Preparation method of lithium ion electrochemical hybrid capacitor

Abstract

The invention discloses a preparation method of a lithium ion electrochemical hybrid capacitor, and particularly relates to the field of lithium ion capacitors. The method comprises the following steps: adding halloysite into a sulfuric acid solution for acid etching, centrifugally washing to be neutral, and drying; the preparation method comprises the following steps: dissolving oxalic acid and V2O5 in deionized water, stirring to obtain a blue solution, adding halloysite subjected to acid etching, Li2CO3 and NH4H2PO4 into the blue solution, stirring in a water bath until gel is formed, and then drying and grinding to obtain blue-green powder; and putting the blue-green powder into a tubular furnace, calcining, cooling to room temperature, grinding, mixing with a binder and acetylene black, adding a solvent, stirring at room temperature, uniformly coating on foamed nickel, drying, and tabletting to obtain the electrode plate. By adopting the technical scheme of the invention, the problem of low electronic conductivity of a lithium ion electronic capacitor prepared from lithium vanadium phosphate is solved, and the prepared halloysite nanotube loaded lithium vanadium phosphate composite material has the advantages of relatively high specific surface area, stable structure, cycling stability and the like.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion capacitors, and in particular to a method for preparing a lithium ion electrochemical hybrid capacitor. Background Art

[0002] Currently, lithium-ion batteries and supercapacitors are considered to be the two most promising electrochemical energy storage devices, but the low energy density of lithium-ion batteries and the low power density of supercapacitors greatly limit their energy storage advantages.

[0003] Lithium-ion hybrid electrochemical capacitors are composed of battery-type electrodes and capacitor-type electrodes. They have high energy density and power density and are an indispensable component of the next generation of energy storage devices. In addition, the charge storage mechanism of lithium-ion hybrid electrochemical capacitors includes the insertion / extraction of Li+ and double-layer adsorption / desorption. Although lithium-ion hybrid electrochemical capacitors have a wide electrochemical window and high energy density in organic electrolytes, their low ionic conductivity and electrolyte loss during charging greatly limit their service life. In aqueous electrolytes, the cycle performance of lithium-ion hybrid electrochemical capacitors can be greatly improved and electrolyte consumption can be reduced.

[0004] A Chinese patent (patent publication number: CN108039284A) discloses a method for preparing a lithium ion capacitor using lithium vanadium phosphate / expanded microcrystalline graphite / carbon composite material, wherein an electrode sheet is made of a mixture of activated carbon and graphite as a negative electrode, a polypropylene diaphragm is sandwiched between the positive and negative electrode sheets, and a lithium ion capacitor is assembled, and a lithium nitrate aqueous solution with a concentration of 1 mol / L is injected between the positive and negative electrode sheets as an electrolyte. In this technical solution, lithium vanadium phosphate / expanded microcrystalline graphite / carbon composite material is used to make an electrode sheet as a positive electrode, and the lithium vanadium phosphate / expanded microcrystalline graphite / carbon composite material uses cheap and readily available expanded microcrystalline graphite instead of graphene as a raw material. The obtained composite material has excellent electrochemical properties and has better cycle stability while maintaining the charge and discharge specific capacity. Although activated carbon has become the most commonly used negative electrode material in lithium ion electrochemical hybrid capacitor components due to its advantages such as high specific surface area, good electronic conductivity and low cost. In order to obtain better electrochemical performance, as a common lithium ion positive electrode material, lithium vanadium phosphate generally has defects such as low electronic conductivity, unstable structure and poor cycle performance due to its own limitations. Therefore, it is urgent to obtain a lithium vanadium phosphate positive electrode material for a lithium ion electrochemical hybrid capacitor with high electronic conductivity, stable structure, simple preparation method and low cost. Summary of the invention

[0005] The present invention aims to provide a method for preparing a lithium ion electrochemical hybrid capacitor, which solves the problem of low electronic conductivity of lithium ion electronic capacitors prepared by lithium vanadium phosphate.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: A method for preparing a lithium ion electrochemical hybrid capacitor comprises the following steps: S1. Grind the halloysite, sieve it, add it to a sulfuric acid solution, acid-etch it in a magnetic stirring water bath, then centrifuge and wash it repeatedly with deionized water until it is neutral, and put it in an oven to dry; S2, dissolving oxalic acid and V2O5 in deionized water at room temperature, stirring to obtain a clear blue solution, then adding the acid-etched halloysite, Li2CO3 and NH4H2PO4 in step S1 to the blue solution, stirring in a water bath until a gel is formed, and then drying the gel, and grinding to obtain a blue-green powder; S3, placing the blue-green powder of step S2 into a tube furnace, performing gradient calcination under N2 atmosphere protection, and then cooling to room temperature; S4, grinding the mixture calcined in step S3, mixing it with a binder and acetylene black, adding a proper amount of alcohol as a solvent, stirring at room temperature, evenly coating it on the nickel foam, and pressing it into sheets after drying to obtain an electrode sheet.

