Electrochemical capacitor having high specific capacitance and low self-discharge, and preparation method for positive electrode

Abstract

A preparation method for a positive electrode. The preparation method comprises: subjecting a three-dimensional porous carbon material and chained conductive carbon black to dry-state mechanical kneading and mixing in a cloth bag, then adding the resulting mixture to deionized water containing a binder in one time, and stirring same at a high speed to form a viscous slurry; coating the slurry onto two surfaces of an aluminum foil current collector, and drying and shaping same to form a first electrode layer; subjecting a multi-element lithium oxide, a P-t-P conductive agent and a binder to dry-state mechanical mixing in a cloth bag, then adding the resulting mixture to a solvent containing 2,5-dimethylpyrrolidine (NMP) in one time, and stirring same at a high speed to form a viscous slurry; coating the slurry onto two surfaces of the first electrode layer, and drying and shaping same to form a second electrode layer; and rolling the obtained electrode on a Cr-coated roller press to a designed thickness, so as to form the positive electrode of an electrochemical capacitor. The prepared electrochemical capacitor has the characteristics of a high specific capacitance and low self-discharge, and has good market application prospects.

Description

A method for preparing a high specific capacitance, low self-discharge electrochemical capacitor and a positive electrode Technical Field

[0001] The present invention belongs to the technical field of capacitor preparation, and in particular relates to an electrochemical capacitor with high specific capacitance and low self-discharge, and a method for preparing a positive electrode. Background Art

[0002] Electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, are a new type of energy storage device that has attracted considerable attention in recent years. They utilize the interfacial electrical double-layer charge separation or Faraday pseudocapacitance principle to rapidly store and release energy. Combining the characteristics of secondary chemical batteries and traditional capacitors, they are an excellent new chemical power source with both high specific power and high safety.

[0003] The earliest electrochemical capacitors used activated carbon (AC) as the main material and the so-called symmetrical electrochemical double layer capacitor (EDLC) with the same positive and negative electrodes. The specific power exceeded 10kW / kg and the cycle life could reach 1 million times, but the specific energy was less than 10Wh / kg and the self-discharge was large, with a monthly self-discharge rate usually above 30%. In 2001, Amatucci et al. first constructed an asymmetric electrochemical capacitor (also known as "lithium ion capacitor, LiC") with activated carbon as the positive electrode and nano-Li4Ti5O12 as the negative electrode. The specific energy reached 18Wh / kg [Amatucci GG, Badway F, DU Pasquier A, et al. An asymmetric hybrid nonaqueous energy storage cell. Journal of the Electrochemical Society, 2001, 148(8):A930-A939], which opened up a new method to explore new ways to improve the specific energy of supercapacitors.

[0004] The electrode is known as the heart of the electrochemical capacitor. It is the core component that determines its performance and is also the key to improving its specific energy. According to the electrochemical capacitor energy formula E=1 / 2CV 2It can be seen that when the operating voltage range is limited, increasing the specific capacitance C of the electrode will be an effective way to increase the specific energy of the entire electrochemical capacitor. However, existing technical conditions limit the increase in C value. Among them, the C value of double-layer capacitor type is limited to 50-300F / g, and the C value of faraday pseudo-capacitor type is limited to 500-1200F / g. As a result, the overall specific energy of electrochemical capacitors is limited to 10-50Wh / kg, which is still a large gap compared to the specific energy of lithium-ion batteries. Technical issues

[0005] Through the above analysis, the problems and defects of the existing technology are: 1) The low specific capacitance of the existing electrode makes it difficult to further improve the overall specific energy of the electrochemical capacitor; 2) The existing electrode structure causes large self-discharge of the electrochemical capacitor. Technical Solutions

[0006] In view of the problems existing in the prior art, the present invention provides an electrochemical capacitor with high specific capacitance and low self-discharge and a method for preparing a positive electrode.

[0007] The present invention adopts the following technical solutions:

[0008] A positive electrode comprises a first electrode layer and a second electrode layer, wherein the first electrode layer is a double-layer electrode layer, and the second electrode layer is a pseudo-capacitive electrode layer.

