0088] The positive electrode prepared in Example 1-4 is used as the positive electrode of the sodium ion battery. 1 Ti2 (PO 4 ) 3 is used as the negative electrode, sodium sulfate is used as the electrolyte to form a sodium-ion battery, and then charge-discharge cycling is carried out under a current condition of 1 A / g. The cycling performance is shown in Figures 3 - 5 .

[0089] Figure 2 is the X-ray diffraction pattern of the positive electrode material of the sodium-ion battery prepared in Example 4; it can be seen from the figure that doping iron and tungsten within 50% does not affect the crystal structure of the material, and maintains the fast-conductor property of its original crystal;

[0090] Figure 3 is the cyclic capacity percentage diagram of the positive electrodes prepared in Example 1 and Example 2; it can be seen from the figure that the capacity retention rate of the electrode doped with tungsten is much higher than that of the electrode without any doping;

[0091] Figure 4 is the cyclic capacity diagram of the positive electrode in Example 4; it can be seen from the figure that the capacity retention rate of the electrode doped with iron during charge-discharge under a large current condition is relatively high, above 90%;

[0092] Figure 5 is the cyclic capacity diagram of the positive electrodes prepared in Example 1, Example 2, Example 3, and Example 4; it can be seen from the figure that the electrode co-doped with iron and tungsten has excellent capacity retention rate.

[0093] Figure 6 is the comparison diagram of the color of the initial electrolyte and the electrolyte after 50 cycles after the positive electrodes prepared in Example 1-4 are assembled; it can be seen from the figure that for the positive electrodes prepared in Example 1-4, the color of the solution dissolved in the electrolyte in the initial state (before charge-discharge) is colorless; after 50 cycles of cycling, the dissolution phenomenon of the undoped electrode is serious; the solution color changes from colorless to colored, while the solution of the electrode doped with iron and tungsten remains colorless after cycling and there is no dissolution at all. And both iron doping and tungsten doping inhibit the dissolution of the electrode to a certain extent compared with the undoped electrode. It can be known that the transition metal doping screened by the present invention can effectively inhibit the dissolution of sodium vanadium phosphate.

Claims

1. A method for preparing an aqueous sodium ion battery positive electrode for an aqueous electrolyte, It is characterized in that The steps include: (1) adding ammonium dihydrogen phosphate, a reducing agent and a carbon source into water, and heating and stirring until the solute is completely dissolved to obtain a transparent solution; (2) adding a metal salt to the transparent solution, and continuing heating and stirring until the solute is completely dissolved; the metal salt is sodium carbonate, ammonium metavanadate, ferric nitrate and sodium tungstate; (3) heating the solution obtained in step (2) in a water bath and stirring until the water is completely evaporated; (4) The sample after dehydration is vacuum dried at 120°C-140°C to obtain a loose block sample; (5) Grind the block sample into powder in a grinding mortar; (6) Place the powdered sample in a tubular furnace and sinter it for more than 6 hours under a protective gas atmosphere at 700 °C - 800 °C to form a carbon-coated sodium-ion fast conductor crystal powder, thus obtaining the positive electrode material Na 3 V 1.5-x Fe 0.5 W x (PO 4 ) 3 ; (7) The carbon-coated sodium ion fast conductor crystal powder is mixed with a conductive agent and a binder to form an aqueous sodium ion battery positive electrode.

2. A method for preparing a positive electrode of an aqueous sodium ion battery for an aqueous electrolyte according to claim 1, It is characterized in that In step (1), the molar ratio of the diammonium phosphate, the reducing agent and the carbon source is 3:(7-14):(1-3).

3. A method for preparing a positive electrode of an aqueous sodium ion battery for an aqueous electrolyte according to claim 1, It is characterized in that The carbon source is one or more of citric acid, glucose and polyvinyl alcohol; and the reducing agent is oxalic acid.

4. A method for preparing a positive electrode of an aqueous sodium ion battery for an aqueous electrolyte according to claim 1, It is characterized in that The molar ratio of ammonium dihydrogen phosphate, sodium carbonate, ammonium metavanadate, ferric nitrate and sodium tungstate in the solution obtained in step (2) is 30:15:15-X:5:X, wherein the range of X is 0<X≤5.

5. A method for preparing a positive electrode for an aqueous sodium ion battery for an aqueous electrolyte according to claim 1 or 4, It is characterized in that The molar ratio of ammonium dihydrogen phosphate, sodium carbonate, ammonium metavanadate, ferric nitrate and sodium tungstate in the solution obtained in step (2) is 30:15:13:5:

2.

6. A method for preparing an aqueous sodium ion battery positive electrode for an aqueous electrolyte according to claim 1, It is characterized in that The water bath heating temperature is 80°C.

7. A method for preparing a positive electrode for an aqueous sodium ion battery for an aqueous electrolyte according to claim 1, It is characterized in that The vacuum drying was carried out at a temperature of 120° C. and for a period of 12 h.

8. A method for preparing an aqueous sodium ion battery positive electrode for an aqueous electrolyte as claimed in claim 1, It is characterized in that The sintering time is 8 hours.

9. A method for preparing an aqueous sodium ion battery positive electrode for an aqueous electrolyte according to claim 1, It is characterized in that The positive electrode material Na 3 V 1.5-x Fe 0.5 W x (PO 4 ) 3 is sodium vanadium phosphate doped with iron and tungsten, wherein the chemical formula of sodium vanadium phosphate is Na 3 V 2 (PO 4 ) 3 .

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