WO2017190417A1 - Method for preparing thick and dense graphene-based electrode - Google Patents

Abstract

Disclosed is a method for preparing a thick and dense graphene-based electrode. The method comprises the following steps for the preparation of a graphene hydrogel, compounding of the graphene and a salt component, gas formation and removal of the salt component, and preparation of the thick and dense graphene-based electrode. According to the method, a three-dimensional porous graphene block material is prepared by using the pore-forming effect of a gas-forming salt on a graphene network during heating. Compared with other pore-forming methods, the gas-forming salt does not etch the graphene during heating, the yield of the resulting graphene is high, and the method is suitable for mass production of porous graphene materials; the gas generated after heating is removed, and therefore, the resulting graphene has few impurities and a high purity; a small quantity of the remaining impurities occupy the pores of the graphene, and a secondary pore-forming effect is achieved on the graphene network after washing. The graphene is of a three-dimensional formed block structure and can be directly applied to an electrode material, the electrode has a higher thickness and a larger density, and the processing step of preparing an electrode from powdery graphene is also avoided.

Description

Method for preparing graphene-based thick and dense electrode Technical field

The invention relates to a preparation method and application of a "high-thickness" and "high-density" electrode based on graphene, and belongs to the technical field of graphene.

Background technique

Graphene is a sp ² hybrid single-layer carbon atom crystal having a two-dimensional honeycomb lattice structure, which is an uneven, wrinkled two-dimensional crystal and is considered as a unit unit for constructing other sp ² carbonaceous materials. The excellent electrical, thermal, mechanical and optical properties of graphene have caused people's research boom in recent years.

Graphene materials have great advantages in the field of electrochemical energy storage due to their microscopic nanometer scale, high activity specific surface area, high reactivity and high electrochemical capacity. Although the graphene material itself has a high energy density, the performance of the graphene-based energy storage device is not satisfactory, and the energy density of the entire device is still at a low level. This is because the energy storage device not only includes the electrode active material, but also includes the current collector, the electrolyte, the separator, the binder, and the package casing. The lower the active layer quality of the graphene electrode material, so that the electrode active material accounts for the device. The proportion is very low, making the device's energy density difficult to exceed current levels. Therefore, designing a thick electrode based on graphene and increasing the specific gravity of the active material in the energy storage device is the key to improving the energy density of the energy storage device.

At present, the discussion of graphene electrode materials mostly focuses on the mass specific capacity characteristics (based on the capacity per unit mass of the electrode material, while ignoring the volume specific capacity caused by the lower density (in most cases 0.3 to 0.5 g·cm ^-3 )). (Based on the capacity per unit volume), the volumetric energy density of the energy storage device is very low. Therefore, the densification of the graphene electrode material and the increase of the density of the graphene electrode are the key to improving the energy density of the energy storage device.

Through the above analysis, the graphene electrode should not only be "thick" but also "tight": design graphite The alkenyl thick electrode, which has the advantage of high electrochemical activity of the graphene material in a limited device volume, is an important way to increase the energy density of the energy storage device. However, excessively thick and too dense electrodes can cause agglomeration of the graphene material itself and hinder ion transport during charge and discharge. That is to say, electrolyte ions are difficult to enter the inside of the thick electrode during charging and discharging, resulting in low utilization of the electrode material, low capacity and large polarization, which affects the energy output of the entire device. Therefore, the pore structure of the graphene-based thick-density electrode is optimized, and studying the electrochemical behavior of the electrolyte ions is of great significance for improving the volumetric energy density of the energy storage device.

In summary, through the design of the graphene electrode material, the pore structure of the electrode is optimized, and the thickness and density of the electrode are taken into consideration, and the mode of transport of the electrolyte ions in the thick electrode during charging and discharging is optimized to solve the energy density in the device application. The problem has important theoretical research value and practical application significance.

Summary of the invention

The problem to be solved by the present invention is the technical problem that the graphene electrode material is easy to agglomerate, the electrolyte ions are blocked in the thick electrode, and the volume energy density of the electrochemical energy storage device is low. Based on this, the present invention provides a method for preparing a once-formed graphene-based thick-dense electrode, which optimizes the electrochemical transport of electrolyte ions in a thick electrode by adjusting the pore, thickness and density of the electrode, and improves the energy of the energy storage device. density.

A method for preparing a graphene-based thick-density electrode comprises the following steps:

Step 1: Preparation of graphene hydrogel: reducing the graphene derivative solution to obtain a graphene hydrogel having a three-dimensional structure;

Graphene hydrogel has a three-dimensional structure of porous channels, which is beneficial to the transfer of electrons and the storage and transport of electrolyte ions.