[0009] Furthermore, the active material of the double-layer electrode layer is a three-dimensional porous carbon material; the three-dimensional porous carbon material is a carbon-containing material with a large specific surface area, and the specific surface area is 1000-3500m 2 / g, the three-dimensional porous carbon material is one or more of porous activated carbon, mesoporous carbon, and porous graphene.

[0010] Furthermore, the active material of the pseudo-capacitive electrode layer is a multinary lithium oxide material; the multinary lithium oxide material is at least two elements selected from nickel, manganese, titanium, iron, cobalt, and vanadium in addition to lithium; and the molar content of lithium in the multinary lithium oxide is 20%-80%.

[0011] Furthermore, the first electrode layer contains chain conductive carbon black, including one or more of Ketjen black, superconducting acetylene black, and VulcanXC carbon black.

[0012] Furthermore, the first electrode layer also includes a fiberizable resin, which is one of polytetrafluoroethylene and modified polytetrafluoroethylene.

[0013] Furthermore, the second electrode layer contains a point-to-point conductive material, including one or both of Super P conductive carbon black and GS conductive carbon black.

[0014] Furthermore, the second electrode layer also includes a high molecular polymer material, which is polyvinylidene fluoride.

[0015] The present invention also provides a method for preparing a positive electrode, comprising the following steps:

[0016] Step 1: The three-dimensional porous carbon material and the chain conductive carbon black are dry-kneaded and mixed in a cloth bag for 5-10 minutes, and then added to deionized water containing a binder at one time, and stirred at high speed for 30-60 minutes to form a viscous slurry;

[0017] Step 2: evenly apply the slurry to both sides of the aluminum foil current collector and dry it at 100°C to form the first electrode layer;

[0018] Step 3: Dry-mix the multi-component lithium oxide, PtP conductive agent, and binder in a bag for 5-10 minutes, then add them all at once to a solvent containing dimethylpyrrolidone (NMP), and stir at high speed for 60-90 minutes to form a viscous slurry;

[0019] Step 4: evenly apply the slurry to both sides of the first electrode layer, and vacuum dry at 105°C to form the second electrode layer;

[0020] Step 5: Roll the electrode obtained in step 4 on a Cr plating roller press to a designed thickness to form a positive electrode.

[0021] The present invention also provides an electrochemical capacitor with high specific capacitance and low self-discharge, comprising a shell, a diaphragm, an electrolyte, a positive electrode and a negative electrode.

[0022] Furthermore, the shell is one of a soft-package aluminum-plastic film, an aluminum shell or a steel shell. Beneficial effects

[0023] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0024] First, during the manufacturing process of the electrochemical capacitor of the present invention, a pseudo-capacitive electrode layer is introduced into the traditional electrode layer. On the one hand, the specific energy of the system is greatly improved by increasing the positive electrode specific capacitance; on the other hand, the charge absorption capacity of the pseudo-capacitive electrode layer is used to greatly reduce the self-discharge of the electrochemical capacitor.

[0025] Second, during the manufacturing process of the electrochemical capacitor of the present invention, by adding a chain-type highly conductive material to the first electrode layer, the interruption of the electron and ion transport paths caused by the porous structure of the three-dimensional porous carbon material is greatly improved, thereby alleviating the retention of overpotential when the electrochemical capacitor operates at a high rate, and maintaining the high power characteristics of the electrochemical capacitor.

[0026] Third, during the manufacturing process of the electrochemical capacitor of the present invention, the thermodynamic and kinetic matching design of the first electrode layer and the second electrode layer is used to improve the coordinated transmission capability of electrons and ions during operation of the electrochemical capacitor, reduce the overall internal resistance of the electrochemical capacitor, and thus ensure its long cycle characteristics.