[0007] Furthermore, in step S1, the particle size is 200 mesh, the concentration of the sulfuric acid solution is 2 mol / L, the water bath temperature is 80° C., the water bath time is 0-6 h, the drying temperature is 100° C., and the drying time is 6 h.

[0008] Furthermore, in step S2, the stirring time is 30 min, the water bath temperature is 80° C., the drying temperature is 100° C., the drying time is 12 h, the stoichiometric molar ratio of the chemical reagents is oxalic acid: V2O5: Li2CO3: NH4H2PO4 = 3:1:1.5:3, and the mass ratio of halloysite to lithium vanadium phosphate is 1:3.

[0009] Furthermore, in step S3, the heating rate is 5°C / min, and the calcination gradient is 350°C for 4h and 750°C for 8h.

[0010] Furthermore, in step S4, the binder is polytetrafluoroethylene, and the mass ratio of the active material, the binder and the acetylene black is 8:1:1, the stirring time is 6 hours, the drying temperature is 100°C, the drying time is 12 hours, the tableting pressure is 10 MPa, and the tableting time is 60 seconds.

[0011] Compared with the prior art, this solution has the following beneficial effects: 1. This scheme provides a method for preparing a lithium-ion electrochemical hybrid capacitor, which is a positive electrode material for a lithium-ion capacitor based on halloysite-loaded lithium vanadium phosphate. The natural mineral halloysite is used as a raw material, which is abundant in source, low in price, and green and pollution-free.

[0012] 2. In the preparation process of this scheme, the halloysite is pretreated by acid etching, which can better load the lithium vanadium phosphate and increase the specific surface area of ​​the lithium vanadium phosphate, providing certain active sites for energy storage, so that it has good energy storage performance.

[0013] 3. In this solution, since halloysite has a stable nanotube structure, after loading lithium vanadium phosphate, the overall structure can be stabilized, and the structural stability can be better guaranteed during the lithium ion extraction / insertion process.

[0014] 4. The nanotube structure of halloysite in this scheme can provide a good extraction / insertion transmission channel for lithium ions, promote the transmission of lithium ions, and improve the ionic conductivity of the material.

[0015] 5. The positive electrode material of lithium ion capacitor prepared based on halloysite-loaded lithium vanadium phosphate in this scheme still has a specific capacitance retention rate of 94.87% after 10,000 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the process of halloysite-loaded lithium vanadium phosphate according to the present invention; Figure 2 is an isothermal adsorption curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material prepared in Example 1; Figure 3 is a pore size distribution curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material prepared in Example 1; Figure 4 is a TEM image of the halloysite nanotubes loaded with lithium vanadium phosphate prepared in Example 1; Figure 5 is an AC impedance curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material obtained in Example 1; Figure 6 1 is a graph showing the capacity retention rate and coulombic efficiency of the lithium ion capacitor prepared in Example 1 after 10,000 cycles. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below through specific embodiments: Example

[0018] like Figure 1 As shown, a method for preparing a lithium ion electrochemical hybrid capacitor comprises the following steps: After grinding the halloysite, sieving it with 200 mesh can prevent the mixing of large agglomerated particles and affect the etching effect. Take 2g of halloysite powder and add it to 200ml of 2mol / L sulfuric acid solution, stir it with magnetic stirring in an 80℃ water bath for acid etching, react for 4h, then wash it repeatedly by centrifugation with deionized water until it is neutral, and put it in an oven at 100℃ for 6h; the etching degree can be controlled by adjusting the water bath time. If the time is too short, there will be no etching effect. If the time is too long, it will cause partial structural damage of the halloysite and lead to decreased stability.

[0019] Take 2g oxalic acid and 1.34g V2O5 and dissolve them in 30ml deionized water at room temperature, stir until a clear blue solution is obtained, then add 1g acid-etched halloysite, 2.25g Li2CO3 and 2.54g NH4H2PO4 to the solution, stir in a water bath at 80℃ for 30min until a gel is formed, then dry the gel at 100℃ for 12h, and grind to obtain a blue-green powder; The sample was placed in a tube furnace under N2 atmosphere protection, with a heating rate of 5°C / min, kept at 350°C for 4h, kept at 750°C for 8h, and then cooled to room temperature; 0.8 g of the calcined material was ground, mixed with 0.1 g of a binder (polytetrafluoroethylene) and 0.1 g of acetylene black, and 5 ml of alcohol was added as a solvent. After stirring at room temperature for 6 hours, the mixture was evenly coated on the nickel foam. After drying at 100°C for 12 hours, the mixture was pressed into a tablet with a pressure of 10 MPa and a pressing time of 60 seconds to obtain an electrode sheet.

