CN104201438B - A kind of lithium-air battery based on graphene oxide-carbon paper gas catalysis electrode - Google Patents

Abstract

The invention provides a lithium-air battery based on a graphene oxide-carbon paper gas catalytic electrode, the positive electrode of the battery is a graphene oxide catalytic electrode supported by carbon paper prepared by the following method, and the preparation method is as follows: graphite oxide The alkene is ultrasonically dispersed in a phosphate buffer solution into a suspension state to prepare an electrolyte; then, the carbon paper is used as the positive electrode and the platinum electrode is used as the negative electrode, and the voltage of the electrolytic cell is controlled at 5-20V. 5 to 30 minutes, after the electrolytic deposition is completed, the graphene oxide is loaded on the carbon paper; the carbon paper is washed with twice distilled water, then vacuum-dried, and finally the graphene oxide loading on the carbon paper is weighed and measured with an analytical balance. The invention has simple preparation steps, easy control of operating parameters, stable and reproducible electrode performance, the first discharge capacity reaches 11553mAh/g at a current density of 0.1mA/ ^cm2 , and the performance of the cycle battery is stable after 520 hours of operation.

Description

A lithium-air battery based on graphene oxide-carbon paper gas catalytic electrode

technical field

The invention provides a lithium-air battery, in particular to a lithium-air battery based on a graphene oxide-carbon paper gas catalytic electrode, which belongs to the lithium-air battery and its preparation technology.

Background technique

A lithium-air battery is a secondary battery that uses metallic lithium as the negative electrode and air as the positive electrode. It has a completely different design from lithium-ion batteries, and its theoretical specific energy is 11140Wh/kg (excluding oxygen mass), which is close to the theoretical specific energy value of gasoline of 13000Wh/kg. Even considering the quality of oxygen, its specific energy is ten times that of ordinary lithium-ion batteries (5210Wh/kg). In 1996, Dr. Abraham of EIC Laboratory in Massachusetts reported for the first time the lithium-air battery of this new polymer electrolyte system, which obtained a discharge specific capacity of 1400Ah/kg, which is close to the actual available specific energy of gasoline of 1700Wh/kg. This achievement has been widely recognized around the world, which has triggered a research upsurge in developing it into automotive power batteries. Lithium-air battery is a kind of metal/air battery, also known as half fuel cell, it is a fuel cell that consumes Li, and it is also a lithium battery in which the positive active material is oxygen. It has both similarities and differences to lithium-ion batteries and fuel cells. Compared with fuel cells, lithium-air batteries use metallic lithium instead of hydrogen, so there is no need to consider the storage of hydrogen, and lithium-air batteries can achieve charge/discharge cycles, which is a convenient energy storage battery; compared with lithium-ion batteries Compared with lithium-air batteries, the positive electrode active material-oxygen can be obtained directly from the air without storing it in the battery system, which greatly reduces the weight of the battery system. - The huge development value of air batteries has attracted widespread attention.

Although lithium-air batteries show good application prospects, their performance is actually limited by various factors, and their energy conversion efficiency is far from the theoretically achievable value. At present, the negative electrode of lithium-air batteries uses metal lithium sheets. In order to prevent metal lithium passivation, it is usually configured with a relatively mature mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC). 1mol/dm ³ LiPF ₆ EC/EMC/DMC (mass ratio 1:1:1) non-aqueous electrolyte (although aqueous electrolyte and solid electrolyte are also under study), the air electrode consists of (carbon powder/catalyst/bonded agent) mixed slurry coated on foamed nickel. Assemble batteries in an air-isolated environment:

(-)Lithium sheet|Organic electrolyte-diaphragm|Gas diffusion electrode(+)