[0027] Fourth, the auxiliary evidence of the inventiveness described in the claims of the present invention is also reflected in the following important aspects:

[0028] (1) The expected benefits and commercial value of the technical solution of the present invention after transformation are as follows: The economic benefits and commercial value of the technical solution of the present invention after transformation are obvious, and more and more manufacturers will introduce this technical solution.

[0029] (2) The technical solution of the present invention fills the technical gap in the industry at home and abroad: This technical solution is an original technical solution, and no such technical solution has been published at home or abroad.

[0030] (3) The technical solution of the present invention solves a technical problem that scientists have always been eager to solve but have never been able to solve: the simultaneous existence of low specific capacity and high self-discharge of electrochemical capacitors.

[0031] In summary, the present invention not only optimizes various performance indicators of the electrochemical capacitor, but also has high practical value and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] FIG1 is a flow chart of a method for preparing a positive electrode of an electrochemical capacitor provided in an embodiment of the present invention;

[0034] FIG2 is a 41-day self-discharge curve of the electrochemical capacitor of Example 1 of the present invention. Modes for Carrying Out the Invention

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] In an embodiment of the present invention, the present invention provides a positive electrode comprising a first electrode layer and a second electrode layer;

[0037] The first electrode layer is a double-layer electrode layer, and the second electrode layer is a pseudo-capacitive electrode layer;

[0038] The active material of the double-layer electrode layer is a three-dimensional porous carbon material;

[0039] The three-dimensional porous carbon material is a carbon-containing material with a large specific surface area, the specific surface area of ​​which is 1000-3500 m2 / g, and is preferably one or more of porous activated carbon, mesoporous carbon, and porous graphene;

[0040] The first electrode layer contains chain conductive carbon black, preferably one or more of Ketjen black, superconducting acetylene black, and VulcanXC carbon black;

[0041] The active material of the pseudo-capacitive electrode layer is a multi-component lithium oxide material;

[0042] The multi-element oxide material is at least two elements selected from nickel, manganese, titanium, iron, cobalt and vanadium except lithium;

[0043] The multinary lithium oxide has an electrochemical pseudocapacitive (also known as "pseudocapacitive") property;

[0044] The molar content of lithium in the multi-component lithium oxide is 20%-80%;

[0045] The second electrode layer contains a point-to-point conductive material (PtP conductive agent), preferably one or both of Super P conductive carbon black and GS conductive carbon black;

[0046] The first electrode layer comprises a fiberizable resin, preferably one of polytetrafluoroethylene or modified polytetrafluoroethylene (binder);

[0047] The second electrode layer includes a high molecular polymer material (binder) that is formed by physical adsorption and chemical bonding, preferably polyvinylidene fluoride.

[0048] As shown in FIG1 , a positive electrode preparation method includes the following steps:

[0049] Step 1: The three-dimensional porous carbon material and the chain conductive carbon black are dry-kneaded and mixed in a cloth bag for 5-10 minutes, and then added to deionized water containing a binder at one time, and stirred at high speed for 30-60 minutes to form a viscous slurry;

[0050] Step 2: evenly apply the slurry to both sides of the aluminum foil current collector and dry it at 100°C to form the first electrode layer;

[0051] Step 3: Dry-mix the multi-component lithium oxide, PtP conductive agent, and binder in a bag for 5-10 minutes, then add them all at once to a solvent containing dimethylpyrrolidone (NMP), and stir at high speed for 60-90 minutes to form a viscous slurry;

[0052] Step 4: evenly apply the slurry to both sides of the first electrode layer, and vacuum dry at 105°C to form the second electrode layer;

[0053] Step 5: Roll the electrode obtained in step 4 on a Cr plating roller press to a designed thickness to form the positive electrode of the electrochemical capacitor of the present invention.

[0054] A high-specific-capacitance, low-self-discharge electrochemical capacitor comprises a shell, a diaphragm, an electrolyte, a positive electrode and a negative electrode, wherein the positive electrode is the positive electrode prepared by the above method.

[0055] The following is explained with more specific examples.

