Controlled Synthesis Of Nickel/Cobalt-based Micro/Nanomaterials And Their Electrochemical Performance

In order to adapt to the further development of the modern advanced weapon systems,the research of high-performance military chemical power supplies has become animportant issue. In the past few decades, the researchers have been pursing chemical powersupplies with higher energy density, higher power density, and higher security. Thermalbatteries have become one of the ideal power supplies for modern weapons, consideringtheir prominent advantages in terms of high-power discharge ability, quick activation andcompact structure. Meanwhile, the role of supercapacitors in military power supplies hasbeen expanding due to their quick charge-discharge rate and high power density. The effectsof electrode materials, as a key part of the chemical power supplies, on the electrochemicalperformance are vital. Among them, nickel/cobalt-based mirco/nano-scaled materials haveattracted more and more attention and are considered to be one of the most promisingmaterisls for their high electrochemical activity and large specific surface area.First of all, to overcome the current defects for the preparation of NiCl2as cathode forthermal batteries, including the complex synthesis technology, the stringent equipmentrequirement, and the uncontrolled particle size and morphology, this paper described asimple and quick recrystallization method for successfully synthesizing NiCl2nanorods.The relation between the microstructure of NiCl2and its electrochemical performance wasexplored. The results show that the nanostructured NiCl2favors for the enhancement of thedischarge performance for thermal batteries. It delivers an energy densigy of249.43Whkg-1and a power density of9.45kW kg-1at0.424A g-1, with a15.8%and2.4%improvement, respectively, when comparing with the bulk NiCl2. Furthermore, thewater-soluble NiCl2nanorods were applied as electrode materials for supercapacitors forthe first time, and the charge storage mechanism was researched. After the transformationfrom NiCl2to Ni(OH)2via an in situ chemical reaction, the electrochemical activity wasactivated. The energy was stored or released through the mutual conversion of Ni(OH)2andNiOOH mediated by OH-.Secondly, this paper demonstrated a simple one-step hydrothermal method forsuccessfully preparing regugar CoS2octahedrons and proposed a growth mechanism thatbegins with a growth and self-aggregation process, followed by an Ostwald ripeningprocess.The octahedron-shaped CoS2crystals were employed as electrode active materials for supercapacitors for the first time, and the electrochemical performance was researchedsystematically. The results show that the specific capacitance of the as-fabricated CoS2electrode is236.5F g-1at1A g-1. It exhibits an excellent cycling stability with only a lossof7.4%in the specific capacitance after2000cycles, making it a practical material forapplication in supercapacitors.Finally, for further improving the specific capacitance of CoS2, thus enhancing theenergy densigy and power density, three different hierarchical CoS2microspheres weresynthesized successfully using the composite system of citric acid monohydrate (CAM) andethanolamine (ETA) as the chelating agent. The influence of the addition of ETA in thechelating agent on the morphology of CoS2was discussed. The electrochemicalperformance of the CoS2samples with differernt morphologies as electrode materials forsupercapacitors was explored. The results show that the hierarchical CoS2nanostructureconstructed by ultrathin nanosheets possesses the maximum specific surface area (66.416m2g-1) with a suitable pore size distribution (2~5nm). The unique hierarchicalnanostructure can facilitate the full contact between the electrode surface and theelectrolytes, and shortens the distance for charge transfer and ions diffusion as well, leadingto its highest specific capacitance (718.7F g-1at1A g-1), excellent rate capability, and goodcycling stability. In this work, the chelating agent assisted hydrothermal method can beextended to the design and synthesis of other micro/nano-scaled metal sulfides with novelstructres for various applications, such as energy storage and catalysis, etc.