[0020] Based on the lithium ion electrochemical hybrid capacitor, the positive electrode material of halloysite nanotubes loaded with lithium vanadium phosphate was used in a three-electrode system with 2M LiNO3 as the electrolyte at 0.1A·g -1 The specific capacitance is as high as 207.4F·g -1 .

[0021] The halloysite nanotube-loaded lithium vanadium phosphate positive electrode material based on the lithium ion electrochemical hybrid capacitor prepared in this embodiment was tested.

[0022] Figure 2 This is the isothermal adsorption curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material prepared in this embodiment. It can be seen from the figure that the adsorption curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material for lithium ion electrochemical hybrid capacitor is a typical type IV adsorption curve, and the hysteresis loop is H3 type, indicating the presence of mesopores, which is conducive to charge transfer.

[0023] Figure 3 This is the pore size distribution curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material prepared in this embodiment. It can be seen from the figure that the pore size distribution of the obtained halloysite nanotube-loaded lithium vanadium phosphate positive electrode material is between 2-50nm, and the mesopore distribution is uniform, so that it has good electrochemical performance.

[0024] Figure 4 This is a TEM image of the halloysite nanotubes loaded with lithium vanadium phosphate prepared in this example. It can be seen from the figure that the particle size of the lithium vanadium phosphate particles is about 100 nm and is evenly loaded on the halloysite nanotubes.

[0025] Figure 5 This is the AC impedance curve of the halloysite nanotube-loaded lithium vanadium phosphate positive electrode material prepared in this example. Through fitting, it can be found that it has a very small charge transfer resistance of 1.09Ω.

[0026] Figure 6 The graph of capacity retention rate and coulombic efficiency of the lithium ion capacitor prepared in this embodiment after 10,000 cycles shows that the capacitance retention rate of the sample is 94.87 and the coulombic efficiency is 100% after 10,000 cycles. Example

[0027] A method for preparing a lithium ion electrochemical hybrid capacitor comprises the following steps: Grind the halloysite and sieve it through 200 mesh. Take 2g oxalic acid and 1.34g V2O5 and dissolve them in 30ml deionized water at room temperature. Stir until a clear blue solution is obtained. Then add 1g of halloysite that has not been acid-etched, 2.25g Li2CO3 and 2.54g NH4H2PO4 to the solution. Stir in a water bath at 80℃ for 30min to form a gel. Then dry the gel at 100℃ for 12h and grind it to obtain a blue-green powder. The sample was placed in a tube furnace under N2 atmosphere protection, with a heating rate of 5°C / min, kept at 350°C for 4h, kept at 750°C for 8h, and then cooled to room temperature; 0.8 g of the calcined material was ground, mixed with 0.1 g of a binder (polytetrafluoroethylene) and 0.1 g of acetylene black, and 5 ml of alcohol was added as a solvent. After stirring at room temperature for 6 hours, the mixture was evenly coated on the nickel foam. After drying at 100°C for 12 hours, the mixture was pressed into a tablet with a pressure of 10 MPa and a pressing time of 60 seconds to obtain an electrode sheet.

[0028] Based on the lithium ion electrochemical hybrid capacitor, the positive electrode material of halloysite nanotubes loaded with lithium vanadium phosphate was used in a three-electrode system with 2M LiNO3 as the electrolyte at 0.1A·g -1 The specific capacitance is 133.1F·g -1 . Example

[0029] A method for preparing a lithium ion electrochemical hybrid capacitor comprises the following steps: Grind the halloysite and sieve it through 200 mesh. Take 2g of the halloysite powder and add it to 200ml of 2mol / L sulfuric acid solution. Acid-etch it in a water bath at 80℃ with magnetic stirring for 2h. Wash it repeatedly by centrifugation with deionized water until it is neutral. Dry it in an oven at 100℃ for 6h. Take 2g oxalic acid and 1.34g V2O5 and dissolve them in 30ml deionized water at room temperature, stir until a clear blue solution is obtained, then add 1g acid-etched halloysite, 2.25g Li2CO3 and 2.54g NH4H2PO4 to the solution, stir in a water bath at 80℃ for 30min until a gel is formed, then dry the gel at 100℃ for 12h, and grind to obtain a blue-green powder; The sample was placed in a tube furnace under N2 atmosphere protection, with a heating rate of 5°C / min, kept at 350°C for 4h, kept at 750°C for 8h, and then cooled to room temperature; 0.8 g of the calcined material was ground, mixed with 0.1 g of a binder (polytetrafluoroethylene) and 0.1 g of acetylene black, and 5 ml of alcohol was added as a solvent. After stirring at room temperature for 6 hours, the mixture was evenly coated on the nickel foam. After drying at 100°C for 12 hours, the mixture was pressed into a tablet with a pressure of 10 MPa and a pressing time of 60 seconds to obtain an electrode sheet.