Step 2: Composite of graphene and salt component: the graphene hydrogel prepared in the first step is immersed in a salt solution having a concentration of c, and statically adsorbed for t hours, and then the graphene hydrogel is taken out and dried to obtain graphite. a complex of an alkene and a salt component;

The graphene hydrogel has a strong liquid phase adsorption capacity, which is favorable for the loading of the salt component on the graphene sheet. Static adsorption also reduces energy consumption during the compounding of salt components with graphene.

Step 3: Gas production of salt component: The composite of graphene and salt component is placed in an oxygen-deficient atmosphere or a reducing atmosphere, heat-treated at a temperature T ₁ , taken out and repeatedly washed and purified with a washing solvent to obtain a three-dimensional graphite. Alkene block material;

Step 4: Preparation of a graphene-based thick-density electrode: directly cutting the three-dimensional graphene block obtained in the third step into an electrode material having a diameter d, a thickness h, and a density ρ;

The salt described in the second step is a salt which generates a gas at a temperature T ₀ and T ₁ ≥ T ₀ .

The method can realize the precise regulation of the pore structure of the graphene bulk material on the three-dimensional scale by using the hydrogel and utilizing the impact on the three-dimensional pore structure during the gas production process of the salt. Therefore, as an electrode, the graphene material can realize efficient storage and rapid transport of ions, and has higher capacity and excellent rate characteristics.

The invention utilizes the pore-forming effect of gas-producing salts on graphene during heating to prepare a three-dimensional porous graphene bulk material. Different from other pore-forming methods, the method starts from graphene hydrogel, and the gas-producing salt does not etch with graphene during heating, and the impact of gas on graphene sheets is utilized.

The obtained graphene has high yield and uniform pores, and is suitable for mass production of porous graphene materials; gas generated after heating is released, and the obtained graphene has less impurities and high purity; Impurities occupy the pores of graphene, and after cleaning, the effect of secondary pore formation on graphene is achieved. Compared with other porous graphenes, the graphene is a three-dimensional shaped bulk structure, which can be directly applied to an electrode material, the electrode has a large thickness and density, and the processing steps of preparing the electrode from the powder graphene are avoided, and Due to its high surface area, it has a high capacity, and because of its three-dimensional controllable structure, it also has good fast charge and discharge characteristics.

In summary, the beneficial effects of the present invention are:

(A) The present invention provides a method for preparing a graphene-based thick-density electrode, and innovatively proposes a gas-generating salt-generating gas to control the microstructure of the graphene material. The graphene material prepared by the method has high yield and large density, and is a formed bulk material, which is free from preparation and processing of the electrode material, and the material can be directly applied to the electrode.

(2) The method can achieve precise regulation of the thickness, density, porosity and specific surface area of the formed graphene block electrode in a large range.

(3) The graphene-based thick-density electrode provided by the invention realizes densification of the electrode material, and greatly increases the thickness of the electrode by adjusting the pore structure of the electrode, thereby effectively solving the low density and thickness of the graphene electrode material. problem. The electrode material can be directly applied to an electrochemical energy storage device, effectively increasing the volume energy density of the device.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the graphene derivative described in the first step is at least one selected from the group consisting of graphene oxide, modified graphene, and porous graphene.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the reduction treatment according to the first step comprises: hydrothermal reduction or chemical reduction, and the reducing agent used for chemical reduction is used. At least one of hydrazine hydrate, urea, thiourea, hydroiodic acid, sodium citrate, and sodium hydrogen sulfite is included.

An improved method for preparing the alkenyl groups of the present invention the graphite electrode is thick and dense, the salt of step II is at a temperature T ₀ sublimable salts or / and salts of the decomposed gas generated at the temperature T _0.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the salt which can be sublimed at the temperature T ₀ includes: potassium chloride, potassium bromide, sodium chloride, sodium bromide, calcium chloride, chlorination. Ferrous, ferrous nitrate, ferrous sulfate, ferric chloride, ferric nitrate, ferric sulfate, zinc chloride, zinc nitrate, zinc sulfate, barium chloride, barium nitrate, silver nitrate, copper chloride, copper nitrate, copper sulfate At least one of magnesium chloride and magnesium nitrate.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the salt which can be decomposed to generate gas at temperature T ₀ includes: calcium carbonate, iron carbonate, barium carbonate, silver carbonate, copper carbonate, sodium hydrogencarbonate, carbonic acid. At least one of potassium hydrogen, ammonium nitrate, ammonium chloride, and ammonium sulfate.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the solvent used in the salt solution described in the second step is water, ethanol, benzene, toluene, acetone, diethyl ether, dioxane, tetrahydrofuran, N-methyl. At least one of pyrrolidone, liquid ammonia, carbon disulfide, carbon tetrachloride, chloroform, inorganic acid, and liquid ammonia.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the concentration c of the salt solution described in the second step is 0.01M-10M, and the adsorption time t is 0.01h-48h.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the anoxic atmosphere described in the third step includes at least one of nitrogen, argon and helium, and the reducing atmosphere includes ammonia, hydrogen and carbon monoxide. At least one of them.