[0056] Example 1

[0057] A high-specific-capacitance, low-self-discharge electrochemical capacitor comprises an aluminum-plastic film housing, a diaphragm, an electrolyte, a positive electrode, and a negative electrode. A method for preparing the positive electrode comprises the following steps:

[0058] Step 1: 93 parts (mass fraction, the same below) of commercially available porous activated carbon (manufactured by Zhejiang Apex, FCO-20A) and 2 parts of chain conductive carbon black (manufactured by Lion, Japan, ECP200L) were kneaded and mixed in a bag dry state for 6 minutes, and then added all at once to 5 parts of deionized water containing modified polytetrafluoroethylene (manufactured by Shanghai Huayi Sanai Fu, PTFE FR303), and stirred at high speed for 45 minutes to form a viscous slurry;

[0059] Step 2: The slurry is evenly coated on both sides of a 15 μm aluminum foil (manufactured by Henan Mingtai Aluminum, 1060H15) current collector with a surface density of 65 g / m2 and dried at 100°C to form the first electrode layer.

[0060] Step 3: 95 parts of commercially available multi-component lithium oxide (6SC2, manufactured by Beijing Dangsheng Technology), 3 parts of a PtP conductive agent (Super P Li, manufactured by Termeco, Switzerland), and 2 parts of a binder (PVDF 5130, manufactured by Solvay, USA) were dry-mixed in a bag for 5 minutes. The mixture was then added all at once to a solvent containing dimethylpyrrolidone (battery-grade NMP, manufactured by Changxin Chemical) and stirred at high speed for 75 minutes to form a viscous slurry.

[0061] Step 4: evenly apply the slurry to both sides of the first electrode layer, control the surface density to 175g / m2, and vacuum dry at 105℃ to form the second electrode layer;

[0062] Step 5: Roll the electrode obtained in step 4 on a Cr plating roller press to a designed thickness (115 μm) to form the positive electrode of the electrochemical capacitor of the present invention.

[0063] The above positive electrodes were assembled into soft-pack electrochemical capacitors.

[0064] Referring to Figure 2, the aluminum-plastic film soft-pack electrochemical capacitor produced under the above conditions was subjected to electrochemical performance testing and self-discharge experiments. The experimental results show that the electrochemical capacitor provided in Example 1 has a capacity of 13.5Ah at 1.0C, a corresponding positive electrode specific capacitance of 941F / g, an electrochemical capacitor specific energy of 119Wh / kg, and a 28-day charge retention capacity of 95.23%. Its specific energy and self-discharge performance are significantly better than those of the existing technology.

[0065] Example 2

[0066] A high-specific-capacitance, low-self-discharge electrochemical capacitor comprises a square aluminum housing, a diaphragm, an electrolyte, a positive electrode, and a negative electrode. A method for preparing the positive electrode comprises the following steps:

[0067] Step 1: 93 parts of commercially available porous activated carbon (manufactured by PCT, South Korea, CEP16) and 2 parts of chain conductive carbon black (manufactured by Lion, Japan, ECP600JD) were kneaded and mixed in a bag dry state for 8 minutes, and then added to 5 parts of deionized water containing polytetrafluoroethylene (manufactured by Daikin, Japan, PTFE D-6B) at one time, and stirred at high speed for 54 minutes to form a viscous slurry;

[0068] Step 2: The slurry is evenly coated on both sides of a 20 μm aluminum foil (manufactured by Huizhou Xinfeile, 1060H20) current collector with a surface density of 61 g / m2 and dried at 100°C to form the first electrode layer.

[0069] Step 3: 95 parts of a commercially available multi-component lithium oxide (XC50C4, manufactured by Zhejiang Haichuang Lithium Battery Technology), 3 parts of a PtP conductive agent (F-200GS, manufactured by Asahi Carbon, Japan), and 2 parts of a binder (PVDF 900, manufactured by Akema, France) were mechanically mixed in a bag for 6 minutes, then added all at once to a solvent containing dimethylpyrrolidone (manufactured by Changxin Chemical, battery-grade NMP) and stirred at high speed for 64 minutes to form a viscous slurry;

[0070] Step 4: evenly apply the slurry to both sides of the first electrode layer, control the surface density to 182g / m2, and vacuum dry at 105℃ to form the second electrode layer;

[0071] Step 5: The electrode obtained in step 4 is rolled on a Cr plating roller press to a designed thickness (118 μm) to form the positive electrode of the electrochemical capacitor of the present invention.

