Positive electrode material for zinc-bromine flow battery as well as preparation method and application of positive electrode material

Abstract

The invention discloses a positive electrode material for a zinc-bromine flow battery and a preparation method and application thereof, and belongs to the technical field of zinc-bromine flow batteries, the preparation method comprises the following steps: crushing and sieving an active carbon source, adding the active carbon source into a graphene oxide aqueous dispersion, stirring, centrifuging, removing supernate, drying, mixing with an activating agent, and activating in an inert atmosphere; washing to be neutral, drying and sieving to obtain a graphene / activated carbon composite material; and attaching the graphene / activated carbon composite material to a carbon-plastic bipolar plate to obtain the positive electrode material for the zinc-bromine flow battery. A graphene / activated carbon composite system is combined with a high-conductivity network, graded holes and surface functional groups, so that the reaction kinetics bottleneck of a traditional carbon material Br2 is broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of zinc-bromine liquid flow batteries, and in particular relates to a positive electrode material for zinc-bromine liquid flow batteries, a preparation method thereof, and an application thereof. Background Art

[0002] With increasing environmental pollution and the depletion of fossil fuels, the proportion of new renewable energy sources such as wind and solar power in power generation continues to increase. However, the random, intermittent, and volatile nature of new energy sources leads to low utilization rates, making distributed storage a key solution to this problem. In recent years, the demand for long-term, capacity-based energy storage has steadily increased for renewable energy generation, making the development of long-term energy storage a key solution to the intermittent nature of renewable energy generation. Flow batteries, with their advantages of high safety, strong scalability, and unrestricted geographical location, have a dominant position in long-term energy storage. Zinc-bromine flow batteries stand out among flow batteries due to their high energy density (theoretical energy density reaches 430 Wh / kg), high safety (using an aqueous electrolyte), and wide operating temperature range (-30°C to 50°C).

[0003] The core principle of zinc-bromine flow battery is based on the redox reaction between zinc negative electrode and bromide positive electrode, and the storage and release of electrical energy are achieved through the circulation of electrolyte. Current research focuses on three major directions: electrode materials, electrolyte formulation and diaphragm technology; in terms of electrode materials, carbon plastic bipolar plates are mostly used because of their good mechanical properties and corrosion resistance. In terms of electrolyte, self-discharge is suppressed by adding bromine complexing agents. For example, tetrapropylammonium bromide can significantly improve the complexing ability of polybromide ions and reduce the decomposition rate of the electrolyte; the introduction of supporting electrolytes such as lithium perchlorate effectively enhances the conductivity of the electrolyte. In terms of diaphragms, in response to the problem of zinc dendrite penetration, researchers have developed a tetrabutylammonium tribromide coated diaphragm, which extends the battery cycle life by chemically dissolving zinc dendrites. Although zinc-bromine flow battery technology has made many breakthroughs, its commercialization process still faces core bottlenecks. The positive electrode Br of zinc-bromine flow battery - The sluggish kinetics of the Br2 redox reaction lead to high electrochemical polarization and low power density in zinc-bromine flow batteries, hindering their further commercial application. Electrode materials significantly influence the performance of zinc-bromine flow batteries. Currently, commercial zinc-bromine flow batteries mostly use carbon-plastic bipolar plates as electrodes, but these plates have poor electrolyte wettability, low conductivity, and a small reactive surface area, which cannot promote the reaction activity of zinc-bromine flow batteries.