In a lithium-air battery in a non-aqueous system, the Li ⁺ produced by the oxidation of the negative lithium sheet migrates to the positive electrode through the electrolyte when the battery is discharged, and the peroxide ion produced by the reduction of oxygen (or oxygen ions O ^2- generated by further reactions) to form lithium oxides. The charging process is opposite to the discharging process. During charging, lithium oxides decompose to produce oxygen and lithium ions. The formation of the discharge product Li ₂ O ₂ does not require the cleavage of the OO bond, so the reaction does not require a high activation energy, and can proceed smoothly without using a catalyst, see Figure 1. The charging process is to decompose the formed lithium oxide, which is an ionic crystal, and its decomposition requires a high activation energy, and when the electrolyte or binder is decomposed, the discharge product becomes lithium carbonate or contains When lithium is an organic compound, the activation energy required for charging is higher, so the use of an oxygen evolution catalyst is essential during charging. Relevant evidence shows that the discharge product Li ₂ O ₂ or Li ₂ O is insoluble in the non-aqueous electrolyte. After a discharge, a large amount of discharge products accumulate disorderly on the air side of the electrode, while there is basically no discharge on the diaphragm side. products, thereby causing the blockage of the oxygen transport channel, resulting in the termination of the discharge. Moreover, solid Li ₂ O ₂ or Li ₂ O ion crystals are almost insulators, once formed and piled up in disorder, the conductivity of the electrode will be destroyed, making charging impossible. It can be seen that the orderly distribution of battery reaction products on the positive electrode can be realized to ensure the uninterrupted conductivity of the electrode during the charging process and accelerate the charging process. Or the conversion rate of O ^2- → O ² is the key problem that must be solved for the positive electrode of the organic electrolyte lithium-air battery. The goal of large-scale exploration in terms of design and experimentation.

Contents of the invention

The invention provides a lithium-air battery based on graphene oxide-carbon paper gas catalytic electrode, which has higher capacity and charge-discharge cycle performance than existing lithium-air batteries; the invention also provides a A method for preparing graphene oxide-carbon paper electrodes by electrophoresis-electrodeposition.

The technical scheme adopted to realize the above-mentioned purpose of the present invention is:

A lithium-air battery based on a graphene oxide-carbon paper gas catalytic electrode, the positive electrode of the battery is a graphene oxide catalytic electrode supported by carbon paper prepared by the following method, and the preparation method is as follows: graphene oxide is mixed at a pH value The electrophoresis-electrolysis cell is assembled by using carbon paper as the positive electrode and the platinum electrode as the negative electrode, and using a DC stabilized power supply to control the voltage of the electrophoresis-electrolysis cell. The temperature of the electrolyte is 5-20V, the temperature of the electrolyte is controlled at 20-50°C, and the electrophoresis-electrolysis time is 5-30 minutes; during the electrolysis process, in order to make the graphene oxide adhere and deposit evenly on the surface of the carbon paper, a uniform stirring device is used. The stirring rate is 1000-4000r/min. After the electrolytic deposition, the graphene oxide is deposited on the carbon paper; then the carbon paper loaded with graphene oxide is washed with twice distilled water, and after washing, it is vacuum-dried at 80-120°C, and finally An analytical balance is used to weigh and measure the loading amount of graphene oxide on the carbon paper, and the loading amount of graphene oxide on the carbon paper is 0.1-1.0 mg/cm ² .

The carbon paper is a carbon paper after hydrophobic and flattening treatment, its thickness is 25-34 μm, and its contact angle with water is 90-140°.

The graphene oxide concentration in the electrolyte is 0.5-3.0 mg/cm ³ .

When preparing a lithium-air battery, the above-mentioned carbon paper loaded with graphene oxide is cut into the required area as the positive electrode, and the lithium sheet is used as the negative electrode, and injected with 1mol/dm LiPF ⁶ EC/EMC/DMC (mass ratio ₁ :1: 1) Non-aqueous electrolyte, assembled into a button battery under the isolation of air, let it stand for 3-24 hours under the open circuit voltage, adopt constant current free discharge mode and control discharge depth mode for discharge test, record voltage-time curve and voltage - Specific capacity curve.