As an improvement of the preparation method of the graphene-based thick-density electrode of the present invention, the electrode material described in the fourth step has a diameter of 0.2 cm ≤ d ≤ 10 cm, a thickness of 10 μm ≤ h ≤ 6 mm, and a density of 0.2 g·cm ^-3 ≤ ρ. ≤1.6g·cm ^-3 .

DRAWINGS

1 is a scanning electron microscope picture of a three-dimensional graphene bulk material prepared in Example 1;

2 is a nitrogen adsorption desorption isotherm (77K) of the graphene electrode prepared in Example 1;

3 is a graph showing the charge and discharge curves of the graphene electrode prepared in Example 1 under an ionic liquid system.

detailed description

The invention provides a preparation method of a graphene-based thick-density electrode, which comprises the following steps:

(1) Preparation of graphene hydrogel

It can be understood that in order to make the graphene sheet layer more fully overlapped and crosslinked into a three-dimensional structure, the selected graphene derivative is selected from at least one of graphene oxide, modified graphene, and porous graphene.

In the embodiment of the invention, graphene oxide is preferred.

The reduction method includes hydrothermal reduction, chemical reduction, and the chemical reducing agent used includes at least one of hydrazine hydrate, urea, thiourea, hydroiodic acid, sodium citrate, and sodium hydrogen sulfite.

In an embodiment of the invention, hydrothermal reduction is preferred in the reduction process.

(2) Composite of graphene and salt components

Salt component should be selected to produce a salt in the gas temperature T _0, temperature T ₀ is divided into at sublimable salts and salts of the decomposed gas generated at the temperature T _0.

In an embodiment of the invention, the salt component is preferably one of zinc chloride, magnesium chloride, and zinc nitrate.

The solvent in the salt solution is water, ethanol, benzene, toluene, acetone, diethyl ether, dioxoperane, tetrahydrofuran, N-methylpyrrolidone, liquid ammonia, carbon disulfide, carbon tetrachloride, chloroform, inorganic acid, liquid ammonia. At least one of them.

In an embodiment of the invention, the solvent of the salt solution is preferably water.

The salt solution concentration c is 0.01M-10M, and the soaking time t is 0.01h-48h. It can be understood that the concentration of the salt solution is too large or the immersion time is too long, and the gas generated by the salt component enhances the pore-forming effect of the three-dimensional graphene block, thereby causing a decrease in electrode density, which is disadvantageous for high-volume energy density energy storage. . Similarly, the concentration of the salt solution is too small or the soaking time is too short, and the gas generated by the salt component has a weak pore-forming effect on the three-dimensional graphene block, and the specific capacity of the electrode is low.

In an embodiment of the invention, it is preferred that the salt solution has a concentration of 0.5 M and a soaking time of 12 h.

(3) Gas production of salt components

The heated anoxic atmosphere includes at least one of nitrogen, argon, and helium. The reducing atmosphere includes at least one of ammonia gas, hydrogen gas, and carbon monoxide.

In the embodiment of the present invention, one of argon gas, nitrogen gas, and ammonia gas is preferred.

It can be understood that in order to utilize the interaction between the gas generated by the salt and the graphene sheet layer, the pore structure of the graphene block is regulated, and the heating temperature T ₁ ≥ T ₀ .

(4) Preparation of graphene-based thick and dense electrode

The electrode material has a diameter of 0.2 cm ≤ d ≤ 10 cm, a thickness of 10 μm ≤ h ≤ 6 mm, and a density of 0.2 g·cm ^-3 ≤ ρ ≤ 1.6 g·cm ^-3 . It can be understood that the thickness of the electrode material is too large or the density is too large, which hinders the transmission of electrolyte ions during charging and discharging of the device, and reduces the specific capacity of the material; and if the thickness of the electrode material is too small or the density is too small, the active material is lowered in the device. The volumetric specific gravity reduces the volumetric energy density of the device.