[0004] For the cathode Br of traditional zinc-bromine flow battery -The sluggish kinetics of the Br2 redox reaction results in high internal resistance and high charge and discharge overpotentials, placing the battery's power density at the level of lead-acid batteries, making it difficult to meet the demands of rapid charge and discharge. A new cathode material for zinc-bromine flow batteries is needed to address the core issues of sluggish cathode kinetics, electrode material performance defects, and low bromine reaction efficiency. This will overcome existing technological bottlenecks and advance zinc-bromine flow batteries towards high-power, long-life commercial applications. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a positive electrode material for zinc-bromine flow battery and its preparation method and application, so as to solve the problem of the positive electrode Br - The kinetics of the / Br2 redox reaction are sluggish, resulting in high internal resistance of the battery, large charge and discharge overpotential, low power density, and difficulty in meeting the technical requirements of fast charging and discharging.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention discloses a method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The activated carbon source is crushed and sieved, and then added to the graphene oxide aqueous dispersion, stirred, centrifuged, and the supernatant is removed and dried to obtain a graphene / activated carbon composite material precursor, which is then mixed with an activator and activated under an inert atmosphere; washed to neutrality, dried, and sieved to obtain a graphene / activated carbon composite material; and the graphene / activated carbon composite material is attached to a carbon-plastic bipolar plate to obtain a positive electrode material for a zinc-bromine liquid flow battery.

[0007] Preferably, the graphene oxide aqueous dispersion is prepared by dispersing graphene oxide in deionized water; the mass percentage of the graphene oxide aqueous dispersion is 5wt%; the activator is KOH; and the inert gas is nitrogen or argon.

[0008] Further preferably, the mass ratio of the activated carbon source to the graphene oxide is (5-20):1; the mass ratio of the graphene / activated carbon composite material precursor to the activator is (1-2):(1-3).

[0009] Preferably, the activation treatment conditions include: a heating rate of 2-10° C. / min; an activation temperature of 800-1000° C.; and an activation time of 2 h.

[0010] Preferably, the sieving condition is to pass through a 100-mesh sieve; the centrifugal speed is 8000-10000 r / min; and the washing condition includes: washing with deionized water 4-8 times.

[0011] Preferably, the specific surface area of ​​the graphene / activated carbon composite material is greater than 1400 m2 / g, pore volume greater than 0.4cm 3 / g.

[0012] Preferably, the method of attaching the graphene / activated carbon composite material to the electrode plate includes: mixing the graphene / activated carbon composite material with a solvent and a binder, and spraying the mixture on one side of the bipolar plate to obtain a positive electrode material for a zinc-bromine flow battery.

[0013] Further preferably, the mass ratio of the graphene / activated carbon composite material to the binder is 8:(2~3); the solvent is N-methylpyrrolidone; and the binder is at least one of Nafion, polyvinylidene fluoride and polytetrafluoroethylene.

[0014] The present invention also discloses a positive electrode material for a zinc-bromine liquid flow battery, which is prepared by adopting the above-mentioned method for preparing the positive electrode material for a zinc-bromine liquid flow battery.

[0015] The present invention also discloses the use of the positive electrode material for zinc-bromine flow battery prepared by the above-mentioned preparation method in the preparation of zinc-bromine flow battery, wherein the negative electrode adopts a carbon plastic bipolar plate; the diaphragm is a microporous polyolefin diaphragm; the electrolyte is a mixed aqueous solution containing zinc bromide, potassium chloride and methacrylate-2-(1-ethyl-2-imidazolinone) ester, and the electrolyte is a mixed aqueous solution containing zinc bromide, potassium chloride and methacrylate-2-(1-ethyl-2-imidazolinone) ester at 20 mA / cm 2 The current density is charged and discharged, and the charging time is 1h; the discharge cut-off voltage is 0.5V, the Coulomb efficiency is 91.3%-95.6%; the energy efficiency is 71.3%-82.2%; and the voltage efficiency is 78.1%-86.9%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for preparing a positive electrode material for zinc-bromine flow batteries. By crushing, the composite uniformity of the material and graphene oxide can be improved, and the loading capacity of graphene oxide can be increased. The introduction of graphene oxide aqueous dispersion, through stirring and centrifugation, allows the graphene to evenly coat the surface of activated carbon, retaining the graphene's flaky structure. After activation, a composite material with both high conductivity (graphene network) and hierarchical pore structure (activated carbon) is formed, which significantly increases the Br2 diffusion rate and the density of reactive active sites. By spraying the graphene / activated carbon composite material on the surface of commercial bipolar plates, the electrode conductivity and electrolyte wettability are improved, the reactive area and active sites are increased, and the positive electrode Br is increased. - The Br2 reaction kinetics of graphene / activated carbon are improved by combining a highly conductive network, hierarchical pores, and surface functional groups in a graphene / activated carbon composite system, thereby overcoming the bottleneck of the Br2 reaction kinetics of traditional carbon materials.

