The chemical reactions leading to precipitation or nucleation of new phase in liquid solution is of interest in many applications ranging from materials synthesis to biologically-induced materials and energy storage systems. A better understanding of these reactions at the nanoscale level requires imaging and spectroscopy of nucleation and growth events in the liquid media. The development of nanotechnology, especially the liquid-cell transmission electron microscopy (TEM) provides new opportunities for direct visualization of dynamic processes in solution in real-time. Liquid phase processes are important in various aspects such as mineral growth, biomineralization process, and even electrochemical reactions. In this thesis, we studied the in-situ liquid cell mineralization of calcium based-minerals including gypsum (CaSO4•2H2O) and hydroxyapatite (HA), as well as electrochemical deposition in lithium-oxygen (Li-O2) batteries. We observed that both classical and non-classical nucleation and growth events can happen during the formation of calcium-based minerals. We showed that the fabrication of gypsum microneedles can bypass the formation of intermediate basanite (CaSO4•0.5H2O). We were able to show the complete pathways for HA formation following both classical and non-classical theories. Interesting, we observed that the growth of HA crystals depended on the dissolution rate of amorphous calcium phosphate phases. For the electrochemical battery study, the (electro)chemical fundamentals in a working Li-O2 battery is explored. This work revealed further details of underlying mechanisms in a working Li-O2 battery and identifies various limiting factors controlling the discharge and charge processes