In the embodiment of the present invention, it is preferred that the electrode material has a diameter of 0.4 cm, a thickness of 400 μm, and a density of 0.87 g·cm ^-3 .

To further disclose the technical solution of the present invention, a number of more specific embodiments are provided below:

Example 1:

(1) Preparation of graphene hydrogel

170 mg of the graphite oxide powder material prepared by the modified Hummer method was weighed, added to 85 mL of deionized water, and ultrasonically dispersed at 200 W for 2 h to obtain a 2 mg·mL ^-1 graphene oxide hydrosol. The above hydrosol was placed in a 100 mL hydrothermal kettle and heated at 180 ° C for 6 h; after cooling in the hydrothermal kettle, the aqueous phase was poured out to obtain a hydrothermally reduced graphene hydrogel.

(2) Composite of graphene and salt components

The above graphene hydrogel was immersed in 20 mL of 0.5 M zinc chloride aqueous solution for 12 h, and then the graphene hydrogel was taken out. At this time, zinc chloride was adsorbed on the graphene sheet layer of the hydrogel, and the graphene was hydrogelated. The gel was dried under vacuum at 70 ° C for 24 h to obtain a zinc chloride and graphene composite.

(3) The salt component generates a gas to regulate the pore structure of the graphene block

Thereafter, the zinc chloride and the graphene composite were placed in a heating furnace, heated at 600 ° C for 1 h in an argon atmosphere, taken out, and repeatedly washed and purified with dilute hydrochloric acid to obtain a three-dimensional graphene bulk material.

(4) Preparation of graphene-based thick and dense electrode

The graphene bulk material was cut, and the thickness of the control electrode was 400 μm, at which time the electrode material diameter was 0.4 cm.

Scanning electron micrograph of the three-dimensional graphene bulk material prepared in Example 1 is shown in FIG. 1. The nitrogen adsorption desorption isotherm (77K) of the graphene electrode prepared in Example 1 is as shown in FIG. 2, and the preparation of Example 1 is as shown in FIG. The charge and discharge curves of the graphene electrode in the ionic liquid system are shown in Fig. 3.

Example 2: The concentration of the zinc chloride aqueous solution in Example 1 was adjusted to 0.1 M, and the rest was the same as in Example 1.

Example 3: The concentration of the zinc chloride aqueous solution in Example 1 was adjusted to 1 M, and the rest was the same as in Example 1.

Example 4: The concentration of the zinc chloride aqueous solution in Example 1 was adjusted to 2 M, and the rest was the same as in Example 1.

Example 5: The concentration of the zinc chloride aqueous solution in Example 1 was adjusted to 4 M, and the rest was the same as in Example 1.

Comparative Example 1: The concentration of the zinc chloride aqueous solution in Example 1 was adjusted to 0 M, and the rest was the same as in Example 1.

Capacitance performance test:

The graphene-based thick-density electrodes prepared in Examples 1-5 and the comparative examples were pressed on a current collector stainless steel mesh, and two were carried out under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. Electrode test. The concentration of the zinc chloride aqueous solution, the density of the electrode, and the mass specific capacity and volume specific capacitance of the electrode are shown in Table 1.

Table I

As shown in Table 1: The concentration of zinc chloride solution has a great influence on the density of the electrode. The volume ratio of the final graphene electrode has a great influence. When the concentration of the solution is too low, the pore structure of the electrode is not rich, which is not conducive to the transport of electrolyte ions. The volumetric specific capacitance is low; when the concentration of the solution is too high, the pore-forming effect of zinc chloride on the graphene electrode is too strong, resulting in a low electrode density, resulting in a lower volume specific capacitance. From the above investigation, we found that the concentration of the salt component has a great influence on the capacity of the graphene-based thick-density electrode.

Example 6: The graphene hydrogel soaking time in Example 1 was adjusted to 1 h, and the rest was the same as in Example 1.

Example 7: The graphene hydrogel soaking time in Example 1 was adjusted to 5 h, and the rest was the same as in Example 1.

Example 8: The graphene hydrogel soaking time in Example 1 was adjusted to 18 h, and the rest was the same as in Example 1.

Example 9: The graphene hydrogel soaking time in Example 1 was adjusted to 24 h, and the rest was the same as in Example 1.