In the present invention, since graphene oxide is a derivative of flaky exfoliated graphite after oxidation treatment, it still maintains the layered structure of graphite, and each carbon atom is covalently connected with sp ² hybrid orbitals, but in each layer Oxygen-containing functional groups were introduced into graphene monoliths. The structure model generally accepted by people at this stage is that hydroxyl groups and epoxy groups are randomly distributed on the two-dimensional plane of graphene oxide, while carbonyl and carboxyl groups are introduced at the edge of the monolith, see Figure 2. Although the number and distribution of these oxygen-containing groups will vary depending on the preparation method, it is certain that the introduction of oxygen-containing functional groups makes graphene oxide amphiphilic, from the edge to the center of the graphene sheet, it is hydrophilic to the center. Hydrophobic properties, thus enabling it to be suspended in aqueous solutions. Therefore consider following factor in the present invention: 1, the carbonyl group of graphene oxide can open double bond by electrolytic oxidation method, forms graphene oxide surface on carbon paper; The group on the electrode surface can be regarded as a kind of "water" in a broad sense, which is provided to the battery reaction product to change from Li ₂ O ₂ or Li ₂ O to LiOH; 3. Since graphene oxide still maintains the layered structure of graphite, it is perpendicular to The delocalized large π bond of the sp ² carbon ring plane can enhance the electronic conductivity of carbon paper; 4. The oxygen-containing functional group of graphene oxide has a strong electron-absorbing ability, which can induce Or O ^2- , or OH ^- tends to discharge toward the positive electrode, and actually acts as a catalyst for oxygen reduction reaction (discharge, ORR) and oxygen evolution conversion reaction (charge, OER).

In the lithium-air battery provided by the present invention, the positive electrode skillfully combines graphene oxide and carbon paper. Corrosion of the current collector after 4.2V, because no carbon powder and catalyst material that affects the electronic conductivity and pore volume of the electrode, nor N-methylpyrrolidone dispersant (NMP) and PVDF binder, greatly reduces the corrosion rate of the positive electrode. ohmic voltage drop, see Figure 4; second, both carbon paper and graphene oxide are carbon materials, graphene oxide is bonded to carbon paper by electrolytic oxidation, and -OH and COOH functional groups are introduced into the positive electrode, which can promote Li The conversion of ₂ O ₂ or Li ₂ O to LiOH can be transformed into OH by the original charging reaction Li ₂ O ₂ → 2Li ⁺ + O ₂ +2e or Li ₂ O → 2Li+O ₂ +4e ^- discharge on the electrode: 4OH ^- →O ₂ +H ₂ O+4e, with the transformation and fluidization of Li ₂ O ₂ or Li ₂ O solid crystals under the action of generalized "water" in the electrode, it overcomes the disordered accumulation of battery reaction products in the electrode pores The resulting electrode conductivity is interrupted, making charging unsustainable; third, the carbonyl, carboxyl and other oxygen-containing functional groups of graphene oxide have the ability to attract electrons, and can induce electrode active materials (Li ₂ O ₂ or Li ₂ O, and then OH ^- ) is adsorbed and discharged on the electrode surface, which actually acts as a catalyst to achieve the purpose of smooth charging reaction, which greatly improves the stability, cycleability and practicability of lithium-air batteries; finally, The lithium-air battery of the present invention is light and stable after assembly, has a high voltage platform, and a large discharge capacity, and realizes a stable charge/discharge cycle under a certain discharge system. Moreover, the preparation process and operating parameters of the present invention are simple and easy to control, and are easy to implement Large-scale production is convenient for industrial promotion.

Description of drawings

Fig. 1 is the first discharge curve contrast figure of carbon paper positive pole (CP) and graphene oxide-carbon paper positive pole (GO-CP) in the present invention;

Fig. 2 is a schematic diagram of graphene oxide structure in the present invention;

Fig. 3 is the carbon paper SEM figure and local enlarged figure of graphene oxide loaded by electrolysis in the present invention;

Fig. 4 is the comparison chart of the first discharge curve of comparative example 1 and embodiment 1 in the present invention;

Fig. 5 is the charge-discharge cycle curve of the lithium-air battery using pure carbon paper as the positive electrode in Comparative Example 3;

Fig. 6 is the Raman spectrum of the graphene oxide-carbon paper electrode (GO-CP) and the carbon paper (CP) used in the present invention;

