A potassium metal capacitor and a method for preparing the same

Abstract

The present invention belongs to the field of electrochemical energy storage technology, and specifically relates to a potassium metal capacitor and a preparation method thereof. The capacitor of the present invention includes a potassium metal negative electrode, a positive electrode with a carbon material or a carbon-based composite material as an active material, and an organic solvent electrolyte dissolved with a potassium salt. Compared with traditional potassium ion capacitors, the preparation process and cost of the device are greatly simplified, and its fast electrochemical reaction kinetics can achieve a good match with the capacitive positive electrode material. Therefore, the potassium metal capacitor assembled by the metal potassium negative electrode and the capacitive carbon positive electrode of the present invention has an energy density close to that of a traditional potassium ion battery, and at the same time can achieve the characteristics of high power density of the capacitor, and can be used in large-scale energy storage systems with high energy and high power density requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and in particular relates to a potassium metal capacitor and a preparation method thereof. Background Art

[0002] In recent years, with the continuous development of new electronic devices and sustainable renewable clean energy, the demand for safe and efficient electrochemical energy storage systems has increased dramatically. At the same time, the existing widely used batteries and secondary batteries cannot meet some special needs in the fields of high-end national defense technology, weapons and equipment, and communications, especially the instantaneous high-power power demand when high-power systems are started. At present, lithium-ion batteries occupy a dominant position in various electrochemical energy storage devices and are widely used in portable devices. Lithium-ion batteries have the advantages of high energy density, high operating voltage and environmental friendliness. However, its power density (<1000W+Kg -1 ) and cycle life (<1000 times) are much lower than those of electrochemical capacitors. Electrochemical capacitors are a type of capacitor with high power density (>10kW+kg -1 ) and long cycle life (>100,000 times), have been widely used in telecommunications, medical equipment, aerospace and military cutting-edge fields. At present, the energy density of electrochemical capacitors is relatively low (<10Wh+kg -1 ), so that it cannot meet the energy density requirements of the device when used alone. Therefore, it is urgent to develop new electrochemical energy storage technologies with high energy and power density, long life and high safety to meet the application needs in different fields.

[0003] Compared with lithium resources, potassium resources are abundant (potassium reserves 1.5 mass% vs lithium reserves 0.0017 mass%) and cheap (potassium carbonate 1000 $ ton -1 vs lithium carbonate 23000$ton -1 ), so potassium ion energy storage devices are extremely advantageous in large-scale energy storage devices. Potassium ion energy storage devices also have the following advantages: (1) commercial graphite can be used as the negative electrode; (2) it has the lowest electrode potential (K + / K: -2.88V vs standard hydrogen electrode vs Li + / Li: -2.79V vs standard hydrogen electrode), which is conducive to achieving high energy density; (3) Potassium ions have the smallest solvation radius (K + : vs Li + : ), which helps to achieve a faster ion diffusion rate and achieve high rate performance. Therefore, the development of potassium ion hybrid capacitors with high energy and high power density has become a research hotspot. At present, the positive electrode materials of potassium ion hybrid capacitors mainly use various capacitive carbon materials with porous structures and large specific surface areas. Suitable pore size and high specific surface area are the key factors as the best positive electrode materials. The negative electrode materials can be divided into three categories according to the different energy storage mechanisms: embedded type, conversion type and alloy type. Among them, the capacity of carbon-based materials as embedded negative electrodes is mainly concentrated in 200-400mA+h+g -1 , the first coulombic efficiency is generally less than 60%. Embedded negative electrodes such as non-carbon materials (such as titanium-based materials) have the advantages of stable structure and good cycle stability, and the embedding potential of potassium ions is relatively low, so they can be used as battery-type negative electrode materials. However, the conductivity of such materials is relatively poor and the capacity is low, which needs to be improved by mixing with other highly conductive materials. Conversion-type and some alloy-type negative electrode materials such as metal oxides and metal sulfides have high specific capacity, but the charging and discharging process will produce a large volume expansion, resulting in rapid capacity decay and poor cycle stability. In addition, these types of battery negative electrodes store energy through the embedding / extraction of potassium ions inside the material. This process is controlled by the diffusion rate of ions inside the electrode material, and the reaction rate is slow, resulting in a large gap between its potassium storage kinetics and that of the capacitive positive electrode, which makes it difficult for the positive and negative electrodes to play a synergistic role, making it difficult for potassium ion capacitors to truly have the characteristics of high energy and high power density. In addition, the synthesis process of the above-mentioned negative electrode materials is complicated and difficult to prepare on a large scale. Therefore, it is still a huge challenge to develop and design negative electrode materials with high specific capacity, low discharge platform and the ability to conduct ions / electrons quickly. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a potassium metal capacitor, which creatively uses potassium metal as the negative electrode material of the capacitor, which is beneficial to improving the conduction rate of ions and electrons, widening the voltage window for stable operation of the capacitor, and achieving good kinetic matching with the capacitive carbon positive electrode. The purpose is to prepare a potassium metal capacitor with high energy and high power density.