Capacitance performance test:

The graphene-based thick-density electrodes prepared in Examples 1, 6-9 and the comparative examples were pressed on a collector stainless steel mesh under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. Perform a two-electrode test. The soaking time of the graphene hydrogel, the density of the electrode, and the mass specific capacity and volume specific capacitance of the electrode are shown in Table 2.

Table II

As shown in Table 2: the soaking time of the graphene hydrogel has a great influence on the density of the electrode and the volumetric capacitance of the final graphene electrode. When the soaking time is too short, the salt component is negative. Insufficient load, the subsequent pore-forming effect is not obvious, and the void structure inside the electrode is not conducive to the transport of electrolyte ions, resulting in a lower volume specific capacitance; when the soaking time is too long, the zinc chloride on the graphene electrode during heating The pore-forming effect is too strong, resulting in a lower electrode density, resulting in a lower volumetric capacitance. Through the above investigation, we found that the immersion time of the graphene hydrogel also has a great influence on the capacity of the graphene-based thick-density electrode.

Example 10: The heating temperature of the graphene and zinc chloride composite in Example 1 was adjusted to 400 ° C, and the rest was the same as in Example 1.

Example 11: The heating temperature of the graphene and zinc chloride complex in Example 1 was adjusted to 500 ° C, and the rest was the same as in Example 1.

Example 12: The heating temperature of the graphene and zinc chloride composite in Example 1 was adjusted to 700 ° C, and the rest was the same as in Example 1.

Example 13: The heating temperature of the graphene and zinc chloride composite in Example 1 was adjusted to 800 ° C, and the rest was the same as in Example 1.

Capacitance performance test:

The graphene-based thick-density electrode prepared in Examples 1, 10-13 was pressed on a current collector stainless steel mesh, and two electrodes were carried out under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. test. The heating temperature of the graphene and zinc chloride complex, the density of the electrode, and the mass specific capacity and volume specific capacitance of the electrode are shown in Table 3.

Table 3

As shown in Table 3: The heating temperature of the graphene and zinc chloride complex has a great influence on the density of the electrode and the volume specific capacitance of the final graphene electrode. When the heating temperature is too low, zinc chloride does not volatilize and remains in the form of a solid in the pores of the three-dimensional graphene, and has almost no pore-forming effect, resulting in a lower mass-to-capacity ratio and volume specific capacity of the final electrode; When the temperature is too high, the evaporation rate of zinc chloride is too fast, and the pore-forming effect on graphene is too strong, resulting in a decrease in electrode density, resulting in a lower volume ratio capacitance. From the above investigation, we found that the heating temperature of the graphene and salt component complex also has a great influence on the capacity of the graphene-based thick-density electrode.

Example 14: The zinc chloride aqueous solution of Example 1 was adjusted to a zinc nitrate aqueous solution, and the heating temperature was lowered to 200 ° C, and the rest was the same as in Example 1.

Example 15: The zinc chloride aqueous solution of Example 1 was adjusted to a magnesium chloride aqueous solution, and the heating temperature was lowered to 500 ° C, and the rest was the same as in Example 1.

Example 16: The aqueous zinc chloride solution of Example 1 was adjusted to an aqueous solution of copper chloride, and the heating temperature was raised to 800 ° C, and the rest was the same as in Example 1.

Capacitance performance test:

The graphene-based thick-density electrodes prepared in Examples 1, 14-16 and the comparative examples were pressed on a collector stainless steel mesh under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. Perform a two-electrode test. The composition of the solute in the salt solution, the density of the electrode, and the mass specific capacity and volume specific capacitance of the electrode are shown in Table 4.

Table 4

As shown in Table 4: different salt components are compounded with graphene, and the pore structure of the three-dimensional graphene block can also be regulated by adjusting the heat treatment temperature of the heated gas. For example, zinc nitrate and magnesium chloride are easily decomposed by heat. From the viewpoint of reducing energy consumption, we should lower the heat treatment temperature to achieve the effect of adjusting the microstructure of the graphene material. Copper chloride is relatively stable in heat and has a high boiling point. Therefore, we need to increase the heat treatment temperature to achieve the purpose of regulating the structure of graphene materials. The above investigations show that the effect of regulating the pore structure of the graphene electrode is achieved by the heated gas produced by the salt, which has great universality.

Example 17: The cut thickness of the graphene electrode in Example 1 was adjusted to 100 μm, and the rest was the same as in Example 1.

Example 18: The cut thickness of the graphene electrode in Example 1 was adjusted to 200 μm, and the rest was the same as in Example 1.

Example 19: The cut thickness of the graphene electrode in Example 1 was adjusted to 300 μm, and the rest was the same as in Example 1.