Fig. 7 is the discharge curve for the first time under the current density of 0.05mA/cm ² and 0.1mA/cm ² in the embodiment 1 of the present invention;

Fig. 8 is a charge-discharge cycle diagram of 81-100 cycles intercepted in Example 2 of the present invention;

Fig. 9 is a charge-discharge cycle diagram of Example 3 of the present invention.

detailed description

In order to better illustrate the content, essential features and remarkable progress of the present invention, the present invention will be further described below in conjunction with relevant comparative examples and examples. It should be noted here that the enumeration of specific comparative examples and examples is to help understand the present invention, but the present invention is not limited to the following examples. The carbon paper described in the following examples is carbon paper after hydrophobic and planarization treatment, its thickness is 25-34 μm, and its contact angle with water is 90-140°.

Comparative example 1

The purchased graphene and polyvinylidene fluoride (PVDF) are modulated into a slurry of a certain viscosity in N-methylpyrrolidone (NMP) medium at a mass ratio of 90:10, and the slurry is coated by a method similar to screen printing. Evenly coated on carbon paper, then placed in a vacuum oven, baked at 80 ° C for 12 hours, weighed after drying, and the coated carbon paper was shot into a disc with a diameter of 8 mm, thus making a positive electrode sheet spare.

In an argon-protected glove box, a CR2032 battery case (the surface of the positive electrode case has been perforated to ensure the transmission channel of oxygen) was used as the battery package, and the metal lithium sheet (Φ15.6×0.45mm), the separator Celgard 2325, The positive electrode sheet is installed layer by layer, and an appropriate amount of commercial 1M LiPF6 (EC:EMC:DMC=1:1:1) electrolyte is added dropwise to infiltrate the electrode and separator, and the battery is sealed on the packaging machine to complete the battery assembly.

The whole operation process of the battery is carried out in dry oxygen. Under the current density of 0.05mA/cm ² , the initial discharge capacity is 6022mAh/g, and the discharge platform is around 2.7V, see Figure 4.

Comparative example 2

The pure carbon paper that dries is used as positive electrode, makes lithium-air battery by the method in comparative example 1, obtains the discharge curve as in accompanying drawing 1, and first discharge capacity is 13830.7mAh/g (pure carbon paper), and discharge platform average The value is around 2.7V.

Comparative example 3

The pure carbon paper of drying is used as the positive electrode, assuming that the loading capacity in Example 1 is the same, the depth of discharge is controlled, that is, the discharge capacity is controlled to be 1000mAh/g, and the cycle curve in the accompanying drawing 5 is obtained. The pure carbon paper electrode passes through 20 times Discharge terminates after charging and discharging.

Example 1

Ultrasonic disperse graphene oxide at a concentration of 1.0 mg/cm ³ in double distilled water, add KH ₂ PO ₄ and K ₂ HPO ₄ to prepare a phosphate buffer solution with pH 9.0, and continue ultrasonic dispersion for 6 hours to make it uniform Dispersed suspension. The electrophoresis-electrolytic cell is assembled with a platinum electrode as the negative electrode and carbon paper as the positive electrode. The voltage of the electrolytic cell is controlled at 20V by the stabilized power supply, and the temperature of the electrolyte is controlled at 45°C. The surface is evenly attached and deposited, using a uniform stirring device, the stirring rate is 2000r/min, and the electrolysis reaction time is 5min. The carbon paper electrode loaded with graphene oxide was washed with double distilled water, and its Raman spectrum is shown in Figure 6. The cleaned carbon paper electrodes loaded with graphene oxide were baked in a vacuum oven at 80°C for 12 hours, weighed, and punched into discs with a diameter of 8 mm to assemble batteries. The discharge curves for the first time are shown in Figure 7 when the constant current discharges are performed at the current densities of 0.05mA/cm ² and 0.1mA/cm ² respectively. The power supply is a two-pole DC power supply.

