TW201914090A - Composite composition for electrodes and manufacturing method thereof - Google Patents

Abstract

Provided is a composite composition for electrodes and the manufacturing method thereof, wherein the manufacturing method comprises: modifying graphene and carbon nanotubes to bare opposite electrical charges; mix one of the graphene and the carbon nanotubes with a precursor of a redox active substance to form a mixture; and adding the other one of the graphene and the carbon nanotubes to the mixture at a predetermined rate to simultaneously perform self-assembly of the graphene and the carbon nanotubes and crystal growth of the redox active substance.

Description

Composite composition for electrode and manufacturing method thereof

The present invention relates to a composite composition for an electrode and a method for producing the same, and, in particular, to a composite composition for an electrode having a three-dimensional structure formed by self-assembly of graphene and a carbon nanotube, and a method for producing the same.

With the advancement of portable devices, the importance of providing batteries for carrying electrical energy is increasing, and in particular, secondary batteries capable of repeated charging and discharging have become the mainstream of current portable devices. However, compared with the advancement of other hardware devices and technologies in the portable device, the storage capacity of the secondary battery has not seen a significant breakthrough for a long time, and gradually fails to meet the demand for more and more complicated portable devices, affecting the high-end portable devices. Endurance has become an important technology that is urgently needed for improvement.

In general, the storage capacity of a secondary battery largely depends on the energy storage material used by the electrode. Therefore, how to develop an energy storage material having high storage capacity and low resistance has become one of the important topics in the field. In this regard, it is generally known that the method for producing an electrode is a slurry method, and the formulation thereof is mostly polyvinylidene difluoride (PVDF), N-methylpyrrolidone (NMP), carbon black, and redox active materials. A mixture in which carbon black and a redox active material are energy storage materials in an electrode, and PVDF and NMP serve as an adhesive and a solvent for the slurry, respectively.

In terms of improvement of energy storage materials, conventional carbon black has been replaced by an improved technical scheme of graphene or carbon nanotubes (CNT) which can improve conductivity and three-dimensional space. However, since the arrangement of the graphene or the carbon nanotubes and the redox active material itself is not directional in the conventional manufacturing method, the redox active material can only adhere to the surface of the graphene or carbon nanotube structure layer, The effect of improving the storage capacity of energy storage materials is still limited. On the other hand, in the slurry for fabricating electrodes, since PVDF and NMP have poor compatibility with water, it is difficult for KOH to be effective in the potassium hydroxide (KOH) aqueous solution which is used as an electrolyte in the battery system. The capacitive material (redox active material) contacts and reacts so as to affect the contact of the electrolyte with the electrode, resulting in lower battery performance.

In view of the above problems in the prior art, an object of the present invention is to provide a composite composition for an electrode having high storage capacity and low electrical resistance, a method for producing the same, and a composite composition for an electrode thereof, to solve the conventional secondary The problem of insufficient battery storage capacity and improved overall battery performance.

According to an aspect of the present invention, a method for producing a composite composition for an electrode, comprising the steps of: modifying a graphene and a carbon nanotube to have opposite charges; and the graphene and the One of the carbon nanotubes is mixed with the precursor of the redox active material to form a mixture; and the other of the graphene and the carbon nanotube is added to the mixture at a predetermined speed to simultaneously perform the graphite Self-assembly of an ene with the carbon nanotube and a growth reaction of the redox active material.

Preferably, a modifier selected for use in the upgrading step comprises a strong oxidizing agent, a surfactant, or a combination thereof.

Preferably, wherein the surfactant comprises a cationic surfactant or an anionic surfactant.

Preferably, the redox active material comprises A _x B _y O _z , A _x B _y S ₄ , A _x B _y F ₄ , AB hydroxide or AB hydrosulfide, wherein A and B are respectively selected Free manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lithium (Li), aluminum (Al), magnesium (Mg), antimony (Rb) A group of components; x and y are integers from 0 to 3 and are not 0 at all, and z is an integer from 1 to 4.

Preferably, wherein the predetermined speed ranges from 0.001 to 600 ml/min (the feed time is about 5 seconds to 10 hours).

According to another object of the present invention, there is provided a composite composition for an electrode which is produced by the above-described production method.

Preferably, the redox active material accounts for 50 to 95% by weight of the total solid content of the composite composition for the electrode, and the graphene and the carbon nanotubes account for the total solid content of the composite composition for the electrode. 5 to 50% by weight.