[0017] Furthermore, by regulating the mass ratio of reactants, the interface bonding between activated carbon and graphene is optimized, while the amount of activator is controlled to balance the etching degree and pore structure, avoiding excessive etching leading to a decrease in mechanical strength.

[0018] Furthermore, at an activation temperature of 800-1000°C, KOH etching at high temperatures creates micropores and mesopores, while also partially reducing graphene oxide and improving conductivity. An activation time of 2 hours ensures sufficient but not excessive etching, maintaining the stability of the material skeleton.

[0019] Furthermore, a centrifugal speed of 8,000-10,000 r / min effectively separates uncompounded graphene oxide fragments, ensuring the purity of the composite material. Deionized water washing 4-8 times thoroughly removes residual KOH and prevents alkaline environment corrosion of battery components.

[0020] Furthermore, the specific surface area is greater than 1400 m 2 / g, pore volume greater than 0.4 cm 3 / g: High specific surface area provides more Br2 adsorption sites, and large pore volume promotes rapid electrolyte infiltration and reduces mass transfer polarization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 SEM images of the graphene / activated carbon composite precursor, graphene / activated carbon composite material, and activated carbon from Comparative Example 1 prepared in Example 2; (a) is the graphene / activated carbon composite precursor prepared in Example 2, (b) is the graphene / activated carbon composite material prepared in Example 2, and (c) is the activated carbon from Comparative Example 1; Figure 2 The pore volume comparison diagram of the graphene / activated carbon composite material prepared in Example 2 and the activated carbon prepared in Comparative Example 1; wherein (a) is the graphene / activated carbon composite material; (b) is the activated carbon; Figure 3 It is the O1s peak in the XPS spectrum of the graphene / activated carbon composite material prepared in Example 2. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0024] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0025] In the present invention, unless otherwise specified, percentages (%) or parts refer to percentages by weight or parts by weight relative to the composition.

[0026] In the present invention, unless otherwise specified, the components involved or their preferred components can be combined with each other to form a new technical solution.

[0027] In this disclosure, unless otherwise specified, the numerical range "a-b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "6-22" indicates that all real numbers between "6-22" are listed herein, and "6-22" is merely an abbreviation for these numerical combinations.

[0028] The "range" disclosed in the present invention is in the form of lower limit and upper limit, which can be one or more lower limits, and one or more upper limits respectively.

[0029] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0030] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in accordance with the order. Preferably, the reaction method herein is carried out sequentially.

[0031] Unless otherwise indicated, the professional and scientific terms used herein are the same as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the present invention.

[0032] The present invention provides a method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: S1. Using biomass or coking coal-based coke as an activated carbon source, crush it with a crusher and add it to a 5% graphene oxide aqueous dispersion, wherein the mass ratio of graphene oxide to activated carbon raw material is 1:5-1:20, stirring for 2 hours, and then centrifuging to remove the supernatant. The product after centrifugation is dried to obtain a graphene / activated carbon composite material precursor; S2. Mixing the graphene / activated carbon composite material precursor with an activator and activating the mixture under an inert atmosphere at a heating rate of 2-10°C / min, an activation temperature of 800-1000°C, and an activation time of 2 h; S3. The activated sample was washed with deionized water until neutral and then dried, and then passed through a 100-mesh sieve to obtain a graphene / activated carbon composite material; S4. The graphene / activated carbon composite material is mixed with a solvent and a binder and then sprayed onto one side of a carbon-plastic bipolar plate for use as a positive electrode of a zinc-bromine flow battery.

[0033] Furthermore, the specific surface area of ​​the graphene / activated carbon composite material is greater than 1400m 2 / g, pore volume greater than 0.4g / cm 3 .

