Preparation Of Several Nanomaterials And Their Application In Aqueous Electrochemical Energy Storage

There are increasing demands for safe and reliable high-performance electrochemical energy storage devices since the growing of energy crisis and environmental problems. Aqueous-based electrochemical devices, which possess relative low cost and reliable safety, show huge advantage on electric vehicles, renewal energy (e.g., solar and wind) storage and grid-energy storage. Among them, pseudocapacitor with high theoretical energy density and cheap nontoxic nickel iron battery, hold the most promise. This thesis mainly focuses on fixing the problems existing in aqueous pseudocapacitor electrode materials (mainly hydrous ruthenium oxide and polyaniline) and iron anode, and developing high-performance, safe and reliable aqueous electrochemical storage electrode material with strong application potential. The main contents of this paper include the following three parts: (1) High-performance aqueous pseudocapacitor electrode materials based on hollow hydrous ruthenium oxideHollow fusiform RuO2·xH2O was prepared through hydrothermal method by using spindle a-Fe2O3 as the template. We found that the introduction of an appropriate amount of acid in the reaction system played a very important role in regulating the dissolution of a-Fe2O3 template and hydrolysis of Ru3+ to form the hollow structure. The obtained hollow structures provided a high specific surface area and shortened the transport distance of protons, and hydrothermal synthesis routes well balanced the water content and crystallinity of the hydrate, which greatly enhanced the electron and proton transfer rate of the product. Test results suggested that the prepared hollow fusiform RuO2·xH2O possess a high rate performance. High capacity retention of 65% and 47% can be obtained at current densities of 20 A g-1 and 40 A g-1, respectively, when compared to the capacity at 0.5 A g-1.In addition, the electrode material also exhibited a good cycling stability, the capacity increase by 19% after cycling for 1000 times at a high current density of 4 A g-1.Inspired by the result that hollow structure could effectively improve the electrochemical performance of the electrode, we also synthesized the hydrous ruthenium dioxide (RuO2) nanotubes directly on Ti substrate by using cobalt-hydroxide-carbonate nanowire array as the template through a water bath process. The prepared product can be directly used as binder-free electrode. The directly built 3-D hydrous RuO2 nanotubes on Ti substrate can significantly decrease the influence of traditional binder involved electrode made process and electronic resistance at the interface between electrode material and current collector; in addition, hollow nanotube structure are very favorable for the fast transfer of electrons and protons, thus give the prepared material a ultra-high rate performance. The test results show that capacity of 745 F g-1 can be obtained at 32 A g-1, only 11.2% loss when compared to the value of 840 F g-1 at 2 A g-1. Meanwhile, the electrode also possesses a good cycling stability.(2) Preparation of biomass derived 3D porous carbon material and its application on polyaniline based pseudocapacior composite electrode material.In order to obtain a continuous porous and low-cost carbon material as a growth substrate and current collector, we prepared the 3D porous rose carbon skeleton by pre-treatment of fresh rose petals and the following N2 protected annealing process. This carbon material had a high graphitization degree with good conductivity, could be an idea carbon substrate for composite electrode material. Then the polyaniline (PANI) nanorod array was assembled on the carbon skeleton through a dilute polymerization method at low temperature. By studying the influence of different aniline monomer concentration on the preparation of PANI nanorod array, we found the best aniline monomer concentration in this reaction system was 0.05 M. Under this condition, the largest loading mass of PANI could be obtained with the least side reaction product. The continuous 3D porous structure could effectively enhance the electron transfer rate and shorten the ion transport distance. The vertical nanowire arrays were facile to strain relaxation, which allowed them to decrease the breaking during the doping/dedoping process of counterions. At the same time, the carbon skeleton undertook some mechanical deformation in the redox process of PANI nanowires, which avoided destroying the electrode material and was benefited to a better stability. Electrochemical tests showed that the prepared composite exhibited a high capacity, high rate performance (capacity retention of 56.6% and 44.8% could be obtained at current densities of 8 A g-1 and 16 A g-1, respectively, when compared to the capacity at 0.5 A g-1) and a good cycling stability (89% of the capacity could be maintained after 2000 cycles at a current density of 2 A g-1). The high capacity and good rate performance, especially the long cycling stability could be further proved through their comparison with the control group of pure PANI. The rose derived 3D porous carbon skeleton used in this experiment had the characteristics such as environmentally-friendly, low cost, easy-made and et al., and the obtained composite displayed a high performance, which provided a new route for the preparation of high performance polyaniline based aqueous pseudocapacior electrode material.(3) Robust iron nanoparticles with graphitic shells for high-performance aqueous Ni-Fe batteryHomogenous polymeric complexes containing iron salts were prepared through electrostatic interaction between the negatively charged carboxylic groups (COO) of PAA and the positively charged iron cations (e.g., Fe(OH)2+, Fe(OH)2+ or iron-chloride complexes). The Fe nanoparticles with graphitic shells were obtained by the simple following drying and pyrolysis process. Such robust carbon coatings and crosslinkings not only provided the Fe anodes with outstanding conductivity, but also retarded the degradation of the Fe nanoparticles during charging/discharging process. The electrochemical test results show that the electrode material had a high capacity (capacity of 314 mAh g-1 at 1 A g-1), good rate capability (224 mAh g-1 can be obtained at 32 A g-1), excellent cycle performance (90% of the capacity retained after 1000 cycles) and a high charging efficiency (> 90%). Meanwhile, the synthesis process was simple and did not involve the expensive graphene and other carbon materials, which provided a better anode material for high-performance nickel-iron battery. In order to match the prepared Fe anode, we synthesized the Ni(OH)2 and nitrogen-doped graphene (NG) composite cathode material through pyrolysis and microwave assistant hydrothermal process, by using urea, sucrose and et al. as the raw material. The assembled full Ni-Fe battery displayed a high electrochemical performance. Energy density of 136.7 Wh kg-1 could be obtained at a power density of 0.7 kW kg-1, and when the power density was increased to 11.7 kW kg-1, energy density could still maintained to 71.4 Wh kg-1. At the same time, the full battery showed an excellent cycling performance with capacity retention of 86% after 1,000 cycles. This excellent performance further proved the great application potential of our Fe anode.In order to prepare large-scale and can be commercialized high performance Fe anode material, inexpensive carbonyl iron was used as raw material. After an alkaline hydrolysis process, large amount of Fe nanoparticles (with the diameter-30 nm) were prepared through a continuous and scalable aerosol assisted process. Then a large number of graphitic carbon coated iron nanoparticles were obtained after mixing the prepared Fe particles with carbon sources (e.g. sucrose), and the following high temperature pyrolysis process. Electrochemical test results showed that the prepared Fe anode material also had an excellent electrochemical performance. Since the relatively low price of raw materials, as well as the preparation process is simple and effective, the prepared product possessed great potentials for large-scale production and marketization.