[0030] Based on the lithium ion electrochemical hybrid capacitor, the positive electrode material of halloysite nanotubes loaded with lithium vanadium phosphate was used in a three-electrode system with 2M LiNO3 as the electrolyte at 0.1A·g -1 The specific capacitance is 133.5F·g -1 . Example

[0031] A method for preparing a lithium ion electrochemical hybrid capacitor comprises the following steps: Grind the halloysite and sieve it through 200 mesh. Take 2g of the halloysite powder and add it to 200ml of 2mol / L sulfuric acid solution. Acid-etch it in a water bath at 80℃ with magnetic stirring for 2h. Wash it repeatedly by centrifugation with deionized water until it is neutral. Dry it in an oven at 100℃ for 6h. Take 2g oxalic acid and 1.34g V2O5 and dissolve them in 30ml deionized water at room temperature, stir until a clear blue solution is obtained, then add 1g acid-etched halloysite, 2.25g Li2CO3 and 2.54g NH4H2PO4 to the solution, stir in a water bath at 80℃ for 30min until a gel is formed, then dry the gel at 100℃ for 12h, and grind to obtain a blue-green powder; The sample was placed in a tube furnace under N2 atmosphere protection, with a heating rate of 5°C / min, kept at 350°C for 4h, kept at 750°C for 8h, and then cooled to room temperature; 0.8 g of the calcined material was ground, mixed with 0.1 g of a binder (polytetrafluoroethylene) and 0.1 g of acetylene black, and 5 ml of alcohol was added as a solvent. After stirring at room temperature for 6 hours, the mixture was evenly coated on the nickel foam. After drying at 100°C for 12 hours, the mixture was pressed into a tablet with a pressure of 10 MPa and a pressing time of 60 seconds to obtain an electrode sheet.

[0032] Based on the lithium ion electrochemical hybrid capacitor, the positive electrode material of halloysite nanotubes loaded with lithium vanadium phosphate was used in a three-electrode system with 2M LiNO3 as the electrolyte at 0.1A·g -1 The specific capacitance is 133.5F·g -1 .

[0033] The above are only embodiments of the present invention, and the common knowledge such as the known specific structures and / or characteristics in the scheme are not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a lithium ion electrochemical hybrid capacitor, characterized in that: The steps include: S1. Grind the halloysite, sieve it, add it to a sulfuric acid solution, acid-etch it in a magnetic stirring water bath, then centrifuge and wash it repeatedly with deionized water until it is neutral, and put it in an oven to dry; S2, dissolving oxalic acid and V2O5 in deionized water at room temperature, stirring to obtain a clear blue solution, then adding the acid-etched halloysite, Li2CO3 and NH4H2PO4 in step S1 to the blue solution, stirring in a water bath until a gel is formed, and then drying the gel, and grinding to obtain a blue-green powder; S3, placing the blue-green powder of step S2 into a tube furnace, performing gradient calcination under N2 atmosphere protection, and then cooling to room temperature; S4, grinding the mixture calcined in step S3, mixing it with a binder and acetylene black, adding a proper amount of alcohol as a solvent, stirring at room temperature, evenly coating it on the nickel foam, and pressing it into sheets after drying to obtain an electrode sheet.

2. The method for preparing a lithium ion electrochemical hybrid capacitor according to claim 1, characterized in that: In step S1, the particle size is 200 mesh, the concentration of the sulfuric acid solution is 2 mol / L, the water bath temperature is 80° C., the water bath time is 0-6 h, the drying temperature is 100° C., and the drying time is 6 h.

3. The method for preparing a lithium ion electrochemical hybrid capacitor according to claim 1, characterized in that: In step S2, the stirring time is 30 minutes, the water bath temperature is 80°C, the drying temperature is 100°C, the drying time is 12 hours, the stoichiometric molar ratio of the reagents is oxalic acid: V2O5: Li2CO3: NH4H2PO4 = 3:1:1.5:3, and the mass ratio of halloysite to lithium vanadium phosphate is 1:

3.

4. The method for preparing a lithium ion electrochemical hybrid capacitor according to claim 1, characterized in that: In step S3, the heating rate is 5°C / min, and the calcination gradient is 350°C for 4h and 750°C for 8h.

5. The method for preparing a lithium ion electrochemical hybrid capacitor according to claim 1, characterized in that: In step S4, the binder is polytetrafluoroethylene, and the mass ratio of the active material, the binder and the acetylene black is 8:1:1, the stirring time is 6 hours, the drying temperature is 100° C., the drying time is 12 hours, the tableting pressure is 10 MPa, and the tableting time is 60 seconds.

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