[0034] Furthermore, the mass ratio of the activated carbon source material to graphene oxide in S1 is 10:1-20:1.

[0035] Furthermore, the sheet diameter of the graphene oxide described in S1 is 5-10 μm.

[0036] Furthermore, the centrifugal rotation speed in S1 is 8000-10000 r / min.

[0037] Furthermore, the activator in S2 is KOH, and the inert gas is nitrogen or argon; the mass ratio of the graphene / activated carbon composite material precursor to the activator is (1-2): (1-3).

[0038] Furthermore, the number of water washing in S3 is 4-8 times.

[0039] Furthermore, the preparation process of the zinc-bromine flow battery positive electrode in S4 is as follows: using N-methylpyrrolidone (NMP) as a solvent, mixing the graphene / activated carbon composite material and the binder in a mass ratio of 8:2 and spraying the mixture on one side of the carbon plastic bipolar plate; the binder is one or more of Nafion, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); The negative electrode of the zinc-bromine single-flow battery adopts a carbon-plastic bipolar plate; the diaphragm is a microporous polyolefin diaphragm, the electrolyte contains a mixed aqueous solution of 2M zinc bromide, 3M potassium chloride and methacrylate-2-(1-ethyl-2-imidazolidinone) ester, the electrode area is 3*3cm, and the current is 20mA / cm 2 The current density is charged and discharged, with the charging cut-off condition being a charging time of 1 hour and the discharge cut-off condition being a cut-off voltage of 0.5 V. The coulombic efficiency is 91.3%-95.6%; the energy efficiency is 71.3%-82.2%; and the voltage efficiency is 78.1%-86.9%.

[0040] The present invention is directed to the positive electrode Br of zinc-bromine flow battery -In order to solve the problem of sluggish kinetics of Br2 / Br2 reaction, a graphene / activated carbon composite material is proposed. By spraying the graphene / activated carbon composite material on the surface of carbon-plastic bipolar plate and using it for the positive electrode of zinc-bromine flow battery, the main effects are as follows: 1. The composite material has high conductivity and hydrophilicity, which can improve the electrode conductivity and electrolyte wettability, and reduce mass transfer impedance; 2. The high specific surface area and ordered hierarchical pore structure of the composite material are conducive to the entry of electrolyte into the micro-mesopores, which can reduce the diffusion resistance of bromine and increase the active reaction area; 3. The carbon-oxygen functional groups such as CO on the surface of the composite material increase the reaction active sites of bromine, thereby improving the Br2 / Br2 reaction of the positive electrode of zinc-bromine flow battery. - / Br2 reaction kinetics.

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Example 1 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The asphalt coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5 wt% graphene oxide aqueous dispersion and stirred for 2 h, wherein the ratio of graphene oxide to asphalt coke was 1:20. The supernatant was removed by centrifugation at a speed of 8000 r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was mixed with KOH in a ratio of 1:3 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 2°C / min, an activation temperature of 800°C, and an activation time of 2 h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1 h, and then filtered, and repeated 4 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with PVDF in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0043] Example 2 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The asphalt coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5 wt% graphene oxide aqueous dispersion and stirred for 2 h, wherein the ratio of graphene oxide to asphalt coke was 1:10. The supernatant was removed by centrifugation at a speed of 9000 r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was mixed with KOH in a ratio of 1:2 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 5°C / min, an activation temperature of 900°C, and an activation time of 2 h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1 h, and then filtered, and the mixture was repeated 6 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with PVDF in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0044] Example 3 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The asphalt coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5 wt% graphene oxide aqueous dispersion and stirred for 2 h, wherein the ratio of graphene oxide to asphalt coke was 1:10. The supernatant was removed by centrifugation at a speed of 10,000 r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was uniformly mixed with KOH in a ratio of 1:2 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 10°C / min, an activation temperature of 1000°C, and an activation time of 2 h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1 h, and then filtered, and the mixture was repeated 6 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with PVDF in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0045] Example 4 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The asphalt coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5wt% graphene oxide aqueous dispersion and stirred for 2h, wherein the ratio of graphene oxide to asphalt coke was 1:10, and the supernatant was removed by centrifugation at a speed of 85000r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was evenly mixed with KOH in a ratio of 1:1.5 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 5°C / min, an activation temperature of 800°C, and an activation time of 2h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and then filtered, and repeated 6 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with PTFE in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0046] Example 5 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The asphalt coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5wt% graphene oxide aqueous dispersion and stirred for 2h, wherein the ratio of graphene oxide to asphalt coke was 1:5. The supernatant was removed by centrifugation at a speed of 9500r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was mixed with KOH in a ratio of 1:1.5 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 5°C / min, an activation temperature of 900°C, and an activation time of 2h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and then filtered, and repeated 6 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with PTFE in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0047] Example 6 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The petroleum coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5wt% graphene oxide aqueous dispersion and stirred for 2h, wherein the ratio of graphene oxide to pitch coke was 1:5. The supernatant was removed by centrifugation at a speed of 8000r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was mixed with KOH in a ratio of 2:1 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 10°C / min, an activation temperature of 1000°C, and an activation time of 2h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and then filtered, and repeated 5 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with Nafion in a ratio of 8:2 and then sprayed on one side of a bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 h for use as the positive electrode of a zinc-bromine flow battery.