Example 2

Ultrasonic disperse graphene oxide at a concentration of 2.0 mg/cm ³ in twice distilled water, add KH ₂ PO ₄ and K ₂ HPO ₄ to prepare a pH 8.0 phosphate buffer solution, and continue ultrasonic dispersion for 6 hours to make it uniform Dispersed suspension. The electrophoresis-electrolytic cell is assembled with a platinum electrode as the negative electrode and carbon paper as the positive electrode. The voltage of the electrolytic cell is controlled at 15V by the stabilized power supply, and the temperature of the electrolyte is controlled at 35°C. During the electrolysis process, in order to make the graphene oxide on the carbon paper The surface is uniformly attached and deposited, using a uniform stirring device, the stirring rate is 3000r/min, and the electrolysis reaction time is 15min. The carbon paper electrode loaded with graphene oxide was cleaned with double distilled water, and the cleaned carbon paper electrode loaded with graphene oxide was dried in a vacuum oven at 100°C for 10 h, weighed, and assembled into a disc with a diameter of 8 mm. .

Using the positive electrode sheet prepared in this example, at a current density of 0.05 mA/cm ² , the discharge capacity is controlled to be 500 mAh/g (calculated based on the amount of supported graphene oxide), and its charge-discharge cycle curve is shown in Figure 8.

Example 3

Ultrasonic disperse graphene oxide at a concentration of 3.0 mg/cm ³ in double distilled water, add KH ₂ PO ₄ and K ₂ HPO ₄ to prepare a pH 7.0 phosphate buffer solution, and continue ultrasonic dispersion for 6 hours to make it uniform Dispersed suspension. The electrophoresis-electrolytic cell is assembled with a platinum electrode as the negative electrode and carbon paper as the positive electrode. The voltage of the electrolytic cell is controlled at 8V by the stabilized power supply, and the temperature of the electrolyte is controlled at 25°C. During the electrolysis process, in order to make the graphene oxide on the carbon paper The surface is uniformly attached and deposited, using a uniform stirring device, the stirring rate is 4000r/min, and the electrolysis reaction time is 25min. The carbon paper electrode loaded with graphene oxide was cleaned with double distilled water, and the cleaned carbon paper electrode loaded with graphene oxide was dried in a vacuum oven at 120°C for 8 hours, weighed, and formed into a disc with a diameter of 8 mm to assemble the battery .

Using the positive electrode sheet prepared in this example, at a current density of 0.05mA/cm ² , the discharge capacity is controlled to be 1000mAh/g (calculated based on the amount of graphene oxide supported), and its charge-discharge cycle curve is shown in Figure 9.

Claims (2)

1. a lithium-air battery based on graphene oxide-carbon paper gas catalytic electrode, is characterized in that: the positive electrode of this battery adopts the graphene oxide catalytic electrode of the carbon paper support that following method is made, and preparation method is as follows: Graphene oxide is ultrasonically dispersed in a phosphate buffer solution with a pH value of 5 to 9 to form an electrolyte solution; then the carbon paper is used as the positive electrode and the platinum electrode is used as the negative electrode to assemble an electrophoresis-electrolytic cell, using a DC stabilized power supply Control the electrophoresis-electrolysis cell voltage to 5-20V, the temperature of the electrolyte to 20-50°C, and the electrophoresis-electrolysis time to 5-30 minutes; during the electrolysis process, in order to make graphene oxide adhere and deposit evenly on the surface of carbon paper, A uniform stirring device was used with a stirring rate of 1000-4000r/min. After the electrolytic deposition, graphene oxide was deposited on the carbon paper; Vacuum drying at ℃, and finally weighing and measuring the load of graphene oxide on the carbon paper with an analytical balance, the load of graphene oxide on the carbon paper is 0.1-1.0 mg/cm ² ; The carbon paper is a carbon paper after hydrophobic and flattening treatment, its thickness is 25-34 μm, and its contact angle with water is 90-140°. 2 . The lithium-air battery based on graphene oxide-carbon paper gas catalytic electrode according to claim 1 , wherein the concentration of graphene oxide in the electrolyte is 0.5-3.0 mg/cm ³ .