Example 20: The cut thickness of the graphene electrode in Example 1 was adjusted to 600 μm, and the rest was the same as in Example 1.

Example 21: The cut thickness of the graphene electrode in Example 1 was adjusted to 800 μm, and the rest was the same as in Example 1.

Capacitance performance test:

The graphene-based thick-density electrode prepared in Examples 1, 14-18 was pressed on a current collector stainless steel mesh, and two electrodes were carried out under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. test. The thickness of the graphene electrode, the mass specific capacity and the volume specific capacitance of the electrode, and the volumetric energy density of the device are shown in Table 5.

Table 5

As shown in Table 5, the thickness of the graphene electrode has a great influence on the mass specific capacity, the volume specific capacity, and the volume energy density of the device. When the electrode is too thin, the electrode has a higher mass specific capacity and volume specific capacity due to the smoother ion transport and storage, but the too thin electrode causes the electrode active material to have a low occupancy rate in the entire device, and the folded device The volumetric energy density is low; when the electrode is too thick, the electrolyte ions are difficult to pass through. The specific capacity of the electrodes is very low, which also leads to a lower volumetric energy density of the device. Through the above investigation, we found that the thickness of the graphene electrode has a great influence on the volumetric energy density of the device. Finding the thickness of the electrode is the key to increasing the volumetric energy density of the device.

Example 22: The zinc chloride aqueous solution in Example 1 was adjusted to an aqueous potassium hydroxide solution, and the obtained graphene and the conductive carbon black and the binder were made into an electrode at a mass ratio of 8:1:1, and the rest were the same as in Example 1. .

Example 23: The zinc chloride aqueous solution of Example 1 was adjusted to an aqueous sodium carbonate solution, and the obtained graphene and the conductive carbon black and the binder were formed into an electrode at a mass ratio of 8:1:1, and the rest were the same as in Example 1.

Capacitance performance test:

The graphene-based thick-density electrode prepared in Examples 1, 22, and 23 was pressed on a current collector stainless steel mesh to carry out two electrodes under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. test. The yield of the porous graphene, the specific surface area of the graphene, the volume specific capacitance of the electrode, and the capacity retention ratio of the electrode material at a large current are shown in Table 6.

Table 6

As shown in Table 6, the etched bases and salts (potassium hydroxide and sodium carbonate in Examples 22 and 23) reacted significantly with graphene during heating, as compared to the gassable salt. Caused a decrease in the yield of graphene, this method is not suitable for a large number of graphene materials Volume production. In addition, due to the strong etching action, the graphene block can not maintain its bulk structure, the density is greatly reduced, but the specific surface area is not significantly improved, so its volumetric specific capacitance is small. In addition, in addition, the graphene material prepared by the etchant requires an electrode preparation process and cannot maintain its three-dimensional structure, so that poor rate performance is exhibited. From the above analysis, we can conclude that compared with the etchant, the gas-forming salt can make the pore-forming effect of graphene more obvious, and the obtained product has higher yield, larger density and superior rate characteristics.

Example 24: The three-dimensional hydrogel precursor in Example 1 was adjusted to a two-dimensional graphene sheet, and a two-dimensional graphene material was prepared by compounding a gas salt with graphene, and the obtained graphene and conductive carbon black were adhered. The junction was made into an electrode at a mass ratio of 8:1:1, and the rest was the same as in Example 1. Capacitance performance test:

The graphene-based thick-density electrodes prepared in Examples 1 and 24 were pressed against a current collector stainless steel mesh, and subjected to a two-electrode test under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. The density of the porous graphene, the specific surface area of the graphene, the volume specific capacitance of the electrode, and the capacity retention ratio of the electrode material at a large current are shown in Table 7.

Table 7

As shown in Table 7, the graphene precursor was adjusted to a sheet of two-dimensional graphene, and the obtained porous graphene was a lamellar graphene, which was a powder graphene, which was light in density and small in volumetric capacity. By introducing a three-dimensional graphene hydrogel, the density of the electrode is significantly improved, and High volume capacity and capacity retention at high rates. From the above analysis, we can get: Compared with the two-dimensional graphene sheet, the three-dimensional graphene hydrogel is used as the precursor, and the obtained product can maintain the bulk morphology, the density is high, the volume specific capacity is high, and the high ratio is high. The capacity retention rate is high.

Example 25: The cleaning solvent in Example 1 was adjusted to deionized water, and the rest was the same as in Example 1.