Preferably, the composite composition for the electrode has a three-dimensional structure in which a graphene layer and a carbon nanotube layer are alternately stacked with a plurality of layers, and the graphene layer and the carbon nanotube layer contain the redox activity. And a substance in which the redox active material and the graphene or the carbon nanotube are arranged in a disordered structure, and the graphene layer and the carbon nanotube layer are arranged in an ordered structure.

As described above, the composite composition for an electrode of the present invention and the method for producing the same can have one or more of the following advantages:

(1) By causing graphene and carbon nanotubes to have opposite positive and negative charges, when one of the solutions drops into the other, the positive and negative charges attract self-assembly and stack a layer of graphene. A three-dimensional structure composed of a plurality of layers of carbon nanotubes alternately stacking a plurality of layers can effectively reduce the electrical resistance of the material than a structure having no directionality in the prior art.

(2) Since the self-assembly of graphene and the carbon nanotubes and the long-crystal reaction of the redox active material are simultaneously performed in a single step, the redox active material can be embedded in the self-assembled three-dimensional structure instead of merely adhering On the surface of the three-dimensional structure, it can effectively disperse the redox active material and help electron conduction, and can increase the nickel-cobalt-oxygen specific capacitance to about 1649F/g (purity of nickel-cobalt oxygen is 521 F/g), and the series impedance can be lower than About 0.74 ohms (pure nickel cobalt oxide is 0.83 ohms).

The invention will now be described in greater detail with reference to the drawings. However, the embodiments described below are only used to enhance the understanding of those skilled in the art, and are not intended to limit the scope of the invention.

Referring to Fig. 1, there is shown a flow chart of a method for producing a composite composition for an electrode of the present invention. As shown in Fig. 1, the manufacturing method of the present invention first (S1) reforms graphene and carbon nanotubes to give opposite charges. In this step, the modifier used for the modification may comprise a strong oxidizing agent and any cationic or anionic surfactant, in order to make the graphene and the carbon nanotubes have positive and negative opposite charges, for example, concentrated sulfuric acid and the like. The oxidant treats the graphene to form a negatively charged graphene oxide, and the positive carbon nanotube is positively charged with a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) modified carbon nanotubes. .

After the modification is completed, (S2) a modified graphene and a carbon nanotube are mixed with a redox active material precursor to form a mixture; in this step, graphene and nanocarbon can be used. The tubes are individually formulated into a solution, and the desired redox active material precursor is mixed into one of the solutions to form a mixed solution, for example, a redox active material precursor is mixed with the graphene oxide solution. The redox active material used herein may include a compound represented by the general formula A _x B _y O _z , A _x B _y S ₄ , A _x B _y F ₄ , AB hydroxide or AB hydrosulfide, wherein A and B Can be selected from manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lithium (Li), aluminum (Al), magnesium (Mg), bismuth (Rb) is a group of components, and x and y are integers of 0 to 3 and are not 0 at the same time, and z is an integer of 1 to 4, for example, NiCo ₂ S ₄ .

Finally, (S3) the other of the graphene and the carbon nanotubes is added to the mixture at a predetermined rate to simultaneously perform self-assembly of the graphene and the carbon nanotubes and a crystal growth reaction of the redox active material. In this step, for example, a carbon nanotube solution is dropped into a mixed solution of a redox active material precursor and graphene oxide at a flow rate. At this time, since the oppositely charged graphene is in contact with the carbon nanotube for the first time, the graphene and the carbon nanotube are self-assembled by the action of the opposite charges attracting each other to form the composite composition for an electrode of the present invention. The basic skeleton, and the redox active material precursor also undergoes a long crystal reaction to cause the redox active material to adhere to the basic skeleton assembled by the graphene and the carbon nanotube. Therefore, the graphene can be made in a single step. The self-assembly of the carbon nanotubes and the long-crystal reaction of the redox active material are simultaneously performed, so that the redox active material can be embedded in the three-dimensional structure of the self-assembled basic skeleton, instead of merely adhering to the surface of the basic skeleton, which is effective. The redox active species are dispersed to aid in electron conduction.

Please refer to Fig. 2, which is an SEM image of the composite composition for an electrode produced by the above steps. In the example shown in Fig. 2, the weight ratio of graphene to carbon nanotubes was 3:1, which was formed by self-assembly and sedimentation in an aqueous solution.