[0072] The above positive electrodes were assembled into square aluminum shell electrochemical capacitors.

[0073] Example 3

[0074] A high-specific-capacitance, low-self-discharge electrochemical capacitor comprises a cylindrical aluminum-plastic film housing, a diaphragm, an electrolyte, a positive electrode, and a negative electrode. A method for preparing the positive electrode comprises the following steps:

[0075] Step 1: 92 parts of commercially available activated carbon (YP-80F, manufactured by Kuraray, Japan) and 3 parts of chain conductive carbon black (Denka black 350, manufactured by Toho, Japan) were kneaded and mixed in a bag dry state for 10 minutes. The mixture was then added all at once to 5 parts of deionized water containing polytetrafluoroethylene (POLYFLON™ PTFE DISP30, manufactured by DuPont, USA) and stirred at high speed for 50 minutes to form a viscous slurry.

[0076] Step 2: The slurry is evenly coated on both sides of a 16 μm aluminum foil (manufactured by Huizhou Xinfeile, 1060H16) current collector with a surface density of 58 g / m2 and dried at 100°C to form the first electrode layer.

[0077] Step 3: 94 parts of commercially available multi-component lithium oxide (manufactured by Ningbo Rongbai, S800), 3 parts of PtP conductive agent (manufactured by Asahi Carbon, Japan, F-200GS), and 3 parts of binder (manufactured by Solvay, USA, PVDF 5130) were mechanically mixed in a bag for 5 minutes. The mixture was then added all at once to a solvent containing dimethylpyrrolidone (manufactured by Changxin Chemical, battery-grade NMP) and stirred at high speed for 80 minutes to form a viscous slurry.

[0078] Step 4: evenly apply the slurry to both sides of the first electrode layer, control the surface density to 188g / m2, and dry it in a vacuum oven at 105℃ to form the second electrode layer;

[0079] Step 5: The electrode obtained in step 4 is rolled on a Cr plating roller press to a designed thickness (121 μm) to form the positive electrode of the electrochemical capacitor of the present invention.

[0080] The above positive electrodes were assembled into cylindrical electrochemical capacitors.

[0081] Example 4

[0082] The same procedures as in Example 1 were followed except that the first positive electrode layer was made of porous graphene (self-made hard template, specific surface area 2250 m2 / g) and stirred at high speed for 60 minutes.

[0083] Example 5

[0084] Except that the second positive electrode layer uses multi-element lithium oxide Hunan Sander New Energy SN2R, is stirred at high speed for 90 minutes, and uses a stainless steel shell, the rest is the same as in Example 1.

[0085] Example 6

[0086] Except the first electrode layer density is controlled at 69g / m 2, except that the electrode thickness is controlled at 123um, the rest are implemented in the same way as 2.

[0087] Example 7

[0088] Except that the density of the second electrode layer is controlled at 195g / m2 and the electrode thickness is controlled at 126um, the rest are implemented in the same way as 2.

[0089] Comparative Example

[0090] A double-layer electrochemical capacitor comprises an aluminum shell, a diaphragm, an electrolyte, a positive electrode and a negative electrode.

[0091] The electrode film is prepared by conventional technology and then wound into a cylindrical double-layer electrochemical capacitor, wherein the positive and negative electrode surface densities are 120g / m 2 , electrode compaction density 0.6g / cm 3 .

[0092] The electrochemical capacitors prepared in the above examples and comparative examples were tested to obtain their basic electrochemical properties. The results are shown in Table 1.

[0093] From the data in FIG. 2 and Table 1, it can be analyzed that the electrochemical capacitor prepared by the present invention is better than the prior art in terms of electrode specific capacitance, specific energy and monthly self-discharge.

