The 21st century has witnessed dramatic changes in the energy harvesting and supply scenario with an appreciable transition from non-renewable energy resources (fossil fuels) to renewable energy resources (wind, solar, hydroelectricity, geothermal), brought on by global efforts to battle climate change associated with elevated greenhouse emissions. This energy transition to meet the world's growing needs for electricity, heating, cooling, and power for transport in a sustainable way is widely considered to be one of the greatest challenges facing humanity in this century. The transition is largely enabled by improvements in generation and storage technologies for energy harvested from renewable, but inherently intermittent supplies. As most of renewable energy technologies provide electricity, development of fast, efficient, and safe electrical energy storage techniques is crucial for further progress. Moreover, growing needs for smaller, lighter, more powerful portable electronic devices, and more powerful electric vehicles suitable for long-range transportation have further fostered the demand for dispatchable and efficient electrical energy storage. In this regard, rechargeable batteries composed of reactive metal anodes such as Lithium, have garnered interest in recent years, primarily due to their potential to significantly improve the energy density compared to current state-of -art Lithium-ion batteries. However, the commercialization of these Lithium metal batteries has received steady challenges from concerns of short-circuiting and fire hazard, brought on by uneven (dendritic, tree-like) electrodeposition of the reactive metal during several charge-discharge cycles of the batteries. The dendritic electrodeposition is thought to be facilitated by an interplay of morphological and chemical instabilities at the Lithium metal anode during battery charge. The work reported in this thesis utilizes theoretical and experimental tools to fundamentally understand the nature of these instabilities at the initiation step and to thereby develop rational designs of Li anode-electrolyte interphases that delay or eliminate the instabilities at their source. Towards this goal, the physics of nucleation and early-stage growth of Lithium electrodeposits is firstly interrogated and is shown to be consistent across different liquid electrolyte chemistries. Next, based on an understanding of nucleation of Li in liquid electrolytes, certain halide rich electrolytes hypothesized to enhance the surface energetics of Lithium electrodeposition are studied to evaluate their influence on the morphology and chemistry of Lithium electrodeposits. It is shown that these electrolytes do in fact eliminate the morphological and chemical instabilities at the initiation step, and the fine control achieved in physical-chemical features of the Lithium electrodeposits can be translated to achieve greater control of electrodeposit morphology at later stages of electroplating. Finally, custom blends of halide rich electrolytes with beneficial additives are developed to eliminate the instabilities and preserve the therein developed physical-chemical features of Lithium electrodeposits through the deep cycling of Lithium metal anodes. Liquid electrolyte blends developed through rational choice of electrolyte chemistry are shown to improve the electrochemical performance of Lithium metal batteries.