[0005] To achieve the above object, the present invention is implemented by the following technical solutions:

[0006] In one aspect, the present invention provides a potassium metal capacitor, which includes a potassium metal negative electrode, a positive electrode using a carbon material or a carbon-based composite material as a positive electrode active material, and an organic solvent electrolyte dissolved with a potassium salt.

[0007] The capacitor of the present invention uses potassium metal as the negative electrode, the active material of carbon material or carbon-based composite material as the positive electrode, and an organic solvent dissolved with potassium salt as the electrolyte. Compared with the traditional potassium ion capacitor, the preparation process and cost of the device are greatly simplified, and its fast electrochemical reaction kinetics can achieve a good match with the capacitive positive electrode material. Therefore, the present invention is a potassium metal capacitor assembled from a metallic potassium negative electrode and a capacitive carbon positive electrode, which has an energy density close to that of a traditional potassium ion battery, and can also achieve the characteristics of high power density of the capacitor, and can be applied in large-scale energy storage systems with high energy and high power density requirements.

[0008] Preferably, the carbon material is selected from at least one of activated carbon, amorphous carbon, graphene, amorphous carbon doped with heteroatoms and graphene doped with heteroatoms, wherein the heteroatoms are non-carbon atoms. Further, the non-carbon atoms include but are not limited to nitrogen, oxygen and sulfur.

[0009] Preferably, the carbon-based composite material is composed of any two or more of activated carbon, amorphous carbon, graphene, heteroatom-doped amorphous carbon and heteroatom-doped graphene, wherein the heteroatom is a non-carbon atom.

[0010] Preferably, the potassium salt includes potassium hexafluorophosphate and bis(fluorosulfonyl)imide potassium salt.

[0011] Preferably, the organic solvent is selected from at least one of ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate and dimethylhexane.

[0012] Preferably, the mass ratio of the organic solvent to the potassium salt is 40:60-99:1. Further, the mass ratio of the organic solvent to the potassium salt is 40:60-90:10.

[0013] Another aspect of the present invention provides a method for preparing the potassium metal capacitor, comprising the following steps:

[0014] S1. Evenly dispersing the carbon material or carbon-based composite material, a binder and a conductive additive in a solvent, then coating the mixture on a current collector, and drying and cutting the mixture to obtain a positive electrode material;

[0015] S2. Roll a pure potassium metal block into a negative electrode material, and then assemble them in the order of negative electrode material, separator, and positive electrode material, and add an organic solvent dissolved with potassium salt as an electrolyte, and finally encapsulate to obtain a potassium metal capacitor.

[0016] Preferably, the carbon material comprises YP-50F activated carbon, and the carbon-based composite material comprises a graphene / amorphous carbon composite and a sulfur-doped graphite amorphous carbon composite.

[0017] Preferably, in terms of mass percentage, the amount of the carbon material or carbon-based composite material is 60-90%, the amount of the binder is 5-20%, and the amount of the conductive additive is 5-20%.

[0018] Preferably, the solvent includes water, ethanol and N-methylpyrrolidone.

[0019] Preferably, the binder includes but is not limited to sodium carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride.

[0020] Preferably, the current collector includes but is not limited to aluminum foil, copper foil and stainless steel mesh.

[0021] Preferably, the conductive additive includes but is not limited to acetylene black, Ketjen black, carbon black, conductive graphite and carbon nanotubes.

[0022] Preferably, the separator includes but is not limited to glass fiber, polyethylene, and polypropylene porous membranes.

