Fabrication and control of crystal structure of $Ni(OH)_2$ nanocrystals by hydrothermal process

Abstract

Ni(OH)2 is one of representative cathode materials due to its proton diffusion property, stability in strong alkaline electrolyte and good reversibility when charged to NiOOH. Ni(OH)2 has been focused with increased due to its applications for alkaline rechargeable batteries which are most widely used in many applications, such as power tools, portable electronics and electric vehicles. The electrochemical utilization and practical capacity of Ni(OH)2 cathodes are directly affected by their morphology and size. In order to fabricate Ni(OH)2 nanocrystals, several chemical processes were proposed during the last decade. In this study, hydrothermal process has been used for the fabrication of Ni(OH)2 nanocrystals. The hydrothermal process is relatively easy to control of process parameters, it provide more versatility to change and control the crystal size and shape during the process. The control of size and shape of Ni(OH)2 nanocrystals and crystal structure engineering of Ni(OH)2 were investigated by using hydrothermal process. Ni(OH)2 nanocrystals was fabricated by addition of NaOH, as a precipitator, in water dissolved Ni acetate hydrate by High Temperature High Pressure (HTHP) reaction. It was possible to control the size of Ni(OH)2 nanocrystals by changing process parameters such as reaction time and reaction temperature. The size of Ni(OH)2 nanocrystals is increased and became saturated as increasing reaction time. reaction temperature is identified as an important to control of saturated nanocrystals size. The saturation size of Ni(OH)2 became larger with increasing reaction temperature. It was possible to control the shape of Ni(OH)2 nanocrystals by changing process parameters such as reaction time, reaction temperature, anion type as a additive and pH of reaction solution before HTHP reaction. The shape of Ni(OH)2 nanocrystals fabricated initially is hexagon due to its crystal structure, while the hexagon changed to disk shared by controlling proces...