[0048] Example 7 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The petroleum coke was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5wt% graphene oxide aqueous dispersion and stirred for 2h, wherein the ratio of graphene oxide to pitch coke was 1:20. The supernatant was removed by centrifugation at a speed of 8000r / min, and the product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was evenly mixed with KOH in a ratio of 1:2 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 2°C / min, an activation temperature of 800°C, and an activation time of 2h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and then filtered, and repeated 8 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with Nafion in a ratio of 8:2 and then sprayed on one side of a bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 h for use as the positive electrode of a zinc-bromine flow battery.

[0049] Example 8 A method for preparing a positive electrode material for a zinc-bromine flow battery, comprising: The pre-carbonized coconut shell was crushed with a crusher, passed through a 60-mesh sieve, and added to a 5wt% graphene oxide aqueous dispersion and stirred for 2h, wherein the ratio of graphene oxide to pitch coke was 1:20, and the supernatant was removed by centrifugation at a speed of 8000r / min. The product after centrifugation was dried to obtain a graphene / activated carbon composite material precursor; the graphene / activated carbon composite material precursor was mixed with KOH in a ratio of 1:1.2 and placed in a nickel boat, and activated in a tube furnace at a heating rate of 2°C / min, an activation temperature of 800°C, and an activation time of 2h; the activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and then filtered, and repeated 7 times. After drying and passing through a 100-mesh sieve, a graphene / activated carbon composite material was obtained; Using NMP as solvent, the material was mixed with Nafion in a ratio of 8:3 and then sprayed on one side of a bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 h for use as the positive electrode of a zinc-bromine flow battery.

[0050] Comparative Example 1 A method for preparing a pitch coke activated carbon positive electrode material for a zinc-bromine flow battery comprises: The pitch coke was crushed with a crusher and passed through a 60-mesh sieve. It was then mixed evenly with KOH in a ratio of 1:2 and placed in a nickel boat. It was activated in a tube furnace at a heating rate of 5°C / min, an activation temperature of 900°C, and an activation time of 2h. After activation, the sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and filtered. This was repeated 7 times. The sample was dried and passed through a 100-mesh sieve to obtain pitch coke activated carbon. Using NMP as solvent, the material was mixed with PTFE in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0051] Comparative Example 2 A method for preparing a petroleum coke activated carbon positive electrode material for a zinc-bromine flow battery comprises: The petroleum coke was crushed with a crusher and passed through a 60-mesh sieve. The mixture was then mixed with KOH in a ratio of 1:2 and placed in a nickel boat. The mixture was activated in a tube furnace at a heating rate of 2°C / min, an activation temperature of 800°C, and an activation time of 2 hours. The activated sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1 hour, and filtered. This process was repeated 7 times. The sample was then dried and passed through a 100-mesh sieve to obtain petroleum coke activated carbon. Using NMP as solvent, the material was mixed with Nafion in a ratio of 8:2 and then sprayed on one side of a bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 h for use as the positive electrode of a zinc-bromine flow battery.

