High-area specific volume battery negative electrode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of energy storage materials, and particularly relates to a battery cathode material as well as a preparation method and application thereof.
Background
With the development of economy and the dramatic increase of world population, the world energy demand is continuously increased, thereby causing serious problems of energy resource competition and environmental pollution[1]. Therefore, in recent years, how to effectively utilize clean energy, including wind energy, solar energy, tidal energy, and the like, has been widely studied. Since these energy sources are intermittently generated, they need to be converted into electrical energy for further use. Therefore, it is necessary to develop an efficient, safe and environmentally friendly energy storage system to utilize energy more efficiently[2]. The secondary battery which can be repeatedly charged and discharged, has high efficiency and is environment-friendly is an important research direction of the energy storage technology.
The water system battery is a secondary battery taking aqueous solution as electrolyte, overcomes the defects of expensive, toxic, flammable and explosive electrolyte, low ionic conductivity and the like of the traditional organic system battery, and has the advantages ofHigh multiplying power, green and environmental protection. Therefore, the water-based battery has important application prospect in the field of large-scale energy storage at the power grid level[3]. With the increasing demand for high-performance electrode materials, there is an urgent need to improve the performance of aqueous batteries by designing energy storage materials.
Metals are generally used as negative electrode materials of aqueous batteries, such as zinc and the like. However, zinc is liable to generate dendrite during charge and discharge cycles, thereby causing short circuit of the battery and having poor cycle stability[4]. Therefore, other suitable anode materials need to be found. The bismuth-based material has good conductivity and a proper negative potential working range, and is a high-performance negative electrode material with development potential. Despite the extensive research of researchers, the energy density of current bismuth-based materials still cannot meet the practical needs[5,6]. On one hand, the specific volume of the bismuth electrode is lower, and the specific volume of the electrode material with the same mass is lower; on the other hand, when the loading capacity per unit area is increased and the electrode material is thickened, the ion diffusion speed and the electron transfer speed of the electrode are reduced, so that the specific area capacity of the electrode is not obviously increased along with the increase of the loading capacity[7]. Therefore, the development of a preparation method of the bismuth-based material with high specific area has great significance for industrial production and practical application of the electrode material.
Graphene was successfully prepared by mechanical exfoliation method since 2004 by Novoseov et al, university of Manchester, UK[8]The research heat tide is raised in the fields of chemistry, physics and materials. Graphene is the most excellent conductive material (10) known at present3~104S/m), the theoretical specific surface area is up to 2630 m2The chemical properties are stable, and the outstanding performances enable the graphene to have wide development prospects in the field of energy storage devices. In order to solve the problem that the specific area is not increased in proportion with the increase of the electrode loading capacity, the three-dimensional framework network structure of the graphene is constructed by an electrochemical deposition method, so that the electrode loading capacity is increased; on the other hand, the ion diffusion speed and the electron transfer speed are improved.
Disclosure of Invention
The invention aims to provide a battery cathode material with high loading capacity, high electric capacity, excellent rate performance and excellent cycle stability, a preparation method thereof and application thereof in a flexible water-based battery.
The high-area specific volume battery cathode material provided by the invention is a reduced graphene oxide/bismuth composite material with a fine three-dimensional structure. According to the invention, the three-dimensional network structure of graphene and bismuth is constructed through co-deposition of graphene and bismuth, and the side wall of the three-dimensional network structure (porous structure) is formed by overlapping bismuth and a reduction-oxidation graphene layer, so that the ionic electron transfer efficiency of the electrode material and the utilization rate of an active material are improved on one hand, and the cycling stability of the electrode is improved due to the physical confinement effect on the other hand.
The invention provides a preparation method of a battery cathode material-reduced graphene oxide/bismuth composite material, which comprises the following steps:
(1) preparation of electroplating baths
Adding a graphene oxide aqueous solution with the volume concentration of 0.01-0.09 mg/mL into a beaker, adding ethylene diamine tetraacetic acid disodium salt to enable the concentration of the ethylene diamine tetraacetic acid disodium salt to be 0.1-0.5 mol/L, and stirring the mixture on a magnetic stirrer to form a solution; adding a certain amount of Bi (NO)3)3·5H2O, enabling the concentration of the O to be 10-100 mmol/L, and dropwise adding a NaOH solution to adjust the pH value until the solution is clear;
(2) electrodeposition
Taking flexible carbon cloth as a working electrode, a graphite rod as a counter electrode, a mercury-mercury oxide electrode as a reference electrode, and taking the prepared solution as electroplating solution to carry out constant-voltage electroplating, wherein the electroplating voltage is-0.9V to-1.6V, and the electroplating time is adjusted according to the required electrode loading capacity; soaking the electroplated carbon cloth in deionized water to remove surface electrolyte, and drying on a hot bench;
(3) surface coated graphene oxide
And slowly dipping the obtained product in a graphene oxide solution for multiple times, drying the sample on a hot table, and repeatedly dipping and hot drying for multiple times to obtain the graphene-bismuth composite material coated with the graphene oxide.
In the step (1), the concentration of the graphene oxide aqueous solution is preferably 0.02-0.05 mg/mL, and more preferably 0.03 mg/mL; preferably, the concentration of the disodium ethylene diamine tetraacetate is 0.2-0.4 mol/L, and more preferably 0.2 mol/L; bi (NO) is preferred3)3·5H2The concentration of O is 20-70 mmol/L, and more preferably 50 mmol/L; the pH of the solution is preferably 4-7. More preferably, the solution has a pH of 5.