As shown in the SEM image, the composite composition for an electrode of the present invention penetrates the self-assembly of graphene and a carbon nanotube to form a multilayer structure in which a plurality of layers of a graphene layer and a carbon nanotube layer are alternately stacked, plus The redox active material is dispersed and distributed in the surface of the graphene layer or the carbon nanotube layer, which can help the conduction and resistance of the electrons to decrease and improve the performance of the energy storage material.

The conventional pure nickel-cobalt oxygen composition is used as a comparative example to compare the electrochemical measurement results with the examples of the composite composition of the present invention.

Comparative Examples 1-3

Add 5 mmole Ni(NO ₃ ) ₂ 6H ₂ O, 10 mmole Ni(NO ₃ ) ₂ 6H ₂ O and 22.5 mmole of cyclohexamethylenetetramine to different ratios of deionized water/ethanol solution and stir until dissolved. The mixture was poured into a reaction flask and reacted at 90 ° C for 4 hours. The solution was sprayed on a foamed nickel substrate and dried in a vacuum oven. Comparative Examples 1 to 3 were deionized water (DL): ethanol solution (EtOH). The results of the electrochemical properties of the solutions having a weight ratio of 3:1 (Comparative Example 1), 5:1 (Comparative Example 2), and 8:1 (Comparative Example 3) are shown in Figs. 3 to 6 .

Examples 1 to 6

Add 5 mmole of Ni(NO ₃ ) ₂ 6H ₂ O, 10 mmole of Ni(NO ₃ ) ₂ 6H ₂ O, 22.5 mmole of cyclohexamethylenetetramine and graphene to a deionized water/ethanol solution (ratio 8:1) Stir evenly to dissolve to form a graphene mixture, and then pour into the reaction flask; then dispose of the carbon nanotube dispersion liquid, the carbon nanotube dispersion liquid is the weight of the carbon nanotubes and cetyltrimethylammonium bromide Add 1:1 water to a solution of deionized water/ethanol (ratio 8:1) until the solution is homogeneous. Add 40 ml of the carbon nanotube dispersion liquid to the above graphene mixture for 2-4 hours. After reacting for 4 hours at ° C, the solution was sprayed onto a foamed nickel substrate and dried in a vacuum oven. In each of the examples, the weight ratio of Ni(NO ₃ ) ₂ 6H ₂ O/Ni(NO ₃ ) ₂ 6H ₂ O to carbon material was fixed at 9:1, and the difference between Examples 1 and 6 was changed by graphene (GO): The weight ratio of carbon nanotubes (CNT) (1:3, 1:1, and 3:1) and the dropping time (2 hours, 4 hours), the electrochemical properties of which are shown in Fig. 7 to Fig. 13 .

For each of the above comparative examples and examples, the electrochemical characteristics were measured by a CHI 608 electrochemical workstation. The standard calomel electrode was used as a reference electrode, and the platinum electrode was used as an auxiliary electrode for cyclic voltammetry, constant current charge and discharge, and AC impedance analysis. And calculate the specific capacitance value using Equation 1: Where I is the current density i, Δt is the charge and discharge time, m is the sample quality, and ΔV is the voltage operating range.

The measurement results are shown in Fig. 3 to Fig. 13, respectively. Among them, in the 3rd to 5th, 7th to 12th, (a) is cyclic voltammetry (CV), and (b) is constant current charge and discharge method (CP). In Fig. 6 and Fig. 13, (a) is the impedance analysis (EIS) and (b) is the specific capacitance value calculated by CP.

Please refer to FIGS. 3 to 5 and 7 to 12, which are electrochemical measurement results of the above respective comparative examples and examples. It can be seen from Fig. 3 to Fig. 5(a) that the conventional composition has an oxidation and reduction peak at 0.3 to 0.45 V and 0 to 0.2 V, and is changed to the composite composition of the present invention, from the 7th to 12th ( a) It can be seen that the oxidation peak and the reduction peak are broad, the oxidation peak is about 0.2-0.45V, and the reduction peak is about -0.1~0.2V, which means that the composite composition of the invention has high reactivity and fully exhibits pseudo capacitance. Redox properties. Further, as can be seen from Fig. 6(a) and Fig. 13(a), at a constant current charge and discharge of 1 A/g, the specific capacitance value is increased from 521 F/g (conventional nickel-cobalt oxygen composition) to 1649 F. /g (composite composition of the present invention) has a growth rate of nearly three times.