Example 26: The mixture after the heat treatment in Example 1 was washed without using a washing solvent, and was directly applied to the electrode material, and the rest was the same as in Example 1.

The graphene-based thick-density electrode prepared in Examples 1, 25, and 26 was pressed on a current collector stainless steel mesh, and subjected to two-electrode test under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. . The density of the obtained graphene material, the specific surface area of graphene, the volume specific capacitance of the electrode, and the capacity retention ratio of the electrode material at a large current are shown in Table 8.

Table eight

As shown in Table 8, the heat-treated mixture was washed with dilute hydrochloric acid and deionized water, respectively, in comparison with the unwashed material, and it can be seen that the step of washing has a secondary pore-forming effect on the graphene material. The cleaning process can increase the specific surface of the electrode material, increase the pore structure of the material, and further improve the electrochemical performance of the electrode.

Example 27: The graphite oxide powder in Example 1 was adjusted to nitrogen-doped graphene, and the rest was the same as in Example 1.

Example 28: The graphite oxide powder in Example 1 was adjusted to porous graphene, and the rest was the same as in Example 1.

The graphene-based thick-density electrode prepared in Examples 1, 27, and 28 was pressed on a current collector stainless steel mesh to perform two-electrode test under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. . The density of the obtained graphene material, the specific surface area of graphene, the volume specific capacitance of the electrode, and the capacity retention ratio of the electrode material at a large current are shown in Table IX.

Table 9

As shown in Table 9, the graphene raw material before hydrothermal reduction is adjusted to modified graphene (nitrogen-doped graphene) and porous graphene, and the obtained electrode material also has a high capacitance value under high current charge and discharge. Has a high capacity retention rate. The method can also be applied to the regulation of three-dimensional pore structure based on precursors of different graphene derivatives, and has certain universality.

Example 29: The hydrothermal reduction in the process of preparing the graphene hydrogel in Example 1 was adjusted to be reduced by urea, and the rest was the same as in Example 1.

Example 30: The hydrothermal reduction in the process of preparing the graphene hydrogel in Example 1 was adjusted to be reduced with sodium hydrogen sulfite, and the rest was the same as in Example 1.

Example 31: The hydrothermal reduction in the process of preparing the graphene hydrogel in Example 1 was adjusted to be reduced with hydroiodic acid, and the rest was the same as in Example 1.

The graphene-based thick-density electrode prepared in Example 1, 29-31 was pressed on a current collector stainless steel mesh and subjected to two-electrode test under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. . The density of the obtained graphene material, the specific surface area of graphene, the volume specific capacitance of the electrode, and the capacity retention ratio of the electrode material are shown in Table 10.

Table ten

As shown in Table 10, the graphene oxide dispersion liquid prepared by the above method has a high capacitance value and excellent rate characteristics in a different reduction form (hydrothermal reduction, reduction of a reducing agent). Therefore, our proposed method of pore regulation is also feasible for three-dimensional graphene hydrogels prepared by different reduction methods.

Example 32: The heating atmosphere in Example 1 was adjusted to nitrogen gas, and the rest was the same as in Example 1.

Example 33: The heating atmosphere in Example 1 was adjusted to ammonia gas, and the rest was the same as in Example 1.

The graphene-based thick-density electrode prepared in Example 1, 30, 31 was pressed on a current collector stainless steel mesh, and subjected to two-electrode test under an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) system. . The density of the obtained graphene material, the specific surface area of graphene, the volume specific capacitance of the electrode, and the capacity retention ratio of the electrode material at a large current are shown in Table 11.

Table XI

As shown in Table 11, the inert atmosphere and the reducing atmosphere in the heat treatment process have little effect on the obtained graphene material, and the electrode materials all exhibit high capacitance values and excellent rate characteristics. Therefore, the method for controlling the pore size of the graphene material has certain universality for different heat treatment atmospheres.

Taking the supercapacitor electrode material as an example, Table 8 lists the mass ratio capacitance, volume ratio capacitance, electrolyte system, electrode thickness, and volume energy density of the device, as shown in Table 12.