[0094] Table 1. Positive electrode specific capacitance, system specific energy and self-discharge performance of the above examples and comparative examples

[0095] Contents Positive electrode structure Positive electrode specific capacitance (F / g) System specific energy (Wh / kg) 41-day self-discharge rate (%) Example 1 Double electric layer / quasi-capacitive layer composite layer 9411194.77 Example 2 Double electric layer / quasi-capacitive layer composite layer 9571214.54 Example 3 Double electric layer / quasi-capacitive layer composite layer 9731234.23 Example 4 Double electric layer / quasi-capacitive layer composite layer 9251174.37 Example 5 Double electric layer / quasi-capacitive layer composite layer 8861124.82 Example 6 Double electric layer / quasi-capacitive layer composite layer 9091154.75 Example 7 Double electric layer / quasi-capacitive layer composite layer 8631094.66 Comparative example Double electric layer single layer 757.932.3

[0096] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A positive electrode, characterized in that It comprises a first electrode layer and a second electrode layer, wherein the first electrode layer is a double-layer electrode layer, and the second electrode layer is a pseudo-capacitive electrode layer.

2. The positive electrode according to claim 1, characterized in that The active material of the double-layer electrode layer is a three-dimensional porous carbon material; the three-dimensional porous carbon material is a carbon-containing material with a large specific surface area, and the specific surface area is 1000-3500m 2 / g, the three-dimensional porous carbon material is one or more of porous activated carbon, mesoporous carbon, and porous graphene.

3. The positive electrode according to claim 1, characterized in that The active material of the pseudo-capacitor electrode layer is a multinary lithium oxide material; the multinary lithium oxide material is at least two of nickel, manganese, titanium, iron, cobalt, and vanadium elements other than lithium; the molar content of lithium in the multinary lithium oxide is 20%-80%.

4. The positive electrode according to claim 1, characterized in that The first electrode layer contains chain conductive carbon black, including one or more of Ketjen black, superconducting acetylene black, and VulcanXC carbon black.

5. The positive electrode according to claim 1, characterized in that The first electrode layer also includes a fiberizable resin, which is one of polytetrafluoroethylene and modified polytetrafluoroethylene.

6. The positive electrode according to claim 1, characterized in that The second electrode layer contains a point-to-point conductive material, including one or both of Super P conductive carbon black and GS conductive carbon black.

7. The positive electrode according to claim 1, characterized in that The second electrode layer also includes a high molecular polymer material, which is polyvinylidene fluoride.

8. A method for preparing a positive electrode according to any one of claims 1 to 7, characterized in that: The steps include: Step 1: knead and mix the three-dimensional porous carbon material and the chain conductive carbon black in a cloth bag in a dry state for 5-10 minutes, then add them into deionized water containing a binder at one time, and stir at a high speed for 30-60 minutes to form a viscous slurry; Step 2: evenly apply the slurry to both sides of the aluminum foil current collector, and dry at 100° C. to form a first electrode layer; Step 3, dry-mix the multi-component lithium oxide, PtP conductive agent and binder in a cloth bag for 5-10 minutes, then add them into a solvent containing dimethylpyrrolidone (NMP) at one time, and stir at high speed for 60-90 minutes to form a viscous slurry; Step 4, evenly apply the slurry to both sides of the first electrode layer, and vacuum dry at 105° C. to form the second electrode layer; Step 5: Roll the electrode obtained in step 4 on a Cr plating roller press to a designed thickness to form a positive electrode.

9. A high specific capacitance, low self-discharge electrochemical capacitor, characterized in that: The invention comprises a shell, a separator, an electrolyte, a positive electrode and a negative electrode, wherein the positive electrode is the positive electrode prepared by the method according to claim 8.

10. The high specific capacitance, low self-discharge electrochemical capacitor of claim 9, characterized in that: The shell is one of a soft-package aluminum-plastic film, an aluminum shell or a steel shell.

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