[0023] Preferably, the drying is carried out at 80-100° C. for 8-12 hours.

[0024] Preferably, rolling the pure potassium metal block into the negative electrode material is to roll the pure potassium metal block into a suitable shape for the negative electrode under anhydrous and oxygen-free conditions, such as a sheet or strip with a suitable thickness.

[0025] Preferably, the entire packaging process is carried out under anhydrous and oxygen-free conditions to ensure the airtightness of the capacitor.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention discloses a potassium metal capacitor, which comprises a potassium metal negative electrode, a positive electrode with a carbon material or a carbon-based composite material as an active material, and an organic solvent electrolyte dissolved with a potassium salt. The present invention uses a potassium metal capacitor which is rich in resources, low in price, has a low electrode potential (-2.92V vs standard hydrogen electrode), a high specific capacity (687mA+h+g -1) and potassium metal with the ability to quickly conduct electrons and ions as the negative electrode to prepare a new type of potassium metal capacitor. Compared with traditional potassium ion capacitors, the use of potassium metal negative electrodes can avoid the pre-embedded potassium process and the complicated steps of negative electrode preparation, greatly simplifying the preparation process and cost of the device. And its fast electrochemical reaction kinetics can achieve a good match with the capacitive positive electrode material. Therefore, the potassium metal capacitor assembled by the metallic potassium negative electrode and the capacitive carbon positive electrode has an energy density close to that of a traditional potassium ion battery, and can also achieve the characteristics of high power density of the capacitor, belonging to a new energy storage technology with both high power and large capacity. It can be used in large-scale energy storage systems with high energy and high power density requirements, and can also be used as a starting power supply for non-portable high-power equipment to meet the needs of instantaneous high power output, and can provide a long-lasting power supply. The potassium metal capacitor in the present invention has not been reported at home and abroad, and is advanced in both energy storage concepts and principles, and meets the requirements of future high-power, high-specific energy, and long-life new electrochemical energy storage technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Graph showing the electrochemical cycle performance of the potassium metal capacitor of Examples 1-3;

[0029] Figure 2 This is the electrochemical cycle performance diagram of the potassium metal capacitor of Comparative Example 1. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0032] In addition, unless otherwise stated, the reagents and solvents disclosed below were purchased from Suzhou Duoduo Chemical Technology Co., Ltd., Shanghai Aladdin Biochemical Technology Co., Ltd., and Shanghai MacLean Biochemical Technology Co., Ltd. The electrochemical performance was completed by using a battery test system CT3002A from Wuhan Blue Electric Electronics Co., Ltd.

[0033] Example 1 A method for preparing a potassium metal capacitor

[0034] (1) Commercial YP-50F carbon material, Ketjen black and polyvinylidene fluoride were uniformly dispersed in N-methylpyrrolidone solution at a mass ratio of 8:1:1, and the mass ratio of electrode material (YP-50F carbon material, Ketjen black and polyvinylidene fluoride) to dispersant (N-methylpyrrolidone) was 1:6. Then, they were uniformly coated on a stainless steel mesh current collector, dried in a vacuum oven at 80°C for 12 hours, and then cut into 12 mm electrode pieces. The loading amount of positive electrode active material was 1-1.5 mg / cm 2 .

[0035] (2) Take an appropriate amount of potassium block and roll it into a potassium sheet with a thickness of 200-500 μm. Put the potassium sheet into a 2032-type negative electrode battery shell as the negative electrode, then put the glass fiber separator and the positive electrode sheet in turn, and inject 200 μL of electrolyte (a solution formed by potassium hexafluorophosphate dispersed in a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio, with a concentration of 0.8 mol / L), then put the gasket and the positive electrode shell in turn, and finally encapsulate to obtain a potassium metal capacitor.

[0036] Example 2 A method for preparing a potassium metal capacitor

[0037] Its preparation method is consistent with that in Example 1, except that the YP-50F carbon material is replaced with a composite material of graphene and amorphous carbon. Among them, graphene and amorphous carbon are prepared by covering the surface of graphene oxide with a layer of phenolic resin and then carbonizing it at high temperature (for specific preparation methods, see "Approaching Superior Potassium Storage of Carbonaceous Anode through a Combined Strategy of Carbon Hybridization and Sulfur Doping[J].Energy&Environmental Materials,2021.").