In the step (2), the flexible carbon cloth is preferably used as a working electrode, and the electroplating voltage of the constant voltage electroplating method is-1.2V to-1.5V, more preferably-1.4V.
In the step (3), the concentration of the graphene oxide solution is preferably 3-8 mg/mL, and more preferably 5 mg/mL; the number of times of slow dipping is 5-15. The dipping-hot drying times are repeated for 2-6 times.
The graphene and bismuth composite material prepared by the invention can be used as an electrode material and can be used in a flexible water-based battery.
The preparation of the electrode material adopts an in-situ electrochemical deposition method on the flexible carbon cloth, so that a conductive agent, a binder and the like do not need to be added for secondary preparation of the electrode. By regulating the electroplating time, the material load of the carbon cloth per unit area can be controlled between 4 and 40 mg/cm2(ii) a As the loading capacity increases, the mass specific volume remains substantially constant; the specific area can be up to 3.5 mAh/cm by testing in a three-electrode system2Exceeding most electrode materials reported at present. After the electrode is tested for 3 ten thousand circles in a circulating way, the capacity is basically not attenuated, and after the electrode is cycled for 5 ten thousand circles, the capacity is still maintained by 90 percent. After the electrode and the nickel oxide anode material are assembled into a full battery, the battery still has 3mAh/cm2The above energy density (calculated from the mass of the anode active material).
According to the invention, the composite material of graphene and bismuth is prepared by adopting an electrochemical codeposition method, the obtained composite material not only has a three-dimensional network structure, but also has a fine structure in the network, the loading capacity of the active material is greatly increased, and the cycling stability of the electrode material is greatly improved due to the domain-limiting effect of graphene on the active material.
The preparation method is simple, low in energy consumption, wide in raw material source and easy for large-scale production.
Drawings
Fig. 1 is a Scanning Electron Microscope (SEM) picture of a reduced graphene oxide/bismuth composite material. Wherein, the magnification a is 150 times, and the magnification b is 20000 times.
Fig. 2 is an X-ray diffraction (XRD) pattern of the reduced graphene oxide/bismuth composite material.
FIG. 3 is a high magnification Scanning Electron Microscope (SEM) picture of a composite material obtained by electroplating for 5 minutes at a graphene oxide concentration of 0.01mg/mL in the electroplating solution.
FIG. 4 is a high magnification Scanning Electron Microscope (SEM) picture of a composite material obtained by electroplating for 5 minutes at a graphene oxide concentration of 0.03mg/mL in the electroplating solution.
FIG. 5 is a high magnification Scanning Electron Microscope (SEM) picture of a composite material obtained by electroplating for 5 minutes at a graphene oxide concentration of 0.06mg/mL in the electroplating solution.
FIG. 6 is a high magnification Scanning Electron Microscope (SEM) picture of a composite material obtained by electroplating for 5 minutes at a graphene oxide concentration of 0.09mg/mL in the electroplating solution.
FIG. 7 is an impedance spectrum of the electrode material plated in different graphene oxide concentrations under an open circuit voltage (-0.05V).
FIG. 8 is an impedance spectrum of the electrode material plated in different graphene oxide concentrations at the working voltage (-0.68V).
Fig. 9 is a graph comparing the ion diffusion resistance and the reaction resistance of electrode materials plated in different graphene oxide concentrations.
FIG. 10 is a discharge curve of the reduced graphene oxide/bismuth composite material obtained under the electroplating condition that the graphene oxide concentration is 0.03mg/mL (the current density is 20 mA/cm)2)。
Fig. 11 is a curve of the area specific capacity of the electrode material changing with the loading capacity under different current densities of the graphene oxide/bismuth composite material.
Fig. 12 is a cycle life curve for a reduced graphene oxide/bismuth composite.
Fig. 13 is a plot of the area capacity of a nickel bismuth battery at different current densities.
Detailed Description
(1) Preparation of electroplating baths
Adding 40 mL of graphene oxide aqueous solution with the concentration of 0.01M, 0.03M, 0.06M and 0.09M into a 50mL beaker, adding certain mass of disodium ethylene diamine tetraacetate (0.1M, 0.2M and 0.5M), stirring into solution on a magnetic stirrer, and adding Bi (NO) (NO is added into the solution3)3·5H2O (10 mmol/L, 20 mmol/L, 50 mmol/L), and the pH was adjusted to about 5 with NaOH solution.
(2) Electrodeposition
The prepared electroplating solution is used as electroplating solution to carry out constant-voltage electroplating by taking flexible carbon cloth as a working electrode, a graphite rod as a counter electrode and a mercury-mercury oxide electrode as a reference electrode. The electroplating voltage is-0.9V, -1.2V-1.4V, and the electroplating time is adjusted to be between 2 minutes and 15 minutes according to the required electrode loading capacity. And soaking the electroplated carbon cloth in deionized water to remove surface electrolyte, and drying on a hot bench.
(3) Surface coating graphene oxide treatment
And slowly dipping the sample obtained after annealing in a graphene oxide solution with the concentration of 2, 5 and 10mg/mL for multiple times, drying the sample on a hot bench, and repeatedly dipping and hot drying to obtain the graphene/bismuth composite material coated with the graphene oxide.
The preparation method of the graphene oxide used in the invention is a Hummers method.
Reference to the literature
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