Table 12

Table 8 shows a comparison of specific capacitance values, electrode thicknesses, and device volume energy densities of the graphene-based thick-density electrode prepared in Example 1 of the present invention and a portion of the reported electrode material. It can be seen from the above table that the graphene-based thick-density electrode prepared by the method proposed in the present invention can achieve a very high electrode thickness of 400 μm and has a high volumetric energy density, which is much higher than the above. Electrode material. Therefore, the method for regulating the pore structure of the three-dimensional graphene bulk material by the gas production of the salt component proposed by the present invention, thereby realizing the controllable preparation of the graphene-based thick-density electrode, is remarkable in the field of high-volume energy density energy storage. Application prospects,

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments, and the above embodiments are merely for explaining the claims. However, the scope of protection of the present invention is not limited to the description. Any changes or substitutions that are easily conceivable within the scope of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A method for preparing a graphene-based thick-density electrode, comprising the steps of:

   Step 1: Preparation of graphene hydrogel: reducing the graphene derivative solution to obtain a graphene hydrogel having a three-dimensional structure;

   Step 2: Composite of graphene and salt component: the graphene hydrogel prepared in the first step is immersed in a salt solution having a concentration of c, and statically adsorbed for t hours, and then the graphene hydrogel is taken out and dried to obtain graphite. a complex of an alkene and a salt component;

   Step 3: Gas production of salt component: The composite of graphene and salt component is placed in an oxygen-deficient atmosphere or a reducing atmosphere, heat-treated at a temperature T ₁ , taken out and repeatedly washed and purified with a washing solvent to obtain a three-dimensional graphite. Alkene block material;

   Step 4: Preparation of a graphene-based thick-density electrode: directly cutting the three-dimensional graphene block obtained in the third step into an electrode material having a diameter d, a thickness h, and a density ρ;

   The salt described in the second step is a salt which generates a gas at a temperature T ₀ and T ₁ ≥ T ₀ .
2. The method for preparing a graphene-based thick-density electrode according to claim 1, wherein the graphene derivative in the first step is at least one selected from the group consisting of graphene oxide, modified graphene and porous graphene. .
3. The method for preparing a graphene-based thick-density electrode according to claim 1, wherein the reduction treatment according to step 1 comprises: hydrothermal reduction or chemical reduction, and the reducing agent for chemical reduction used comprises (hydrazine hydrate, urea). At least one of thiourea, hydroiodic acid, sodium citrate and sodium hydrogen sulfite).
4. The method for preparing dense and thick graphene electrode according to claim 1, wherein: said step II salt is at a temperature T ₀ sublimable salts and / or decomposed generate a gas at the temperature T ₀ Salt.
5. The method for preparing a graphene-based thick-density electrode according to claim 4, wherein the salt which can be sublimed at a temperature T ₀ comprises potassium chloride, potassium bromide, sodium chloride, sodium bromide, and chlorination. Calcium, ferrous chloride, ferrous nitrate, ferrous sulfate, ferric chloride, ferric nitrate, ferric sulfate, zinc chloride, zinc nitrate, zinc sulfate, barium chloride, barium nitrate, silver nitrate, copper chloride, nitric acid At least one of copper, copper sulfate, magnesium chloride, and magnesium nitrate.
6. The method for preparing a graphene-based thick-density electrode according to claim 4, wherein the salt which can be decomposed to generate gas at a temperature T ₀ comprises: calcium carbonate, iron carbonate, barium carbonate, silver carbonate, copper carbonate, carbonic acid. At least one of sodium hydrogen, potassium hydrogencarbonate, ammonium nitrate, ammonium chloride, and ammonium sulfate.
7. The method for preparing a graphene-based thick-density electrode according to claim 1, wherein the solvent used in the salt solution in the second step is water, ethanol, benzene, toluene, acetone, diethyl ether, dioxane, At least one of tetrahydrofuran, N-methylpyrrolidone, liquid ammonia, carbon disulfide, carbon tetrachloride, chloroform, inorganic acid, and liquid ammonia.
8. The method for preparing a graphene-based thick-density electrode according to claim 1, wherein the concentration c of the salt solution in the second step is 0.01 M-10 M, and the adsorption time t is 0.01 h-48 h.
9. The method for preparing a graphene-based thick-density electrode according to claim 1, wherein the cleaning solvent in the third step comprises at least one of dilute hydrochloric acid or/and water; and the oxygen-deficient atmosphere described in the third step The at least one of nitrogen, argon, and helium is included, and the reducing atmosphere includes at least one of ammonia, hydrogen, and carbon monoxide.
10. The method for preparing a graphene-based thick-density electrode according to claim 1, wherein the electrode material in the fourth step has a diameter of 0.2 cm ≤ d ≤ 10 cm, and a density of 0.2 g·cm ^-3 ≤ ρ ≤ 1.6 g. · cm ^-3 , when the electrode thickness is 10 μm ≤ h ≤ 6 mm, the electrode ion transmission impedance is 0.1 Ω to 200 Ω.

Images