[0038] Example 3 A method for preparing a potassium metal capacitor

[0039] The preparation method is consistent with that in Example 1, except that the YP-50F carbon material is replaced with a composite carbon material of sulfur-doped graphene and amorphous carbon. The sulfur-doped graphene amorphous carbon composite is obtained by mixing the prepared graphene and amorphous carbon composite with sulfur powder and then treating them at high temperature (for a specific preparation method, see "[1] Approaching Superior Potassium Storage of Carbonaceous Anode through a Combined Strategy of Carbon Hybridization and Sulfur Doping [J]. Energy & Environmental Materials, 2021.").

[0040] Comparative Example 1: Preparation method of a potassium ion hybrid capacitor

[0041] The preparation method is the same as that of Example 1, except that the potassium metal negative electrode is replaced with a common negative electrode material, that is, hard carbon as an active material, and assembled into a potassium ion hybrid capacitor. The preparation method of the hard carbon electrode is:

[0042] Hard carbon, Ketjen black and sodium carboxymethyl cellulose were used as electrode materials, and water was used as a dispersant in a mass ratio of 8:1:1 to disperse them evenly. The ratio of electrode material to dispersant was about 1:6. The obtained slurry was coated on copper foil, dried at 80℃ for 12h, and then cut into 12mm pole pieces. The loading amount of hard carbon active material was 1-1.5mg / cm 2 The obtained electrode piece was placed in a 2032 type negative electrode battery shell as the negative electrode, and then the glass fiber separator and YP-50F positive electrode piece were placed in turn, and 200μL of electrolyte (a solution formed by potassium hexafluorophosphate dispersed in a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio, with a concentration of 0.8mol / L) was injected, and then the gasket and positive electrode shell were placed in turn, and finally packaged to obtain a hybrid capacitor.

[0043] Experimental Example 1 Electrochemical Performance Test of Potassium Metal Capacitor

[0044] The electrochemical performance of the potassium metal capacitors prepared in Examples 1-3 was tested, and the potassium ion hybrid capacitor of Comparative Example 1 was used as a control.

[0045] It can be seen from Table 1 that, compared with the traditional potassium ion hybrid capacitor, the potassium metal capacitor of the present invention can have both high energy and high power density.

[0046] at the same time, Figure 1 is the electrochemical cycle performance diagram of Examples 1-3, Figure 2 The electrochemical cycle performance diagram of the comparative example. Figure 1 and Figure 2 It can be concluded that, under the same test conditions, Examples 1-3 can obtain higher specific capacity than the comparative example, and thus can achieve higher energy and power.

[0047] Table 1 Electrochemical properties of various potassium metal capacitors

[0048]

[0049] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A potassium metal capacitor, characterized in that: The capacitor comprises a potassium metal negative electrode, a positive electrode with a carbon-based composite material as a positive electrode active material, and an organic solvent electrolyte dissolved with a potassium salt; the carbon-based composite material is selected from a graphene / amorphous carbon composite or a sulfur-doped graphite amorphous carbon composite; the potassium salt comprises potassium hexafluorophosphate and bis(fluorosulfonyl)imide potassium salt, the organic solvent is selected from at least one of ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate and dimethylhexane, and the mass ratio of the organic solvent to the potassium salt is 40:60-99:

1.

2. The method for preparing the potassium metal capacitor according to claim 1, characterized in that: The following steps are involved: S1, uniformly dispersing the carbon-based composite material, the binder and the conductive additive in a solvent, then coating the same on a current collector, and obtaining a positive electrode material through drying and cutting; S2. Roll a pure potassium metal block into a negative electrode material, and then assemble them in the order of negative electrode material, separator, and positive electrode material, and add an organic solvent dissolved with potassium salt as an electrolyte, and finally encapsulate to obtain a potassium metal capacitor.

3. The method for preparing a potassium metal capacitor according to claim 2, characterized in that: Calculated by mass percentage, the amount of the carbon-based composite material is 60-90%, the amount of the binder is 5-20%, and the amount of the conductive additive is 5-20%.

4. The method for preparing a potassium metal capacitor according to claim 2, characterized in that: The solvents include water, ethanol and N-methylpyrrolidone.

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