[0052] Comparative Example 3 A method for preparing a coconut shell activated carbon positive electrode material for a zinc-bromine flow battery comprises: The pre-carbonized coconut shell was crushed with a crusher and passed through a 60-mesh sieve. It was then mixed evenly with KOH in a ratio of 1.2:1 and placed in a nickel boat. It was activated in a tube furnace at a heating rate of 2°C / min, an activation temperature of 800°C, and an activation time of 2h. After activation, the sample was added to deionized water 5 times the mass of the activated carbon, stirred for 1h, and filtered. This was repeated 7 times. The coconut shell activated carbon was obtained after drying and passing through a 100-mesh sieve. Using NMP as solvent, the material was mixed with PVDF in a ratio of 8:2 and then sprayed on one side of the bipolar plate. The mixture was placed in a forced air oven at 60° C. and dried for 8 hours for use as the positive electrode of a zinc-bromine flow battery.

[0053] Table 1 is a comparison of key parameters in Examples 1-8 and Comparative Examples 1-3. From the table, the selection of preparation conditions for each Example and Comparative Example can be clearly seen.

[0054] Table 1 Comparison of key parameters in Examples 1-8 and Comparative Examples 1-3

[0055] The zinc-bromine flow battery performance test was carried out using a single cell for the zinc-bromine flow battery cathode materials prepared in Examples 1-8 and Comparative Examples 1-3. The specific data are shown in Table 2.

[0056] Table 2 Comparison of performance test results of zinc-bromine flow batteries prepared using cathode materials for zinc-bromine flow batteries prepared in Examples 1-8 and Comparative Examples 1-3

[0057] Table 2 compares the performance test results of zinc-bromine flow batteries made from the positive electrode materials for zinc-bromine flow batteries prepared in Examples 1-8 and Comparative Examples 1-3. As can be seen from the above table, the coulombic efficiency of the zinc-bromine flow battery made from the positive electrode material for zinc-bromine flow battery prepared by the present invention is 91.3%-95.6%; the energy efficiency is 71.3%-82.2%; and the voltage efficiency is 78.1%-86.9%. The values ​​of coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) in Examples 1-5 are all greater than those in Comparative Example 1. The values ​​of coulombic efficiency, voltage efficiency and energy efficiency in Examples 6-7 are all greater than those in Comparative Example 2. The values ​​of coulombic efficiency, voltage efficiency and energy efficiency in Example 8 are all greater than those in Comparative Example 3. This shows that the addition of graphene can improve the performance of activated carbon, thereby improving the performance of the battery.

[0058] Figure 1SEM electron microscope images of the graphene / activated carbon composite material precursor, graphene / activated carbon composite material and activated carbon of comparative example 1 prepared in Example 2; wherein, (a) is the graphene / activated carbon composite material precursor prepared in Example 2, (b) is the graphene / activated carbon composite material prepared in Example 2, and (c) is the activated carbon of comparative example 1; Figure 1 It can be seen from the electron microscope image that graphene oxide is evenly coated on the surface of asphalt coke. The activated carbon formed after high-temperature activation is rougher than the activated carbon surface without graphene composite, providing a larger reaction area for bromine on the surface of the material and reducing the electrode impedance.

[0059] Figure 2 The pore volume comparison diagram of the graphene / activated carbon composite material prepared in Example 2 and the activated carbon prepared in Comparative Example 1 is shown; wherein (a) is the graphene / activated carbon composite material; (b) is the activated carbon; Figure 2 From the pore structure diagram, the pore volume of the graphene / super activated carbon composite material increases at larger pore sizes, which is more conducive to the entry of the electrolyte into the pores, effectively reducing the diffusion resistance of bromine and reducing the internal resistance of the battery.