On the other hand, from the impedance analysis of Figs. 4(a) and 7(a), the internal impedance of the conventional composition is about 0.83 Ω, and the composite composition of the present invention can be reduced to 0.74 Ω. The conventional composition is about 0.1 Ω lower, which also demonstrates that the composite composition of the present invention is more compatible than the conventional composition.

From the above results, it is understood that the composite composition for an electrode of the present invention can effectively increase the specific capacitance value of the nickel-cobalt oxygen battery and at the same time reduce the series resistance, and can greatly improve the storage capacity of the secondary battery.

Further, in the above embodiments, the graphene and the carbon nanotube are used as the conductive material of the composite composition, but the invention is not limited thereto. As is known to those skilled in the art, the above graphene and carbon nanotubes can also be replaced with other conductive materials such as activated carbon, conductive polymers, nanometals and their derivatives, or the like. A combination of two or more materials can also exert at least a part of the effects of the present invention.

The above is intended to be illustrative only and not limiting. Any equivalent modifications or alterations to the spirit and scope of the invention are intended to be included in the scope of the appended claims.

no.

Fig. 1 is a flow chart showing a method of producing a composite composition for an electrode of the present invention. Fig. 2 is an SEM image of the composite composition for an electrode of the present invention. Fig. 3 is a result of electrochemical measurement of a conventional pure nickel-cobalt oxygen composition (Comparative Example 1). Fig. 4 is an electrochemical measurement result of a conventional pure nickel-cobalt oxygen composition (Comparative Example 2). Fig. 5 is an electrochemical measurement result of a conventional pure nickel-cobalt oxygen composition (Comparative Example 3). Fig. 6 shows the results of impedance measurement and capacitance calculation of a conventional pure nickel-cobalt oxygen composition (Comparative Examples 1 to 3). Fig. 7 is a result of electrochemical measurement of the composite composition of the present invention (Example 1). Fig. 8 is a result of electrochemical measurement of the composite composition of the present invention (Example 2). Fig. 9 is a result of electrochemical measurement of the composite composition of the present invention (Example 3). Fig. 10 is a result of electrochemical measurement of the composite composition of the present invention (Example 4). Fig. 11 is a result of electrochemical measurement of the composite composition of the present invention (Example 5). Fig. 12 is a result of electrochemical measurement of the composite composition of the present invention (Example 6). Fig. 13 is a graph showing the results of impedance measurement and capacitance calculation of the composite composition (Examples 1 to 6) of the embodiment of the present invention.

Claims (8)

A method for producing a composite composition for an electrode, comprising the steps of: modifying a graphene and a carbon nanotube to have opposite charges; and combining the graphene with the carbon nanotube The redox active material precursor is mixed to form a mixture; and the other of the graphene and the carbon nanotube is added to the mixture at a predetermined rate to simultaneously perform the graphene and the carbon nanotube Self-assembly and long crystal reaction of the redox active material. The manufacturing method of claim 1, wherein the modifier used in the upgrading step comprises a strong oxidizing agent, a surfactant, or a combination thereof. The method of manufacture of claim 2, wherein the surfactant comprises a cationic surfactant or an anionic surfactant. The manufacturing method according to claim 1, wherein the redox active material comprises A _x B _y O _z , A _x B _y S ₄ , A _x B _y F ₄ , AB hydroxide or AB hydrosulfide. And A and B are each selected from the group consisting of manganese, iron, cobalt, nickel, copper, zinc, lithium, aluminum, magnesium and strontium; x and y are integers of 0 to 3 and are not simultaneously It is 0, and z is an integer of 1-4. The manufacturing method according to claim 1, wherein the predetermined speed ranges from 0.001 to 600 ml/min. A composite composition for an electrode, which is produced by the production method according to any one of claims 1 to 5. The composite composition for an electrode according to claim 6, wherein the redox active material accounts for 50 to 95% by weight of the total solid content of the composite composition for the electrode, and the graphene and the carbon nanotube occupy The electrode is used in the composite composition in an amount of 5 to 50% by weight based on the total solid content. The composite composition for an electrode according to claim 6, wherein the composite composition for the electrode has a three-dimensional structure in which a graphene layer and a carbon nanotube layer are alternately stacked with a plurality of layers, the graphene layer and The carbon nanotube layer contains the redox active material, wherein the redox active material and the graphene or the carbon nanotube are arranged in a disordered structure, and the graphene layer and the carbon nanotube layer are arranged. It is an ordered structure.