[0060] Figure 3 is the O1s peak in the XPS spectrum of the graphene / activated carbon composite material obtained in Example 2; Figure 3 The XPS results show that the composite material surface contains more oxygen functional groups (the O content is 11.5%). The oxygen functional groups increase the reactive sites of bromine and improve the wettability of the electrolyte, thus improving the Br - / Br2 reaction kinetics.

[0061] In summary, the present invention provides a positive electrode material for zinc-bromine flow batteries, its preparation method, and application. By combining graphene with activated carbon and optimizing the activation process, a positive electrode material with high conductivity, hierarchical porous structure, and rich surface functional groups is prepared. Graphene constructs a continuous conductive network to improve charge transfer efficiency, the micro / mesopores of activated carbon synergistically reduce bromine diffusion resistance, and the surface CO functional groups enhance electrolyte wettability and anchor bromine species, significantly improving Br - / Br2 reaction kinetics, the prepared zinc-bromine flow battery at 20mA / cm 2 The energy efficiency is 82.2% and the coulombic efficiency is 95.6%.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode material for a zinc-bromine flow battery, characterized in that: include: The activated carbon source is crushed and sieved, and then added to the graphene oxide aqueous dispersion, stirred, centrifuged, and the supernatant is removed and dried to obtain a graphene / activated carbon composite material precursor, which is then mixed with an activator and activated under an inert atmosphere; washed to neutrality, dried, and sieved to obtain a graphene / activated carbon composite material; The graphene / activated carbon composite material is attached to the carbon-plastic bipolar plate to obtain the positive electrode material for zinc-bromine flow battery.

2. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 1, wherein: The graphene oxide aqueous dispersion is prepared by dispersing graphene oxide in deionized water; the mass percentage of the graphene oxide aqueous dispersion is 5wt%; the activator is KOH; and the inert gas is nitrogen or argon.

3. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 2, wherein: The mass ratio of the activated carbon source to the graphene oxide is (5-20):1; the mass ratio of the graphene / activated carbon composite material precursor to the activator is (1-2):(1-3).

4. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 1, wherein: The activation treatment conditions include: a heating rate of 2-10°C / min; an activation temperature of 800-1000°C; and an activation time of 2h.

5. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 1, wherein: The screening condition is to pass through a 100-mesh screen; the centrifugal speed is 8000-10000 r / min; and the washing condition includes: washing with deionized water 4-8 times.

6. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 1, wherein: The specific surface area of ​​the graphene / activated carbon composite material is greater than 1400 m 2 / g, pore volume greater than 0.4cm 3 / g.

7. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 1, wherein: The method for attaching a graphene / activated carbon composite material to a bipolar plate includes: mixing the graphene / activated carbon composite material with a solvent and a binder, and spraying the mixture on one side of the bipolar plate to obtain a positive electrode material for a zinc-bromine liquid flow battery.

8. The method for preparing a positive electrode material for a zinc-bromine flow battery according to claim 7, wherein: The mass ratio of the graphene / activated carbon composite material to the binder is 8:(2-3); the solvent is N-methylpyrrolidone; and the binder is at least one of Nafion, polyvinylidene fluoride, and polytetrafluoroethylene.

9. A positive electrode material for zinc-bromine flow battery, characterized in that The positive electrode material is prepared by the method for preparing the positive electrode material for zinc-bromine flow battery according to any one of claims 1 to 8.

10. Use of a zinc-bromine flow battery cathode material prepared by the method for preparing a zinc-bromine flow battery cathode material according to any one of claims 1 to 8 in preparing a zinc-bromine flow battery, characterized in that: The negative electrode uses a carbon plastic bipolar plate; the diaphragm is a microporous polyolefin diaphragm, and the electrolyte is a mixed aqueous solution containing zinc bromide, potassium chloride and methacrylate-2-(1-ethyl-2-imidazolidinone) ester. 2 The current density is charged and discharged, and the charging time is 1h; the discharge cut-off voltage is 0.5V, the Coulomb efficiency is 91.3%-95.6%; the energy efficiency is 71.3%-82.2%; and the voltage efficiency is 78.1%-86.9%.

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